3G CDMA200 Wireless System Engineering

280

Transcript of 3G CDMA200 Wireless System Engineering

Page 1: 3G CDMA200 Wireless System Engineering
Page 2: 3G CDMA200 Wireless System Engineering
Page 3: 3G CDMA200 Wireless System Engineering

3G CDMA2000Wireless System Engineering

Page 4: 3G CDMA200 Wireless System Engineering

For a listing of recent titles in the Artech HouseMobile Communications Library, turn to the back of this book.

Page 5: 3G CDMA200 Wireless System Engineering

3G CDMA2000Wireless System Engineering

Samuel C. Yang

Artech House, Inc.Boston • London

www.artechhouse.com

Page 6: 3G CDMA200 Wireless System Engineering

Library of Congress Cataloging-in-Publication DataA catalog record for this book is available from the U.S. Library of Congress.

British Library Cataloguing in Publication DataYang, Samuel C.

3G CDMA2000 wireless system engineering.—(Artech House mobile communicationslibrary)1. Wireless communication systems. 2. Code division multiple accessI. Title621.3'845

ISBN 1-58053-757-x

Cover design by Yekaterina Ratner

© 2004 ARTECH HOUSE, INC.685 Canton StreetNorwood, MA 02062

All rights reserved. Printed and bound in the United States of America. No part of this bookmay be reproduced or utilized in any form or by any means, electronic or mechanical, includ-ing photocopying, recording, or by any information storage and retrieval system, withoutpermission in writing from the publisher.

All terms mentioned in this book that are known to be trademarks or service marks havebeen appropriately capitalized. Artech House cannot attest to the accuracy of this informa-tion. Use of a term in this book should not be regarded as affecting the validity of any trade-mark or service mark.

International Standard Book Number: 1-58053-757-x

10 9 8 7 6 5 4 3 2 1

Page 7: 3G CDMA200 Wireless System Engineering

To my wife Jenny and my son Daniel

Page 8: 3G CDMA200 Wireless System Engineering

.

Page 9: 3G CDMA200 Wireless System Engineering

Contents

Preface xiii

Acknowledgments xvii

CHAPTER 1Introduction to 3G CDMA 1

1.1 Third Generation Systems 11.2 Protocol Architecture 21.3 Other Elements of Protocol Architecture 31.4 Spreading Rate 1 and Spreading Rate 3 51.5 Differences Between IS-2000 and IS-95 7

1.5.1 Signaling 71.5.2 Transmission 81.5.3 Concluding Remarks 8References 9

CHAPTER 2Physical Layer: Forward Link 11

2.1 Introduction 112.2 Radio Configurations 142.3 Signaling Channels 15

2.3.1 Forward Dedicated Control Channel (F-DCCH) 152.3.2 Quick Paging Chanel (F-QPCH) 162.3.3 Forward Common Control Channel (F-CCCH) 192.3.4 Broadcast Control Channel (F-BCCH) 202.3.5 Common Assignment Channel (F-CACH) 212.3.6 Common Power Control Channel (F-CPCCH) 222.3.7 Pilot Channels 24

2.4 User Channels 262.4.1 Forward Fundamental Channel (F-FCH) 262.4.2 Forward Supplemental Channel (F-SCH) 27

2.5 Channel Structure 312.6 Modulation 322.7 Capacity Gain: Forward Link 34

References 35Selected Bibliography 35

vii

Page 10: 3G CDMA200 Wireless System Engineering

CHAPTER 3Physical Layer: Reverse Link 37

3.1 Introduction 373.2 Radio Configurations 393.3 Signaling Channels 40

3.3.1 Reverse Dedicated Control Channel (R-DCCH) 403.3.2 Reverse Common Control Channel (R-CCCH) 413.3.3 Enhanced Access Channel (R-EACH) 423.3.4 Reverse Pilot Channel (R-PICH) 45

3.4 User Channels 493.4.1 Reverse Fundamental Channel (R-FCH) 503.4.2 Reverse Supplemental Channel (R-SCH) 50

3.5 Channel Structure 503.6 Modulation 513.7 Capacity Gain: Reverse Link 52

References 53Selected Bibliography 53

CHAPTER 4Medium Access Control 55

4.1 Introduction 554.2 Primitives 554.3 Multiplex Sublayers 574.4 Radio Link Protocol (RLP) 60

4.4.1 Overview of Layer 2 Protocols 604.4.2 llustration of the RLP 614.4.3 Concluding Remarks 62

4.5 Signaling Radio Burst Protocol (SRBP) 634.6 System Access 64

4.6.1 Basic Access Mode 654.6.2 Reservation Access Mode 654.6.3 Power Controlled Access Mode 674.6.4 Designated Access Mode 68References 68

CHAPTER 5Signaling Link Access Control 71

5.1 Introduction 715.2 LAC Sublayers 71

5.2.1 Authentication and Addressing Sublayers 715.2.2 ARQ Sublayer 735.2.3 Utility Sublayer 735.2.4 Segmentation and Reassembly Sublayer 74

5.3 Sublayer Processing 745.3.1 Common Signaling: Forward Link 745.3.2 Common Signaling: Reverse Link 765.3.3 Dedicated Signaling: Forward Link 77

viii Contents

Page 11: 3G CDMA200 Wireless System Engineering

5.3.4 Dedicated Signaling: Reverse Link 805.4 Interaction of Layer and Sublayers 80

5.4.1 Transmit Side 815.4.2 Receive Side 82References 83

CHAPTER 6Signaling: Upper Layers 85

6.1 Overview 856.2 State Transitions: Call Processing 87

6.2.1 Initialization State 886.2.2 Mobile Station Idle State 896.2.3 System Access State 916.2.4 Mobile Station Control on the Traffic Channel State 94

6.3 Mode Transitions: Packet Data Transmission 966.3.1 Active Mode 966.3.2 Control Hold Mode 966.3.3 Dormant Mode 966.3.4 Transitions 97

6.4 Channel Setup 976.4.1 Example 1: Base Station-Originated Voice Call 986.4.2 Example 2: Mobile Station-Originated Voice Call 996.4.3 Example 3: Mobile Station-Originated Packet Data Call 1006.4.4 Example 4: Supplemental Channel Request During a6.4.4 Packet Data Call 1016.4.5 Concluding Remarks 104References 104

CHAPTER 7Power Control 107

7.1 Introduction 1077.2 Power Control of the Forward Link 107

7.2.1 Inner Loop and Outer Loop 1077.2.2 Power Control of Multiple Forward Traffic Channels 110

7.3 Power Control of the Reverse Link: Open Loop 1137.3.1 Power Control of Multiple Reverse Channels 1137.3.2 Summary 116

7.4 Power Control of the Reverse Link: Closed Loop 1177.4.1 Inner Loop and Outer Loop 1187.4.2 Power Control of Multiple Reverse Channels 119References 121

CHAPTER 8Handoff 123

8.1 Introduction 1238.2 Soft Handoff 123

8.2.1 Active Set 124

Contents ix

Page 12: 3G CDMA200 Wireless System Engineering

8.2.2 Candidate Set 1278.2.3 Neighbor Set 1288.2.4 Remaining Set 1298.2.5 Set Transitions 1298.2.6 Example: Soft Handoff 129

8.3 Idle Handoff 1338.3.1 Active Set 1338.3.2 Neighbor Set 1348.3.3 Private Neighbor Set 1348.3.4 Remaining Set 1348.3.5 Idle Handoff Process 134

8.4 Access Entry Handoff 1348.5 Access Handoff 135

8.5.1 Active Set 1368.5.2 Neighbor Set 1368.5.3 Remaining Set 1368.5.4 Access Handoff Process 136

8.6 Access Probe Handoff 1388.7 Concluding Remarks 139

References 140

CHAPTER 9System Performance 141

9.1 Introduction 1419.2 Channel Supervision 141

9.2.1 Forward Link: Traffic Channel 1419.2.2 Forward Link: Common Channel 1429.2.3 Reverse Link 142

9.3 Code Management 1429.3.1 Generation of Walsh Codes 1439.3.2 Assignment of Walsh Codes: Forward Link 1449.3.3 Quasi-Orthogonal Functions 1479.3.4 Assignment of Walsh Codes: Reverse Link 147

9.4 Turbo Codes 1509.5 Transmit Diversity 152

9.5.1 Orthogonal Transmit Diversity 1529.5.2 Space Time Spreading 1549.5.3 Concluding Remarks 156References 156Selected Bibliography 157

CHAPTER 10System Design: Coverage 159

10.1 Introduction 15910.2 Forward Pilot Channel 16110.3 Forward Fundamental Channel 16210.4 Forward Supplemental Channel 163

x Contents

Page 13: 3G CDMA200 Wireless System Engineering

10.5 Upper Bounds of Interference: Forward Link 16510.6 Reverse Fundamental Channel 16510.7 Reverse Supplemental Channel 16710.8 Upper Bounds of Interference: Reverse Link 16810.9 Eb/N0 and Receiver Sensitivity 16910.10 Concluding Remarks 169

Reference 170

CHAPTER 11System Design: Capacity 171

11.1 Introduction 17111.2 Mathematical Definitions 171

11.2.1 Received Signal Power 17111.2.2 Loading Factor 173

11.3 Reverse Link 17411.3.1 Capacity 17411.3.2 Capacity Improvements in IS-2000 17611.3.3 Capacity Improvements in a System 177

11.4 Forward Link 17811.4.1 Capacity 17911.4.2 Capacity Improvements in IS-2000 18211.4.3 Capacity Improvements in a System 183References 185

CHAPTER 12Network Architecture 187

12.1 Introduction 18712.2 2G Network 187

12.2.1 Network Elements 18712.2.2 Protocols 189

12.3 3G Network 18912.3.1 Network Elements 19012.3.2 Protocols 191

12.4 Simple IP 19212.5 Mobile IP 19312.6 Concluding Remarks 196

References 197

CHAPTER 131xEV-DO Network 199

13.1 Introduction 19913.2 1xEV-DO Network 20113.3 Protocol Architecture 202

13.3.1 Application Layer 20413.3.2 Stream Layer 205

13.3.3 Session Layer 20513.3.4 Connection Layer 206

Contents xi

Page 14: 3G CDMA200 Wireless System Engineering

13.3.5 Security Layer 21013.3.6 Concluding Remarks 210References 211

CHAPTER 141xEV-DO Radio Interface: Forward Link 213

14.1 Introduction 21314.2 MAC Layer 213

14.2.1 Forward Traffic Channel MAC Protocol 21414.2.2 Control Channel MAC Protocol 215

14.3 Physical Layer 21514.3.1 Pilot Channel 21514.3.2 Forward Traffic Channel/Control Channel 21614.3.3 MAC Channel 21914.3.4 Time Division Multiplexing 22114.3.5 Modulation 225

14.4 Concluding Remarks 226References 226Selected Bibliography 226

CHAPTER 151xEV-DO Radio Interface: Reverse Link 227

15.1 Introduction 22715.2 MAC Layer 227

15.2.1 Reverse Traffic Channel MAC Protocol 22715.2.2 Access Channel MAC Protocol 228

15.3 Physical Layer 22915.3.1 Reverse Traffic Channel 23115.3.2 Access Channel 23615.3.3 Modulation 238

15.4 Reverse Power Control 23915.4.1 Open-Loop Power Control 23915.4.2 Closed-Loop Power Control 240References 240Selected Bibliography 240

About the Author 241

Index 243

xii Contents

Page 15: 3G CDMA200 Wireless System Engineering

Preface

Over the past few years, many fundamental changes have taken place in wirelesscommunications that will influence the future of this dynamic field. One phenome-non driving these changes has been the integration of wireless communicationdevices in people’s lives. While the 1990s were the years when wireless voice teleph-ony became popular, the 2000s should be the time when wireless data applicationsare truly un-tethered from homes and offices. As more people adopt wireless com-munication devices and applications effected by these devices, the demand on wire-less networks will continue to grow.

Although code division multiple access (CDMA) has become an integral part ofthe ensemble of third generation (3G) standards, many wireless network operatorshave found the implementation of IS-2000 affords a good balance between cost andperformance of providing 3G services, especially if an operator evolves its networkfrom IS-95 to IS-2000. As such, IS-2000 has become a popular choice of 3G foroperators around the world, notably in Asia and the Americas.

This book has been written to address the technical concepts of IS-2000. Thefocus is on basic issues, and every effort has been made to present the material in anexpository and interesting fashion. One strategy is to utilize examples not to offerproofs (as they cannot) but to help the reader grasp the fundamental issues at hand.In this regard, mathematical details and models have an important role but serve asmeans to an end. While CDMA is by nature theory-intensive, every attempt is madeto strike a balance between theory and practice. In addition, to minimize the dupli-cation of foundational material of spread spectrum communications and IS-95, thisbook does not describe those introductory concepts (e.g., synchronization of PNcodes) in detail and assumes that the reader is familiar with basic material such asthose found in CDMA RF System Engineering (Samuel Yang, Artech House, 1998).Furthermore, this book assumes that the reader is familiar with the layered frame-works of the Internet Model and OSI Model.

In 3G, the system requires the full participation of not only the physical layerbut also medium access control, link access control, and upper layers to provide notonly circuit voice call but also packet data call functions. Hence in 3G, one needs tofocus on the entire system rather than just on a particular layer. To that end, thebook starts with a layer-by-layer treatment of IS-2000. In Chapters 1 to 6, it followsthe protocol layer framework and describes IS-2000 from Layers 1 to 3. Chapter 1introduces basic concepts and requirements of 3G and highlights key differencesbetween IS-2000 and IS-95. Chapters 2 and 3 describe physical layers of forwardand reverse links, respectively. The channel structure and functions of differentchannels are described in these two chapters. Chapter 4 covers medium access

xiii

Page 16: 3G CDMA200 Wireless System Engineering

control and focuses on radio link protocol, signaling radio burst protocol, and sys-tem access. Then, Chapter 5 goes into link access control; this chapter first reviewsthe functions of the sublayers of link access control, then it illustrates sublayer proc-essing on both forward and reverse links. Chapter 6 goes over Layer 3 or upper layersignaling of IS-2000; the emphasis here is on call processing, state transition, andmode transitions.

After building the foundation of the structure of an IS-2000 system, the bookproceeds to the systems aspects of IS-2000 in Chapters 7 to 12. Since IS-2000 con-tains power control and handoff functions that are superior to those in IS-95-A,Chapters 7 and 8 describe in detail power control and handoff functionalities,respectively. Chapter 9 then proceeds to cover system performance and describesthose features adopted by IS-2000 to increase performance such as code manage-ment, turbo codes, and transmit diversity.

Since a CDMA system essentially trades off coverage versus capacity, thesedesign aspects are presented in Chapters 10 and 11. In particular, Chapter 10 coverscoverage, and Chapter 11 covers capacity. These two chapters contain systematicdevelopments of key concepts, and necessary mathematical developments areincluded where necessary to clarify the material.

Chapter 12 is on network architecture and serves as a capstone on all the chap-ters presented thus far. It describes the IS-2000 architecture from a network perspec-tive and shows how a 3G network differs and evolves from a 2G network. Thischapter introduces how IS-2000 works and interacts with other elements in the net-work. Advanced concepts such mobile IP are also introduced here.

The last three chapters concern a special topic that is of particular inter-est—1xEV-DO (1x Evolution for Data Optimized), which has gained popularity inrecent years and is designed to work with an IS-2000 system. The topics related1xEV-DO are included to make the book a more complete reference. Specifically,Chapter 13 focuses on the top five layers of 1xEV-DO (i.e., application, stream, ses-sion, connection, and security), and Chapters 14 and 15 cover medium access con-trol and physical layers of forward and reverse links, respectively.

Without a loss generality, this book emphasizes Spreading Rate 1 at 1.25 MHz.The discussions on Spreading Rate 1 can be readily extended to direct-spread ormultiple-carrier options of wider bandwidths. In addition, throughout the book wecite specific examples of radio configurations instead of exhaustively describe thedetails of every radio configuration. These selective descriptions serve to illustratemore fully the reason for a particular implementation. Overall, the emphasis of thebook is on the conceptual understanding of the salient points, focusing on the“how” and “why” instead of the “what.” It is hoped that the mastery of the materialpresented will serve as a strong foundation from which readers can further explorethe technology.

This book is intended as a reference for radio frequency (RF) and system engi-neers, technical managers, and short-course students who desire to quickly get up tospeed on the essential technical issues of IS-2000. The material covered in the bookis broad enough to serve students of various backgrounds and interests and to allowteachers much flexibility in designing their course material. As such, this bookshould be a good complement to advanced undergraduate or first-year graduatelevel courses in wireless communications as well.

xiv Preface

Page 17: 3G CDMA200 Wireless System Engineering

Finally, the material presented in this book is given for informational purposeand instructional value and is not guaranteed for any particular purpose. The pub-lisher or the author does not offer any warranties or representations and does notaccept any liabilities with respect to the material presented in this book. Further-more, as technical information changes quickly, the purchaser of the book or user ofthe information contained in this book should seek updated information from othersources. The publisher or the author assumes no obligation to update or modify theinformation, nor does the publisher or the author undertake any obligation tonotify the purchaser of the book or user of the information contained in the book ofany update. The purchase of the book or the use of the information contained in thebook signifies the purchaser’s or user’s agreement to the above.

Preface xv

Page 18: 3G CDMA200 Wireless System Engineering

.

Page 19: 3G CDMA200 Wireless System Engineering

Acknowledgments

As always, the completion of a book would not be possible without the support ofmany people. I would like to thank Barry Pasternack who has given me encourage-ment during this project as well as guidance in other areas, Mabel Kung who hasspent many hours giving me support and words of wisdom, Paul Minh who hasgiven me advice during the writing of this book, and Joseph Sherif who is alwayswilling to make himself available for conversations. I appreciate Samir Chatterjeewho often meets with me to discuss various technical topics, and Lorne Olfman whohas continued to give me guidance out of his busy schedule. I also thank the reviewerwhose suggestions have made this a better book.

I am also grateful to the editors at Artech: Mark Walsh who has given me muchvaluable feedback in the initial formulation of this project, and Barbara Lovenvirthwho has done a great job managing the project and keeping me on track. I alsothank Jill Stoodley and the staff at Artech for their help in the production of thebook.

No acknowledgment will be complete without mentioning my wife, Jenny, whohas supported all my endeavors with a gentle spirit and has always encouraged me. Ican always count on her for being there, and I am very much thankful for her. Lastand not the least, I would like to mention my son, Daniel, who has been a source ofmy joy; his laughter and cheerful spirit have always given me strength during chal-lenging parts of this project, and this book is also dedicated to him.

xvii

Page 20: 3G CDMA200 Wireless System Engineering

.

Page 21: 3G CDMA200 Wireless System Engineering

C H A P T E R 1

Introduction to 3G CDMA

1.1 Third Generation Systems

While there are several wireless standards and systems that qualify as third genera-tion (3G) systems, this book specifically deals with the IS-2000 implementation of3G. In the mid-1990s, the International Telecommunication Union (ITU) initiatedan effort to develop a framework of standards and systems that will provide wirelessand ubiquitous telecommunications services to users anywhere at anytime. Subse-quently, International Mobile Telecommunications-2000 (IMT-2000), a subgroupof the ITU, published a set of performance requirements of 3G. It is useful to reviewthe performance requirements of a 3G wireless system, which are as follows (forboth packet-switched and circuit-switched data):

• A minimum data rate of 144 Kbps in the vehicular environment;• A minimum data rate of 384 Kbps in the pedestrian environment;• A minimum data rate of 2 Mbps in the fixed indoor and picocell environment.

In addition, in all environments the system must support same data rates forboth forward and reverse links (symmetric data rates), as well as support differentdata rates for both forward and reverse links (asymmetric data rates) [1].

Some standards and systems such as Universal Mobile Telephone System(UMTS) are implemented in the new 3G spectrum (e.g., in Europe). While otherstandards and systems such as IS-2000 can introduce 3G services in spectrumsalready used by second generation (2G) systems (e.g., in North America). The lattercase takes into account those investments already deployed in the field where usefuland necessary [2]. The correction in the valuation of high-technology assets in early2000 underscores the importance of making calculated infrastructure investmentwhile taking into account the market demand for these services. This considerationis one reason why IS-2000 has gained popularity in the initial deployment of 3G [3].

In addition, as will be seen in later chapters of this book, IS-2000 is backwardcompatible with existing 2G IS-95 systems. This backward compatibility givesIS-2000 two important advantages. First, IS-2000 is able to support the reuse ofexisting IS-95 infrastructure equipment and hence requires only incremental invest-ment to provide 3G services. Second, because IS-2000 represents a natural technicalevolution from its predecessor, there is a lower implementation risk when transi-tioning to 3G.

1

Page 22: 3G CDMA200 Wireless System Engineering

1.2 Protocol Architecture

One architectural difference between the IS-2000 standard and the IS-95 standard isthat IS-2000 calls out explicitly the functions of four different protocol layers. Theselayers are the physical layer, medium access control, signaling link access control,and upper layer.

Physical layer (Layer 1) [4]: The physical layer is responsible for transmittingand receiving bits over the physical medium. Since the physical medium in this caseis over the air, the layer would have to convert bits into waveforms (i.e., modulation)to enable their transmission through air. In addition to modulation, the physicallayer also carries out coding functions to perform error control functions at the bitand frame levels.

Medium access control (MAC) sublayer (Layer 2) [5]: The MAC sublayer con-trols higher layers’ access to the physical medium that is shared among differentusers. In this regard, MAC carries out analogous functions as a MAC entity thatcontrols a local area network (LAN). Whereas a LAN MAC controls different com-puters’ access to the shared bus, the IS-2000 MAC sublayer manages the access ofdifferent (low-speed voice and high-speed data) users to the shared air interface.

Signaling link access control (LAC) sublayer (Layer 2) [6]: The LAC sublayeris responsible for the reliability of signaling (or overhead) messages that areexchanged. Recall that the over-the-air medium is extremely error-prone, and infor-mation messages are at times received (and accepted) with errors. On the otherhand, since signaling messages provide important control functions, these messageshave to be reliably transmitted and received. The LAC sublayer performs a set offunctions that ensure the reliable delivery of signaling messages.

Upper layer (Layer 3) [7]: The upper layer carries out the overall control of theIS-2000 system. It exercises this control by serving as the point that processes all andoriginates new signaling messages. The information (both data and voice) messagesare also passed through Layer 3.

Recall that the IS-95 standard does not explicitly and separately describe thefunctions of each layer. However in IS-95 those functions that are carried out by thelayers do exist. For example, in IS-95 mobile access is logically a function of theMAC sublayer, but its descriptions are lumped together with the other functionswithin a single standard.

At this point the reader may ask why the layered architecture was not employedin IS-95 but now used in IS-2000. The layered architecture is now used in IS-2000because it brings the system into conformance with the 3G architecture delineated inIMT-2000. The IMT-2000 framework calls for different networks to cooperate toprovide services to end users, and the level and extent of these cooperation are moreclearly organized if viewed from the perspective of the layered architecture. Well-defined layer functions provide modularity to the system. As long as a layer still per-forms its functions and provides the expected services, the specific implementation

2 Introduction to 3G CDMA

Page 23: 3G CDMA200 Wireless System Engineering

of its functions can be modified or replaced without requiring changes to the layersabove and below it [8].

Figure 1.1 shows the structure of the protocol architecture used by IS-2000.Without a loss of generality, this figure is shown from the perspective of the mobilestation; a similar figure can also be drawn from the perspective of the base station byreversing the direction of some arrows and changing the placement of some entities.Figure 1.1 is a rather important figure and we will refer to it from time to timethroughout the book. For now, note the three different layers (Layers 1, 2, and 3),the two sublayers in Layer 2 (MAC and LAC), the entities in the layers [e.g., Signal-ing Radio Burst Protocol (SRBP)], and the communication paths among the layersand entities. Also note that the layer structure shown in Figure 1.1 resembles that ofthe Open Systems Interconnection (OSI) Reference Model [9].

1.3 Other Elements of Protocol Architecture

In addition to the individual layers themselves, other important elements of the pro-tocol architecture are described as follows:

Physical channels: The physical channels are the communication paths betweenthe physical layer and the common/dedicated channel multiplex sublayers. Thephysical channels are designated by uppercase letters. In the designation, the first

1.3 Other Elements of Protocol Architecture 3

Reverse link: coding and modulationForward link: demodulation and decoding

Common channelmultiplex sublayer

Dedicated channelmultiplex sublayer

SRBP

f-cs

ch

f-cs

ch

r-cs

chLA

CPD

U

RLP

f-dt

ch

f-ds

ch

r-dt

ch

r-ds

ch

Signaling LAC

f-dt

chvo

ice

r-dt

chvo

ice

Signaling

RLP

SDU

RLP

SDU

L3PD

UL3

PDUUp

per

laye

rsLA

Csu

blay

erM

AC

subl

ayer

Phys

ical

laye

r

Laye

r3

Laye

r2

Laye

r1

Dataservices

Voiceservices

Data burst

Data burst

RL

FL

R-C

CC

HR-

EAC

HR-

AC

H

F-D

CC

HF-

SCH

F-FC

HR-

DC

CH

R-SC

HR-

FCH

F-BC

CH

F-C

CC

HF-

PCH

F-C

PCC

HF-

CA

CH

F-SY

NC

H

Figure 1.1 Structure of the protocol architecture used by IS-2000. (Note that this structure isshown from the perspective of the mobile station. After: [5].)

Page 24: 3G CDMA200 Wireless System Engineering

letter and the dash stand for either forward link (F-) or reverse link (R-), and the lasttwo letters “CH” always stand for “channel.” For example, R-ACH stands forreverse access channel, and F-FCH stands for forward fundamental channel. A listof physical channel names and their designations is shown in Table 1.1; note thatlegacy IS-95 physical channels are denoted with asterisks.

Logical channels: The logical channels are the communication paths between thecommon/dedicated channel multiplex sublayers and higher layer entities. One canthink of logical channels as carrying the logical units of signaling or user informa-tion. Contrast those with physical channels which can be thought of as the actualphysical vehicles that transport the signaling or user information over the air.

The logical channels are designated by lower-case letters. The first letter and thedash stand for either forward link (f-) or reverse link (r-), and the last two letters“ch” always stand for “channel.” For example, r-csch stands for reverse commonsignaling channel, and f-dtch stands for forward dedicated traffic channel. A list oflogical channel names and their designations are shown in Table 1.2.

Data unit: The data units are logical units of signaling and user information thatare exchanged between SRBP entity/Radio Link Protocol (RLP) entity and higherlayer entities. There are two types of data units: payload data units (PDU) and serv-ice data units (SDU). PDU is used to designate those data units that are accepted by a

4 Introduction to 3G CDMA

Table 1.1 Physical Channel Designations in IS-2000

Forward LinkChannelDesignation Channel Name

Reverse LinkChannelDesignation Channel Name

F-SCH Forward supplemental channel R-SCH Reverse supplemental channel

F-SCCH Forward supplemental code channel R-SCCHReverse supplemental codechannel

F-FCH* Forward fundamental channel R-FCH* Reverse fundamental channel

F-DCCH Forward dedicated control channel R-DCCHReverse dedicated control chan-nel

F-PCH* Paging channel

F-QPCH Quick paging channel

R-ACH* Access channel

R-EACH Enhanced access channel

F-CCCH Forward common control channel R-CCCHReverse common controlchannel

F-BCCH Broadcast control channel

F-CPCCH Common power control channel

F-CACH Common assignment channel

F-SYNCH* Sync channel

F-PICH* Forward pilot channel R-PICH Reverse pilot channel

F-TDPICH Transmit diversity pilot channel

F-APICH Auxiliary pilot channel

F-ATDPICHAuxiliary transmit diversity pilotchannel

Page 25: 3G CDMA200 Wireless System Engineering

provider of service from a requester of service, and SDU those data units that aregiven to a provider of service by a requester of service1. The use of PDUs and SDUs isdiscussed in more detail later in Chapter 4 (medium access control), Chapter 5 (linkaccess control), and Chapter 6 (upper layer signaling).

In the MAC sublayer, there are four different entities: SRBP, RLP, commonchannel multiplex sublayer, and dedicated channel multiplex sublayer. Commonchannel multiplex sublayer performs the mapping between the logical com-mon channels (channels that are shared among multiple users) and the physicalcommon channels. Dedicated channel multiplex sublayer performs the mappingbetween the logical dedicated channels (channels that are dedicated to specificusers) and the physical dedicated channels. Note that while dedicated channelscan be used for both signaling and user data, common channels are only usedfor signaling.

SRBP and RLP are protocol entities in the MAC sublayer. They are described inmore detail in Chapter 4. It suffices to say now that SRBP handles common-channelsignaling (as opposed to dedicated-channel signaling) and RLP handles user infor-mation that is packetized in nature.

1.4 Spreading Rate 1 and Spreading Rate 3

Without a loss of generality, this book will focus on Spreading Rate 1 (also knownas “1x”) of IS-2000. Spreading Rate 1 by definition uses one times the chip rate ofIS-95 (i.e., 1.2288 Mcps). See Figure 1.2. In addition, the IS-2000 standard also sup-ports Spreading Rate 3 (also known as “3x”). Spreading Rate 3 is used when higherdata rates are desired. Spreading Rate 3 has two implementation options: directspread (DS) or multicarrier (MC).

On the forward link, Spreading Rate 3 uses the MC option by utilizing threeseparate RF carriers, each spread using a chip rate of 1.2288 Mcps. In this case, theuser data is multiplexed onto three separate RF carriers that are received by themobile. On the reverse link, Spreading Rate 3 uses the DS option. The DS optionallows the mobile to directly spread its data over a wider bandwidth using a chiprate of 3.6864 Mcps. See Figure 1.3. To harmonize with other 3G systems such as

1.4 Spreading Rate 1 and Spreading Rate 3 5

Table 1.2 Logical Channel Designations in IS-2000

Forward LinkChannelDesignation Channel Name

Reverse LinkChannelDesignation Channel Name

f-csch Forward common signaling channel r-cschReverse common signalingchannel

f-dsch Forward dedicated signaling channel r-dschReverse dedicated signalingchannel

f-dtch Forward dedicated traffic channel r-dtch Reverse dedicated traffic channel

1. In the OSI Reference Model, a higher layer entity typically requests services from a lower-layer entity.

Page 26: 3G CDMA200 Wireless System Engineering

UMTS, a Spreading Rate 3 signal can have 625 kHz of guard band on each sideresulting in a total RF bandwidth of 5 MHz.

These options for the forward and reverse links are included in the standard inorder to reduce the complexity of the mobile’s receiver. As readers may have alreadynoticed, the above-stated configurations mean that the mobile’s receiver only has toreceive and demodulate 1x carriers and does not have to receive and demodulate any3x carrier.

Incidentally, a mobile can also receive at Spreading Rate 3 and transmit atSpreading Rate 1. See Figure 1.4. This particular arrangement takes advantage ofthe fact that data rates required for downstreaming are typically higher than thoserequired for upstreaming.

Wider bandwidth options such as 6x, 9x, and 12x are under consideration foreven higher data rate applications. As far as 3G systems are concerned, SpreadingRate 3 satisfies all the performance requirements as set forth by IMT-2000.

6 Introduction to 3G CDMA

Basestation

Mobilestation

1.25 MHz

Forward link

Reverse link

1.25 MHz

Figure 1.2 Spreading Rate 1. A chip rate of 1.2288 Mcps occupies an RF bandwidth of 1.25MHz.

Basestation

Mobilestation

3.75 MHz

Forward link

Reverse link

3.75 MHz

Figure 1.3 Spreading Rate 3.

Page 27: 3G CDMA200 Wireless System Engineering

As a final note: The original intention of the IS-2000 family of standards is toevolve progressively to higher data rates using wider bandwidths (i.e., 3x…12x).However, the current trend seems to be one of deploying high data rate solutionsthat use 1.25 MHz of bandwidth (e.g., 1xEV-DO). There are several advantages ofusing solutions like 1xEV-DO, one of which is that wireless operators can carve outselected 1.25 MHz carriers dedicated to and optimized for high rate data. 1xEV-DOis covered later in Chapters 13–15.

1.5 Differences Between IS-2000 and IS-95

IS-2000 represents a natural technical extension from its IS-95 predecessor, and thisextension can be seen in the fact that IS-2000 users and IS-95 users can coexist in thesame carrier. Although IS-2000 is backward compatible with IS-95, there are manydifferences between IS-2000 and IS-95. We will point out now, by way of introduc-tion, those differences that represent a substantial departure from IS-95. Since therequirement of 3G and IS-2000 is transmitting and receiving at a higher data rate,two types of improvements are needed to enable data rates at or above 144 Kbps:improvements in signaling and improvements in transmission.

1.5.1 Signaling

In order to implement high-rate packet-switched data, IS-2000 needs to dynami-cally acquire and release air link resources, and efficient signaling is required to per-form quick acquisitions and releases of these resources. These new signalingmechanisms include:

• On the forward link, there are new overhead/signaling physical channels.They are quick paging channel (F-QPCH), forward common control channel(F-CCCH), broadcast control channel (F-BCCH), common power controlchannel (F-CPCCH), and common assignment channel (F-CACH).

1.5 Differences Between IS-2000 and IS-95 7

Basestation

Mobilestation

3.75 MHz

Forward link

Reverse link

1.25 MHz

Figure 1.4 Spreading Rate 3 on forward link and Spreading Rate 1 on reverse link.

Page 28: 3G CDMA200 Wireless System Engineering

• On the reverse link, there are new overhead/signaling physical channels. Theyare reverse dedicated control channel (R-DCCH), enhanced access channel(R-EACH), and reverse common control channel (R-CCCH).

• On the reverse link, there are shorter signaling messages. IS-2000 can transmitshorter 5-ms frames on the enhanced access channel (R-EACH). This is doneto reduce the probability of access collision.

• On the forward link, IS-2000 can also transmit shorter signaling messages. Itcan use shorter 5-ms frames (i.e., 1/8 rate) on the forward fundamental chan-nel for this purpose.

In addition, an IS-2000 mobile can now be in one of several modes (e.g., dor-mant mode) to accommodate bursty packet data transmissions and to conserve airlink resources. These modes are described in more detail in Chapter 6 on upper layersignaling.

The new overhead/signaling physical channels on the forward link are discussedin Chapter 2, and the new overhead/signaling physical channels on the reverse linkare discussed in Chapter 3.

1.5.2 Transmission

A higher air link capacity is obviously needed to implement high-rate data, and vari-ous changes are made to improve air link capacity to beyond that of IS-95. Thesechanges are also made to effect a more efficient use of air link resources. Some majorchanges are listed below:

• Forward supplemental channel (F-SCH) and reverse supplemental channel(R-SCH) are added to transport high-rate user data.

• Reverse link now has a reverse pilot channel (R-PICH) to support coherentmodulation on the reverse link.

• Forward link now has fast closed-loop power control (compared with theslower power control in IS-95). Power control groups are transmitted on thereverse pilot channel to enable fast closed-loop power control of the forwardlink.

• In addition to power controlling the traffic channels, IS-2000 can also powercontrol the signaling channel (i.e., forward dedicated control channel[F-DCCH]).

Supplemental channels are discussed in more detail in Chapter 2 and Chapter 3.IS-2000 power controls are discussed in more detail in Chapter 7. Other transmis-sion improvements include the implementation of a more efficient quadraturephase-shift keying (QPSK) in the modulation stage and the use of more efficientturbo codes for high date rate transmissions.

1.5.3 Concluding Remarks

The differences between IS-2000 and IS-95 are not limited to those introducedabove. Throughout the book, we will regularly point out, where appropriate, more

8 Introduction to 3G CDMA

Page 29: 3G CDMA200 Wireless System Engineering

differences to which system engineers and planners should pay attention. Notingthese differences is important because being aware of them not only facilitates theunderstanding of 3G IS-2000, but also leverages the experience already gained inoperating 2G IS-95 systems.

References

[1] ITU-R Recommendation M.1225, Guidelines for Evaluation of Radio Transmission Tech-nologies for IMT-2000, International Telecommunication Union, 1997.

[2] Prasad, R., W. Mohr, and W. Konhauser (eds.), Third Generation Mobile CommunicationSystems, Norwood, MA: Artech House, 2000, p. 2.

[3] The Economist, “Mobile Telecoms: Time for plan B,” Economist, September 28–October4, 2002, pp. 57–58.

[4] TIA/EIA/IS-2000.2-A, Physical Layer Standard for cdma2000 Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

[5] TIA/EIA/IS-2000.3-A, Medium Access Control (MAC) Standard for cdma2000 SpreadSpectrum Systems, Telecommunications Industry Association, March 2000.

[6] TIA/EIA/IS-2000.4-A, Signaling Link Access Control (LAC) Standard for cdma2000Spread Spectrum Systems, Telecommunications Industry Association, March 2000.

[7] TIA/EIA/IS-2000.5-A, Upper Layer (Layer 3) Signaling Standard for cdma2000 SpreadSpectrum Systems, Telecommunications Industry Association, March 2000.

[8] Forouzan, B. A., Data Communications and Networking, New York: McGraw-Hill, 2004.[9] ITU-T Recommendation X.210, Information Technology–Open Systems Interconnec-

tion–Basic Reference Model: Conventions for the Definition of OSI Services, InternationalTelecommunication Union, 1993.

1.5 Differences Between IS-2000 and IS-95 9

Page 30: 3G CDMA200 Wireless System Engineering

.

Page 31: 3G CDMA200 Wireless System Engineering

C H A P T E R 2

Physical Layer: Forward Link

2.1 Introduction

The physical layer is responsible for transmitting and receiving bits (organized inframes) over the physical medium. The physical layer carries out coding functions toenable error correction and detection at the bit and frame levels. Besides coding, thelayer would have to convert bits into waveforms (i.e., modulation) and vice versa toenable their transmission over the air.

In addition to coding and modulation, the physical layer also carries out thechannelization function by which different users of the system can be distinguishedfrom one another. In a shared direct sequence spread spectrum system (such asIS-2000 and IS-95), channelization is done via the use of orthogonal and near-orthogonal codes.

This chapter deals with the physical channels that exist on the forward link inthe IS-2000 system, and their descriptions are organized into two broad categories:signaling channels and user channels.

Signaling channels, described in Section 2.3, are those channels that carry sig-naling and control information. Signaling channels can be further classified into twotypes: dedicated and common channels. The F-DCCH is a dedicated signaling chan-nel because this channel, once assigned, is only used by one user. The remaining sig-naling channels, such as the F-CCCH and F-QPCH are examples of commonsignaling channels because they are shared among multiple users.

User channels, described in Section 2.4, are those channels that carry user infor-mation. The user information may be voice, low-rate data (e.g., short message serv-ice or SMS), or high-rate data (e.g., video streaming). There are three physicalchannels primarily used to carry user information: (1) F-FCH which is equivalent toforward traffic channel in IS-95, (2) F-SCCH which is equivalent to forward supple-mental code channel in IS-95 (more specifically, IS-95-B [1]), and (3) F-SCH whichis a new channel in IS-2000. Figure 2.1 shows the categorization of these forwardlink channels, both signaling and user.

Table 2.1 is a list of physical channels used by the physical layer. Both forwardlink and reverse link channels and their descriptions are shown for completeness.Also, for each forward link physical channel, its counterparts on the reverse link areshown in the same row for correspondence. Asterisked channel designations showthose channels that also exist in IS-95 systems. Note that (forward and reverse) fun-damental channels are equivalent to the IS-95 traffic channels. In addition, bold-faced channel names show those channels that are collectively known as the

11

Page 32: 3G CDMA200 Wireless System Engineering

12 Physical Layer: Forward Link

Signalingchannels

Userchannels

Commonchannels

Forward dedicated control channel (F-DCCH)

Paging channel (F-PCH*)Quick paging channel (F-QPCH)Forward common control channel (F-CCCH)Broadcast control channel (F-BCCH)Common assignment channel (F-CACH)Common power control channel (F-CPCCH)Sync channel (F-SYNCH*)Forward pilot channel (F-PICH*)Transmit diversity pilot channel (F-TDPICH)Auxiliary pilot channel (F-APICH)Auxiliary transmit diversity pilot channel (F-ATDPICH)

Forward fundamental channel (F-FCH*)Forward supplemental channel (F-SCH)Forward supplemental code channel (F-SCCH*)

Dedicatedchannels

Figure 2.1 Categories of forward link physical channels. Legacy IS-95 physical channels aredenoted with asterisks.

Table 2.1 Forward Link Physical Channels and Their Reverse Link Counterparts

Channel Channel Name Description Channel Channel Name Description

F-SCHForwardsupplementalchannel

For transmitting userdata while a call isactive; uses convolu-tional or turbo coding

R-SCHReversesupplementalchannel

For transmittinguser data while acall is active;uses convolu-tional or turbocoding

F-SCCH*Forwardsupplementalcode channel

For transmitting userdata while a call isactive; uses convolu-tional coding

R-SCCH*Reversesupplementalcode channel

For transmittinguser data while acall is active;uses convolu-tional coding

F-FCH*Forwardfundamentalchannel

For transmitting userand signaling datawhile a call is active;uses convolutionalcoding

R-FCH*Reversefundamentalchannel

For transmittinguser and signal-ing data while acall is active;uses convolu-tional coding

F-DCCHForwarddedicatedcontrol channel

For transmitting sig-naling and user datawhile a call is active

R-DCCHReversededicatedcontrol channel

For transmittingsignaling anduser data while acall is active

F-PCH* Paging channel

For transmitting MS-specific and systemoverhead data

Page 33: 3G CDMA200 Wireless System Engineering

2.1 Introduction 13

Table 2.1 (continued)

Channel Channel Name Description Channel Channel Name Description

F-QPCHQuick pagingchannel

For telling MS (oper-ating in slotted modewhile in the idle state)whether or not itshould receiveF-CCCH or F-PCHstarting in the nextF-CCCH or F-PCHslot

R-ACH* Access channel

For initialcommunicationswith BS, i.e.,initiating accessand respondingto pages

R-EACHEnhanced accesschannel

For initialcommunicationswith BS, i.e.,initiating accessor responding toMS-specificmessages

F-CCCHForward commoncontrol channel

For transmitting sig-naling data whenF-FCH, F-SCCH,F-SCH, or F-DCCHis not active

R-CCCHReverse commoncontrol channel

For transmittingsignaling anduser data whenR-FCH,R-SCCH,R-SCH, orR-DCCH is notactive

F-BCCHBroadcast controlchannel

For transmittingsignaling data whenF-FCH, F-SCCH,F-SCH, or F-DCCHis not active

F-CPCCHCommon powercontrol channel

For transmittingcommon power con-trol subchannels (onebit per subchannel) topower-control multi-ple R-CCCHs andR-EACHs

F-CACHCommon assign-ment channel

For transmitting sig-naling data to allocateR-CCCH resources

F-SYNCH* Sync channelFor providing MStime and framesynchronization

F-PICH*Forward pilotchannel

For assisting MS toacquire initial timesynchronization

R-PICHReverse pilotchannel

For assisting BSto detect MStransmission

F-TDPICHTransmit diversitypilot channel

For implementingtransmit diversity onthe forward link

Page 34: 3G CDMA200 Wireless System Engineering

“IS-2000 traffic channels” (not to be confused with IS-95 traffic channels) sincethese channels can all carry user traffic data in IS-2000 systems.

2.2 Radio Configurations

In IS-2000, each traffic channel (i.e., forward fundamental channel, forward supple-mental code channel, forward supplemental channel, and forward dedicated controlchannel) can assume different configurations to implement different data rates. Forany one configuration, the associated coding rate, modulation characteristics, andspreading rate would have to be matched to achieve a specified final transmitteddata rate. Table 2.2 shows these different radio configurations [2]. For these radioconfigurations, the data rates shown in the table are maximum data rates. For agiven radio configuration, data rates lower than the maximum are possible.

Note that Radio Configuration 1 and Radio Configuration 2 are backwardcompatible with IS-95 in that they are equivalent to Rate Set 1 and Rate Set 2 ofIS-95. For each radio configuration, the table shows the maximum achievable datarate (instead of all possible data rates). For example, for Radio Configuration 1 thesystem is capable of transmitting at 1.2 Kbps, 2.4 Kbps, 4.8 Kbps, and 9.6 Kbps;only the maximum data rate of 9.6 Kbps is shown. In addition, for each radio

14 Physical Layer: Forward Link

Table 2.1 (continued)

Channel Channel Name Description Channel Channel Name Description

F-APICHAuxiliary pilotchannel

For supporting theuse of spot beam

F-ATDPICHAuxiliary transmitdiversitypilot channel

For implementingtransmit diversity inthe spot beam

Table 2.2 Radio Configurations on the Forward Link

RadioConfiguration Coding Rate R Modulation Spreading Rate

MaximumData Rate

1 1/2 BPSK 1 9.6 Kbps

2 1/2 BPSK 1 14.4 Kbps

3 1/4 QPSK 1 153.6 Kbps

4 1/2 QPSK 1 307.2 Kbps

5 1/4 QPSK 1 230.4 Kbps

6 1/6 QPSK 3 307.2 Kbps

7 1/3 QPSK 3 614.4 Kbps

8 1/4 (20 ms) QPSK 3 460.8 Kbps

1/3 (5 ms)

9 1/2 (20 ms) QPSK 3 1.0368 Mbps

1/3 (5 ms)

Page 35: 3G CDMA200 Wireless System Engineering

configuration the coding rate R is normally the same regardless of the size of theframe (20 ms or 5 ms). But for Radio Configurations 8 and 9 (i.e., Spreading Rate3), the coding rate is dependent on the size of the frame transmitted.

2.3 Signaling Channels

One of the key requirements of 3G is high-data rate. In order to meet this require-ment one needs to make the physical layer more efficient. Recall that in 2G IS-95,while a call is active signaling information is typically carried by the traffic channel(i.e., fundamental channel). In doing so, signaling bits rob traffic channel’s ability tocarry user data bits.

3G IS-2000 deals with this issue by implementing separate signaling channelsthat carry signaling information. Although signaling data can still be carried by thefundamental channel, IS-2000 has the option of sending signaling data on separatesignaling channels. This frees up fundamental channel’s and supplemental channel’scapability to transport more user data.

2.3.1 Forward Dedicated Control Channel (F-DCCH)

The F-DCCH is a unique signaling channel in two respects:

• Unlike other signaling channels, the F-DCCH is a dedicated signaling channel.Once assigned, the F-DCCH is only allocated to one designated user. All othersignaling channels (to be described later) are common to and shared withother users.

• Just as the forward fundamental channels can carry signaling data (throughdim-and-burst and blank-and-burst), the F-DCCH can carry user data. Thekind of user data that the F-DCCH carries is typically low-rate (such as SMS).Such data service requests are sporadic in nature and short in duration. Forsuch transmission requests, instead of expending resources to set up a full-fledge fundamental channel or supplemental channel, the system can chooseto temporarily suspend transmitting signal data and start sending user dataover the F-DCCH.

In addition, both 20-ms and 5-ms frame formats are supported by the F-DCCH.For example, one 20-ms frame format for the F-DCCH is 192 bits in length consist-ing of 172 information bits, 12 cyclic redundancy check (CRC) bits, and 8 encodertail bits. This gives an F-DCCH data rate of (192 bits/20 ms) 9.6 Kbps. See Figure2.2. Note that in this case, this F-DCCH frame has the same capacity as an IS-95Rate Set 1 paging channel frame. On the other hand, a 5-ms frame structure for theF-DCCH is 48 bits in length consisting of 24 information bits, 16 CRC bits, and 8encoder tail bits. This gives an F-DCCH data rate of (48 bits/5 ms) also 9.6 Kbps.Also see Figure 2.2. Note that a 5-ms frame obviously does not have as much data-carrying capacity as a 20-ms frame.

The reason why 5-ms frames are necessary is that at times a signaling messageis short and cannot fill up the entire (traditional) 20-ms frame, and it would be

2.3 Signaling Channels 15

Page 36: 3G CDMA200 Wireless System Engineering

inefficient to transmit a short minimessage using a 20-ms frame. Using a 5-ms frameto transport a short signaling message is a more efficient use of the air link resources.

An important type of signaling data that the F-DCCH carries is power controlbits used to power-control the reverse link. Recall that in IS-95 the power controlbits are multiplexed onto the forward traffic channel at 800 bps in power controlgroups. In a similar fashion, the power control bits can be multiplexed onto theF-DCCH as well. The structure and organization of the power control groups on theF-DCCH is referred to as forward power control subchannel. In effect, a forwardpower control subchannel exists on the F-DCCH to transport the power controlbits.

The mobile uses these power control bits to perform closed-loop power controlof the reverse dedicated control channel, reverse fundamental channel, and reversesupplemental channel.

2.3.2 Quick Paging Channel (F-QPCH)

The F-QPCH is a new physical channel used in IS-2000 to improve the efficiencyof sending page messages. The IS-95 F-PCH, while effective, does have somedrawbacks:

• In the nonslotted mode the mobile has to monitor continuously the entire pag-ing channel slot, which in IS-95 lasts 80 ms. As a result, the mobile expends alot of battery power to perform this continuous monitoring.

• In the slotted mode the mobile monitors only those time slots that are assignedto it. While this does save some battery power, it is still inefficient. From thebase station’s perspective, it is inefficient because when the base station has a

16 Physical Layer: Forward Link

20-ms frame (9.6 Kbps)

5-ms frame (9.6 Kbps)

172 information bits

24informationbits

8encodertail bits

12CRCbits

8encodertail bits

16CRCbits

Figure 2.2 Examples of 20-ms and 5-ms F-DCCH frames.

Page 37: 3G CDMA200 Wireless System Engineering

mobile-specific page to send, it cannot immediately send it. The base stationhas to wait for the correct slot to come along to send the page. As a result, themobile often does not receive its designated pages immediately. From themobile’s perspective, while the mobile saves some battery power by onlymonitoring its assigned slot, the assigned slot still lasts 80 ms. At the begin-ning of its assigned slot, the mobile still has to wake up to monitor the entire80-ms slot, and most of the time there is no page directed at the mobile.

In IS-2000, the F-QPCH is added to alleviate the drawbacks cited above. If thereis a page directed to a mobile, the base station first uses the F-QPCH to send shorterpaging indicator bits to the mobile. The mobile monitors its designated paging indi-cators. If the paging indicators show that there is no mobile-specific page, then themobile does nothing. If the paging indicators show that there is a mobile-specificpage coming in, then the mobile wakes up and monitors its assigned paging channelslot. Note that in this regard, the F-QPCH works with a paging channel operating inslotted mode. In addition, the F-QPCH can also work with a forward common con-trol channel operating in slotted mode.

2.3.2.1 Paging Indicators

Figure 2.3 shows in more detail how the F-QPCH works in conjunction with theF-PCH. As one can see in the figure, a paging channel slot and a quick paging chan-nel slot both last 80 ms, and quick paging channel slots are offset from (ahead of)paging channel slots by 20 ms. Each quick paging channel is divided into four 20-msportions. In this case, let’s assume that a mobile’s assigned paging channel slot is slotY. Instead of always monitoring paging channel slot Y, the mobile would monitor

2.3 Signaling Channels 17

Paging channel slot (Y)

Quick paging channel slot (y)

Z

20-msportion

y2 y4 z2 z4y1 y3 z1 z3

YX

p p

p: Paging indicator

80-ms

80-ms

Figure 2.3 Channel format: F-QPCH. As an example, the figure shows two paging indicatorslocated in the second and fourth 20-ms portions of the quick paging channel slot (y).

Page 38: 3G CDMA200 Wireless System Engineering

its paging indicators in the quick paging channel slot (y) that comes before theassigned paging channel slot (Y).

In a quick paging channel slot, the mobile always monitors two paging indica-tors. The two paging indicators either fall in the first 20-ms portion and in the third20-ms portion (e.g., y1 and y3), or fall in the second 20-ms portion and in the fourth20-ms portion (e.g., y2 and y4). So in our example, if two mobiles are both assignedpaging channel slot Y, the first mobile may monitor a paging indicator in y1 and apaging indicator in y3; the second mobile may monitor a paging indicator in y2 anda paging indicator in y4. In actuality, the exact position of a paging indicator in the20-ms portion is determined by a hash algorithm, the same type of algorithm thatdetermines the assigned paging channel slot for a mobile operating in the slottedmode.

2.3.2.2 Other Indicators

In addition to carrying paging indicators, the F-QPCH also carries two other typesof indicators: broadcast indicators and configuration change indicators. The mobilemonitors its broadcast indicators to check if it needs to monitor its assigned slot (forbroadcast messages) on the forward common control channel or paging channel.Furthermore, all mobiles monitor configuration change indicators; these indicatorsare used to inform mobiles of a change in configuration parameters (e.g., neighborlist) [2].

The relative positions of broadcast and configuration change indicators areshown in Figure 2.4. As shown in the figure, the number of broadcast and configura-tion change indicators depends on the data rate of the F-QPCH.

2.3.2.3 Characteristics of Quick Paging Channel

One distinguishing feature of the F-QPCH is that this physical channel has no errorprotection. This means that the bits sent on the F-QPCH do not have CRC bits

18 Physical Layer: Forward Link

Quick paging channel slot (y)

20-msportion

y2 y4 z2 z4y1 y3 z1 z3

b bc cb bc c

b: Broadcast indicatorc: Configuration change indicator

b=4 and c=4 if F-QPCH data rate = 4.8 bpsKb=2 and c=2 if F-QPCH data rate = 2.4 bpsK

80-ms

Figure 2.4 Broadcast and configuration change indicators on the F-QPCH.

Page 39: 3G CDMA200 Wireless System Engineering

added, are not convolutionally coded, and are not block-interleaved. The reason forthis design choice is that paging indicator bits need to be quickly demodulated at thereceiver so a decision can be made quickly regarding whether or not to monitor thepaging channel slot that follows. Not needing to check the CRC bits, convolution-ally decode all the bits, and deinterleave save a lot of processing time. Note that thisis the same reason for not error-protecting the power control bits in IS-95 (and inIS-2000). Power control bits need to be demodulated quickly so that power controldecisions can be made quickly to adapt to changing channel conditions.

An IS-2000 carrier can have up to three quick paging channels. However, con-figuration change indicators and broadcast indicators are only used on the firstquick paging channel [2].

2.3.3 Forward Common Control Channel (F-CCCH)

To further improve the signaling efficiency of the link, IS-2000 added two addi-tional physical signaling channels: F-CCCH and F-BCCH. Recall that the functionsof the paging channel in IS-95 are to deliver (1) specific messages that are intendedfor specific mobiles (e.g., channel assignment message), and (2) broadcast messagesthat are intended for all mobiles (e.g., system parameters message and neighbor listmessage).

Using a single paging channel for these two functions is not very efficientbecause of the queuing characteristics of these two types of messages. The broadcastmessages are sent at more regular intervals, while the specific messages are sentmore irregularly on-demand. As a result, mixing two statistically different types ofmessages on the same channel results in less-than-optimal scheduling of the pagingchannel. Furthermore, recall that IS-95 allows up to seven paging channels per car-rier; since each mobile only monitors one paging channel, if there are more than onepaging channels in the carrier then broadcast system messages would have to beduplicated on all paging channels.

To alleviate the responsibilities of the paging channel, IS-2000 added two addi-tional channels: F-CCCH and F-BCCH. The F-CCCH is used to transmit specificmessages intended for specific mobiles, while the F-BCCH is used to transmitbroadcast system messages intended for all mobiles. Note that although theF-CCCH is “common” in the sense that it is shared by many mobiles, its purpose isto carry mobile-specific messages. The broadcast control channel is described inSection 2.3.4.

Since the function of the F-CCCH is to carry messages (e.g., channel assignmentmessage) that are previously carried by the paging channel, it is no surprise that thestructure of the F-CCCH is similar to that of the paging channel. For example, theF-CCCH consists of F-CCCH slots each lasting 80 ms. What is new in IS-2000 isthat it supports three different frame duration: 20 ms, 10 ms, and 5 ms. For exam-ple, a 20-ms frame for the F-CCCH may be 192 bits in length consisting of 172information bits, 12 CRC bits, and 8 encoder tail bits. This gives an F-CCCH datarate of (192 bits/20 ms) 9.6 Kbps. See Figure 2.5. Note that in this case, thisF-CCCH frame has the same capacity as an IS-95 Rate Set 1 paging channel frame.Other data rates of 19.2 Kbps and 38.4 Kbps are also supported. Figure 2.5 givessome examples of F-CCCH frame structures.

2.3 Signaling Channels 19

Page 40: 3G CDMA200 Wireless System Engineering

The F-CCCH can also be used in conjunction with the F-QPCH. Recall that thequick paging channel is a new physical channel used in IS-2000 to improve the effi-ciency of sending page messages. For example, a mobile does not have to monitorthe F-CCCH all the time for page messages intended for it. Rather, by monitoring itspaging indicators on the quick paging channel, the mobile knows whether or not itshould start receiving the F-CCCH in the next F-CCCH slot [2].

2.3.4 Broadcast Control Channel (F-BCCH)

As mentioned previously, the purpose of the F-BCCH is transmitting broadcast sys-tem messages (e.g., system parameters message and access parameters message) tothose mobiles in a base station’s coverage area. Although the F-BCCH performs afunction that is previously carried out by the IS-95 paging channel, the structure ofthe F-BCCH is somewhat different. See Figure 2.6.

20 Physical Layer: Forward Link

20-ms frame (9.6 Kbps)

5-ms frame (38.4 bps)K

172 information bits

172informationbits

8encodertail bits

12CRCbits

8encodertail bits

12CRCbits

20-ms frame (38.4 bps)K

744 information bits8encodertail bits

16CRCbits

10-ms frame (38.4 bps)K

8encodertail bits

16CRCbits

360Informationbits

Figure 2.5 Examples of 20-ms, 10-ms, and 5-ms F-CCCH frames.

Page 41: 3G CDMA200 Wireless System Engineering

As shown in Figure 2.6 instead of using a single slot duration of 80 ms (like thepaging channel and the forward common control channel), the F-BCCH can haveslots that last 40 ms, 80 ms, or 160 ms. In addition, unlike the paging channel andthe forward common control channel the F-BCCH has only one frame format thatlasts 40 ms. Therefore, it is obvious that a 160-ms slot always contains four frames,an 80-ms slot always contains two frames, and a 40-ms slot always contains oneframe.

An F-BCCH frame always lasts 40 ms and always contains 744 informationbits, 16 CRC bits, and 8 encoder tail bits, resulting in a total of 768-bits-per-frame.This gives a (peak) F-BCCH data rate of (768 bits/40 ms) 19.2 Kbps. With sequencerepetition (similar to symbol repetition in IS-95), this peak data rate of 19.2 Kbpscan be throttled down. For example, 2x sequence repetition drops the data rate byhalf to 9.6 Kbps, and 4x sequence repetition drops the data rate by a quarter to 4.8Kbps [2].

2.3.5 Common Assignment Channel (F-CACH)

The function of the F-CACH is for the base station to quickly allocate reverse com-mon control channel (R-CCCH) resources to the different mobiles. As will be dis-cussed in Section 3.3.2, the R-CCCH is used by mobiles to transmit signalinginformation when the R-DCCH or the R-FCH is not active. The scheduling infor-mation for the use of the reverse common control channel is transmitted by theF-CACH.

Because the F-CACH is used to control another signaling channel R-CCCH, theF-CACH is really a signaling channel for a signaling channel. In other words, theF-CACH has to quickly transmit signaling information (to the mobile) so that an

2.3 Signaling Channels 21

40-ms frame(19.2 Kbps peak)

744informationbits

8encodertail bits

16CRCbits

40-ms F-BCCH slot

80-ms F-BCCH slot

160-ms F-BCCH slot

Figure 2.6 F-BCCH structure and frame.

Page 42: 3G CDMA200 Wireless System Engineering

R-CCCH resource can be quickly allocated to transmit some other signaling infor-mation (back to the base station). As such, the F-CACH uses 5-ms frames exclu-sively. Figure 2.7 shows the frame format of the F-CACH. As shown in Figure 2.7,the F-CACH frame consists of 48 bits which yield 9.6 Kbps (= 48 bits/5 ms) [2].

2.3.6 Common Power Control Channel (F-CPCCH)

In addition to power controlling the reverse fundamental channel (R-FCH) and thereverse supplemental channel (R-SCH), IS-2000 has the ability to power control sig-naling channels to further improve air link capacity. The function of the F-CPCCHis to carry signaling information to power control the following reverse link signal-ing channels:

• Reverse common control channel (R-CCCH);• Enhanced access channel (R-EACH).

The F-CPCCH consists of a stream of (power control) bits that is not error-protected. This is because power control bits need to be demodulated rapidly so thatpower control decisions can be made quickly to adapt to changing channel condi-tions. Not needing to check the CRC bits, convolutionally decode all the bits, andde-interleave save a lot of processing time. Note that this is the same reason for noterror-protecting the power control bits in IS-95 (and in IS-2000).

Figure 2.8 shows an example format of the F-CPCCH. Here each F-CPCCHframe (which lasts 20 ms) consists of 16 power control groups. Each power controlgroup lasts 1.25 ms, hence the transmission rate of the power control groups is800-times-per-second (= 1 / 1.25 ms). Each power control group contains 12 powercontrol bit positions. This gives a total of 192 power control bit positions per 20-msframe.

In IS-2000, the forward link uses QPSK modulation which consists of twopaths: the in-phase (I) path and the quadrature (Q) path. The F-CPCCH is struc-tured in such a way that each path contains separate and distinct power control bits.As Figure 2.8 shows, in the I path the first bit position of each power control group isused to transmit power control subchannel 0; the second bit position is used to

22 Physical Layer: Forward Link

5-ms frame(9.6 bps)K

32informationbits

8encodertail bits

8CRCbits

Figure 2.7 F-CACH frame.

Page 43: 3G CDMA200 Wireless System Engineering

transmit power control subchannel 1, and so on. In the Q path the first bit positionof each power control group is used to transmit power control subchannel 12, andthe last bit position in the same power control group is used to transmit power con-trol subchannel 23. Therefore, in this example each power control group is capableof carrying 24 power control subchannels (0–23). Since the same 24 power controlsubchannels are replicated in subsequent common power control groups1, the trans-mission rate of the power control bits for each subchannel is 800-times-per-second.

2.3 Signaling Channels 23

1.25-ms

I (path)

0

11

Power controlsubchannels

12

23

20-ms frame (9.6 Kbps)

PCG 0

PCB

11PC

B11

PCB

2PC

B2

PCB

1PC

B1

PCB

0PC

B0

PCG 1 PCG 15

Q (path)

PCG 0 PCG 1 PCG 15

Figure 2.8 F-CPCCH: 16 power control groups per 20-ms frame.

1. IS-2000 refers to a power control group in the I path and its corresponding power control group in the Qpath as a common power control group.

Page 44: 3G CDMA200 Wireless System Engineering

In actuality, the power control bit positions (and their corresponding powercontrol subchannels) are not arranged sequentially in a power control group.Rather, they are arranged pseudorandomly in a power control group. The long codemask and the long code generator are used to pseudorandomize the bit positions in apower control group. Since the mobile also possesses the same long code mask andthe same long code generator, the exact position of a given power control subchan-nel is known perfectly to the mobile.

In addition to supporting 16 power control groups per 20-ms frame, IS-2000can also support 8 power control groups per 20-ms frame and 4 power controlgroups per 20-ms frame. It is an easy exercise then to calculate the number of powercontrol subchannels supported by these formats:

• For 8 power control groups per 20-ms frame, the F-CPCCH can support atotal of 48 power control subchannels.

• For 4 power control groups per 20-ms frame, the F-CPCCH can support atotal of 96 power control subchannels.

For a F-CCCH, a CDMA carrier can have a maximum of 32 R-CCCHs and amaximum of 32 R-EACHs. Plus if an F-CACH is also active, the same carrier canhave another (maximum) set of 32 R-CCCHs. For each carrier, this gives a maxi-mum total of 96 reverse common control channels and enhanced access channels.These 96 channels can all be power controlled using the 96 power control subchan-nels provided by the 4 power control groups per 20-ms frame on the F-CPCCH [2].Note that each common power control subchannel is used to control the power ofa single mobile.

2.3.7 Pilot Channels

In IS-2000, there are actually four types of pilot channels on the forward link. Theyare:

• Forward pilot channel (F-PICH);• Transmit diversity pilot channel (F-TDPICH);• Auxiliary pilot channel (F-APICH);• Auxiliary transmit diversity pilot channel (F-ATDPICH).

2.3.7.1 Forward Pilot Channel (F-PICH)

The F-PICH is equivalent to the IS-95 pilot channel. This channel is identified byWalsh code w 0

128 . It contains no baseband information in that the basebandsequence is a stream of 1s that are spread by Walsh code w 0

128 , which is also asequence of 1s2. The resulting sequence (still all 1s) is then multiplied by a pair ofquadrature PN codes. Thus the forward pilot channel is effectively the PN codeitself. As in IS-95, the forward pilot channel provides the mobile with timing andphase reference. Each base station sector has only one forward pilot channel.

24 Physical Layer: Forward Link

2. See Chapter 9 on the generation of Walsh codes.

Page 45: 3G CDMA200 Wireless System Engineering

2.3.7.2 Transmit Diversity Pilot Channel (F-TDPICH)

The F-TDPICH is a new signaling channel in IS-2000. This channel is identified byWalsh code w16

128 . It also carries no baseband information in that the basebandsequence is a stream of 1s that are spread by Walsh code w16

128 . The transmit diver-sity pilot channel works with the forward pilot channel to support transmit diver-sity on the forward link (see Chapter 9).

Each base station sector can have at most one transmit diversity pilot channel. Ifthere is one, then the transmit diversity pilot channel is transmitted continuously ata power level that is the same as or lower than that of the forward pilot channel.

2.3.7.3 Auxiliary Pilot Channel (F-APICH)

The F-APICH is a new signaling channel in IS-2000. This channel can be identifiedby a Walsh code or by a quasi-orthogonal function . It carries no baseband informa-tion in that the baseband sequence is a stream of 1s that are spread by its assignedWalsh code or quasi-orthogonal function. The auxiliary pilot channel supports theuse of spot beam on the forward link. If a base station sector has a spot beam(formed by a single antenna or an array antenna) within the coverage area definedby its forward pilot channel, then that spot beam must have an auxiliary pilotchannel.

The auxiliary pilot channel is optional in that IS-2000 does not specify howmany auxiliary pilot channels (or spot beams) a base station sector can have. If thereis one, then the auxiliary pilot channel is transmitted continuously. In addition, ifthere are more than one spot beams then each spot beam is assigned a different aux-iliary pilot channel (which is in turn spread by a different Walsh code or quasi-orthogonal function).

From the mobile’s perspective, the mobile reports the number of auxiliarypilots that it sees using the NUM_AUX_PILOTS field in the origination messageand page response message. For each reported auxiliary pilot, the mobilealso reports parameters such as the phase (PILOT_PN_PHASE), strength(PILOT_STRENGTH), and Walsh code (PILOT_WALSH) if a Walsh code is usedto spread the auxiliary pilot. If a quasi-orthogonal function is used to spread theauxiliary pilot, then the mobile reports that quasi-orthogonal function (QOF)3. Inaddition, the mobile can report information regarding its received auxiliary pilots inthe supplemental channel request message and extended pilot strength measure-ment message.

From the base station’s perspective, the base station specifies informationregarding the auxiliary pilots in messages such as the extended channel assignmentmessage, general neighbor list message, extended neighbor list update message, andcandidate frequency search request message.

2.3.7.4 Auxiliary Transmit Diversity Pilot Channel (F-ATDPICH)

A spot beam itself can also support its own transmit diversity to increase forwardlink gain. If it does, then the spot beam uses the F-ATDPICH in addition to its

2.3 Signaling Channels 25

3. See Chapter 9 for more details on quasi-orthogonal functions.

Page 46: 3G CDMA200 Wireless System Engineering

auxiliary pilot channel. The auxiliary transmit diversity pilot channel can be identi-fied by a Walsh code or by a quasi-orthogonal function. It carries no baseband infor-mation in that the baseband sequence is a stream of 1s that are spread by its assignedWalsh code or quasi-orthogonal function. The auxiliary transmit diversity pilotchannel works with the auxiliary pilot channel to provide orthogonal transmitdiversity to the mobiles using the spot beam.

IS-2000 does not specify how many auxiliary pilot channels a base station sectorcan have. But if a spot beam supports transmit diversity then it has to transmit anauxiliary transmit diversity pilot channel. In addition, if a spot beam uses an auxil-iary transmit diversity pilot channel, then the auxiliary transmit diversity pilot chan-nel transmits at a power level that is the same as or lower than that of the auxiliarypilot channel.

2.4 User Channels

There are three user channels in IS-2000: F-FCH, F-SCCH, and F-SCH. TheF-SCCH is provisioned to provide backward compatibility with IS-95 (more specifi-cally, IS-95-B [1]). Here we focus our discussions on the forward fundamental andsupplemental channels.

2.4.1 Forward Fundamental Channel (F-FCH)

2.4.1.1 Functions

The IS-2000 F-FCH is similar to the IS-95 forward traffic channel in that the pri-mary function of the F-FCH is to carry user data. The following lists the main pur-poses of the IS-95 forward traffic channel:

• Transmission of voice traffic;• Transmission of low-rate data traffic;• Transmission of signaling traffic via dim-and-burst and blank-and-burst

schemes;• Transmission of power control bits to power control the reverse link.

In IS-2000, the F-FCH is also capable of carrying out all the responsibilitieslisted above, but the main advantage is that the IS-2000 F-FCH does not have toperform all of them. Specifically, the transmission of signaling traffic is optional inthat it can be done by the F-FCH or, more efficiently, by other signaling channelsprovided by IS-2000. For example, the F-DCCH can be used to carry signalinginformation; therefore, if both the F-FCH and the F-DCCH are active, then signal-ing information can travel on the F-DCCH, freeing the F-FCH to carry more usertraffic.

Although in IS-2000 signaling messages can be carried by separate signalingchannels, the F-FCH is endowed with improved capabilities to transport signalingmessages. One such capability is the support of shorter 5-ms frames in addition tothe conventional 20-ms frames. Recall that both F-DCCH and F-CCCH alsosupport 5-ms frames to carry shorter signaling messages. The F-FCH has the same

26 Physical Layer: Forward Link

Page 47: 3G CDMA200 Wireless System Engineering

ability to transmit short signaling messages in 5-ms frames as these other signalingchannels.

2.4.1.2 Forward Fundamental Channel Frames

In terms of carrying user traffic, in IS-95 the traffic channel can only support tworadio configurations (or rate sets) and two peak data rates. At Rate Set 1 or a peakdata rate of 9.6 Kbps, the IS-95 traffic channel can support 1.2 Kbps, 2.4 Kbps, 4.8Kbps, and 9.6 Kbps. At Rate Set 2 or a peak data rate of 14.4 Kbps, the IS-95 trafficchannel can support 1.8 Kbps, 3.6 Kbps, 7.2 Kbps, and 14.4 Kbps. In IS-2000, theF-FCH can use one of nine different radio configurations to support rates from 0.75Kbps to 14.4 Kbps.

Regardless of the radio configuration, an IS-2000 F-FCH can support only20-ms and 5-ms frames. Figure 2.9 shows some examples of F-FCH frames (at peakdata rates) for the different radio configurations. Note that Radio Configurations 1and 2 are equivalent to the IS-95 Rate Sets 1 and 2. Readers are referred to Section3.1.3.11.2 of [2] for an exhaustive list of radio configurations, corresponding datarates and frame formats supported by the F-FCH.

2.4.2 Forward Supplemental Channel (F-SCH)

2.4.2.1 Functions

The purpose of IS-2000 F-SCH is to serve as a dedicated transport pipe for high-ratepacket data. Because of the requirement of transmitting packet data at high rates,the F-SCH has two unique characteristics:

• Because it is acting as a high data rate transport pipe, the F-SCH only carriesuser traffic data and does not carry any signaling traffic.

• Because it is used to transmit packet data which is bursty in nature, the exis-tence of the F-SCH is itself bursty. This means that the F-SCH is set up andtorn down rather quickly.

These two characteristics in turn lead to two obvious implications for theF-SCH. First, because the F-SCH cannot carry any signaling traffic, the F-SCH hasto coexist with another physical channel that is able to carry signaling traffic for theF-SCH. In other words, while the F-SCH is active, one of these other physical chan-nels has to be active as well. Some possible operating configurations are:

• F-SCH operating with an F-DCCH: Here the most likely scenario is that themobile is conducting a data-only packet data session, and the forward dedi-cated control channel is used to carry signaling traffic between the base stationand the mobile, while the forward supplemental channel is carrying high-ratetraffic data between them.

• F-SCH operating with an F-FCH: The most likely scenario here is that in addi-tion to conducting a packet data session, the mobile is also having a voice callat the same time. In this scenario the forward supplemental channel is carryinghigh-rate traffic data, and the forward fundamental channel is carrying bothuser voice traffic and signaling traffic.

2.4 User Channels 27

Page 48: 3G CDMA200 Wireless System Engineering

The readers should now recognize the merits of using shorter signaling messagesthat can be carried by small 5-ms frames. In order to support the transmission ofpacket data which is bursty in nature, the F-SCH has to be set up and torn downquickly. These fast assignment and de-assignment of F-SCH resources are done byquick exchanges of these short signaling messages that last no longer than 5 ms. Thenecessity to quickly set up and tear down the F-SCH is why both the forward funda-mental channel and the forward dedicated control channel support 5-ms frames (forquick signaling).

2.4.2.2 Forward Supplemental Channel Frames

In IS-2000, the F-SCH can use one of seven different radio configurations (RadioConfigurations 3 through 9) to support rates from 0.6875 Kbps to 1.0368 Mbps.

28 Physical Layer: Forward Link

20-ms frame (14.4 bps)K

268 information bits

8encodertail bits

12CRCbits

5-ms frame (9.6 bps)K

24informationbits

8encodertail bits

16CRCbits

(Radio Configurations 3, 4, 6, 7 and 5, 8, 9)

20-ms frame (9.6 bps)K

172 information bits

8encodertail bits

12CRCbits

(Radio Configurations 1, 3, 4, 6, 7)

(Radio Configurations 2, 5, 8, 9)

Figure 2.9 Examples of 20-ms and 5-ms F-FCH frames. Note that in the 20-ms frame (14.4Kbps), the 268 information bits include one reserved bit.

Page 49: 3G CDMA200 Wireless System Engineering

It can also support three different frame duration: 20 ms, 40 ms, and 80 ms.Figure 2.10 shows examples of different 20-ms frames for Radio Configuration 4.Figure 2.11 shows examples of different 40-ms frames for Radio Configuration 4,and Figure 2.12 shows examples of different 80-ms frames for RadioConfiguration 4.

In Figures 2.10, 2.11, and 2.12, readers may have noticed that for a given radioconfiguration (e.g., Radio Configuration 4), the longer the frame duration, thelower the peak data rate. For example, the peak data rate supported by a 20-msframe is 307.2 Kbps; this peak date rate drops to 153.6 Kbps for a 40-ms frame, anddown further to 76.8 Kbps for an 80-ms frame. It seems counterintuitive that longerframe duration support lower peak data rates.

It turns out that in IS-2000, longer frame duration (e.g., 40 ms and 80 ms) arenot used for higher data-carrying capacity but for data protection. As the frameduration increases, the corresponding interleaver size can increase as well. The

2.4 User Channels 29

20-ms frame (307.2 bps)K

6,120 information bits 16 CRCbits

8 encodertail bits

20-ms frame (153.6 bps)K

3,048 information bits 16 CRCbits

8 encodertail bits

20-ms frame (76.8 bps)K

1,512 information bits 16 CRCbits

8 encodertail bits

20-ms frame (38.4 bps)K

744 information bits 16 CRCbits

8 encodertail bits

20-ms frame (19.2 bps)K

360 information bits 16 CRCbits

8 encodertail bits

Figure 2.10 Examples of 20-ms F-SCH frames: Radio Configuration 4.

Page 50: 3G CDMA200 Wireless System Engineering

30 Physical Layer: Forward Link

40-ms frame (153.6 bps)K

6,120 information bits 16 CRCbits

8 encodertail bits

40-ms frame (76.8 bps)K

3,048 information bits 16 CRCbits

8 encodertail bits

40-ms frame (38.4 Kbps)

1,512 information bits 16 CRCbits

8 encodertail bits

40-ms frame (19.2 bps)K

744 information bits 16 CRCbits

8 encodertail bits

Figure 2.11 Examples of 40-ms F-SCH frames: Radio Configuration 4.

80-ms frame (76.8 Kbps)

6,120 information bits 16 CRCbits

16 CRCbits

16 CRCbits

8 encodertail bits

8 encodertail bits

8 encodertail bits

80-ms frame (38.4 bps)K

3,048 information bits

80-ms frame (19.2 bps)K

1,512 information bits

Figure 2.12 Examples of 80-ms F-SCH frames: Radio Configuration 4.

Page 51: 3G CDMA200 Wireless System Engineering

consequence of having a longer interleaver size is that the system can combat fadesof longer duration. This results in a better ability to correct burst errors comingfrom longer-term fades [3].

Given their better error-protection properties, why are 40-ms and 80-ms framesnot used in IS-95? The reason is that IS-95 is intended primarily for voice applica-tions, and 20-ms frames are used is because speech statistics are nearly stationary(do not vary much) over a 20-ms interval. In addition, decoding 20-ms frames doesnot result in much noticeable voice delay. On the other hand, using longer durationframes would result in delays that are noticeable during a conversation. This is why40 ms and 80 ms are used by supplemental channels for data transmissions only.

Readers are referred to Section 3.1.3.12.2 of [2] for an exhaustive list of radioconfigurations, corresponding data rates and frame formats supported by theF-SCH.

2.5 Channel Structure

After a physical channel generates a frame, then the physical layer performs theusual functions such as:

• Adding the CRC bits for detecting frame errors;• Coding the bits for correcting bit errors;• Interleaving for combating fades.

These functions are similar to those of IS-95. After block interleaving, the sym-bols undergo long code scrambling, then a gain for that physical channel is applied(the gain is determined by forward power control). In addition, if the physical chan-nel is a forward dedicated control channel or a forward fundamental channel thenpower control bits can be punctured into the symbol stream. Figure 2.13 shows ageneral block diagram up to just before modulation for broadcast control channel,

2.5 Channel Structure 31

Demux

I

Q

Blockinterleaver

Long codescrambling

Channelgain

Modulationsymbols

Long code mask

Figure 2.13 Conceptual block diagram of broadcast control channel4, common assignmentchannel, and forward common control channel.

4. Broadcast control channel has a sequence repetition function between block interleaver and long codescrambler.

Page 52: 3G CDMA200 Wireless System Engineering

common assignment channel, and forward common control channel; Figure 2.14shows a general block diagram up to right before modulation for forward dedicatedcontrol channel, forward fundamental channel, and forward supplemental channel.

As shown in Figures 2.13 and 2.14, the demultiplexer converts one input symbolstream into two output symbol streams. It assigns input symbols alternately to thetwo outputs. As a result, symbols are transmitted using two different paths: I and Q.As we will see later, this quadrature arrangement is one of the reasons why IS-2000has a capacity higher than that of IS-95.

Figures 2.13 and 2.14 show those functions that are unique to IS-2000, and onlythose channels of Spreading Rate 1 are shown. Note that a forward supplementalchannel cannot have power control bits punctured into it.

2.6 Modulation

After demultiplexing, the I and the Q symbols are channelized and spread by aWalsh code (or quasi-orthogonal function) assigned to that physical channel. TheWalsh code (or quasi-orthogonal function) runs at the chip rate of 1.2288 Mcps forSpreading Rate 1.

After channelization, the chip stream undergoes another layer of spreading bythe short PN codes. Similar to IS-95, there are two short PN codes (pI and pQ), andthey are the same as those used to spread the forward pilot channel (for identifying aspecific base station sector). pI and pQ are different short PN codes in that they areproduced by two different generator polynomials. However, both codes start at thesame time and are offset by the same amount of chips. This is important becauseeach base station sector is uniquely identified by its short PN code offset. Figure 2.15shows how the I and the Q symbols are channelized and spread in a complexmanner.

Although Figure 2.15 may look complex at first, it is really just a way to dia-grammatically implement the multiplication of two complex numbers. Because

32 Physical Layer: Forward Link

Demux

I

Q

Blockinterleaving

Long codescrambling

Channelgain

Modulation symbols

Powercontrolpuncturing*

Power control bitsLong code mask

*Only active for F-DCCH and F-FCH

Figure 2.14 Conceptual block diagram of forward dedicated control channel, forward funda-mental channel, and forward supplemental channel5.

5. Forward supplemental channel does not have punctured power control bits.

Page 53: 3G CDMA200 Wireless System Engineering

there are now two baseband symbol streams I and Q, these two symbol streams canbe succinctly represented by one complex number

I jQ+

After multiplying with the Walsh code (or quasi-orthogonal function), the com-plex number becomes

w (I jQ) w I jw Qi i i+ = + (2.1)

To spread the above using the two short PN codes, we multiply the above com-plex number (wi I + jwi Q) by another complex number made up of the two shortPN codes (pI + jpQ),

(w I jw Q)(p jp )w Ip jw Ip jw Qp w Qpw (

i i I Q

i I i Q i I i Q

i

+ + =+ + − =

Ip Qp ) jw (Ip jQp )I Q i Q I− + +(2.2)

Note that the real part of (2.2) corresponds to the input into the in-phase branchof the QPSK modulator, and the imaginary part of (2.2) corresponds to the inputinto the quadrature branch of the QPSK modulator (see Figure 2.15).

As a last note, it is easy to see that if Q is zero (as in the case of IS-95), the modu-lation in Figure 2.15 collapses back to that of IS-95. See Figure 2.16. In this case, I isthe only symbol stream, which is duplicated on both the in-phase and the quadra-ture branches of the QPSK modulator. In fact, Radio Configurations 1 and 2 areimplemented in IS-2000 by zeroing out the Q symbol stream.

2.6 Modulation 33

I

wi or QOF

Q

pI

pQ

pQ

pI

BF

BF

BF: Baseband filter

cos f t(2 )π c

sin(2 )πf tc

Y t( )

+

+

+

w Ii

w Qi

w Ipi I

w Qpi Q

w Ipi Q

w Qpi I

w Ip w Qpi I i Q−

w Ip w Qpi Q i I+

Figure 2.15 Complex modulation: Forward link. For the sake of simplicity, Walsh rotation is notshown.

Page 54: 3G CDMA200 Wireless System Engineering

2.7 Capacity Gain: Forward Link

One reason IS-2000 has a higher physical layer capacity than IS-95 is becauseIS-2000 uses QPSK whereas IS-95 uses BPSK6. Both QPSK and BPSK have the samebandwidth because both have the same transmission symbol rate. However, QPSKencodes two chips-per-symbol whereas BPSK encodes only one chip-per-symbol. Bytransmitting two independent symbol streams in two dimensions, QPSK can doublethe data rate using the same bandwidth.

To take advantage of this higher physical layer capacity on the forward link,IS-2000 also increased the maximum length of its Walsh codes from 64 to 128(Spreading Rate 1). The increased length means that there are now more Walshcodes available, and more available Walsh codes means that the forward link cannow support more physical channels at the same time. With the increased number ofavailable codes, an IS-2000 base station likely would become interference limited(exhaust its power resources at the base station) first before it becomes code limited(exhausts its available codes). However, an IS-2000 base station likely wouldbecome code limited first if a user demands high data rate and thus requires a shortWalsh code (i.e., low spreading factor). See Chapter 9 for more details on the con-straints of Walsh code assignment.

34 Physical Layer: Forward Link

I

wi or QOF

pI

pQ

BF

BF

cos(2 )πf tc

sin(2 )πf tc

Y t( )

+

w Ii

w Ipi I

w Ipi Q+

Figure 2.16 Collapsed complex modulation as in the cases of Radio Configuration 1 and RadioConfiguration 2.

6. Although IS-95 also has a QPSK modulator, its in-phase and quadrature branches carry identical symbols.Thus strictly speaking, IS-95 uses two identical BPSK modulators.

Page 55: 3G CDMA200 Wireless System Engineering

References

[1] TIA/EIA-95-B, Mobile Station-Base Station Compatibility Standard for Wideband SpreadSpectrum Cellular Systems, Telecommunications Industry Association, March 1999.

[2] TIA/EIA/IS-2000.2-A, Physical Layer Standard for cdma2000 Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

[3] Yang, S. C., CDMA RF System Engineering, Norwood, MA: Artech, 1998.

Selected Bibliography

TIA-97, Recommended Minimum Performance Standards for cdma2000 Spread Spectrum BaseStations, Telecommunications Industry Association, February 2003.

TIA-98, Recommended Minimum Performance Standards for cdma2000 Spread SpectrumMobile Station, Telecommunications Industry Association, February 2003.

Garg, V. K., IS-95 CDMA and cdma2000: Cellular/PCS Systems Implementation, Upper SaddleRiver, NJ: Prentice Hall PTR, 2001.

2.7 Capacity Gain: Forward Link 35

Page 56: 3G CDMA200 Wireless System Engineering

.

Page 57: 3G CDMA200 Wireless System Engineering

C H A P T E R 3

Physical Layer: Reverse Link

3.1 Introduction

As described in Chapter 2, the physical layer is responsible for transmitting andreceiving bits (organized in frames) over the physical medium. As such, the layerperforms functions such as coding, modulation, and channelization. This chapterdeals with the physical channels that exist on the reverse link of the IS-2000 system,and their descriptions are organized into two broad categories: signaling channelsand user channels.

Like their forward link counterparts, the signaling channels can also be classi-fied into two types, dedicated and common channels, depending on whether or notthe channel is assigned to only one user or can be used by multiple users. TheR-DCCH is an example of a dedicated signaling channel. On the other hand, theR-CCCH, the R-ACH, and the R-EACH are examples of common signaling chan-nels. The signaling channels are described in Section 3.3.

On the reverse link, user channels are used to carry user information from themobile back to the base station. There are three physical channels used primarily forthis purpose: (1) R-FCH which is equivalent to the reverse traffic channel in IS-95,(2) R-SCCH which is equivalent to the reverse supplemental code channel in IS-95(more specifically, IS-95-B [1]), and (3) R-SCH which is a new channel in IS-2000.Figure 3.1 shows the categorization of these reverse link channels.

37

Signalingchannels

Userchannels

Commonchannels

Reverse pilot channel (R-PICH)Reverse dedicated control channel (R-DCCH)

Access channel (R-ACH*)Enhanced access channel (R-EACH)Reverse common control channel (R-CCCH)

Reverse fundamental channel (R-FCH*)Reverse supplemental channel (R-SCH)Reverse supplemental code channel (R-SCCH*)

Dedicatedchannels

Figure 3.1 Categories of reverse link physical channels. Legacy IS-95 physical channels aredenoted with asterisks.

Page 58: 3G CDMA200 Wireless System Engineering

Table 3.1 shows a list of physical channels used by the physical layer. This tableis identical to Table 2.1 and is reproduced here for completeness. Note that aster-isked channel designations show those channels that also exist in IS-95. Also, bold-faced channel names show those channels that are collectively known as the IS-2000traffic channels since these channels can all carry user traffic data in IS-2000systems.

38 Physical Layer: Reverse Link

Table 3.1 Reverse Link Physical Channels and Their Forward Link Counterparts

Channel Channel Name Description Channel Channel Name Description

F-SCHForwardsupplementalchannel

For transmitting userdata while a call isactive; uses convolu-tional or turbocoding

R-SCHReverse supple-mental channel

For transmittinguser data while acall is active; usesconvolutional orturbo coding

F-SCCH*Forwardsupplementalcode channel

For transmitting userdata while a call isactive; uses convolu-tional coding

R-SCCH*Reversesupplementalcode channel

For transmittinguser data while acall is active; usesconvolutionalcoding

F-FCH*Forwardfundamentalchannel

For transmitting userand signaling datawhile a call is active;uses convolutionalcoding

R-FCH*Reversefundamentalchannel

For transmittinguser and signalingdata while a call isactive; uses convo-lutional coding

F-DCCHForwarddedicated controlchannel

For transmitting sig-naling and user datawhile a call is active

R-DCCHReverse dedicatedcontrol channel

For transmittingsignaling and userdata while a call isactive

F-PCH* Paging channelFor transmittingMS-specific and sys-tem overhead data

F-QPCHQuick pagingchannel

For telling MS (oper-ating in slotted modewhile in the idlestate) whether or notit should receiveF-CCCH or F-PCHstarting in the nextF-CCCH or F-PCHslot

R-ACH* Access channel

For initial commu-nications with BS,i.e., initiatingaccess andresponding topages

R-EACHEnhanced accesschannel

For initial commu-nications with BS,i.e., initiatingaccess or respond-ing to MS-specificmessages

Page 59: 3G CDMA200 Wireless System Engineering

3.2 Radio Configurations

Similar to the forward link, the reverse link traffic channels (i.e., reverse fundamen-tal channel, reverse supplemental code channel, reverse supplemental channel, andreverse dedicated control channel) can also assume different configurations toimplement different data rates. But the difference here is that the number of radioconfigurations on the reverse link is less than those on the forward link. While theforward link can have up to nine different radio configurations, the reverse link canonly have up to six. Table 3.2 shows these different radio configurations [2]. Forthese radio configurations, the data rates shown in the table are maximum

3.2 Radio Configurations 39

Table 3.1 (continued)

Channel Channel Name Description Channel Channel Name Description

F-CCCHForward commoncontrol channel

For transmittingsignaling data whenF-FCH, F-SCCH,F-SCH, or F-DCCHis not active

R-CCCHReverse commoncontrol channel

For transmittingsignaling and userdata when R-FCH,R-SCCH, R-SCH,or R-DCCH is notactive

F-BCCHBroadcast controlchannel

For transmittingsignaling data whenF-FCH, F-SCCH,F-SCH, or F-DCCHis not active

F-CPCCHCommon powercontrol channel

For transmittingcommon powercontrol subchannels(one bit per sub-channel) to power-control multipleR-CCCHs andR-EACHs

F-CACHCommon assign-ment channel

For transmittingsignaling data toallocate R-CCCHresources

F-SYNCH* Sync channelFor providing MStime and framesynchronization

F-PICH*Forward pilotchannel

For assisting MS toacquire initial timesynchronization

R-PICHReverse pilotchannel

For assisting BSto detect MStransmission

F-TDPICHTransmit diversitypilot channel

For implementingtransmit diversity onthe forward link

F-APICHAuxiliary pilotchannel

For supporting theuse of spot beam

F-ATDPICHAuxiliary transmitdiversity pilotchannel

For implementingtransmit diversity inthe spot beam

Page 60: 3G CDMA200 Wireless System Engineering

data rates. For a given radio configuration, data rates lower than the maximum arepossible.

Radio Configuration 1 and Radio Configuration 2 are backward compatiblewith IS-95 in that they are equivalent to Rate Set 1 and Rate Set 2 of IS-95. In fact,Radio Configurations 1 and 2 differ from the rest of the radio configurations in thatRadio Configurations 1 and 2 use the 64-ary orthogonal modulation to be compati-ble with IS-95, while Radio Configurations 3 through 6 use the coherent binaryphase shift keying (BPSK). The use of coherent modulation is now possible inIS-2000 because of the addition of the R-PICH.

For each radio configuration, the table shows the maximum achievable data rate(instead of all possible data rates). For example, for Radio Configuration 4 the sys-tem is capable of transmitting at 1.8 Kbps, 3.6 Kbps, 7.2 Kbps, 14.4 Kbps, 28.8Kbps, 57.6 Kbps, 115.2 Kbps, and 230.4 Kbps; only the maximum data rate of230.4 Kbps is shown.

3.3 Signaling Channels

This section describes the physical signaling channels (both dedicated and common)that exist in an IS-2000 system.

3.3.1 Reverse Dedicated Control Channel (R-DCCH)

The R-DCCH is a dedicated signaling channel in that once assigned, it is only allo-cated to one designated user. In addition, just as the reverse fundamental channelscan carry signaling data (through dim-and-burst and blank-and-burst), theR-DCCH can carry user data (i.e., low-rate data such as SMS).

The R-DCCH supports both 20-ms and 5-ms frame formats. Examples of 20-msand 5-ms frame formats are shown in Figure 3.2. Readers may notice that theseframe formats are similar to those for the F-DCCH shown in Figure 2.2. In fact, the

40 Physical Layer: Reverse Link

Table 3.2 Radio Configurations on the Reverse Link

RadioConfiguration Coding Rate R Modulation Spreading Rate

MaximumData Rate

1 1/3 64-ary 1 9.6 Kbps

Orthogonal

2 1/2 64-ary 1 14.4 Kbps

Orthogonal

3 1/4 BPSK 1 153.6 Kbps

1/2 BPSK 1 307.2 Kbps

4 1/4 BPSK 1 230.4 Kbps

5 1/4 BPSK 3 153.6 Kbps

1/3 BPSK 3 614.4 Kbps

6 1/4 BPSK 3 460.8 Kbps

1/2 BPSK 3 1.0368 Mbps

Page 61: 3G CDMA200 Wireless System Engineering

frame formats are symmetrical between the forward link and the reverse link (i.e.,the frame formats of the R-DCCH are identical to those of the F-DCCH1) [2].

3.3.2 Reverse Common Control Channel (R-CCCH)

In IS-95, if a mobile wants to send information back to the base station when a callis not active (i.e., when there is no traffic channel assigned), the mobile has to use theonly other physical channel that is available–the access channel. But the problem isthat the access channel is a random-access channel. This means that mobiles trans-mit on the access channel more or less randomly; if there is a collision, then the mes-sages are not received by the base station, and the colliding mobiles would have totransmit again. Further complicating the situation is that some full-fledge messages,such as the authentication challenge response message and the origination message,are sent on the access channel. The transmission of these longer signaling messagesis best done over a channel whose resources are scheduled rather than over onewhose accesses are contention-based.

To minimize the problem of random collisions of long signaling messages on theaccess channel, IS-2000 added two new signaling physical channels–the R-CCCH

3.3 Signaling Channels 41

20-ms frame (9.6 Kbps)

5-ms frame (9.6 bps)K

172 information bits

24informationbits

8encodertail bits

12CRCbits

8encodertail bits

16CRCbits

Figure 3.2 Examples of 20-ms and 5-ms R-DCCH frames.

1. Since the forward link and the reverse link have asymmetrical radio configurations, some mapping of radioconfigurations are needed. The frame structures are identical if we map forward link Radio Configurations3, 4, 6, and 7 to reverse link Radio Configurations 3 and 5, and forward link Radio Configurations 5, 8, and9 to reverse link Radio Configurations 4 and 6.

Page 62: 3G CDMA200 Wireless System Engineering

and the R-EACH. The R-EACH is described in the next section. The R-CCCH is“common” in that it is shared among many mobiles, but the key difference here isthat the use of this channel is scheduled among the different mobiles2. Note that theR-CCCH is only used when there is no R-DCCH or no R-FCH active on the reverselink. As soon as a reverse dedicated control channel and/or reverse fundamentalchannel become active, signaling messages are then sent on either one or both ofthese channels.

In a given CDMA carrier, there is a one-to-one correspondence between anF-CCCH and an R-CCCH. Therefore, it is not surprising that the frame formatssupported by the R-CCCH are exactly the same as its forward link counterpart.Similar to the forward common control channel, the R-CCCH supports three differ-ent frame duration (20 ms, 10 ms, and 5 ms) as well as three different data rates (9.6Kbps, 19.2 Kbps, and 38.4 Kbps). See Figure 3.3.

Despite the identical frame formats used by both the F-CCCH and theR-CCCH, the transmission of the R-CCCH does differ from its forward link coun-terpart. First, before transmitting the actual R-CCCH frame(s) the mobile transmitsa preamble. This is done to help the base station in acquiring the R-CCCH. Second,because the R-CCCH is coherently modulated, a reverse pilot is transmitted at thesame time to aid in its coherent demodulation at the base station. Figure 3.4 illus-trates the transmission of the R-CCCH.

As shown in Figure 3.4, the preamble preceding the R-CCCH frame(s) is noth-ing more than a series of gated reverse pilot channel transmissions. In other words,gated reverse pilot channel transmissions are used as the preamble for R-CCCH.The duration of the gated transmissions t1, the duration of the off time t3, the dura-tion of the last gated transmission t2, the total number of gated transmissions(N + 1), and the total duration of the preamble Tpreamble are completely specified bythe appropriate R-CCCH parameters. Note that to further facilitate the acquisitionof the R-CCCH, the mobile transmits the reverse pilot during the preamble at ahigher power level [2].

3.3.3 Enhanced Access Channel (R-EACH)

Although scheduling mobile transmissions on the R-CCCH (when the reverse fun-damental channel and/or reverse dedicated control channel are not active) solves theproblem of collisions when transmitting large signaling messages, there is still theissue of a mobile’s very first transmission of its access request. This issue is impor-tant because the mobile does not (yet) have any assigned channels or resources whenit first transmits its access request. To transmit its access request, the mobile uses theR-EACH.

The R-EACH is similar to the IS-95 access channel (R-ACH) in that the mobiles’R-EACH transmissions are randomized. Although collisions are still possible, amobile’s R-EACH transmission is typically shorter in duration than a mobile’sR-ACH transmission3. Hence the probability of collisions is smaller on theR-EACH.

42 Physical Layer: Reverse Link

2. In reservation access mode.3. In reservation access mode, only a short 5 ms “header” frame and its preamble are transmitted on the

R-EACH.

Page 63: 3G CDMA200 Wireless System Engineering

In terms of frame formats, the frame formats supported by the R-EACH areidentical to those supported by the R-CCCH with one important exception. In addi-tion to supporting 20-ms, 10-ms, and 5-ms data frames, the R-EACH also supportsa special 5-ms header frame which is used to transmit these short initial accessrequests4. Figure 3.5 shows the format of this 5-ms header frame and some exam-ples of the 20-ms, 10-ms, and 5-ms data frames.

3.3 Signaling Channels 43

20-ms frame (9.6 Kbps)

5-ms frame (38.4 bps)K

172 information bits

172informationbits

8encodertail bits

12CRCbits

8encodertail bits

12CRCbits

20-ms frame (38.4 bps)K

744 information bits8encodertail bits

16CRCbits

10-ms frame (38.4 bps)K

8encodertail bits

16CRCbits

360Informationbits

Figure 3.3 Examples of 20-ms, 10-ms, 5-ms R-CCCH frames.

4. In reservation access mode.

Page 64: 3G CDMA200 Wireless System Engineering

Similar to the R-CCCH transmission, the R-EACH also transmits a preamblebefore transmitting the actual R-EACH frame(s). This is done to help the base sta-tion in acquiring the R-EACH. In addition, because the R-EACH is coherentlymodulated, a reverse pilot is transmitted at the same time to aid in its coherentdemodulation at the base station. Figures 3.6, 3.7, and 3.8 show the different typesof R-EACH transmissions.

Similar to the R-CCCH transmission, the R-EACH preamble consists of a seriesof gated reverse pilot channel transmissions. The mobile transmits the reverse pilotduring preamble at a higher power to facilitate acquisition of the R-EACH. For thepreamble, the duration of the gated transmissions t1, the duration of the off time t3,the duration of the last gated transmission t2, the total number of gated transmis-sions (N + 1), and the total duration of the preamble Tpreamble are completely specifiedby the appropriate R-EACH parameters. Note that in the IS-2000 standard, eachR-EACH transmission shown in Figures 3.6 through 3.8 is referred to as anR-EACH probe [2].

As illustrated in Figures 3.6 through 3.8, the actual R-EACH transmissiondepends on the operative access mode at the time. In reservation access mode (wherethe mobile first transmits a short message on the R-EACH and then gets assigned anR-CCCH), the R-EACH transmission consists of only the preamble and the 5-msheader frame (see Figure 3.6). In basic access mode (where the mobile immediatelytransmits access messages), the R-EACH transmission consists of the preamble andthe longer data frames (see Figure 3.7). In power controlled access mode (where thebase station power controls the R-EACH), the R-EACH transmission consists of thepreamble, the header frame, and the data frames (see Figure 3.8). These differentaccess modes are described in more detail in Chapter 4 on medium access control.

44 Physical Layer: Reverse Link

R-PICH N N+121

R-CCCH

t1 t1 t1 t2

t3

Tpreamble

t3

Preamble R-CCCH frame(s)

Figure 3.4 R-CCCH transmission.

Page 65: 3G CDMA200 Wireless System Engineering

3.3.4 Reverse Pilot Channel (R-PICH)

The R-PICH is a new physical channel used in IS-2000 to help the base station indetecting the reverse link. Recall that in IS-95, the access channel (R-ACH) and thereverse traffic channel (R-FCH) both use 64-ary modulation that does not requirecoherent demodulation. To improve the signal-to-noise ratio performance, IS-2000uses BPSK for the new IS-2000 channels (i.e., reverse dedicated control channel,reverse supplemental channel, etc.). The R-PICH is used to help coherently demodu-late these new channels.

Similar to the forward pilot channel (F-PICH), the R-PICH is an unmodulatedsignal. But the R-PICH differs from the forward pilot channel in some importantaspects:

3.3 Signaling Channels 45

20-ms data frame (9.6 Kbps)

5-ms data frame (38.4 Kbps)

172 information bits 12 CRCbits

8 encodertail bits

172 informationbits

20-ms data frame (38.4 Kbps)

744 information bits16 CRCbits

8 encodertail bits

10-ms data frame (38.4 Kbps)

360 Informationbits 16 CRC

bits8 encodertail bits

12 CRCbits

8 encodertail bits

5-ms header frame (9.6 Kbps)

32 informationbits

8 CRCbits

8 encodertail bits

Figure 3.5 R-EACH header frame and examples of 20-ms, 10-ms, 5-ms R-EACH data frames.

Page 66: 3G CDMA200 Wireless System Engineering

46 Physical Layer: Reverse Link

R-PICH N+1N21

R-EACH

t1 t1 t1 t2

t3

Tpreamble

t3

Preamble R-EACHheaderframe

5 ms

Figure 3.6 R-EACH transmission: Reservation access mode.

R-PICH N+1N21

R-EACH

t1 t1 t1 t2

t3

Tpreamble

t3

Preamble R-EACH data frame(s)

Figure 3.7 R-EACH transmission: Basic access mode.

Page 67: 3G CDMA200 Wireless System Engineering

• Unlike the forward pilot channel, which does not carry any information, theR-PICH does carry information. This information is power control feedbackthat the mobile sends back to the base station. The base station uses this feed-back to power control the forward link.

• To reduce interference, the R-PICH can transmit in gated mode in which someparts of the pilot stream are turned off while others turned on.

These differences are described in the following sections.

3.3.4.1 Power Control Subchannel

The R-PICH is used to carry power control information. The power control signal-ing information carried by the R-PICH helps power control the forward link. Buthere lies a major difference between IS-95 and IS-2000. In IS-95 Rate Set 1, forwardlink power control is done by using information contained in the power measure-ment report messages transmitted by the mobile. Since these messages are carriedin-traffic on the reverse traffic channel, the frequency of these message transmis-sions and hence of forward link power control updates is low. In IS-95 Rate Set 2,forward link power control is done by using the erasure indicator bits contained ineach reverse traffic channel frame. While also a form of in-traffic signaling, the era-sure indicator bits are transmitted at a higher rate (i.e., at the rate of transmission ofeach reverse traffic channel frame); this is once every 20 ms, or 50 times a second.

3.3 Signaling Channels 47

R-PICH N+1N21

R-EACH

t1 t1 t1 t2

t3

Tpreamble

t3

Preamble R-EACHdata frame(s)

R-EACHheaderframe

Figure 3.8 R-EACH transmission: Power controlled access mode.

Page 68: 3G CDMA200 Wireless System Engineering

In IS-2000 (specifically Radio Configurations 3 through 6), the R-FCH and theR-SCH have no facility provisioned to carry any power control feedback back to thebase station. Therefore, power control signaling, in the form of power control bits, iscarried entirely by the R-PICH. One area of improvement in IS-2000 is that the fre-quency of power control update has increased from that in IS-95. In Radio Configu-rations 3 through 6, the power control bits carried by the R-PICH are transmitted ata maximum rate of 800-times-per-second, enabling the rate of forward link powercontrol to increase from a maximum of 50-times-per-second (in IS-95) to a maxi-mum of 800-times-per-second.

Figure 3.9 shows the format of the R-PICH transmission. The power controlsubchannel can be thought of as a structure provided by the R-PICH in which powercontrol bits can be transported. This structure is shown in Figure 3.9. An R-PICHcan be divided into 16 segments called power control groups. Each power controlgroup lasts 1.25 ms. It can then be inferred that for Spreading Rate 1, each powercontrol group contains 1,536 chips (=1.2288 Mcps × 1.25 ms). IS-2000 specifiesthat the first 1,152 chips of a power control group constitute the pilot signal, and thelast 384 chips of the same power control group constitute a power control bit.

As Figure 3.9 shows, if the power control bit is 0 then the last 384 chips of thepower control group are all zeros. If the power control bit is 1 then the same chipsare all ones. Note that in Figure 3.9 since the R-PICH is being transmitted continu-ously, the rate of feedback of power control bits in this case is 1/1.25 ms, or 800-times-per-second.

3.3.4.2 Gating

To reduce interference to other reverse physical channels, the R-PICH can be gated.If the parameter PILOT_GATING_USE_RATE = 1 then the R-PICH operates ingated mode. In this case the gating rate is specified by the parameterPILOT_GATING_RATE. When gating rate = 1, all power control groups are on.When gating rate = 1/2, half of all power control groups are on. When gating rate =1/4, only one quarter of all power control groups are on. Figure 3.10 shows threepossible gating rates.

48 Physical Layer: Reverse Link

all 0sorall 1s

all 0sall 0sorall 1s

all 0sall 0sorall 1s

all 0sall 0sorall 1s

all 0s

0 1 2 15

1.25 ms

16 power control groups

1,152chips

384chips

Figure 3.9 R-PICH format.

Page 69: 3G CDMA200 Wireless System Engineering

On the other hand, if PILOT_GATING_USE_RATE = 0 then the R-PICH oper-ates in nongated mode and there is no gating on the R-PICH. In this case the systemignores the PILOT_GATING_RATE parameter.

It is important to note that the gating rate does not necessarily determine therate of power control feedback. For example, even when the gating rate = 1 the sys-tem has the option of combining all 16 power control bits in a 20-ms period to yieldone single power control feedback. In this case, the rate of feedback of power con-trol is 1/20 ms, or 50-times-per-second. The rate of power control feedback is speci-fied by the parameter FPC_MODE (forward power control operating mode) [2].See Chapter 7 for more details on power control.

3.4 User Channels

There are three user channels on the IS-2000 reverse link: R-FCH, R-SCCH,and R-SCH. The R-SCCH is provisioned to provide backward compatibility withIS-95 (more specifically, IS-95-B [1]). The purposes and structures of the reverse

3.4 User Channels 49

16 power control groups

1 2 3 4 5 6 7 8 9 10 11 12 13 14 150

Gating rate = 1

1 3 5 7 9 11 13 15

Gating rate = 1/2

3 7 11 15

Gating rate = 1/4

Figure 3.10 R-PICH gating.

Page 70: 3G CDMA200 Wireless System Engineering

fundamental channel and reverse supplemental channel are similar to their counter-parts on the forward. Therefore only important features are described in the follow-ing sections.

3.4.1 Reverse Fundamental Channel (R-FCH)

The IS-2000 R-FCH is similar to the IS-95 reverse traffic channel in that its primaryfunction is to carry user data. The following are the main functions of the IS-2000R-FCH:

• Transmission of voice traffic;• Transmission of low-rate data traffic;• Transmission of signaling via dim-and-burst and blank-and-burst schemes.

The R-FCH does not carry power control bits (in Radio Configurations 3through 6). The R-FCH can carry signaling traffic and supports the shorter 5-msframes in addition to the conventional 20-ms frames. Readers are referred to Section2.1.3.7.2 of [2] for an exhaustive list of radio configurations, corresponding datarates, and frame formats supported by the R-FCH.

3.4.2 Reverse Supplemental Channel (R-SCH)

The purpose of IS-2000 R-SCH is to serve as a dedicated transport pipe for high-ratepacket data. In performing this function, the R-SCH has two unique characteristics:

• Because it is acting as a high data rate transport pipe, the R-SCH only carriesuser traffic data and does not carry any signaling traffic.

• Because it is used to transmit packet data which is bursty in nature, the exis-tence of the R-SCH is itself bursty. This means that the R-SCH is set up andtorn down rather quickly.

Because the R-SCH does not carry any signaling, it has to coexist with anotherphysical channel that is able to carry signaling traffic for the R-SCH (i.e., reversefundamental channel or reverse dedicated control channel). In other words, whilethe R-SCH is active, one of these other physical channels has to be active as well.Since both the reverse fundamental channel and reverse dedicated control channelsupport 5-ms frames, signaling traffic can be transmitted on these channels quicklyto set up and tear down the R-SCH.

The R-SCH can use one of four different radio configurations (Radio Configu-rations 3 through 6) to support rates from 0.6875 Kbps to 1.0368 Mbps. It can alsosupport three different frame duration: 20 ms, 40 ms, and 80 ms. Readers arereferred to Section 2.1.3.8.2 of [2] for an exhaustive list of radio configurations, cor-responding data rates, and frame formats supported by the R-SCH.

3.5 Channel Structure

After a physical channel generates a frame, then the physical layer performs theusual functions such as:

50 Physical Layer: Reverse Link

Page 71: 3G CDMA200 Wireless System Engineering

• Adding the CRC bits for detecting frame errors,• Coding the bits for correcting bit errors,• Interleaving for combating fades,

These functions are similar to those of IS-95. After block interleaving, the sym-bols of a physical channel undergo a channel gain. The gain is determined by reversepower control. Figure 3.11 depicts a general block diagram up to right beforemodulation for enhanced access channel, reverse common control channel, reversededicated control channel, reverse fundamental channel, and reverse supplementalchannel. The figure shows the function that is unique to IS-2000 and corresponds toSpreading Rate 1.

3.6 Modulation

After being applied a channel gain, the symbol stream of a physical channel (exceptthe reverse pilot channel) is multiplied and spread by its assigned Walsh code forchannelization. The Walsh code runs at the chip rate of 1.2288 Mcps for SpreadingRate 1.

After channelization, the chip streams of the reverse pilot channel, reverse dedi-cated control channel, and the second reverse supplemental channel are addedtogether, and the chip streams of the reverse fundamental channel and enhancedaccess channel, reverse common control channel, or the first reverse supplementalchannel are added together. See Figure 3.12. These two summations undergoanother layer of spreading by a pair of spreading codes: sI and sQ. These two spread-ing codes are derived from the long PN code, which in turn is derived from themobile’s unique identity5. To reiterate, the Walsh codes provide channelization ofthe different physical channels transmitted by the mobile, while the long PN codeprovides identification of the mobile to the base station. Figure 3.12 depicts how thetwo summations of the physical channels are spread and fed into two separate BPSKmodulators.

3.6 Modulation 51

Blockinterleaver

Channelgain

Modulationsymbols

Z

Figure 3.11 Conceptual block diagram of enhanced access channel, reverse common controlchannel, reverse dedicated control channel, reverse fundamental channel, and reverse supplemen-tal channel.

5. These spreading codes are derived from the long PN code, in contrast to the spreading codes used onforward link that are short PN codes.

Page 72: 3G CDMA200 Wireless System Engineering

Figure 3.12 shows that the chip stream of any particular physical channel isalways fed into both BPSK modulators. For example, the reverse dedicated controlchannel is transmitted by both BPSK signals. The two BPSK signals are two inde-pendent signals separated by phase. This method of using two independent BPSKsignals to transmit a single physical channel is similar to that used by IS-95 forwardlink.

3.7 Capacity Gain: Reverse Link

One reason IS-2000 has a higher physical layer capacity than IS-95 is becauseIS-2000 uses coherent BPSK whereas IS-95 uses 64-ary orthogonal modulation. SeeChapter 5 of [3] for a review of 64-ary orthogonal modulation. Because IS-2000now has a pilot on the reverse link, it is able to coherently demodulate BPSK signals.For a given probability of bit error, coherent BPSK requires less Eb/N0 than 64-aryorthogonal modulation, and a lower required Eb/N0 means higher RF capacity in adirect sequence spread spectrum system.

In addition, the existence of a pilot on the reverse link allows Walsh codes to beused for channelization. This is because the reverse pilot channel enables the basestation to synchronize the Walsh codes so that they are orthogonal to each other

52 Physical Layer: Reverse Link

Z

wi forR-DCCH

(R-DCCH)

Z

wi forR-SCH 2

(R-SCH 2)

(R-PICH)

Z

wi forR-FCH

(R-FCH)

Z

wi forR-EACH,R-CCCH,orR-SCH 1

(R-EACH),(R-CCCH),or(R-SCH 1)

sI

sQ

sQ

sI

BF

BF

BF: Baseband filter

cos(2 )πf tc

sin(2 )πf tc

Y t( )

+

+

+

Figure 3.12 Modulation: Reverse link. (After: [2]. See Chapter 9 for the assigned Walsh codes ofphysical channels.)

Page 73: 3G CDMA200 Wireless System Engineering

with respect to a common start time; the maintenance of orthogonality is essentialfor channelization. The use of Walsh codes for channelization also means thatIS-2000 can now have multiple channels active at the same time (whereas IS-95 canonly have one channel active at a time) on the reverse link.

References

[1] TIA/EIA-95-B, Mobile Station-Base Station Compatibility Standard for Wideband SpreadSpectrum Cellular Systems, Telecommunications Industry Association, March 1999.

[2] TIA/EIA/IS-2000.2-A, Physical Layer Standard for cdma2000 Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

[3] Yang, S. C., CDMA RF System Engineering, Norwood, MA: Artech, 1998.

Selected Bibliography

TIA-97, Recommended Minimum Performance Standards for cdma2000 Spread Spectrum BaseStations, Telecommunications Industry Association, February 2003.

TIA-98, Recommended Minimum Performance Standards for cdma2000 Spread SpectrumMobile Station, Telecommunications Industry Association, February 2003.

3.7 Capacity Gain: Reverse Link 53

Page 74: 3G CDMA200 Wireless System Engineering

.

Page 75: 3G CDMA200 Wireless System Engineering

C H A P T E R 4

Medium Access Control

4.1 Introduction

The MAC sublayer serves as an interface between the physical layer below it andLAC sublayer and upper layers above it. In this regard, the MAC sublayer controlshigher layers’ access to the physical medium (i.e., the air link) that is inevitablyshared among different users. The IS-2000 MAC sublayer acts in the same way as aMAC entity controlling a LAN. Whereas a LAN MAC controls different comput-ers’ access to the shared cable medium, the IS-2000 MAC sublayer controls differ-ent users’ access to the shared air medium.

The MAC sublayer logically belongs to Layer 2 of the OSI Reference Model [1].Figure 4.1 shows that there are four different entities in the MAC sublayer: commonchannel multiplex sublayer, dedicated channel multiplex sublayer, SRBP, and radiolink protocol (RLP). The primary function of the MAC sublayer is to multiplex(transmitted) logical channels onto different physical channels and to demultiplex(received) physical channels into different logical channels. This is done by the twomultiplex sublayers of the MAC. On the other hand, RLP handles user packet data,and SRBP handles common-channel signaling which is inserted into the air interfaceusing radio burst techniques.

4.2 Primitives

Before describing the entities in the MAC sublayer, we need to review how the MACsublayer as a whole communicates with the LAC sublayer above it and with thephysical layer below it. The layers communicate using messages. In fact, theselayer/sublayers behave like objects in an object-oriented computer program in thatthey pass messages amongst themselves to communicate.

Primitives are a form of these communication messages that travel back andforth between the layer/sublayers. A primitive contains both payload informationand control information and resembles a procedure call made by one computer pro-gram to another computer program. In the case of IS-2000, a primitive may be usedby a layer/sublayer (i.e., service requester) to request a service or resource fromanother layer/sublayer (i.e., service provider). Or a primitive may be used by alayer/sublayer (i.e., service provider) to indicate to another layer/sublayer (i.e., serv-ice requester) that an event has occurred. Two widely used types of primitives are:

55

Page 76: 3G CDMA200 Wireless System Engineering

• Request: It is sent from a service requester to a service provider. A servicerequester uses request primitives to request a service or a resource.

• Indication: It is sent from a service provider to a service requester. A serviceprovider uses indication primitives to indicate that an event for the servicerequester has occurred.

A primitive can be written in the form:

Layer/Sublayer-Primitive_Name.Primitive_Type (Parameters)

A primitive has four parts which are:

• Layer/Sublayer: It shows the service provider associated with the primitive. Itcan be either PHY (for physical layer) or MAC (for MAC sublayer)

• Primitive_Name: It is the name of the specific primitive call.

56 Medium Access Control

Reverse link: coding and modulationForward link: demodulation and decoding

Common channelmultiplex sublayer

Dedicated channelmultiplex sublayer

SRBP RLP

Signaling LAC

Laye

r3

Laye

r2

Laye

r1

Signaling

LAC

subl

ayer

MA

Csu

blay

er

L3PD

U

L3PD

U

f-dt

ch(v

oice

)

r-dt

ch(v

oice

)RLP

SDU

RLP

SDU

LAP

PDU

f-dt

ch

r-dt

ch

f-ds

chr-

dsch

f-cs

ch

f-cs

ch

r-cs

ch

F-D

CC

HF-

SCH

F-FC

HR-

DC

CH

R-SC

HR-

FCH

F-BC

CH

F-C

CC

H

F-PC

HF-

CA

CH

F-C

PCC

HF-

SYN

CH

R-C

CC

H

R-EA

CH

R-A

CH

Up

per

laye

rsPh

ysic

alla

yer

Dataservices

Voiceservices

Data burst

Data burst

RL

FL

Figure 4.1 Structure of the protocol architecture in IS-2000 as shown from the perspective of themobile. (After: [2].)

Page 77: 3G CDMA200 Wireless System Engineering

• Primitive_Type: It shows the type of the primitive. It can be either a request orindication. Other primitives types are confirm and response.

• Parameters: They contain the actual parameters carried by the primitive. Theparameters may include the actual user/signaling data and the size of the data.

For example, when the MAC sublayer wants the physical layer to transmit somesignaling data on the F-CCCH, the MAC sublayer sends a request primitive to thephysical layer:

PHY-FCCCH.Request (sdu,…, num_bits)

where the designation PHY shows that it is the physical layer that is performing theservice (of transmitting the signaling data over the air interface). FCCCH.Request isthe name and the type of the primitive used to request data transmission. Theparameters of the primitive include the actual signaling data (sdu) and the size of thedata (num_bits) [2].

On the other hand, when the physical layer delivers signaling data to the MACsublayer, the physical layer sends a primitive to the MAC sublayer. For example,when the physical layer delivers signaling data to the MAC sublayer on theF-CCCH, the physical layer sends an indication primitive to the MAC sublayer:

PHY-FCCCH.Indication (sdu,…, num_bits, frame_quality)

where the designation PHY shows that it is the physical layer that is performing theservice (of delivering the signaling data over the air interface). FCCCH.Indication isthe name and the type of the primitive used to indicate that data is received anddelivered. The parameters of the primitive include the actual signaling data (sdu),the size of the data (num_bits), and frame quality (frame_quality) [2].

4.3 Multiplex Sublayers

The multiplex sublayers, both common channel and dedicated channel, are respon-sible for the mapping between logical channels and physical channels. Table 4.1shows this mapping on the forward link. For example, the f-dsch can use both theforward dedicated control channel and forward fundamental channel for physicaltransport. This is so because both are designed to carry dedicated signaling data. Onthe other hand, both the f-dsch and the f-dtch can use the forward dedicated controlchannel for physical transport. This is so because the forward dedicated controlchannel can carry both dedicated user and signaling data.

Table 4.2 shows the mapping between logical channels and physical channelson the reverse link.

Needless to say, logical channel data should be reliably delivered from themobile (or base station) to the base station (or mobile). In executing reliable deliv-ery, the MAC sublayer assembles data received from higher layers and passes theassembled data to the physical layer for transmission. The MAC sublayer alsoreceives data from the physical layer, disassembles the data and passes the disassem-bled data to higher layers. Figure 4.2 illustrates these functions of the multiplex

4.3 Multiplex Sublayers 57

Page 78: 3G CDMA200 Wireless System Engineering

sublayer. On the transmit side, the MAC sublayer assembles data blocks (receivedfrom a higher layer) into an SDU and delivers the SDU to the physical layer for trans-mission. On the receive side, the MAC sublayer receives an SDU, dissembles theSDU into data blocks, and delivers them to higher layers. While the multiplexsublayer can only interact with the physical layer below, the multiplex sublayer caninteract with four entities above it: RLP, voice services, LAC, and SRBP.

58 Medium Access Control

Table 4.1 Mapping Between Logical Channels and Physical Channels: Forward Link

Logical ChannelsChannel Designation Channel Name

Physical ChannelsChannel Designation Channel Name

f-cschForward commonsignaling channel

F-SYNCH Sync channel

F-PCH Paging channel

F-CCCHForward common controlchannel

F-BCCH Broadcast control channel

F-CPCCHCommon power controlchannel

F-CACH Common assignment channel

f-dschForward dedicatedsignaling channel

F-DCCHForward dedicated controlchannel

F-FCHForward fundamentalchannel

f-dtchForward dedicatedtraffic channel

F-DCCHForward dedicated controlchannel

F-FCHForward fundamentalchannel

F-SCHForward supplementalchannel

Table 4.2 Mapping Between Logical Channels and Physical Channels: Reverse Link

Logical ChannelsChannel Designation Channel Name

Physical ChannelsChannel Designation Channel Name

r-cschReverse commonsignaling channel

R-ACH Access channel

R-EACH Enhanced access channel

R-CCCHReverse common controlchannel

r-dschReverse dedicatedsignaling channel

R-DCCHReverse dedicated controlchannel

R-FCH Reverse fundamental channel

r-dtchReverse dedicatedtraffic channel

R-DCCHReverse dedicated controlchannel

R-FCH Reverse fundamental channel

R-SCH Reverse supplemental channel

Page 79: 3G CDMA200 Wireless System Engineering

Figure 4.3 shows an example of the assembling operation of the multiplexsublayer at the mobile. Here the mobile is transmitting. The multiplex sublayerreceives two different data blocks at the same time from two higher layer entities:LAC and RLP. The LAC entity (which handles signaling) passes a signaling datablock to the multiplex sublayer on the r-dsch. The RLP entity (which handles user

4.3 Multiplex Sublayers 59

Higher layerentities

Higher layerentities

Multiplex sublayer(common channelor dedicated channel)

Physical layer

SDUs SDUs

Data blocks Data blocks

Figure 4.2 Inputs and outputs of the multiplex sublayer.

LAC RLP

Data block

Dedicatedchannelmultiplexsublayer

Physicallayer

Header

SDU

Data block

Data block

R-D

CC

H

r-dt

ch

r-ds

ch

Data block

Figure 4.3 Assembling an R-DCCH SDU.

Page 80: 3G CDMA200 Wireless System Engineering

data) passes a user data block to the multiplex sublayer on the reverse r-dtch. Themultiplex sublayer assembles the two data blocks and adds a header to form anR-DCCH SDU. It then passes the R-DCCH SDU to the physical layer for transmis-sion on the R-DCCH. The R-DCCH is used here because it can carry both user anddedicated signaling data.

Note that the MAC sublayer (of which the multiplex sublayer is a part) passesits SDUs down to the physical layer as request primitives, and the MAC sublayerdelivers data blocks up to higher layer entities over the appropriate logical channels.In delivering data blocks to higher layer entities, the MAC sublayer chooses theappropriate logical channels based on the mapping described in Tables 4.1 and 4.2.

Although IS-2000 defines the mapping between logical channels and physicalchannels, the standard does not specify any rule regarding service priority [2]. Forexample, IS-2000 does not specify any prioritization rules to resolve contentionwhen multiple data blocks simultaneously arrive at the multiplex sublayer compet-ing for limited physical channel resources (i.e., SDUs). Therefore, the equipmentvendors are free to implement their own prioritization rules.

4.4 Radio Link Protocol (RLP)

4.4.1 Overview of Layer 2 Protocols

The RLP is a Layer 2 [1] protocol that is responsible for the delivery and receipt ofuser packet data [2]. As packets are transported from the transmitter to the receiver,some will be received in error. Thus, an important function of a Layer 2 entity is tocontrol errors introduced by the physical layer. In general, a Layer 2 entity uses oneof several mechanisms to control packet errors [3]:

• Positive acknowledgment. For error-free packet(s) received, the receiver sendsto the transmitter an acknowledgment indicating that packet(s) has/have beenreceived successfully. This positive acknowledgment is sometimes referred toas an “ACK.”

• Negative acknowledgment. For packet(s) received in error, the receiver sendsto the transmitter an acknowledgment indicating that packet(s) has/havenot been received successfully. This negative acknowledgment is sometimesknown as a “NAK.”

• Retransmission. The transmitter may retransmit packet(s) if, (1) it has notreceived a positive acknowledgment after a predetermined amount of time, or(2) it has received a negative acknowledgment.

Some examples of Layer 2 protocols (also known as data link control protocols)are the logical link control (LLC) protocol and the link access protocol-balanced(LAPB). LLC is used as a part of the IEEE 802 family of standards for operating overa LAN, and LAPB is used as part of the X.25 standard to connect a device to apacket-switching network [3]. These protocols use a combination of positiveand negative acknowledgments and retransmission to provide reliable delivery ofpackets.

60 Medium Access Control

Page 81: 3G CDMA200 Wireless System Engineering

4.4.2 llustration of the RLP

The IS-2000 standard makes use of the RLP for the delivery of user packet data. TheRLP is a data link control protocol that is designed especially for use over an airinterface [4]. The RLP can be viewed as a scheme that “shields” the errors and prob-lems of the air interface from higher layer entities (e.g., TCP/IP). Without the RLP,higher layer entities such as TCP/IP would be rendered useless if they interfaceddirectly with the error-prone air interface.

Since the air link is inherently error-prone, the RLP does not attempt to providea guaranteed delivery of packets over the air link because doing so would cost toomany retransmissions and render Layer 2 inefficient. Instead, the RLP provides abest effort delivery in that it will attempt to deliver a packet up to a point, then giveup. Note that in adopting the best effort strategy, the RLP (and the system) is implic-itly relying on error-control mechanisms at higher layers to guarantee the delivery ofuser data, if such a quality of service (QoS) is required.

To further minimize the transmission of control packets (e.g., ACK and NAK)over the air link, the RLP uses only negative acknowledgment (NAK) and retrans-mission mechanisms. Figure 4.4 shows an example of the negative acknowledgmentand retransmission processes.

4.4 Radio Link Protocol (RLP) 61

Transmitter Receiver

NAK 2NAK 2

NAK 2

Tim

e

NAK 1SEQ 3

SEQ 3

SEQ 3

SEQ 2

SEQ 2

SEQ 2

SEQ 2

SEQ 2

SEQ 2

SEQ 1

SEQ 1

SEQ 1

SEQ 1

SEQ 0

SEQ 0

SEQ 0

a1

a2

a3

a4

b1

b2

b3

b4a5

b5D

D

a6

a7

a8

b6

b7a9

a10

b8

b9

b10

a11

a12

a13

D

b11

b12

b13

b14a14

a15

D

D

Figure 4.4 Example of using negative acknowledgment and retransmission.

Page 82: 3G CDMA200 Wireless System Engineering

In Figure 4.4, the transmitter bursts a series of four packets, numbered withsequence numbers 0, 1, 2, and 31. These four packets are transmitted at times a1, a2,a3, and a4, respectively. The receiver receives sequence 0 (SEQ 0) at time b1, sequence2 at time b3, and sequence 3 at time b4, but it does not receive the packet withsequence 1. At time b3, the receiver realizes it has missed the packet with sequence 1because it has received the packet with sequence 2 (out of sequence). So at time b3,the receiver sends a negative acknowledgment NAK 1 back to the transmitter indi-cating that the receiver did not receive sequence 1. At time a5, the transmitterreceives NAK 1 and retransmits the packet with sequence number 1. The receiverreceives sequence 1 successfully at time b5.

After a roundtrip time delay D, the transmitter does not receive any NAK fromthe receiver, so the transmitter infers that the receiver must have received sequence 1correctly. Then the transmitter proceeds to burst a new set of four packets; here thesequence counter resets, and the sequence number is cycled from 0 to 3 again. Thistime sequence 2 is lost. At b10, the receiver realizes that it has received sequence 3 outof sequence and it has missed sequence 2. So at b10, the receiver sends NAK 2 back tothe transmitter.

At a11, the transmitter receives NAK 2 and retransmits sequence 2. Unfortu-nately, sequence 2 is again lost. At b11, the receiver should have received the retrans-mission of sequence 2 but did not, so it sends negative acknowledgment again. Butthis time it sends two copies of negative acknowledgment NAK 2 (at b11 and b12) toincrease the probability of successful reception. At a12 and a13, the transmitterreceives both copies of NAK 2 and resends two copies of sequence 2.

At b14, the receiver realizes that it should have received two copies of sequence 2by now, but it does not. So it decides to stop sending retransmission requests anddoes not send any more negative acknowledgment. At a15, the transmitter does notreceive any negative acknowledgment from the receiver. The transmitter assumesthat everything is fine and bursts out a new set of four packets.

Note that at a6 (after roundtrip delay D), the transmitter does not immediatelytransmit a new set of packets. Rather it waits for another incremental time step untila7. This is so because the transmitter expects that if there is a packet error then itshould receive two NAK copies from the receiver. This is why the transmitter waitsuntil a7 to start transmitting the new sequences.

4.4.3 Concluding Remarks

It is important to note that the above example serves only to illustrate NAK andretransmission processes, not to describe detailed operations of the RLP. In actual-ity, the RLP uses three classes of frames: control frames, retransmitted data frames,and new data frames. Understandably, control frames carrying control informationhave the highest priority; old data frames that need to be retransmitted are second inpriority, then new data frames that have not been transmitted have the lowest prior-ity [4]. In addition, RLP (more specifically, RLP 3) uses 8-bit and 12-bit sequencenumbers (instead of the 2-bit sequence number used in the above example).

62 Medium Access Control

2. The handoff capability is actually for the soft handoff of common power control channels that powercontrol the mobile’s transmission of R-CCCH.

Page 83: 3G CDMA200 Wireless System Engineering

The RLP family of standards [4] includes three types of RLPs. RLP 3 is the RLPthat implements packet data service over IS-2000 traffic channels; it is used for datarates up to 2 Mbps. Other types of RLPs include RLP 1 and RLP 2. RLP 1 imple-ments packet data service over IS-95-A traffic channel; it operates over the funda-mental channel at 9.6 or 14.4 Kbps. RLP 2 implements packet data service overIS-95-B traffic channels; it operates over IS-95-B fundamental and supplementalcode channels.

4.5 Signaling Radio Burst Protocol (SRBP)Whereas as the RLP controls the processing of user packet data that travel on dedi-cated user channels, the SRBP controls the processing of signaling messages thattravel on the common signaling channels. The SRBP controls the processing of thefollowing common signaling channels:

• F-SYNCH;• F-PCH;• F-CACH;• F-CCCH;• F-BCCH;• R-ACH;• R-EACH;• R-CCCH.

For example, during a mobile’s access attempt [5] on the access channel, theSRBP is the entity that computes the power level of each successive access probe,performs the persistence test, and calculates the randomization delay for each accesssubattempt.

In addition to generating and computing parameters needed for the transmis-sion and reception of common signaling messages, the SRBP also assembles SDUsfor the physical layer to transmit on the physical channels, as well as pass thereceived SDUs from the physical layer to the LAC sublayer. Figure 4.5 shows anexample of the processing of the F-CCCH at the base station.

As shown in Figure 4.5, when the SRBP is ready to process the F-CCCH, theSRBP sends to the LAC sublayer the following primitive:

MAC-Availability.Indication (channel_type, max_size, system_time)

where channel_type is set to “F-CCCH frame,” max_size is the maximum numberof information bits that can be transmitted in the next F-CCCH frame (i.e.,FCCCH_FRAME_SIZE), and system_time specifies the time that the physical layerwill start transmitting the next F-CCCH frame (i.e., “departure time”). This showsthe LAC that SRBP is ready to receive more information for transmission on theF-CCCH.

The LAC sublayer then sends to the MAC sublayer the following primitive:

MAC-Data.Request (channel_type, data, size)

where channel_type is set to “F-CCCH frame,” data contains the actual data to betransmitted on the F-CCCH, and size is the length of the actual data (in bits). Here

4.5 Signaling Radio Burst Protocol (SRBP) 63

Page 84: 3G CDMA200 Wireless System Engineering

the LAC sublayer is requesting the SRBP to assemble an SDU to be transmitted onthe F-CCCH.

After receiving the MAC-Data.Request primitive, the SRBP examines its sizeparameter and appends (FCCCH_FRAME_SIZE – size) zeros to the end of data toform an SDU to be transmitted on the F-CCCH. Then the common channel multi-plex sublayer sends the following primitive to the physical layer:

PHY-FCCCH.Request (sdu, fccch_id, frame_duration, num_bits)

where sdu is the assembled F-CCCH SDU, frame_duration is set to 20 ms, 10 ms, or5 ms depending on the data rate and the number of information bits in the frame,and num_bits is the number of bits in the sdu.

After receiving the PHY-FCCCH.Request primitive, the physical layer proceedsto transmit the F-CCCH frame over the air interface.

4.6 System Access

The IS-2000 standard has the ability to operate in one of four different accessmodes: basic access mode, reservation access mode, designated access mode, andpower controlled access mode. These four access modes are described in the follow-ing sections.

64 Medium Access Control

PHY MAC LAC

SRBPMAC-Availability.Indication

SRBPMAC-Data.Request

CCMPHY-FCCCH.Request

PHY: Physical layerMAC: Medium access control sublayerLAC: Link access control sublayerSRBP: Signaling radio burst protocolCCM: Common channel multiplex sublayer

(Pro

cess

ing)

(Tim

e)

Figure 4.5 Example of SRBP processing at the base station: Forward common control channel.

Page 85: 3G CDMA200 Wireless System Engineering

4.6.1 Basic Access Mode

The access procedure in the basic access mode is similar to that used in IS-95.Namely, the mobile keeps transmitting access probes at increasing power levelsuntil it gets a response back from the base station. Mobiles also transmit pseudoran-domly in their attempts to gain access. In addition, a mobile can transmit accessprobes on the R-EACH instead of the R-ACH. Furthermore, to improve the prob-ability of probe detection, a mobile cannot transmit the probe on the R-EACHunless the primary sector’s Ec/I0 exceeds the parameter EACH_ACCESS_THRESH.

As shown in Figure 4.6, each R-EACH probe contains a preamble and enhancedaccess data. The preamble consists of a series of gated reverse pilot channel trans-missions, which are used to facilitate the acquisition of the R-EACH by the base sta-tion. The reverse pilot channel transmission also continues during the transmissionof enhanced access data.

In the basic access mode, each R-EACH probe carries an entire set of enhancedaccess data, which may require several 20-ms, 10-ms, or 5-ms frames to transport(recall that the R-EACH supports 20-ms, 10-ms, and 5-ms frame formats). Inother words, the enhanced access data portion of the probe may last a long time ascompared to, say, a single 5-ms frame. Therefore, in the basic access mode theR-EACH still has the issue of random collisions of long probes, an issue similar tothat in IS-95.

4.6.2 Reservation Access Mode

In the reservation access mode, a mobile transmits a short (5 ms) burst of messageon the R-EACH to attempt to “reserve” a space on the R-CCCH. After securing thereservation, the mobile transmits the rest of access data on the R-CCCH whose

4.6 System Access 65

R-EACH

Preamble Enhanced access data

R-PICH

Figure 4.6 An R-EACH probe: Basic access mode.

Page 86: 3G CDMA200 Wireless System Engineering

resources are scheduled by the base station and are free of collision problems. Fur-thermore, because the transmitted probe on the R-EACH is now shorter, the colli-sion problem on the R-EACH is minimized as well. To improve the probability ofprobe detection, a mobile cannot transmit the probe on the R-EACH unless the pri-mary sector’s Ec/I0 exceeds the parameter EACH_ACCESS_THRESH.

When a mobile wishes to gain access or has information to send to the base sta-tion while there is no active R-DCCH or no R-FCH, it sends a probe on the R-EACH(see Figure 4.7). In the reservation access mode, this probe consists of the preambleand enhanced access header. The header lasts only 5 ms and contains only the fol-lowing fields [2]:

• HASH_ID or hash identifier. The mobile uses this field to identify itself to thebase station. This field is 16-bits long.

• RATE_WORD or rate and frame size indicator. The mobile uses this field torequest the data rate and frame format on the R-CCCH. This field is 3-bitslong.

• MODE_ID or mode identifier. Its default value is 0.• HO_REQ_ID or handoff request identifier. The mobile uses this field to

request handoff capability on the R-CCCH2 if such a capability is supportedand if a candidate sector’s Ec/I0 is greater than a predetermined threshold. Thisfield has a maximum length of 1 bit.

• NEIGHBOR_PN or neighbor pilot PN offset. The mobile uses this field toreport the neighbor pilot PN offset if it is requesting handoff capability on theR-CCCH. This field has a maximum length of 9 bits.

• RESERVED or reserved bits.

As one can see, all fields excluding the RESERVED field add up to a maximumof 30 bits. Including the RESERVED field brings the total number of bits in theheader to 32 bits, which can be easily transmitted in the 5-ms header.

After receiving the header, the base station uses the received HASH_ID andRATE_WORD parameters to schedule an R-CCCH resource for the mobile. Thebase station then transmits an early acknowledgment channel assignment message

66 Medium Access Control

Preamble Enhancedaccessheader

5 ms

R-EACH

R-PICH

Figure 4.7 An R-EACH probe: Reservation access mode.

1. The sequence number is a part of the control (or header) information that the RLP attaches to the packet itsends. In this simplified example, the sequence number used is a 2-bit field that cycles from 0 to 3.

Page 87: 3G CDMA200 Wireless System Engineering

(EACAM) back to the mobile on the forward common assignment channel(F-CACH). The EACAM contains the following fields [2]:

• MSG_TYPE or message type. This field is set to “000” to indicate that thismessage is an EACAM. This field is 3-bits long.

• HASH_ID or hash identifier. The base station uses this field to retransmit thehash identifier that it received in the enhanced access header. This field is 16-bits long.

• RATE_WORD or rate and frame duration indicator. The base station usesthis field to indicate to the mobile the data rate and frame format on theR-CCCH that it grants to the mobile. This field is 3-bits long.

• RCCCH_ID or reverse common channel identifier. The base station uses thisfield to let the mobile know the R-CCCH index that it grants to the mobile totransmit. This field is 5-bits long.

• CPCCH_ID or common power control channel identifier. The base stationuses this field to let the mobile know the R-CPCCH index that the mobileshould monitor. This field is 2-bits long.

• HO_FLAG or handoff flag. The base station sets this field to 1 if the mobilehad previously requested handoff capability in the header and the base stationgrants the request. This field is 1-bit long.

• RESERVED or reserved bits.

As one can see, the EACAM is 32-bits long which can just fit into a 5-msR-CACH frame (which, readers may recall, contains 32 information bits and 8CRC bits). The mobile knows that the EACAM is intended for it by examining theHASH_ID field in the EACAM; this HASH_ID should be identical to the one trans-mitted previously on the enhanced access header.

After verifying that the received EACAM is intended for it, the mobile starts totransmit the enhanced access data on the allocated R-CCCH specified by theRCCCH_ID field. In doing so, the mobile uses the data rate and frame durationspecified by the RATE_WORD field. In addition, the mobile starts to monitor theF-CPCCH specified by the CPCCH_ID field. The base station uses the specifiedF-CPCCH to send power control bits to power control the mobile’s transmittedpower on the R-CCCH.

4.6.3 Power Controlled Access Mode

In the power controlled access mode, the base station uses the F-CPCCH to powercontrol the R-EACH (instead of to power control the R-CCCH as in the case of res-ervation access mode). The enhanced access probe used in the power controlledaccess mode also differs from those used in the basic access mode and reservationaccess mode. Here the probe consists of a preamble, the header, and the enhancedaccess data. See Figure 4.8.

The base station uses the F-CACH to provide a fast acknowledgment to themobile and to let the mobile know the specific F-CPCCH (i.e., CPCCH_ID) tomonitor. The mobile uses the power control bits it receives on the F-CPCCH toadjust the power it transmits on the R-EACH [2].

4.6 System Access 67

Page 88: 3G CDMA200 Wireless System Engineering

4.6.4 Designated Access Mode

The designated access mode is a mode of operation where the mobile, in response torequests received on the F-CCCH from the base station, responds using theR-CCCH. Similar to the reservation access mode, the R-CCCH is power controlledin the designated access mode. Here the base station uses the F-CPCCH to powercontrol the R-CCCH.

However, there are differences between the designated access mode and the res-ervation access mode. First and foremost, in the designated access mode the mobiledoes not initiate access or autonomously send access request, rather the mobileresponds to requests received on the F-CCCH from the base station (hence the termdesignated access). For example, the mobile may receive a status request message onthe F-CCCH that requires a response. In this case, the mobile may respond in thedesignated access mode on the R-CCCH.

Second, the R-EACH is not used at all in designated access mode. Only theR-CCCH is used. Third, while IS-2000 allows for the support of soft handoff ofR-CCCH in the reservation access mode, it does not provision for soft handoffof R-CCCH in the designated access mode [2].

References

[1] ITU-T Recommendation X.210, Information Technology–Open Systems Interconnec-tion–Basic Reference Model: Conventions for the Definition of OSI Services, InternationalTelecommunication Union, 1993.

[2] TIA/EIA/IS-2000.3-A, Medium Access Control (MAC) Standard for cdma2000 SpreadSpectrum Systems, Telecommunications Industry Association, March 2000.

68 Medium Access Control

Preamble Enhancedaccessdata

Enhancedaccessheader

R-EACH

R-PICH

Figure 4.8 An R-EACH probe: Power controlled access mode.

Page 89: 3G CDMA200 Wireless System Engineering

[3] Stallings, W., Business Data Communications, Upper Saddle River, NJ: Prentice-Hall,2005.

[4] TIA/EIA/IS-707-A, Data Service Options for Wideband Spread Spectrum Systems, Tele-communications Industry Association, February 2003.

[5] Yang, S. C., CDMA RF System Engineering, Norwood, MA: Artech, 1998.

4.6 System Access 69

Page 90: 3G CDMA200 Wireless System Engineering

.

Page 91: 3G CDMA200 Wireless System Engineering

C H A P T E R 5

Signaling Link Access Control

5.1 Introduction

The signaling LAC entity executes a data link protocol; this data link protocolensures that signaling data generated by upper layers are correctly delivered acrossthe air link (see Figure 5.1). In some ways, LAC is analogous to the RLP entity,which is responsible for the delivery of user packet data across the air interface.Both LAC and RLP implement data link protocols. However, LAC differs from RLPin one important respect: while RLP provides a best effort transport of user packetdata whose delivery is not assured, LAC provides a reliable delivery of signalingdata. The reliable delivery of signaling data is needed in any communication net-work to ensure its smooth operation. Note in Figure 5.1 that the LAC entity inter-faces (either directly or indirectly) with both common channel multiplex sublayerand dedicated channel multiplex sublayer. This means that LAC is responsible fordelivering signal data reliably over both common and dedicated signaling channels.

In many ways, LAC is just an interface between the MAC sublayer and Layer 3.The use of LAC enables software and hardware in the MAC sublayer to be sepa-rated from the logical functions of the LAC sublayer. By separating the LACsublayer from the MAC sublayer, it is simpler to change the MAC software andhardware without affecting the software in Layer 3 [1].

To ensure reliable delivery of signaling data, the LAC entity depends on fivesublayers to perform a variety of functions. These sublayers are (1) authenticationsublayer, (2) addressing sublayer, (3) automatic repeat request (ARQ) sublayer, (4)utility sublayer, and (5) segmentation and reassembly (SAR) sublayer. Figure 5.2shows the structure of these sublayers in the LAC entity [2].

5.2 LAC Sublayers

5.2.1 Authentication and Addressing Sublayers

The authentication sublayer’s function is to authenticate mobiles that try to gainaccess to the network. In doing so, this sublayer processes authentication-relatedfields. The addressing sublayer’s function is to process addressing information, suchas a mobile’s electronic serial number (ESN) and mobile identification number(MIN).

71

Page 92: 3G CDMA200 Wireless System Engineering

72 Signaling Link Access Control

f-cs

ch

f-cs

ch

r-cs

ch

f-dt

ch

f-ds

ch

r-dt

ch

r-ds

ch

f-dt

ch(v

oice

)r-

dtch

(voi

ce)

RLP

SDU

RLP

SDU

L3PD

U

L3PD

UUp

per

laye

rsLA

Csu

blay

er

LAC

PDU

MA

Csu

blay

erPh

ysic

alla

yer

Laye

r3

Laye

r2

Laye

r1 R-

CC

CH

R-EA

CH

R-A

CH

F-D

CC

H

F-SC

HF-

FCH

R-D

CC

H

R-SC

H

R-FC

H

F-BC

CH

F-C

CC

HF-

PCH

F-C

PCC

HF-

CA

CH

F-SY

NC

H

Reverse Link: coding and modulationForward Link: demodulation and decoding

Common channelmultiplex sublayer

Dedicated channelmultiplex sublayer

SRBP RLP

Signaling LAC

Signaling Dataservices

Voiceservices

Data burst

Data burst

Reverse link

Forward link

Figure 5.1 Structure of the protocol architecture in IS-2000 as shown from the perspective of themobile. (After: [1].)

Utility

SAR

Addressing

ARQ

Authentication

LAC

subl

ayer

Figure 5.2 Structure of the LAC sublayer.

Page 93: 3G CDMA200 Wireless System Engineering

One important characteristic of the authentication and addressing sublayers isthat they are only active in common signaling1. This is so because authentication isneeded only when a mobile is first trying to access the network using common sig-naling channels2. Once it has access, the mobile has the use of dedicated traffic chan-nels and authentication is no longer required. Similarly, addressing is only neededwhen a mobile communicates on common signaling channels. If a mobile gains useof a dedicated traffic channel, then it is identified by the assigned code (e.g., Walshcode).

5.2.2 ARQ Sublayer

The ARQ sublayer is the sublayer that is responsible for the reliable delivery of sig-naling data. ARQ is a term that collectively refers to a mechanism in which areceiver automatically requests for retransmission if it detects an error in thereceived data. In general, ARQ uses retransmission and positive and/or negativeacknowledgment to provide reliable delivery.

The ARQ sublayer in LAC can deliver Layer 3 PDUs in two modes: assureddelivery and unassured delivery. Layer 3 specifies the type of delivery (usingparameters in the request primative) when requesting delivery service from the LACsublayer. In assured delivery, the transmitting LAC repeatedly sends signaling dataat fixed intervals until it receives a positive acknowledgment from the receivingLAC. If after a predetermined number of transmissions the transmitting LAC doesnot receive any positive acknowledgment, then the transmitting LAC aborts anyfurther transmissions.

In unassured delivery, the transmitting LAC sends signaling data, but the receiv-ing LAC does not send any positive acknowledgment. To improve the probability ofsuccessful delivery, Layer 3 may request the transmitting LAC to send signaling datamultiple times; here, the receiving LAC detects and discards duplicate messages. Butno positive acknowledgment is sent by the receiving LAC [2].

5.2.3 Utility Sublayer

The utility sublayer is best described as one whose function is to perform those mis-cellaneous functions that are not done by other sublayers in LAC. Some examples ofthe utility sublayer’s functions are:

• Assembling the radio environment report fields and attaching them tothe PDU, if required. They are fields such as the Ec/I0 of the active pilot(ACTIVE_PILOT_STRENGTH) and the number of pilots in addition to theactive set that the mobile sees (NUM_ADD_PILOTS). This function is onlyperformed by the utility sublayer at the mobile.

• Padding the PDU to bring it to the required number of bits.

5.2 LAC Sublayers 73

1. One exception is the sync channel (F-SYNCH), which is technically a forward common signaling channelbut does not require authentication and addressing functions.

2. The mobiles typically do not authenticate a base station. Hence authentication is not active in common sig-naling on the forward link.

Page 94: 3G CDMA200 Wireless System Engineering

5.2.4 Segmentation and Reassembly Sublayer

On the transmit side, the segmentation and reassembly (SAR) sublayer segments thePDUs (that have been encapsulated by the LAC sublayers) into PDU fragments ofsizes that can be transferred by the MAC sublayer. The SAR sublayer may also com-pute the CRC and append it to the PDU.

On the receive side, the SAR sublayer reassembles the encapsulated PDU frag-ments (received from the MAC sublayer) into encapsulated PDUs. In addition, theSAR may check the CRC to verify valid receipts. The SAR sublayer then presents theencapsulated PDUs to the sublayers above in LAC for further processing [2].

5.3 Sublayer Processing

On the transmit side, the LAC entity as a whole accepts Layer 3 PDUs from theupper layers, and the different sublayers perform their functions in sequence andattach their own control information to the data unit. At the end the SAR sublayersegments the PDU (that has been encapsulated by the LAC sublayers) into PDU frag-ments of sizes that can be transferred by the MAC sublayer. It then outputs thesePDU fragments to the MAC sublayer for transport [2]. On the receive side, thereverse process takes place.

The following sections describe the processing done by the different sublayers inLAC for four scenarios: (1) common signaling on the forward link, (2) common sig-naling on the reverse link, (3) dedicated signaling on the forward link, and (4) dedi-cated signaling on the reverse link.

5.3.1 Common Signaling: Forward Link

Figure 5.3 shows the processing done by the different LAC sublayers (at the base sta-tion) when the base station transmits common signaling data to the mobile. In thiscase, all LAC sublayers are involved with the exception of the authenticationsublayer. This is so because while the base station needs to authenticate the mobiles(e.g., to prevent fraud), there is rarely a need for a mobile to authenticate the basestation.

At the base station, a Layer 3 PDU is first passed on to the ARQ sublayer. TheARQ sublayer adds the appropriate acknowledgment fields, and the addressingsublayer adds the appropriate address parameters [for addressing the mobile(s)].Then the utility sublayer finishes the assembly of the LAC PDU by performing pad-ding (if necessary) and other relevant functions.

After receiving the data unit, the SAR sublayer first calculates the CRC andappends it to the data unit. Then, in communicating with the MAC sublayer (usingprimatives), the SAR sublayer is notified of whether there is capacity available on theappropriate physical channels (e.g., forward common control channel). Once capac-ity becomes available, the SAR sublayer transfers the encapsulated PDU fragmentsto the MAC sublayer for delivery. Note that common signaling data on the forwardlink logically travels on the f-csch.

Figure 5.4 shows the processing done by the LAC sublayers (at the mobile) whenthe mobile receives common signaling data from the base station. Here the reverse

74 Signaling Link Access Control

Page 95: 3G CDMA200 Wireless System Engineering

5.3 Sublayer Processing 75

Utility

SAR

ARQ

Layer 3 PDU

LAC SDU Encapsulated PDU

EncapsulatedPDU fragments

MAC SDUs

MAC sublayer

f-cs

ch

LAC SDU

LAC SDU

Partially-formedLAC PDU

LAC PDU

Addressing

LAC SDU

LAC SDU

Upper layers

Figure 5.3 Common signaling-forward link processing: Base station. (After: [2].)

Utility

SAR

ARQ

Layer 3 PDU

LAC SDU Encapsulated PDU

EncapsulatedPDU fragments

MAC SDUs

Upper layers

MAC sublayer

f-cs

ch

LAC SDU

LAC SDU LAC PDU

Addressing

LAC SDU

LAC SDU

Figure 5.4 Common signaling-forward link processing: Mobile station. (After: [2].)

Page 96: 3G CDMA200 Wireless System Engineering

process takes place. At the mobile, the SAR sublayer first concatenates the encapsu-lated PDU fragments received from the MAC sublayer. It strips off the CRC and per-forms the CRC check. After forming the LAC PDU, it passes the LAC PDU to theutility sublayer.

After the utility sublayer performs its functions3, the PDU is passed to theaddressing sublayer which processes the address fields for address matching. Thenthe data unit is passed to the ARQ sublayer. The ARQ sublayer processes the ARQfields. If the received PDU requires an acknowledgment, then the (receiving) ARQsublayer notifies its counterpart on the transmit side. Finally, the data unit is deliv-ered to Layer 3. Note that, on the forward link, a mobile logically receives commonsignaling data on the f-csch.

5.3.2 Common Signaling: Reverse Link

Figure 5.5 shows the processing done by the different LAC sublayers when themobile transmits common signaling data to the base station. Note that in this case,

76 Signaling Link Access Control

Utility

SAR

Addressing

Authentication

Layer 3 PDU

LAC SDU Encapsulated PDU

EncapsulatedPDU fragments

MAC SDUs

MAC sublayer

r-cs

ch

LAC SDU

LAC SDU

LAC SDU

Partially-formedLAC PDU

LAC PDU

ARQ

LAC SDU

LAC SDU

Upper layers

Figure 5.5 Common signaling-reverse link processing: Mobile station. (After: [2].)

3. For example, if the received PDU contains a universal page message, then the utility sublayer processes themessage.

Page 97: 3G CDMA200 Wireless System Engineering

all LAC sublayers are involved. When the mobile transmits on the reverse commonsignaling channel, there is a definite need for the base station to authenticate themobile, as well as a need for that mobile to identify itself to the base station usingaddressing fields.

At the mobile, a Layer 3 PDU is first passed on to the authentication sublayer,which adds the authentication fields to the data unit. Afterwards, the ARQ sublayertakes over and appends the acknowledgment fields. Then the addressing sublayeradds the appropriate address fields.

After processing of the addressing field, the partially formed LAC PDU is passedto the utility sublayer. Here the utility sublayer adds the radio environment reportfields to the PDU, and then it finishes the assembly of the encapsulated PDU by per-forming padding (if necessary) and other relevant functions.

After receiving the data unit from the utility sublayer, the SAR sublayer first cal-culates the CRC and adds it to the data unit. Then the SAR sublayer, in communi-cating with the MAC sublayer (using primitives), is notified of whether there iscapacity available on the appropriate physical channels (e.g., reverse common con-trol channel). Once capacity becomes available, the SAR sublayer transfers theencapsulated PDU fragments to the MAC sublayer for delivery. Note that commonsignaling data on the reverse link logically travels on the r-csch.

Figure 5.6 shows the processing done by the LAC sublayers when the base sta-tion receives common signaling data from the mobile. Here the reverse process takesplace. At the base station, the SAR sublayer first concatenates the encapsulated PDUfragments received from the MAC sublayer. It strips off the CRC and performs theCRC check. After forming the PDU, it passes the PDU to the utility sublayer.

After the utility sublayer performs its functions4, the PDU is passed to theaddressing sublayer which processes the address fields for address matching. Thenthe PDU is passed to the ARQ sublayer. The ARQ sublayer processes the ARQfields and passes the data unit to the authentication sublayer. The authenticationsublayer processes the authentication fields and tests for authentication. If theauthentication passes, the remaining Layer 3 SDU is delivered to Layer 3. Note that,on the reverse link, the base station logically receives common signaling data on ther-csch.

5.3.3 Dedicated Signaling: Forward Link

Figure 5.7 shows the processing done by the different LAC sublayers (at the basestation) when the base station transmits dedicated signaling data to the mobile. Inthis case, only the ARQ, utility, and SAR sublayers are involved; the addressing andauthentication layers are not active. The addressing sublayer is not needed becausewhen receiving dedicated traffic channels, mobiles are uniquely identified by theirassigned codes (e.g., Walsh codes). The authentication sublayer is not neededbecause there is no need for mobiles to authenticate the base station.

At the base station, the Layer 3 PDU is first passed to the ARQ sublayer. TheARQ sublayer adds the appropriate acknowledgment fields, then the utility

5.3 Sublayer Processing 77

4. For example, the utility sublayer may interpret the MSG_ID field to see what kind of message is carriedby the received PDU (e.g., if MSG_ID = 000110 then the message is an authentication challenge responsemessage).

Page 98: 3G CDMA200 Wireless System Engineering

sublayer performs padding (if necessary) and other relevant functions. After the dataunit is passed to the SAR sublayer, SAR calculates the CRC and appends it to thedata unit. The SAR sublayer, in communicating with the MAC sublayer (usingprimitives), is notified of whether there is capacity available on the appropriatephysical channels (e.g., forward dedicated control channel). Once capacity becomesavailable, the SAR sublayer transfers the encapsulated PDU fragments to the MACsublayer for delivery. Note that dedicated signaling data on the forward link logi-cally travels on the f-dsch.

Figure 5.8 shows the processing done at the mobile when the mobile receivesdedicated signaling data from the base station. Here the reverse process takes place.At the mobile, the SAR sublayer first concatenates the encapsulated PDU fragmentsreceived from the MAC sublayer. It strips off the CRC and performs the CRC check.The completed LAC PDU is then passed to the utility sublayer.

After the utility sublayer performs its functions5, the data unit is passed to theARQ sublayer which processes the ARQ fields and removes them from the data unit.

78 Signaling Link Access Control

Utility

SAR

Addressing

Authentication

Layer 3 PDU

LAC SDU Encapsulated PDU

EncapsulatedPDU fragments

MAC SDUs

MAC sublayer

r-cs

ch

LAC SDU

LAC SDU

LAC SDU LAC PDU

ARQ

LAC SDU

LAC SDU

Upper layers

Figure 5.6 Common signaling-reverse link processing: Base station. (After: [2].)

5. For example, the utility sublayer may interpret the MSG_TYPE field to see what kind of message is carriedby the received PDU (e.g., if MSG_TYPE = 00000010 then the message is an authentication challengemessage).

Page 99: 3G CDMA200 Wireless System Engineering

5.3 Sublayer Processing 79

Utility

SAR

ARQ

Layer 3 PDU

LAC SDU Encapsulated PDU

EncapsulatedPDU fragments

MAC SDUs

MAC sublayer

f-ds

chLAC SDU

Partially-formedLAC PDU

LAC PDU

LAC SDU

LAC SDU

Upper layers

Figure 5.7 Dedicated signaling-forward link processing: Base station. (After: [2].)

Utility

SAR

ARQ

Layer 3 PDU

LAC SDU Encapsulated PDU

EncapsulatedPDU fragments

MAC SDUs

MAC sublayer

LAC SDU

LAC PDU

LAC SDU

LAC SDU

Upper layers

f-ds

ch

Figure 5.8 Dedicated signaling-forward link processing: Mobile station. (After [2].)

Page 100: 3G CDMA200 Wireless System Engineering

Note that, on the forward link, a mobile logically receives dedicated signaling dataon the f-dsch.

5.3.4 Dedicated Signaling: Reverse Link

The LAC processing of dedicated signaling data on the reverse link is similar andsymmetrical to those done for dedicated signaling data on the forward link. For thesake of completeness, Figures 5.9 and 5.10 are included to show the processing doneat the mobile and at the base station, respectively. Readers can see that the process-ing shown in these figures resemble those performed for dedicated signaling data onthe forward link (i.e., only the ARQ, utility, and SAR sublayers are active). In thiscase, the dedicated signaling data travels on r-dsch [2].

5.4 Interaction of Layer and Sublayers

As readers can see from the above discussion, the LAC sublayer as a whole is in con-stant communication with Layer 3 above it and with the MAC sublayer below it. Incarrying out this communication, Layer 3, LAC, and MAC use primitives to passdata units and control information between Layer 3 and LAC and between LAC andMAC. Note that the actual data unit transferred is simply one of the parameters ofthe primitive (see Chapter 4).

80 Signaling Link Access Control

Utility

SAR

ARQ

Layer 3 PDU

LAC SDU Encapsulated PDU

EncapsulatedPDU fragments

MAC SDUs

MAC sublayer

r-ds

ch

LAC SDU

Partially-formedLAC PDU

LAC PDU

LAC SDU

LAC SDU

Upper layers

Figure 5.9 Dedicated signaling-reverse link processing: Mobile station. (After: [2].)

Page 101: 3G CDMA200 Wireless System Engineering

5.4.1 Transmit Side

Figure 5.11 shows the interaction of primitives when sending signaling data. WhenLayer 3 has a PDU to send, Layer 3 requests this service from the LAC sublayer byinvoking the L2-Data.Request primitive. L2 is the name of the service provider.From the perspective of Layer 3 the entity that provides the service is the entireLayer 2, not just LAC or MAC. Data is the name of this particular primitive, andRequest denotes that this primitive is a request for service.

When the LAC sublayer (or specifically the SAR sublayer) wants to send a PDU,the LAC sublayer invokes the MAC-SDUReady.Request primitive. This primitivelets MAC know that there is a PDU ready for transmission. Here MAC is the entitythat provides the service. SDUReady is the name of the primitive, and Requestdenotes that this primitive is a request for service.

If space is available for data transfer on the physical channel(s), MAC sendsLAC the MAC-Availability.Indication primitive. This primitive lets LAC know thatthere is space available as well as how much space is available (i.e., how many bitsare available on the physical channel(s)). This primitive shows that MAC is the serv-ice provider, and Availability is the name of the primitive. This Indication primitivelets the service requester (i.e., LAC) know that some event has occurred (i.e., there istransport space available). In addition, MAC may also invoke the MAC-Availability.Indication primitive to “advertise” to the LAC sublayer that there isspace available on the physical channel(s).

5.4 Interaction of Layer and Sublayers 81

Utility

SAR

ARQ

Layer 3 PDU

LAC SDU Encapsulated PDU

EncapsulatedPDU fragments

MAC SDUs

MAC sublayer

r-ds

chLAC SDU

LAC PDU

LAC SDU

LAC SDU

Upper layers

Figure 5.10 Dedicated signaling-reverse link processing: Base station. (After: [2].)

Page 102: 3G CDMA200 Wireless System Engineering

After receiving the MAC-Availability.Indication primitive, LAC sends theMAC-Data.Request primitive to MAC. This primitive requests a data transportservice from MAC by carrying the actual data (as one of its parameters). Here MACis the entity that performs the service. Data is the name of the primitive and signifiesthat the primitive carries actual data. As usual, Request denotes that the primitive isused to request a service, in this case one of data transport [2].

5.4.2 Receive Side

Figure 5.12 shows the interaction of primitives when receiving signaling data. TheMAC sublayer sends the SAR sublayer each encapsulated PDU fragment usingthe MAC-Data.Indication primitive. In this case, MAC is the entity that performsthe service (i.e., receiving signaling data and passing it onto LAC). Data signifies thatthis is a primitive that carries the actual data, and Indication is a primitive that issent from a service provider (e.g., MAC) to a service requester (e.g., LAC). MACuses this primitive to “indicate” to LAC that signaling data has been received byMAC and delivered to LAC.

After processing, LAC sends Layer 3 PDU to Layer 3 using the L2-Data.Indica-tion primitive. In this case, L2 (the entire Layer 2) is designated as the service pro-vider. This is because from the perspective of Layer 3, Layer 2 is the entity thatprovides the service to Layer 3 [2].

82 Signaling Link Access Control

Upper layers

MA

C-S

DU

Read

y.Re

que

st

MA

C-A

vaila

bilit

y.In

dica

tion

MA

C-D

ata.

Req

uest

Sign

alin

gda

ta

Laye

r3

Laye

r2

LAC sublayer

L2-D

ata.

Req

uest

MAC sublayer

Figure 5.11 Interaction of primitives: Transmit side. Note that primitives used in notifyingextraordinary and error conditions are not shown.

Page 103: 3G CDMA200 Wireless System Engineering

References

[1] Fitzgerald, J., and A. Dennis, Business Data Communications and Networking, New York:John Wiley and Sons, 2004.

[2] TIA/EIA/IS-2000.4-A, Signaling Link Access Control (LAC) Standard for cdma2000Spread Spectrum Systems, Telecommunications Industry Association, March 2000.

[3] TIA/EIA/IS-2000.1-A, Introduction to cdma2000 Standards for Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

5.4 Interaction of Layer and Sublayers 83

Upper layers

MA

C-D

ata.

Indi

catio

n

Sign

alin

gda

ta

Laye

r3

Laye

r2

LAC sublayer

L2-D

ata.

Req

uest

MAC sublayer

Figure 5.12 Interaction of primitives: Receive side. Note that primitives used in notifying extraor-dinary and error conditions are not shown.

Page 104: 3G CDMA200 Wireless System Engineering

.

Page 105: 3G CDMA200 Wireless System Engineering

C H A P T E R 6

Signaling: Upper Layers

6.1 Overview

The signaling entity (see Figure 6.1) is the one that effectively controls the operationof the entire IS-2000 system. In doing so it follows state transitions that have beenspecified by the IS-2000 standard. In addition, the signaling entity also controls andexecutes those functions that are necessary for the setup, maintenance, and teardown of a call.

85

f-cs

ch

f-cs

ch

r-cs

ch

f-dt

ch

f-ds

ch

r-dt

ch

r-ds

ch

f-dt

ch(v

oice

)r-

dtch

(voi

ce)

RLP

SDU

RLP

SDU

L3PD

U

L3PD

UUp

per

laye

rsLA

Csu

blay

er

LAC

PDU

MA

Csu

blay

erPh

ysic

alla

yer

Laye

r3

Laye

r2

Laye

r1 R-

CC

CH

R-EA

CH

R-A

CH

F-D

CC

H

F-SC

HF-

FCH

R-D

CC

H

R-SC

H

R-FC

H

F-BC

CH

F-C

CC

HF-

PCH

F-C

PCC

HF-

CA

CH

F-SY

NC

H

Reverse link: coding and modulationForward link: demodulation and decoding

Common channelmultiplex sublayer

Dedicated channelmultiplex sublayer

SRBP RLP

Signaling LAC

Signaling Dataservices

Voiceservices

Data burst

Data burst

Reverse link

Forward link

Figure 6.1 Structure of the protocol architecture in IS-2000 as shown from the perspective of themobile. (After: [1].)

Page 106: 3G CDMA200 Wireless System Engineering

Overall, the operation of the signaling entity can be viewed along two dimen-sions: states and functions. See Figure 6.2. From the perspective of states and statetransitions, the signaling entity enters and exits states and substates depending onwhich stage of the call processing cycle it is in. At the top level, the IS-2000 standardspecifies four states: (1) mobile station initialization, (2) mobile station idle, (3) sys-tem access, and (4) mobile station control on the traffic channel. These states aresimilar to those in IS-95. Furthermore, in packet data transmission a mobile may bein one of several modes and transition between these modes. These modes areunique to IS-2000 and are implemented to accommodate bursty packet data trans-missions and to conserve air link resources.

The dimension of functions provides another perspective on the operation of thesignaling entity. Here, the signaling entity effectively controls and executes differentfunctions that are required for call processing. These functions include but are notlimited to registration, handoff, and power control. In performing these functions,the signaling entity originates and receives messages. In originating a message, thesignaling entity (e.g., at the mobile) requests Layer 2 to deliver the message to itscounterpart at the other side (e.g., at the base station). In receiving a message, thesignaling entity takes delivery of the message from Layer 2 that was transmitted bythe other side.

Before we begin, it would be instructive to highlight the difference between theterms “message” and “data unit” (e.g., PDU or SDU). For example when the signal-ing entity at the mobile sends an origination message, the message is sent as a PDU,and its first physical destination is the LAC sublayer. However, the message itself isreally intended logically for the signaling entity across the link at the base station.Therefore, the best way to distinguish between message and data unit is to use mes-sage in a logical and semantic context and to use data unit in a physical and protocolcontext. When referring to interactions between two entities, such as between thesignaling entity at the base station and the signaling entity at the mobile, use theterm message since a message is logically sent from one entity to another. Whenreferring to interactions between two protocol layers, such as between Layer 3 andLayer 2, use the term data unit (e.g., PDU or SDU) since a data unit sent by a higherlayer is successively processed by lower layers for the eventual transmission overthe air.

86 Signaling: Upper Layers

Functions andmessage processing

Stat

esan

dst

ate

tran

sitio

ns

Figure 6.2 Two dimensions of signaling operation.

Page 107: 3G CDMA200 Wireless System Engineering

The next section (Section 6.2) describes the states and state transitions related tocall processing. Then Section 6.3 focuses on packet data transmission and covers theassociated modes and mode transitions. Finally, Section 6.4 solidifies the materialslearned on signaling by going through several call flow examples, including bothvoice calls and packet data calls.

6.2 State Transitions: Call Processing

The IS-2000 standard specifies four states for the signaling entity (or Layer 3) at themobile: (1) mobile station initialization state, (2) mobile station idle state, (3) sys-tem access state, and (4) mobile station control on the traffic channel state. Similarto IS-95, the IS-2000 standard largely specifies the states and substates for themobile station. But it is obvious that whatever functions the base station performs,they must work with the specified mobile states and substates. The infrastructurevendors have flexibility here to implement their own functions at the base station tosatisfy specified call processing requirements [2, 3].

Figure 6.3 shows these top-level states and their transitions. After power up, themobile enters the initialization state. After a call is finished, the mobile returns to theinitialization state.

6.2 State Transitions: Call Processing 87

Power-upMSinitializationstate

MSidlestate

Systemaccessstate

MS controlon the trafficchannelstate

Mobileselectsandacquiressystem

Mobilemonitorsmessageson f-csch

Mobilesendsmessageson r-cschandreceivesmessageson f-csch

Mobilecommunicateswith basestation ontrafficchannel

Mobile hasacquired system

Mobile responds toorder or message,originates a call, orperforms registration

Mobile is directedto traffic channel

Call is terminated

Power-down

Mobile needsto reacquiresystem

Mobile performs registrationor responds without making call

Figure 6.3 State and state transitions at the mobile. (After: [2] and [4].)

Page 108: 3G CDMA200 Wireless System Engineering

While in the initialization state, the mobile selects and acquires a system. Afterthe mobile acquires the system, it enters the idle state where the mobile monitorsmessages on the f-csch. The mobile stays in the idle state until it receives a message(on the f-csch) or originates a call or performs registration (on the r-csch). If any oneof these three events occurs, then the mobile enters the system access state where itsends messages on the r-csch and receives messages on the f-csch. If call originationis successful, the mobile is directed to a traffic channel1 by the base station, in whichcase the mobile enters the mobile station control on the traffic channel state. In thisstate, the mobile communicates with the base station using the traffic channel [4].

There are events that can cause the mobile to return to a previous state. If amobile loses the paging channel, forward common control channel, or broadcastcontrol channel, or if it goes from CDMA to AMPS, then the mobile transitionsfrom the idle state back to the initialization state to reacquire the system or toacquire another system. In addition, if a mobile performs a registration withoutmaking a call, it returns from the system access state back to the idle state. Note thatideally power down provides an exit from the idle state, but in reality power downcan cause an exit from any one of the four states.

6.2.1 Initialization State

After powering up, the mobile enters the initialization state, which contains foursubstates. The mobile goes through these four substates in sequence:

• System determination substate;• Pilot channel acquisition substate;• Sync channel acquisition substate;• Timing change substate.

These substates are similar to those previously specified by IS-95.

6.2.1.1 System Determination Substate

The system determination substate is the first substate that the mobile enters uponentering the initialization state. In this substate, the mobile selects which system touse (e.g., system A or system B in the cellular band). Alternatively, the mobile canalso be redirected to a different system using the information received in the serviceredirection message, global service redirection message, or extended global serviceredirection message.

6.2.1.2 Pilot Channel Acquisition Substate

In the pilot channel acquisition substate, the mobile demodulates and acquires theforward pilot channel of the selected system. The mobile has to acquire the pilotwithin a specific time limit T20m (defined by [4] as 15 seconds). If it does, then it

88 Signaling: Upper Layers

1. In terms of logical channels, a “traffic channel” is either forward or reverse dedicated traffic channel (f-dtchor r-dtch) or forward or reverse dedicated signaling channel (f-dsch or r-dsch).

Page 109: 3G CDMA200 Wireless System Engineering

enters the sync channel acquisition substate. If it does not, then it goes back to thesystem determination substate.

6.2.1.3 Sync Channel Acquisition Substate

In the sync channel acquisition substate, the mobile proceeds to acquire the syncchannel and receive the sync channel message. The mobile obtains the system timinginformation, such as the pilot PN offset (PILOT_PN), the system time (SYS_TIME),and long code state (LC_STATE), from the sync channel message. These enable themobile to sync up its long PN code [2] and to acquire subsequent common signalingchannels (e.g., paging channel or forward common control channel) later.

In addition, the mobile also obtains system configuration information, such asthe minimum protocol revision level supported by the base station (MIN_P_REV)and whether or not the base station supports broadcast control channel(SR1_BCCH_SUPPORTED), from the sync channel message. In general, a protocolrevision level of six or greater shows that the mobile or the system supports 3Gcapabilities.

The mobile needs to receive the sync channel message within a specific timelimit T21m (defined by [4] as 1 second) upon entering this substate. If it does not, thenthe mobile returns to the system determination substate.

6.2.1.4 Timing Change Substate

In the timing change substate, the mobile synchronizes its own timing and long PNcode phase to those of the system. It does this by using three parameters obtainedfrom the sync channel message (i.e., PILOT_PN, SYS_TIME, and LC_STATE).After the mobile has fully acquired the system, it enters the mobile station idle state.

6.2.2 Mobile Station Idle State

A mobile typically spends a majority of its time in the mobile station idle state, Inthis state, the mobile primarily monitors for messages sent on the F-PCH, F-QPCH,F-CCCH, or F-BCCH. The following sections describe different ways the mobilecan monitor these channels.

6.2.2.1 Monitoring Paging Channel

If a mobile operates in the IS-95 mode, then it monitors only the F-PCH. The pagingchannel transmission is divided into slots that are 80 ms in length (see Chapter 2).The mobile monitors the paging channel for two types of messages: (1) specific mes-sages that are intended for specific mobiles (e.g., page message), and (2) broadcastmessages that are intended for all mobiles (e.g., system parameters message).

There are two ways that the mobile can monitor the paging channel: nonslottedmode or slotted mode. In nonslotted mode, the mobile monitors the paging channelat all times. In slotted mode, the mobile monitors the paging channel only during itsassigned paging channel slots. Because the mobile doesn’t have to monitor all theslots all the time, the mobile operating in slotted mode uses less battery power.

6.2 State Transitions: Call Processing 89

Page 110: 3G CDMA200 Wireless System Engineering

6.2.2.2 Monitoring Quick Paging Channel

In IS-95, using slotted mode on the paging channel does have a couple of disadvan-tages. From the base station’s perspective, it is inefficient because when the base sta-tion has a mobile-specific page to send, it cannot immediately send it. The basestation has to wait for the right slot to come along to send the page. As a result, themobile often does not receive its designated page immediately. From the mobile’sperspective, while the mobile saves some battery power by only monitoring itsassigned slot, the assigned slot still lasts 80 ms. At the beginning of its assigned slot,the mobile still has to wake up to monitor the entire 80-ms slot, and most of the timethere is no page directed at the mobile in the slot.

In IS-2000, the F-QPCH is added to alleviate the drawbacks described above. Aquick paging channel slot also lasts 80 ms. But the mobile monitors only its desig-nated (and shorter) paging indicator bits in the quick paging channel slot. The exactpositions of a mobile’s paging indicators are determined by a hash algorithm. If thepaging indicators show that there is no mobile-specific message, then the mobiledoes nothing. If the paging indicators show that there is a mobile-specific messagecoming in, then the mobile wakes up and monitors the paging channel slot thatcomes after the end of the current quick paging channel slot. In this regard, theF-QPCH works with a paging channel in slotted mode.

In addition to working with the paging channel, the F-QPCH can also workwith a F-CCCH operating in slotted mode. The use of the F-CCCH is described inmore detail in the next section.

6.2.2.3 Monitoring Forward Common Control Channel (F-CCCH )and BroadcastControl Channel (F-BCCH)

In IS-95, a mobile monitors the paging channel for both specific and broadcast mes-sages. But using a single paging channel to transmit these two types of messages isnot very efficient because of their different queuing characteristics. The broadcastmessages are sent at more regular intervals, while the specific messages are sent on-demand. Mixing two statistically different types of messages on the same channelresults in less-than-optimal scheduling of the paging channel. Furthermore, recallthat IS-95 allows up to seven paging channels per carrier; since each mobile onlymonitors one paging channel, if there are more than one paging channels in thecarrier then broadcast system messages would have to be duplicated on all pagingchannels.

IS-2000 added two additional channels: F-CCCH and F-BCCH to alleviate theresponsibilities of the paging channel. The F-CCCH is used to transmit specific mes-sages intended for particular mobiles, and the F-BCCH is used to transmit broadcastsystem messages intended for all mobiles. The mobile needs to monitor both theF-CCCH and F-BCCH for both types of messages.

In monitoring the F-CCCH, the mobile may operate in either nonslotted modeor slotted mode. In nonslotted mode, a mobile needs to monitor the F-CCCH at alltimes for the specific message intended for it. In slotted mode, the mobile only moni-tors the F-CCCH during its assigned forward common control channel slots, each ofwhich also lasts 80 ms. In addition, a quick paging channel may be used in conjunc-tion with the F-CCCH in slotted mode. This way a mobile only has to monitor thoseF-CCCH slots that actually contain messages intended for it.

90 Signaling: Upper Layers

Page 111: 3G CDMA200 Wireless System Engineering

In monitoring the F-BCCH, a mobile operating in nonslotted mode would haveto monitor the F-BCCH at all times for broadcast messages. In slotted mode, themobile first monitors its specially assigned slots on the forward common controlchannel called broadcast slots. The mobile monitors these broadcast slots forenhanced broadcast pages, which are nothing more than general page messages oruniversal page messages. These broadcast pages then in turn tell the mobile whichfuture broadcast control channel slot to monitor for the broadcast message.

6.2.2.4 Other Functions

In addition to performing those functions described above, the mobile can also per-form other functions in the mobile station idle state. These functions include origi-nating a call, transmitting a user message, and performing a registration. When themobile originates a call, transmits a user message, or performs a registration themobile transitions from the mobile station idle state to the update overhead infor-mation substate of the system access state.

In addition, the mobile can also perform idle handoff in the mobile station idlestate. Idle handoff is described in more detail in Chapter 8.

6.2.3 System Access State

In the system access state, the mobile sends messages to the base station and receivesmessages from the base station. If the mobile receives messages on the paging chan-nel only, then it sends messages on the access channel. If the mobile receives mes-sages on the forward common control channel and broadcast control channel, thenthe mobile sends messages on the enhanced access channel.

There are seven substates in the system access state: (1) update overhead infor-mation substate, (2) page response substate, (3) mobile station origination attemptsubstate, (4) registration access substate, (5) mobile station order/message responsesubstate, (6) mobile station message transmission substate, and (7) priority accessand channel assignment (PACA) cancel substate. Figure 6.4 shows the nominaltransitions among these substates. It is important to note that while in the systemaccess state, the mobile monitors the paging channel or the forward common con-trol channel at all times [4].

6.2.3.1 Update Overhead Information Substate

In this substate, the mobile monitors for broadcast overhead messages on either thepaging channel (IS-95) or the broadcast control channel (3G). These messagesinclude:

• System parameters message, extended system parameters message, andANSI-41 system parameters message;

• Access parameters message and enhanced access parameters message;• Neighbor list message, extended neighbor list message, general neighbor list

message, private neighbor list message, and universal neighbor list message;• CDMA channel list message and extended CDMA channel list message.

6.2 State Transitions: Call Processing 91

Page 112: 3G CDMA200 Wireless System Engineering

If the mobile receives a general page message, then it transitions from this sub-state to the page response substate.

6.2.3.2 Page Response Substate

The mobile moves to this substate after receiving a general page message. While inthis substate, the mobile transmits to the base station a page response message [4].

After receiving the page response message, the base station may send a channelassignment message or extended channel assignment message to the mobile. InIS-2000, the extended channel assignment message contains parameters that themobile uses to start receiving on a forward traffic channel. These parametersinclude information such as the forward and reverse traffic channel radio config-urations (FOR_RC and REV_RC), CDMA_FREQ (frequency assignment),FRAME_OFFSET (frame offset), CODE_CHAN_FCH (fundamental channel codechannel), and QOF_MASK_ID_FCH (quasi-orthogonal function mask). Themobile also receives in the extended channel assignment message some power con-trol parameters. After updating its internal parameters, the mobile then enters the

92 Signaling: Upper Layers

IS

UpdateoverheadinformationsubstateMS

idlestate

MScontrolon thetrafficchannelstate

Pageresponsesubstate

MSmessagetransmissionsubstate

PACAcancelsubstate

Registration accesssubstate

MSoriginationattemptsubstate

MS order/messageresponsesubstate

IS

IS

IS

IS

IS

Receives orderor message thatrequires response

Performsregistrationaccess

Generatesdata burstmessage

Receives generalpage message

Originates call

CancelsPACA call

Receives generalpage message

Receivesgeneralpagemessage

Originates callor reoriginatesPACA call

Receivesgeneralpagemessage

IS: Idle state

Figure 6.4 Nominal transitions among substates in the system access state. (After: [4].)

Page 113: 3G CDMA200 Wireless System Engineering

traffic channel initialization substate of the mobile station control on the trafficchannel state.

6.2.3.3 Mobile Station Origination Attempt Substate

In this substate, the mobile transmits to the base station an origination message [4].After receiving the origination message, the base station may send a channel assign-ment message or extended channel assignment message to the mobile. In IS-2000,the extended channel assignment message contains parameters that the mobile usesto start receiving on a forward traffic channel. The mobile also receives in theextended channel assignment message some power control parameters. After updat-ing its internal parameters, the mobile then enters the traffic channel initializationsubstate of the mobile station control on the traffic channel state.

6.2.3.4 Registration Access Substate

In this substate, the mobile transmits to the base station a registration message [4].The mobile typically enters this substate from the update overhead information sub-state. For example, in performing a power-up registration (without making a call) amobile would transition from mobile station initialization state to mobile stationidle state, then to update overhead information substate and finally to registrationaccess substate. After sending the registration message, it would then return tomobile station idle state.

In addition, while in the idle state the mobile may receive a registration requestorder from the base station. In performing this ordered registration, the mobilewould transition to update overhead information substate and onto registrationaccess substate. After sending the registration message, the mobile would return tomobile station idle state.

6.2.3.5 Mobile Station Order/Message Response Substate

In this substate, the mobile transmits to the base station a response or acknowledg-ment in response to an order or message received. An example of an order from thebase station that requires a response is the base station challenge confirmationorder. This order tells the mobile to update the shared secret data (SSD) as part ofthe authentication procedure. After updating, the mobile then sends back to thebase station a response called SSD update confirmation order indicating a successfulSSD update [4]. Other examples include a status request message from the base sta-tion; the mobile responds to this message by nominally sending a status responsemessage back to the base station.

After sending the required response, the mobile returns to the mobile stationidle state.

6.2.3.6 Mobile Station Message Transmission Substate

In this substate, the mobile transmits to the base station a data burst message. Thesupport of this substate is optional.

6.2 State Transitions: Call Processing 93

Page 114: 3G CDMA200 Wireless System Engineering

6.2.3.7 PACA Cancel Substate

In this substate, the mobile transmits to the base station a PACA cancel message. APACA call is a priority call originated by the mobile for which no traffic channel isavailable, so the call is queued for a priority channel assignment [4]. After receivingan origination message, the base station may send a PACA message to the mobile.This serves to inform the mobile of the queue position of the PACA call or to instructthe mobile to reoriginate the PACA call. PACA is supported for protocol revisionlevels greater than four.

While in queue, the user may direct the mobile to cancel the PACA call, in whichcase the mobile proceeds to PACA cancel substate through update overhead infor-mation substate. After sending the PACA cancel message to the base station, themobile returns to mobile station idle state.

6.2.4 Mobile Station Control on the Traffic Channel State

In this state, the mobile exchanges user information with the base station using for-ward traffic channels and reverse traffic channels. This state contains three sub-states: (1) traffic channel initialization substate, (2) traffic channel substate, and (3)release substate. The mobile nominally goes through these three substates sequen-tially, and it exits from release substate back to system determination substate ofmobile station initialization state [4].

6.2.4.1 Traffic Channel Initialization Substate

In this substate, the mobile checks that it can correctly receive the forward trafficchannel and starts to transmit on the reverse traffic channel. Upon entering this sub-state, the mobile first initialize its variables. For example, the mobile sets its forwardtraffic channel power control variables (e.g., TOT_FRAMES, BAD_FRAMES,DCCH_TOT_FRAMES, DCCH_BAD_FRAMES, SCH_TOT_FRAMES, andSCH_BAD_FRAMES) to zero. While still monitoring all the pilots in the active set,the mobile tunes to the assigned CDMA channel and the assigned forward trafficcode channel, as well as sets its forward and reverse traffic channel frame offsets tothose that are assigned [4].

If the mobile can receive consecutive good frames for a period of 40 ms (2 × 20ms) within one second after entering traffic channel initialization substate, then themobile proceeds to transmit the traffic channel preamble, which is really a sequenceof all-zero frames on the reverse traffic channel. The traffic channel preamble is usedto help the base station acquire the reverse traffic channel. At the same time, if Layer3 at the mobile receives a forward dedicated channel acquired indication from Layer2 within two seconds after receiving those consecutive good frames, then Layer 3enters the traffic channel substate.

6.2.4.2 Traffic Channel Substate

In this substate, the mobile actively exchanges user and/or signaling informationwith the base station. In doing so, the mobile exchanges user information onthe traffic channel and processes dedicated signaling messages. It also performs

94 Signaling: Upper Layers

Page 115: 3G CDMA200 Wireless System Engineering

functions such as traffic channel supervision, pilot monitoring and reporting, powercontrol, and handoff processing.

Recall that in IS-95, the mobile can only transmit on one physical channel at atime. It transmits on the access channel to respond to messages or to access the sys-tem, then it transmits on the traffic channel when a call becomes active. But inIS-2000, the mobile can transmit on more than one physical channel at a time. It cantransmit and receive on the fundamental channel during a voice call, and it can, atthe same time, initiate a packet data call by using the dedicated control channel orsupplemental channel. This means that IS-2000 can support multiple simultaneoussessions.

Each one of these calls (which may occur simultaneously) is characterized by itsservice option connection, which is nothing more than a logical set of parametersthat characterizes that particular call or session. Each service option connection isidentified by a:

• Service option connection reference (CON_REF), which is a unique identifierfor a specific service option connection.

• Service option (SERVICE_OPTION), which specifies the kind of serv-ice/application that is used by this service option connection. For example, theservice option in use may be a voice service using enhanced variable rate coder(service option 3) or high-speed packet data service (service option 33).SERVICE_OPTION is a 16-bit parameter. For a complete list of serviceoptions, consult [5].

• Forward traffic channel traffic type (FOR_TRAFFIC), which specifies thetype of forward traffic channel traffic used to support the service option. Thiscan be either primary traffic or secondary traffic.

• Reverse traffic channel traffic type (REV_TRAFFIC), which specifies the typeof reverse traffic channel traffic used to support the service option. This can beeither primary traffic or secondary traffic.

Supporting simultaneous sessions means that there can be more than one serviceoption connection at any given time. If Layer 3 at the mobile receives a request torelease a call, then one of two things can occur. First, if the corresponding serviceoption connection is not the only one connected (e.g., there is another service optionconnection connected), then the mobile requests the release of this service optionconnection by sending a resource release request message, resource release requestminimessage, or service request message. Second, if the corresponding serviceoption connection is the only one connected, then the mobile enters the release sub-state [4].

6.2.4.3 Release Substate

In this substate, the mobile releases the call and releases its occupation of the physi-cal channel(s). It does so by sending a release order, extended release response mes-sage, or extended release response minimessage back to the base station. Afterreleasing the call, the mobile nominally returns to system determination substate ofmobile station initialization state.

6.2 State Transitions: Call Processing 95

Page 116: 3G CDMA200 Wireless System Engineering

6.3 Mode Transitions: Packet Data Transmission

The state transitions described above are used to manage over-the-air resources inan IS-2000 system. In particular, it is in the traffic channel substate (of the mobilestation control on the traffic channel state) when the system actively exchanges userdata over the air. A distinguishing feature of IS-2000 is that it can exchange high-rate packet data over the air. Packet data transmissions are bursty in nature withtransmissions followed by quiet periods, and it is not desirable to hold on to over-the-air resources during quiet periods.

IS-2000 accommodates intermittent packet data transmissions by using twomodes while the mobile is in the traffic channel substate: active mode and controlhold mode2 [4].

6.3.1 Active Mode

In the active mode, there is an active exchange of user packet data and dedicated sig-naling data between the mobile and the base station. As such, the reverse pilot chan-nel is not gated (i.e., PILOT_GATING_USE_RATE = 0). User data can only beexchanged in the active mode, and user data is exchanged using the supplementalchannel and could be simultaneously exchanged using the dedicated control channel(or fundamental channel) with the supplemental channel [6]. In addition, dedicatedsignaling data is exchanged using the dedicated control channel.

6.3.2 Control Hold Mode

In the control hold mode, there is no exchange of user packet data between themobile and the base station, and the reverse pilot channel may be gated to minimizeinterference on the air link (i.e., PILOT_GATING_USE_RATE = 1 andPILOT_GATING_RATE ≠ ‘00’). However, the dedicated control channel is activein this mode. Here, the system maintains MAC control and power control (throughthe dedicated control channel) and saves the parameters (e.g., Walsh code) related tothis call. This is done to allow the next packet data (burst) transmission to beginimmediately with no delay (due to power control stabilization and call setup) [7]. Tofurther minimize interference, the dedicated control channel may operate in discon-tinuous (DTX) mode, which allows its transmissions to be gated [6].

6.3.3 Dormant Mode

In addition to active and control hold modes, there is the dormant mode. In the dor-mant mode, there is no exchange of user packet data and no exchange of signalingdata between the mobile and the base station. In other words, no over-the-airresources are assigned. However, information regarding the user’s packet data serv-ice registration and PPP connection is still kept [7]. Since no air link resources areassigned in this mode, the dormant mode by definition should coincide with themobile station idle state.

96 Signaling: Upper Layers

2. The packet option that uses both of these modes is known as packet option P2. Packet option P1 has no con-trol hold mode [6].

Page 117: 3G CDMA200 Wireless System Engineering

6.3.4 Transitions

The mobile enters the active mode if there is packet data to send. Signaling messagesthat effect the transition to the active mode include the extended supplementalchannel assignment message, forward supplemental channel assignment mini-message, or reverse supplemental channel assignment minimessage. The messageassigns a supplemental channel for packet data burst and moves the mobile into theactive mode (see Section 6.4.4).

The mobile may exit the active mode to the control hold mode through timeout,which triggers the necessary signaling (e.g., extended release message or extendedrelease minimessage). There exists a timer setting the maximum time the mobilemay be in the active mode after sending a packet data transmission [6]. If the timerexpires, the mobile must give up its supplemental channel and transitions to the con-trol hold mode.

The mobile may exit from the control hold mode to the dormant mode alsothrough timeout which triggers the associated signaling (e.g., extended release mes-sage, extended release minimessage, or release order). There exists a timer settingthe maximum time the mobile may spend in the control hold mode (and keep thededicated control channel) after first entering the control hold mode [6]. If thetimer expires, the mobile must give up its dedicated control channel and transitionsto the dormant mode. Figure 6.5 depicts the different modes and the transitionsbetween them.

6.4 Channel Setup

In this section we provide another perspective on call processing and packet datatransmission by going through four different call setup examples. The first exampleis a standalone voice call that is initiated by the base station. The second example isa standalone voice call that is initiated by the mobile. The third example is a standa-lone packet data call that is initiated by the mobile. Since the base station rarely ini-tiates a standalone packet data call by itself, the mobile-initiated example is the onlystandalone packet data call setup we describe. Finally, the fourth example dealswith how the mobile and the base station request for supplemental channelresources during a packet data call.

6.4 Channel Setup 97

Activemode

Controlholdmode

Dormantmode

Timeout

There is data to send

There is data to send

Timeout

Figure 6.5 Active, control hold, and dormant modes and transitions.

Page 118: 3G CDMA200 Wireless System Engineering

6.4.1 Example 1: Base Station-Originated Voice Call

When initiating a call that is terminated at the mobile, the base station first sends ageneral page message on the F-PCH or F-CCCH. See Figure 6.6. The general pagemessage specifies the service option for voice call through the SERVICE_OPTIONfield (e.g., service option 3 for enhanced variable rate voice service). The mobileresponds by sending a page response message on the R-ACH or R-EACH. Uponreceiving the page response message, the base station sends the base stationacknowledgment order on the F-PCH or F-CCCH. At the same time, the base sta-tion sets up the traffic channel and starts to send null traffic channel data on theF-FCH. Then the base station sends a channel assignment message or extendedchannel assignment message on F-PCH or F-CCCH.

The mobile also sets up the traffic channel using the information it receives inthe channel assignment message or extended channel assignment message. It firstverifies that it can receive N5m consecutive good frames, then it begins transmittingthe traffic channel preamble and null traffic channel data on the R-PICH. After

98 Signaling: Upper Layers

Basestation

Channel assignment message or extended channel assignment message

Base station acknowledgment order

F -PCH or F -CCCH

Null traffic channel data

F-FCH

F-PCH or F-CCCH

Traffic channel preamble and null traffic channel data

R-PICH

Service connect completion message

R-FCH

User voice data

F-FCH and R-FCH

Set up trafficchannel

Set up trafficchannel

Receive Nconsecutivegood frames

5m

Service connect message

Base station acknowledgment order

F-FCH

F-FCH

Acquire reversetraffic channel

General page message

F-PCH or F-CCCH

Page response message

R-ACH or R-EACH

Mobilestation

Figure 6.6 Example 1: Setup of voice call initiated by the base station.

Page 119: 3G CDMA200 Wireless System Engineering

receiving the traffic channel preamble, the base station sends the base stationacknowledgment order on the F-FCH.

The service parameters are finalized when the base station transmits the serviceconnect message on the F-FCH. The mobile responds with a service connect com-pletion message on the R-FCH, after which the mobile and the base station begin toactively exchange user voice data over the air link. The user voice data may includevoice traffic, as well as in-traffic messages sent over the F-FCH and R-FCH such asalert with information message (i.e., ring) and connect order [4].

6.4.2 Example 2: Mobile Station-Originated Voice Call

As shown in Figure 6.7, after the user presses the SEND key the mobile transmits theorigination message on the R-ACH or R-EACH. The origination message specifiesthe service option for voice call through the field SERVICE_OPTION (e.g., serviceoption 3 for enhanced variable rate voice service). The base station responds bysending a base station acknowledgment order on the F-PCH or F-CCCH. At thesame time, the base station sets up the traffic channel and starts to send null traffic

6.4 Channel Setup 99

Basestation

Channel assignment message or extended channel assignment message

Null traffic channel data

F-FCH

F-PCH or F-CCCH

Traffic channel preamble and null traffic channel data

R-PICH

Service connect completion message

R -FCH

User voice data

F-FCH and R-FCH

Set up trafficchannel

Set up trafficchannel

Receive Nconsecutivegood frames

5m

Service connect message

Base station acknowledgment order

F-FCH

F-FCH

Acquire reversetraffic channel

Origination message

F-ACH or R-EACH

Base station acknowledgment order

F-PCH or F-CCCH

Mobilestation

Figure 6.7 Example 2: Setup of voice call initiated by the mobile station.

Page 120: 3G CDMA200 Wireless System Engineering

channel data on the F-FCH. Then the base station sends a channel assignment mes-sage or extended channel assignment message on F-PCH or F-CCCH.

The mobile also sets up the traffic channel using the information it receives inthe channel assignment message or extended channel assignment message. It firstverifies that it can receive N5m consecutive good frames, then it begins transmittingthe traffic channel preamble and null traffic channel data on the R-PICH. Afterreceiving the traffic channel preamble, the base station sends the base stationacknowledgment order on the F-FCH.

The service parameters are finalized when the base station transmits the serviceconnect message on the F-FCH. The mobile then responds with a service connectcompletion message on the R-FCH, after which the mobile and the base stationbegin to actively exchange user voice data over the air link [4].

6.4.3 Example 3: Mobile Station-Originated Packet Data Call

The setup of a packet data call is similar to that of the voice call. See Figure 6.8. Themobile first transmits an origination message on the R-ACH or R-EACH. The origi-nation message specifies the service option for a high-speed packet data call (e.g.,service option 33); unlike the origination message for a voice call, the originationmessage for a packet data call contains no dialed digits. The base station responds by

100 Signaling: Upper Layers

Basestation

Channel assignment message or extended channel assignment message

Null traffic channel data

F-FCH or F-DCCH

F-PCH or F-CCCH

Traffic channel preamble and null traffic channel data

R-PICH

Service connect completion message

User packet dataF-FCH and R-FCH, or F-DCCH and R-DCCH

Set up PDSNresources

Set uptrafficchannel

Service connect message

Base station acknowledgment order

F-FCH or F-DCCH

Acquire reversetraffic channel

Origination message

F-ACH or R-EACH

Base station acknowledgment order

F-PCH or F-CCCH

Mobilestation

F-FCH or F-DCCH

F-FCH or F-DCCH

A

Figure 6.8 Example 3: Packet data call setup.

Page 121: 3G CDMA200 Wireless System Engineering

sending a base station acknowledgment order on the F-PCH or F-CCCH. At thesame time, the base station initiates the setup of packet data service node (PDSN)resources and starts to send null traffic channel data on the F-FCH or F-DCCH. Thebase station then sends a channel assignment message or extended channel assign-ment message on F-PCH or F-CCCH.

The mobile sets up the traffic channel using the information it receives in thechannel assignment message or extended channel assignment message. It beginstransmitting the traffic channel preamble and null traffic channel data on theR-PICH. After receiving the traffic channel preamble, the base station sends thebase station acknowledgment order on the F-FCH or F-DCCH.

The service parameters are finalized when the base station transmits the serviceconnect message on the F-FCH or F-DCCH. The mobile responds with a serviceconnect completion message on the R-FCH or R-DCCH, after which the mobileand the base station begin to exchange user packet data traffic on the forward andreverse fundamental channels or dedicated control channels.

6.4.4 Example 4: Supplemental Channel Request During a Packet Data Call

If the base station and mobile need to exchange bursts of high-rate packet data dur-ing a packet data call, either the base station or the mobile may initiate the requestfor supplemental channel resources. The following two sections describe each ofthese two cases: base station-initiated request and mobile station-initiated request.

6.4.4.1 Base Station-Initiated Request of Supplemental Channels

If the base station wishes to send a burst of high-rate packet data during a packetdata call, it may request a temporary use of the supplemental channel. The base sta-tion sets up supplemental channel resources by sending an extended supplementalchannel assignment message (ESCAM) on the F-FCH or F-DCCH. The ESCAM is arather large message that, among other things, updates the supplemental channelcode list (SCCL). The SCCL specifies a list of F-SCH configurations that canbe used.

The ESCAM may also include forward and reverse supplemental channelassignments that are to be immediately used. For the R-SCH, the ESCAM may spec-ify fields such as:

• REV_SCH_ID (reverse supplemental channel identifier);• REV_SCH_START_TIME (start time of the assignment of the reverse supple-

mental channel);• REV_SCH_DURATION (duration of the assignment of the reverse supple-

mental channel);• REV_SCH_NUM_BITS_IDX (index of the reverse supplemental channel

number of bits per frame).

These tell the mobile that it may transmit supplemental channel REV_SCH_IDstarting at time REV_SCH_START_TIME for a period of REV_SCH_DURATIONusing the configuration specified by REV_SCH_NUM_BITS_IDX.

6.4 Channel Setup 101

Page 122: 3G CDMA200 Wireless System Engineering

For the F-SCH, the ESCAM may specify fields such as:

• FOR_SCH_ID (forward supplemental channel identifier);• FOR_SCH_START_TIME (start time of the assignment of the forward sup-

plemental channel);• FOR_SCH_DURATION (duration of the assignment of the forward supple-

mental channel);• SCCL_INDEX (index of the supplemental channel code list).

These tell the mobile that it may receive supplemental channel FOR_SCH_IDstarting at time FOR_SCH_START_TIME for a period of FOR_SCH_DURATIONusing the configuration specified by SCCL_INDEX.

After the successful reception of ESCAM, the subsequent assignments of theF-SCH and R-SCH can be done by the use of forward supplemental channel assign-ment mini message (FSCAMM) and reverse supplemental channel assignmentmini message (RSCAMM). These messages are very short, each containing onlyfour fields totaling 14 bits. For assigning the R-SCH, the RSCAMM containsonly those four R-SCH assignment fields mentioned above (i.e., REV_SCH_ID,REV_SCH_START_TIME, REV_SCH_DURATION, and REV_SCH_NUM_BITS_IDX). For assigning the F-SCH, the FSCAMM contains only thosefour F-SCH assignment fields mentioned above (i.e., FOR_SCH_ID,FOR_SCH_START_TIME, FOR_SCH_DURATION, and SCCL_INDEX). Theseshort minimessages enable a very quick allocation of supplemental channels. In fact,the base station and the mobile do not even have to send “release orders” for supple-mental channels because their assignments only last FOR_SCH_DURATION andREV_SCH_DURATION. Hence using minimessages quickens supplemental chan-nel assignments and conserves air link resources.

Figure 6.9 shows an example of the assignment of supplemental channels that isfirst initiated by the base station. The base station first sends an ESCAM to the

102 Signaling: Upper Layers

A

Basestation

Mobilestation

Extended supplemental channel assignment messageF-FCH or F-DCCH

High-rate user packet dataF-SCH and/or R-SCH

Forward supplemental channel assignment minimessageand/or

Reverse supplemental channel assignment minimessageF-FCH or F-DCCH

High-rate user packet dataF-SCH and/or R-SCH

Figure 6.9 Supplemental channel assignment initiated by the base station.

Page 123: 3G CDMA200 Wireless System Engineering

mobile. The ESCAM updates the SCCL that specifies a list of F-SCH configurationsthat can be used. The mobile later can quickly refer to which F-SCH configurationto use by referencing the SCCL_INDEX. In the same ESCAM, the base station mayelect to include those F-SCH assignment fields (e.g., FOR_SCH_START_TIME)and R-SCH assignment fields (e.g., REV_SCH_START_TIME) that are to be usedimmediately for an exchange of high-rate packet data.

If the ESCAM contains assignment fields that are to be immediately used, thenthe mobile uses those parameters to exchange bursts of high-rate packet data withthe base station on the F-SCH and R-SCH. After this initial exchange, there may bea quiet period when there is no high-rate data exchange. During this time, the physi-cal supplemental channel resources are released and assigned to other users in thesame carrier. However, if after a period of time the base station elects to transmitanother burst of high-rate packet data, it sends the FSCAMM and/or RSCAMM toquickly assign forward and/or reverse supplemental channels. Then the base stationand the mobile may again exchange high-rate packet data on the assigned supple-mental channels.

6.4.4.2 Mobile Station-Initiated Request of Supplemental Channels

Figure 6.10 shows an example of mobile-initiated request for supplemental chan-nels. If during a packet data call the mobile wishes to set up supplemental channelresources for the first time (i.e., it has not received an ESCAM), then the mobile first

6.4 Channel Setup 103

Basestation

Mobilestation

Extended supplemental channel assignment message

F-FCH or F-DCCH

High-rate user packet data

F-SCH and/or R-SCH

Forward supplemental channel assignment minimessageand/or

Reverse supplemental channel assignment minimessage

F-FCH or F-DCCH

High-rate user packet data

Supplemental channel request minimessage

R-FCH or R-DCCH

F-SCH and/or R-SCH

Supplemental channel request minimessage

R-FCH or R-DCCH

A

Figure 6.10 Supplemental channel assignment initiated by the mobile station.

Page 124: 3G CDMA200 Wireless System Engineering

transmits a supplemental channel request mini message (SCRMM). This minimes-sage contains only one field that is 16-bits long. The field is REQ_BLOB or thereverse supplemental channel request block of bytes. REQ_BLOB contains informa-tion specifying the characteristics of the reverse supplemental channel requests [4].

The base station responds by transmitting an ESCAM. The ESCAM updates theSCCL that contains a list of F-SCH configurations that can be used. The mobile canlater quickly identify a specific F-SCH configuration to use by referencing theSCCL_INDEX. If the ESCAM contains the F-SCH assignment information (e.g.,FOR_SCH_START_TIME) and/or R-SCH assignment information (e.g.,REV_SCH_START_TIME) that is to be immediately used, then the mobile and thebase station starts exchanging high-rate packet data for a period ofFOR_SCH_DURATION and/or REV_SCH_DURATION.

The mobile’s subsequent requests for supplemental channels can be accom-plished by sending another SCRMM. The base station responds by transmitting theFSCAMM and/or RSCAMM. The FSCAMM and RSCAMM contain assignmentinformation for F-SCH and R-SCH, and the mobile can use this information toagain exchange high-rate packet data for a given period.

6.4.5 Concluding Remarks

Although the above examples describe voice and packet data calls that are standa-lone, the IS-2000 standard supports simultaneous voice and packet data calls. Forexample, if during a voice call the mobile wishes to initiate a packet data call, themobile may send an enhanced origination message (typically as an in-traffic messageon the R-FCH) to request a simultaneous packet data call. After the base stationresponds with a service connect message, a separate packet data call becomes active.

In addition, the IS-2000 standard also supports the power control of supplemen-tal channels that is independent of fundamental channels. When the base station ini-tially transmits the (large) ESCAM, the ESCAM also contains power control fieldsthat are used to power control supplemental channels. These fields includeFPC_SCH_FER (the target frame error rate of supplemental channel),FPC_SCH_MIN_SETPT (the minimum outer loop Eb/N0 set point of supplementchannel), and FPC_SCH_MAX_SETPT (the maximum outer loop Eb/N0 set point ofsupplemental channel) [4].

References

[1] TIA/EIA/IS-2000.1-A, Introduction to cdma2000 Standards for Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

[2] Yang, S. C., CDMA RF System Engineering, Norwood, MA: Artech House, 1998.[3] Garg, V. K., K. Smolik, and J. E. Wilkes, Applications of CDMA in Wireless/Personal Com-

munications, Upper Saddle River, NJ: Prentice Hall, 1997.[4] TIA/EIA/IS-2000.5-A, Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread

Spectrum Systems, Telecommunications Industry Association, March 2000.[5] TIA/EIA/TSB-58, Administration of Parameter Value Assignments for cdma2000 Spread

Spectrum Standards, Telecommunications Industry Association, January 2002.

104 Signaling: Upper Layers

Page 125: 3G CDMA200 Wireless System Engineering

[6] Yoon, S. Y., and S. W. Lee, “Forward Link Performance of Medium Access Control forIS-2000,” Proceedings of Vehicular Technology Conference, 2001, pp. 2759–2762.

[7] Knisely, D. N., et al., “Evolution of Wireless Data Services: IS-95 to cdma2000,” IEEECommunications, October 1998, pp. 140–149.

6.4 Channel Setup 105

Page 126: 3G CDMA200 Wireless System Engineering

.

Page 127: 3G CDMA200 Wireless System Engineering

C H A P T E R 7

Power Control

7.1 Introduction

The IS-2000 standard has added a host of new features to the function of powercontrol, all aimed at improving its speed and accuracy, which have direct conse-quences on capacity and quality. In terms of capacity, fast and accurate power con-trol minimizes the variances of powers received from multiple transmitters, andminimizing the variances of received powers in the same band allows more users tobe on the system. In terms of quality, fast and accurate power control ensures thateach user has its share of power resources that maintains adequate link quality.These important benefits warrant a separate chapter on power control. In this chap-ter, we focus on those power control topics that are unique to IS-2000.

The IS-95 power control had two limitations. First, the system could onlypower control one physical channel (i.e., traffic channel on the forward link andtraffic channel on the reverse link). Second, power control rate was asymmetricbetween forward and reverse directions. While it could power control (closed loop)reverse traffic channel at a rate of 800-times-per-second, it could only power con-trol (closed loop) forward traffic channel at a peak rate of 50-times-per-second (forRate Set 2).

The IS-2000 standard improves upon these two limitations. First, the systemcan power control multiple physical channels on the forward and reverse links. Sec-ond, the system can now power control (closed loop) both the forward link and thereverse link at 800-times-per-second.

7.2 Power Control of the Forward Link

Since IS-2000 can now also power control the forward link at 800-times-per-second, it is no surprise that power control of the forward link is approximately amirror image of the IS-95 reverse link. Note that since Radio Configurations 1 and 2in IS-2000 correspond to Rate Sets 1 and 2 in IS-95, forward link power control at amaximum rate of 800-times-per-second is only available for Radio Configurations3 through 6.

7.2.1 Inner Loop and Outer Loop

Once the mobile starts to receive the forward traffic channel and begins to commu-nicate with the base station, the mobile continuously monitors the forward link and

107

Page 128: 3G CDMA200 Wireless System Engineering

measures its link quality. If the link quality starts to get worse, then the mobile willrequest the base station, via the reverse link, to power up. If the link quality becomestoo good, then there is excess signal power on the forward link. In this case, themobile will request the base station to power down. Ideally, FER is a good indica-tion of link quality, but it takes a long time for the mobile to accumulate enough bitsto calculate FER. Thus some signal-to-noise ratio measure (e.g., Eb/N0 that can bequickly calculated) can be used as an indicator of forward link quality [1, 2].

The closed-loop power control of the forward link is done as follows:

1. The mobile continuously monitors Eb/N0 on the forward link.2. If Eb/N0 is too high (i.e., if it exceeds a certain threshold), then the mobile

requests the base station to decrease the base station transmit power.3. If Eb/N0 is too low (i.e., if it drops below a certain threshold), then the mobile

requests the base station to increase the base station transmit power.

The mobile requests the base station to power up and down using power controlbits (PCBs) that are multiplexed onto the R-PICH. Hence these PCBs are not errorprotected. Recall that the reason why PCBs are not error protected is to reducedelays that are inherent in decoding error protected bits. Since PCBs are used tocombat fast Rayleigh fading, PCBs are not error protected so that the base stationcan quickly recover them and adjust its transmit power accordingly.

The above describes the inner loop of the closed-loop power control of the for-ward link. The assumption of the inner loop is that there exists a predeterminedEb/N0 threshold by which power-up and power-down decisions are made. Butbecause in a mobile environment the relationship between Eb/N0 and FER is con-stantly changing, the Eb/N0 threshold has to be dynamically adjusted to maintain anacceptable FER. This dynamic adjustment of the Eb/N0 threshold (i.e., Eb/N0 set-point) is referred to as the outer loop of the closed-loop power control [3].

Figures 7.1 and 7.2 show a conceptual illustration of the closed-loop forwardlink power control. Figure 7.1 depicts those functions carried out by the mobile.Here the mobile implements the entire outer loop and part of the inner loop. Themobile receives the forward link from the base station. The mobile first demodulatesthe signal and estimates the FER of the forward link. This information on the for-ward link quality is fed into the outer loop. The outer loop, using current FER andEb/N0 estimates, dynamically computes the new Eb/N0 setpoint required to maintainan acceptable FER. The new Eb/N0 setpoint and the current Eb/N0 estimate are thencompared. If the estimate is greater than the setpoint, then the link Eb/N0 is higherthan what is necessary to maintain a good FER; a PCB of 1 is thus sent to the basestation to request power down. If the estimate is less than the setpoint, then the linkEb/N0 is lower than what is necessary; a PCB of 0 is then sent to request the base sta-tion to power up. The PCBs are multiplexed onto the reverse pilot channel andtransmitted to the base station at a maximum rate of 800-times-per-second.

Figure 7.2 shows the corresponding illustration of the closed-loop forwardlink power control as carried out by the base station. Here the base station has therest of the inner loop. The base station receives the reverse pilot channel signal. Itrecovers the PCB and, based on the PCB, makes a decision to power up or to powerdown [3].

108 Power Control

Page 129: 3G CDMA200 Wireless System Engineering

Note that in Figure 7.1, the outer loop(s) can monitor all forward traffic chan-nels that the mobile is receiving (i.e., forward fundamental channel, forward dedi-cated control channel, and forward supplemental channel). If the outer loop ismonitoring the F-FCH, the outer loop uses as its inputs current Eb/N0 and FER esti-mates of the F-FCH. In addition, the outer loop also takes into account the follow-ing parameters:

• FPC_FCH_FER or the target frame error rate of the F-FCH;• FPC_FCH_INIT_SETPT or the initial setpoint of the F-FCH;

7.2 Power Control of the Forward Link 109

E Nb/ 0estimate

OUTER LOOP

RCVR

Demod FERestimate

Adjust

setpointE Nb/ 0

E Nb/ 0setpoint

FERestimate

Decision:If estimate>setpointthen PCB=1

If estimatesetpointthen PCB=0

<

E Nb/estimate

0

R-PICH Transmitter

RxAntenna

TxAntenna

PCB

Mobile station

E Nb/ 0estimate

Figure 7.1 Forward link power control functions carried out by the mobile.

TxAntenna

RxAntennaBase station

Transmitter Forward traffic channel

Demod

Decision:If PCB=0 thenpower downIf PCB=1 thenpower up

PCB

Powercontroldecisions

RCVR

Figure 7.2 Forward link power control functions carried out by the base station.

Page 130: 3G CDMA200 Wireless System Engineering

• FPC_FCH_MIN_SETPT or the minimum setpoint of the F-FCH;• FPC_FCH_MAX_SETPT or the maximum setpoint of the F-FCH.

Obviously, the new Eb/N0 setpoint computed by the outer loop has to be boundby FPC_FCH_MIN_SETPT and FPC_FCH_MAX_SETPT. These parameters arepart of the nonnegotiable service configuration parameters to be used by the mobile.They are sent in messages like service connect message, general handoff directionmessage, and universal handoff direction message. They can also be sent to themobile in extended channel assignment message and power control message.

If the outer loop is monitoring the F-DCCH, in addition to using as its inputscurrent Eb/N0 and FER estimates of the F-DCCH the outer loop also takes intoaccount the following:

• FPC_DCCH_FER or the target frame error rate of the F-DCCH;• FPC_DCCH_INIT_SETPT or the initial setpoint of the F-DCCH;• FPC_DCCH_MIN_SETPT or the minimum setpoint of the F-DCCH;• FPC_DCCH_MAX_SETPT or the maximum setpoint of the F-DCCH.

The new Eb/N0 setpoint of the F-DCCH computed by the outer loop has to bebound by FPC_DCCH_MIN_SETPT and FPC_DCCH_MAX_SETPT. Theseparameters are part of the nonnegotiable service configuration parameters to beused by the mobile and are sent in messages like service connect message, generalhandoff direction message, and universal handoff direction message. They can alsobe sent to the mobile in extended channel assignment message and power controlmessage.

If the outer loop is monitoring the F-SCH, in addition to using as its inputs cur-rent Eb/N0 and FER estimates of the F-SCH the outer loop also considers the follow-ing parameters1:

• FPC_SCH_FER or the target frame error rate of the F-SCH;• FPC_SCH_INIT_SETPT or the initial setpoint of the F-SCH;• FPC_SCH_MIN_SETPT or the minimum setpoint of the F-SCH;• FPC_SCH_MAX_SETPT or the maximum setpoint of the F-SCH.

The new Eb/N0 setpoint of the F-SCH calculated by the outer loop has to bebound by FPC_SCH_MIN_SETPT and FPC_SCH_MAX_SETPT. These parame-ters are sent in extended supplemental channel assignment message and power con-trol message2 [4].

7.2.2 Power Control of Multiple Forward Traffic Channels

PCBs are carried by the R-PICH using the power control subchannel. The powercontrol subchannel is a structure provided by the R-PICH (or another host physicalchannel) by which PCBs can be transported (see Chapter 3). In addition, the powercontrol subchannel is structured in such as way so that more than one forward

110 Power Control

1. These parameters can be different for the different forward supplemental channels.2. Power control message does not contain FPC_SCH_INIT_SETPT.

Page 131: 3G CDMA200 Wireless System Engineering

traffic channels can be power controlled. IS-2000 uses the parameter forwardpower control operating mode (FPC_MODE) to specify how multiple forward traf-fic channels are power controlled and the rate of power control feedback.

Table 7.1 shows the seven configurations specified by the seven forward powercontrol operating modes when the R-PICH operates in nongated mode. When theR-PICH is not gated, its power control subchannel can be further divided into twostreams (i.e., primary power control subchannel and secondary power control sub-channel). For example, if FPC_MODE = 000 then the power control subchannel isnot divided, and all 16 power control groups are used for a single power controlsubchannel. Here the rate of power control feedback is 800-times-per-second.

However, if FPC_MODE = 001 then the power control subchannel is dividedinto two subchannels; eight of the 16 power control groups are used for the primarysubchannel, and the other eight of the 16 power control groups are used for the sec-ondary subchannel. In this case, the rate of power control feedback is 400-times-per-second for the primary subchannel and 400-times-per-second for the secondarysubchannel.

If FPC_MODE = 010 then again the power control subchannel is divided intotwo subchannels. But here only four of the 16 power control groups are used for theprimary subchannel, while the other 12 power control groups are used for the sec-ondary subchannel. This division yields a rate of power control feedback of 200-times-per-second for the primary subchannel and 600-times-per-second for the sec-ondary subchannel.

7.2 Power Control of the Forward Link 111

Table 7.1 Forward Power Control Operating Modes

FPC_MODE

Primary PCSubchannel onR-PICH

Secondary PCSubchannelon R-PICH Outer Loop

Primary InnerLoop

Secondary InnerLoop

000 PCB @ 800 Hz Not usedF-DCCH;F-FCH; F-SCH

F-FCH orF-DCCH

Not applicable

001 PCB @ 400 Hz PCB @ 400 HzF-DCCH;F-FCH; F-SCH

F-FCH orF-DCCH

F-SCH

010 PCB @ 200 Hz PCB @ 600 HzF-DCCH;F-FCH; F-SCH

F-FCH orF-DCCH

F-SCH

110 PCB @ 400 Hz

EIB @ 50 Hz forF-SCH (20 ms);EIB @ 25 Hz forF-SCH (40 ms);EIB @ 12.5 Hz forF-SCH (80 ms)

F-DCCH;F-FCH

F-FCH orF-DCCH

Not applicable

011EIB @ 50 Hz forF-FCH orF-DCCH

Not used Not applicable Not applicable Not applicable

100QIB @ 50 Hz forF-FCH orF-DCCH

Not used Not applicable Not applicable Not applicable

101QIB @ 50 Hz forF-FCH orF-DCCH

EIB @ 50 Hz forF-SCH (20 ms);EIB @ 25 Hz forF-SCH (40 ms);EIB @ 12.5 Hz forF-SCH (80 ms)

Not applicable Not applicable Not applicable

Page 132: 3G CDMA200 Wireless System Engineering

Furthermore, the primary and secondary power control subchannels can beused to transmit erasure indicator bits (EIBs) or quality indicator bits (QIBs). InRadio Configurations 3 through 6, the mobile uses the EIB to tell the base stationthat a received F-FCH or F-DCCH frame is bad. Recall that in IS-95 Rate Set 2 (orIS-2000 Radio Configuration 2), the mobile uses an EIB to tell the base station that areceived forward traffic channel (or F-FCH) frame is bad. On the other hand, themobile uses a QIB to tell the base station that a received F-DCCH frame is bad.

An EIB or a QIB is transported by combining different power control groups onthe power control subchannel. For example, when FPC_MODE = 011 the systemcombines all 16 power control groups in a 20-ms period to yield one single EIB,resulting in an EIB feedback rate of 1/20 ms or 50-times-per-second.

If FPC_MODE = 000 then the mobile’s outer loop estimates the Eb/N0 setpointfor all forward traffic channels (i.e., F-DCCH, F-FCH, and F-SCH). The mobiletransmits PCBs at 800 bps on the primary (and only) power control subchannel onthe R-PICH. These PCBs are used to perform inner-loop power control for either theF-FCH or the F-DCCH.

If FPC_MODE = 001 then the mobile’s outer loop estimates the Eb/N0 setpointfor all forward traffic channels (i.e., F-DCCH, F-FCH, and F-SCH). The mobiletransmits a stream of PCBs at 400 bps on the primary power control subchannel.This stream of PCBs is used to perform inner-loop power control for either theF-FCH or the F-DCCH. In addition, the mobile also transmits a separate stream ofPCBs at 400 bps on the secondary power control subchannel. These PCBs are usedto perform inner-loop power control for the F-SCH.

The case of FPC_MODE = 010 is similar to that of FPC_MODE = 001, excepthere the PCBs are transmitted at 200 bps on the primary subchannel and at 600 bpson the secondary subchannel.

If FPC_MODE = 110 then the mobile’s outer loop estimates the Eb/N0 setpointfor the F-DCCH and F-FCH. The mobile transmits a stream of PCBs at 400 bps onthe primary power control subchannel. This stream of PCBs can be used to performinner-loop power control for either the F-FCH or the F-DCCH. On the secondarypower control subchannel, the mobile sends EIBs to indicate to the base station thequality of received F-SCH frames. Since one EIB is sent for every received F-SCHframe, the rate of EIB feedback is 1/20 ms or 50 bps for 20-ms F-SCH frames, 1/40or 25 bps for 40-ms SCH frames, and 1/80 ms or 12.5 bps for 80-ms F-SCH frames.The base station uses these EIBs to adjust its transmit power for the F-SCH.

If FPC_MODE = 011 then the mobile does not perform any outer loopestimates of the Eb/N0 setpoint. The mobile only transmits EIBs at 50 bps. TheseEIBs indicate to the base station the quality of the received frames on the F-FCH orthe F-DCCH.

The case of FPC_MODE = 100 is similar to that of FPC_MODE = 011, excepthere the QIBs are transmitted instead of the EIBs.

Lastly, if FPC_MODE = 101 then the mobile does not perform any outer loopestimates of the Eb/N0 setpoint. On the primary power control subchannel, themobile transmits QIBs at 50 bps. These QIBs indicate to the base station the qualityof the received frames on the F-FCH or the F-DCCH. On the secondary power con-trol subchannel, the mobile sends EIBs to indicate to the base station the quality ofreceived F-SCH frames. The EIBs are sent at 50 bps for 20-ms F-SCH frames, 25 bps

112 Power Control

Page 133: 3G CDMA200 Wireless System Engineering

for 40-ms SCH frames, and 12.5 bps for 80-ms F-SCH frames. The base station usesthese EIBs to adjust its transmit power for the F-SCH [3].

In closing, why would a system engineer choose a slower power control feed-back rate (e.g., 50 Hz) using EIBs or QIBs when a faster power control feedback rate(e.g., 800 Hz) is available using PCBs? One advantage of using PCBs in outer-loopand inner-loop power controls is obviously the faster feedback rate. But rememberthat PCBs are not error protected, thus it is possible that many PCBs may bereceived in error and hence degrade forward power control performance. On theother hand, as many as 16 PCBs may be combined to yield one EIB or QIB. There-fore, one advantage of using EIBs and QIBs is that they have lower error rates (allthings being equal). The decision between these two choices reflects a classictradeoff between data transmission rate (feedback rate) and bit-error probability(feedback accuracy).

7.3 Power Control of the Reverse Link: Open Loop

Reverse link power control for IS-2000 Radio Configurations 1 and 2 is identical tothat of IS-95 Rate Sets 1 and 2. Readers can refer to references such as [5–7] for itsdescription. For other radio configurations, the IS-2000 power control of thereverse link is conceptually similar to the one in IS-95, with some enhancements.One significant difference in IS-2000 is that the R-PICH now has a prominent rolein reverse link power control.

We will focus our discussion on those reverse radio configurations (Radio Con-figurations 3 and 4) that support Spreading Rate 1. The discussions are readilygeneralizable to the Spreading Rate 3 radio configurations (Radio Configurations5 and 6). Section 7.3 discusses the open-loop part of the reverse link power control.Section 7.4 discusses the closed-loop part.

7.3.1 Power Control of Multiple Reverse Channels

When a mobile moves around in a cell, the path loss between the mobile and thebase station continues to change, hence the received power at the mobile also con-tinues to change. In open-loop power control, the mobile monitors its receivedpower continuously and adjusts its transmit power accordingly. Note that open-loop power control is done solely by the mobile and does not involve the base sta-tion at all. In IS-2000, the mobile can perform open-loop power control on threetypes of reverse physical channels:

• R-EACH;• R-CCCH;• Reverse traffic channel, including R-DCCH, R-FCH, and R-SCH.

For each of these channels, the open-loop power control is done in two separateparts. In the first part, the mobile calculates the pilot channel transmit power of theR-PICH, which is almost always active. In the second part, the mobile calculates thecode channel transmit power of the reverse channels themselves. See Table 7.2.

7.3 Power Control of the Reverse Link: Open Loop 113

Page 134: 3G CDMA200 Wireless System Engineering

7.3.1.1 Enhanced Access Channel (R-EACH)

Recall from Chapter 3 that an R-EACH transmission consists of two parts: (1) pre-amble, and (2) R-EACH header and/or R-EACH data. The preamble is nothingmore than a reverse pilot channel transmission. Therefore during the transmission ofR-EACH preamble, the mobile (in performing open-loop power control of theR-PICH) calculates the transmit power of the R-PICH. Here the mobile calculates itsR-PICH transmit power based on the following general equation (in decibels):

p p sum of correction factorst,R RICH r− = − + ( ) (7.1)

where pt,R-PICH is the open-loop estimate of the transmit power, and pr is the receivedpower at the mobile. IS-2000 has added some new correction factors that are used incalculating the mobile transmit power. The description of these correction factorscan be found in Section 2.1.2.3.1 of [3] and is not repeated here.

The R-PICH is also active during the transmission of R-EACH header and data.The transmit power of R-PICH during R-EACH header and data transmission is (indecibels)

p p sum of correction factorssumof at,R PICH r− = − + +( )

( ll closed loop powercontrol corrections)(7.2)

The correction factors used here differ slightly from those in (7.1). If the systemperforms closed-loop power control on R-EACH, then the transmit power ofR-PICH also includes the sum of all closed-loop power control corrections. SeeSection 7.4 for more details on closed-loop power control. As the next paragraphwill describe, by controlling the transmit power of R-PICH during R-EACH headerand data transmission, the mobile also controls the transmit power of R-EACHheader and data transmission itself.

The R-EACH header and R-EACH data frames contain data (for signaling).Therefore, during header and data frame transmission, the transmit power of theR-EACH code channel itself needs to be calculated. The transmit power of theR-EACH code channel during header and data frame transmission is (in decibels)

p p sum of gain factorst,R EACH t,R-PICH− = − + ( ) (7.3)

where pt,R-PICH is the transmit power of R-PICH during R-EACH header and dataframe transmission, shown in (7.2). The gain factors are those factors used to adjust

114 Power Control

Table 7.2 Open-Loop Power Control of Reverse Physical Channels

Enhanced AccessChannel

Reverse CommonControl Channel

Reverse TrafficChannel

Reverse Pilot ChannelTransmit Power

Calculate pt of preamble Calculate pt of preamble Calculate pt of reverse pilot

Reverse Code ChannelTransmit Power

Calculate pt of R-EACHheader and R-EACHdata

Calculate pt of R-CCCHdata

Calculate pt of reverse traf-fic channel

Page 135: 3G CDMA200 Wireless System Engineering

the transmit power of the R-EACH code channel based on a variety of parameters,such as data rate and frame length. The description of these gain factors can befound in Section 2.1.2.3.3 of [3] and is not repeated here. As one can see, the trans-mit power of the R-EACH code channel is clearly dependent on the current transmitpower of the R-PICH. In other words, the transmit power of the R-EACH codechannel references that of the R-PICH; as the R-PICH transmit power changes, sodoes the R-EACH transmit power.

7.3.1.2 Reverse Common Control Channel (R-CCCH)

An R-CCCH transmission also consists of two parts: (1) preamble, and (2)R-CCCH data. The R-CCCH preamble is also a reverse pilot channel transmission(see Chapter 3). Therefore, the mobile performs open-loop power control of theR-PICH during the transmission of R-CCCH preamble. Here the mobile calculatesits R-PICH transmit power based on the following general equation (in decibels):

p p sum of correction factorst,R PICH r− = − + ( ) (7.4)

where pt,R-PICH is the open-loop estimate of the transmit power, and pr is the receivedpower at the mobile. The correction factors here have some that are used specificallyfor the transmission of R-CCCH preamble. The description of these correction fac-tors can be found in Section 2.1.2.3.1 of [3] and is not repeated here.

The R-PICH is also active during the transmission of R-CCCH header and data.The transmit power of R-PICH during R-CCCH header and data transmission is (indecibels)

p p sum of correction factorssumof at,R PICH r− = − + +( )

( ll closed loop powercontrol corrections)(7.5)

The description of the correction factors used here can be found in Section2.1.2.3.1 of [3] and is not repeated here. If the system performs closed-loop powercontrol on R-CCCH, then the transmit power of R-PICH also includes the sum ofall closed-loop power control corrections. See Section 7.4 for more details onclosed-loop power control. By power controlling the transmit power of R-PICHduring R-CCCH header and data transmission, the mobile also power controls thetransmit power of R-CCCH header and data transmission itself.

The R-CCCH data frames also contain signaling data. Therefore, during dataframe transmission, the transmit power of the R-CCCH code channel itself needs tobe calculated. The transmit power of the R-CCCH code channel during data frametransmission is (in decibels)

p p sum of gain factorst,R CCCH t,R-PICH− = + ( ) (7.6)

where pt,R-PICH is the transmit power of R-PICH during R-CCCH data frame trans-mission, shown in (7.5). The gain factors here are identical to those used in theR-EACH [i.e., in (7.3)]. Again, the transmit power of the R-CCCH code channel isdependent on the current transmit power of the R-PICH.

7.3 Power Control of the Reverse Link: Open Loop 115

Page 136: 3G CDMA200 Wireless System Engineering

7.3.1.3 Reverse Traffic Channel

During the transmission of reverse traffic channels (i.e., R-DCCH, R-FCH, andR-SCH), the R-PICH is also active to aid their coherent demodulation. Thus themobile power controls the R-PICH during the transmission of reverse traffic chan-nels. Here the mobile calculates its R-PICH transmit power based on the followinggeneral equation (in decibels):

p p sum of correction factorssumof at,R PICH r− = − + +( )

( ll closed loop powercontrol corrections)(7.7)

The correction factors here are different from those used in either the R-EACHor the R-CCCH. The description of these correction factors can be found in Section2.1.2.3.1 of [3].

In addition to controlling the transmit power of the R-PICH, the mobile alsoneeds to power control the reverse traffic channels themselves. Since the reverse traf-fic channels carry user data, the transmit power of the reverse traffic channel codechannel itself needs to be calculated. The transmit power of the reverse traffic chan-nel is (in decibels)

p p sum of gaint,reverse traffic channel t,R-PICH= + ( factors) (7.8)

where pt,R-PICH is the transmit power of R-PICH during the transmission of reversetraffic channel, shown in (7.7). The gain factors here are all specific to reverse trafficchannels and are different from those used in R-EACH and R-CCCH. The descrip-tion of these gain factors can be found in Section 2.1.2.3.3 of [3] and is not repeatedhere. As one can see, the transmit power of the reverse traffic channel references thatof the R-PICH; as the R-PICH transmit power changes, so does the reverse trafficchannel transmit power.

7.3.2 Summary

Figure 7.3 summarizes the power control discussions thus far. The received power,together with the various correction factors, plays a part in determining the transmitpower of the R-PICH. The transmit power of the R-PICH in turn determines thetransmit power of R-EACH, R-CCCH, and reverse traffic channel. The closed-looppower control corrections are first applied to the R-PICH and subsequently mani-fested in the R-EACH, R-CCCH, and reverse traffic channel.

By using the received power as a decision metric, the open-loop power control isbased on an estimate of the forward path loss. This power control thus compensatesfor slow-varying and log-normal shadowing effects where there is a correlationbetween the forward link and reverse link fades. However, since forward andreverse links are at different frequencies, the open-loop power control is too slow tocompensate for fast Rayleigh fading (recall Rayleigh fading depends on the fre-quency). Therefore, closed-loop power control is used in addition to open-loop tocombat Rayleigh fading.

116 Power Control

Page 137: 3G CDMA200 Wireless System Engineering

7.4 Power Control of the Reverse Link: Closed Loop

For the reverse link, the closed-loop power control of IS-2000 is similar to that ofIS-95. Readers can refer to references such as [5–7] for its description, and we willhighlight only significant differences here. To power control the reverse link, thebase station continuously monitors the reverse link and measures its link quality. Ifthe link quality starts to get worse, then the base station will command the mobile,via the forward link, to power up. If the link quality becomes too good, then there isexcess power on the reverse link. In this case, the base station will command themobile to power down.

7.4 Power Control of the Reverse Link: Closed Loop 117

Σ

Σ

RxAntenna

TxAntennaMobile station

Σ

CFs

Closed loopcorrections

Σ

CFs

Closed loopcorrections

CFs

Closed loopcorrections

pt,R-PICH to beused for R-EACH

pt,R-PICH to beused for R-CCCH

pt,R-PICH to beused for reversetraffic channel

R-PICH

prRCVR

Σ

GFs

GFs

Σ

GFs

Σ

R-EACH Tran

smitt

er

R-CCCH

Reversetraffic channel

pt,R-PICH

pt,R-EACHto be used

pt,R-CCCHto be used

pt,rev traffic chto be used

Figure 7.3 Reverse link power control. CF stands for correction factor, and GF stands for gainfactor.

Page 138: 3G CDMA200 Wireless System Engineering

7.4.1 Inner Loop and Outer Loop

The IS-2000 standard (and the IS-95 standard) itself does not explicitly specify howthe reverse link closed-loop power control is to be performed. It only states that thebase station should ascertain the received signal quality of a mobile’s signal, and thatthe base station should transmit the PCB based the received signal quality. Oneimplementation is measuring the Eb/N0 of one of the reverse traffic channels to ascer-tain reverse link quality [8, 9]. For example:

1. The base station continuously monitors Eb/N0 of the reverse traffic channel.2. If Eb/N0 is too high (i.e., if it exceeds a certain threshold), then the base

station commands the mobile to decrease the mobile transmit power.3. If Eb/N0 is too low (i.e., if it drops below a certain threshold), then the base

station commands the mobile to increase the mobile transmit power.

The base station commands the mobile to power up and power down usingPCBs that are multiplexed onto the forward link. The actual forward physical chan-nel that carries PCBs depends on the reverse physical channel to be power con-trolled. Regardless of the forward physical channel that carries PCBs, PCBs are noterror protected. They are not error protected for the reason that the mobile canquickly recover the PCB and adjust its transmit power accordingly.

The above describes the inner loop of the closed-loop power control of thereverse link. The assumption of the inner loop is that there exists a predeterminedEb/N0 threshold by which power-up and power-down decisions are made. The func-tion of the outer loop, then, is to adjust the Eb/N0 threshold (i.e., Eb/N0 setpoint) tomaintain an acceptable FER.

Figures 7.4 and 7.5 both show a conceptual illustration of the closed-loopreverse link power control. Figure 7.4 depicts those functions carried out by the basestation. Here the base station implements the entire outer loop and part of the innerloop. The base station receives the reverse traffic channel from the mobile. The basestation first demodulates the signal and estimates the FER. This information on thereverse link quality is fed into the outer loop. The outer loop, using current FER andEb/N0 estimates, dynamically computes the new Eb/N0 setpoint required to maintainan acceptable FER. The new Eb/N0 setpoint and the current Eb/N0 estimate are thencompared. If the estimate is greater than the setpoint, then the link Eb/N0 is higherthan what is necessary to maintain a good FER; a PCB of 1 is thus sent to the mobileto command power down. If the estimate is less than the setpoint, then the link Eb/N0

is lower than what is necessary; a PCB of 0 is then sent to command the mobile topower up. PCBs are multiplexed onto the F-CPCCH, F-DCCH, or F-FCH depend-ing on which reverse physical channel is to be power controlled (see Figure 7.5).PCBs are transmitted to the mobile at a maximum rate of 800-times-per-second.

Figure 7.5 shows the corresponding implementation of the closed-loop reverselink power control as carried out by the mobile. Here the mobile has the rest of theinner loop. The mobile receives the F-CPCCH, F-DCCH, and F-FCH signals andrecovers the PCBs. Based on the PCB, the mobile makes a decision to power-up or topower-down [3]. Note that closed-loop power control corrections applied to reversephysical channels (shown in Figure 7.5) correspond to those shown in Figure 7.3.

118 Power Control

Page 139: 3G CDMA200 Wireless System Engineering

7.4.2 Power Control of Multiple Reverse Channels

IS-2000 has the ability to perform closed-loop power control of R-EACH,R-CCCH, and reverse traffic channels. To adjust the transmit power of thesereverse physical channels, the mobile makes use of the different streams of PCBs itreceives on the forward link.

7.4.2.1 Enhanced Access Channel (R-EACH)

To further apply closed-loop correction to the transmit power of the R-EACH, themobile demodulates the F-CPCCH and recover the PCBs assigned. See Chapter 2for details on how power control groups and power control subchannels are organ-ized on the F-CPCCH. The mobile uses these PCBs to adjust the transmit power ofthe R-EACH.

7.4.2.2 Reverse Common Control Channel (R-CCCH)

To power control an R-CCCH, the mobile demodulates the F-CPCCH and recoversthe PCBs assigned to that particular R-CCCH. The mobile uses these PCBs to applyclosed-loop correction to the transmit power of the R-CCCH.

7.4 Power Control of the Reverse Link: Closed Loop 119

PCB

RCVR

DemodFERestimate

Adjust/

setpointE Nb 0

E Nb/estimate

0

E Nb/setpoint

0FERestimate

Decision:If estimate>setpointthen PCB=1

If estimate<setpointthen PCB=0

E Nb/estimate

0

OUTER LOOP

RxAntenna

TxAntennaBase station

E Nb/estimate

0

R-FCH

ΣR-DCCH

R-CPCCH

PCB

PCB

Tran

smitt

er

Figure 7.4 Reverse link power control functions carried out by the base station.

Page 140: 3G CDMA200 Wireless System Engineering

7.4.2.3 Reverse Traffic Channels

To apply closed-loop correction to the transmit power of the reverse traffic channel,the mobile demodulates the F-DCCH or F-FCH and recovers the assignedPCBs. The mobile uses these PCBs to adjust the transmit power of the reverse trafficchannel.

It is worth noting that PCBs are inserted into the F-DCCH and F-FCH by punc-turing them into these channels. PCBs carried by the F-DCCH and F-FCH are trans-mitted at a peak rate of 800 bps if the R-PICH is not gated. If the R-PICH is gated,then the transmission rate of the PCBs is reduced accordingly. If the R-PICH is gatedat 1/2 rate, then PCBs are transmitted at 400 bps. IF the R-PICH is gated at 1/4 rate,then PCBs are transmitted at 200 bps.

The actual forward physical channel that carries the PCBs is determined asfollows:

• If the R-PICH is gated, then only the F-DCCH carries PCBs for the closed-looppower control of the reverse traffic channel.

• If the R-PICH is not gated, then either the F-DCCH or the F-FCH carriesPCBs. The parameter FPC_PRI_CHAN specifies exactly which forward physi-cal channel (F-DCCH or F-FCH) carries them.

120 Power Control

Transmitter

TxAntenna

RxAntennaMobile station

RCVR

Demod

Decision:If PCB=0then power downIf PCB=1then power up

PCB

Decision:If PCB=0then power downIf PCB=1then power up

Decision:If PCB=0then power downIf PCB=1then power up

F-FCH

DemodPCB

F-DCCH

Demod

PCB

F-CPCCHDecision:If PCB=0then power downIf PCB=1then power up

PCB

Closed-loopcorrectionfor R-EACH

Closed-loopcorrectionfor R-CCCH

Closed-loopcorrectionfor reversetraffic channel

Closed-loopcorrectionfor reversetraffic channel

DEM

UX

Figure 7.5 Reverse link power control functions carried out by the mobile.

Page 141: 3G CDMA200 Wireless System Engineering

Recall that in IS-95, PCBs are multiplexed onto the forward traffic channel inpower control groups. In a similar fashion, IS-2000 multiplexes the PCBs onto theF-DCCH and F-FCH. The structure and organization of the power control groupson the F-DCCH is referred to as the forward power control subchannel. In effect, aforward power control subchannel exists on the F-DCCH and F-FCH to transportthe PCBs. The position and duration of these puncturing PCBs (carried by the for-ward power control subchannel) on the F-DCCH and F-FCH are completely speci-fied [3], so the mobile knows exactly where to recover the PCBs.

The parameter FPC_PRI_CHAN is one of the nonnegotiable service configura-tion parameters to be used by the mobile. They are sent in messages like service con-nect message, general handoff direction message, and universal handoff directionmessage. They can also be sent to the mobile in power control message, extendedchannel assignment message, and extended supplemental channel assignmentmessage.

References

[1] Paranchych, D. W., “On the Performance of Fast Forward Link Power Control in IS-2000CDMA Networks,” Proceedings of Wireless Communications and Networking Confer-ence, Chicago, IL, September 23–28, 2000, pp. 603–607.

[2] Chulajata, T., and H. M. Kwon, “Combinations of Power Controls for cdma2000 WirelessCommunications System,” Proceedings of Vehicular Technology Conference, Boston, MA,September 24–28, 2000, pp. 638–645.

[3] TIA/EIA/IS-2000.2-A, Physical Layer Standard for cdma2000 Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

[4] TIA/EIA/IS-2000.5-A, Upper Layer (Layer 3) Signaling Standard for cdma2000 SpreadSpectrum Systems, Telecommunications Industry Association, March 2000.

[5] Yang, S. C., CDMA RF System Engineering, Norwood, MA: Artech House, 1998.[6] Lee, S., Spread Spectrum CDMA: IS-95 and IS-2000 for RF Communications, New York:

McGraw-Hill, 2002.[7] Lee, J. S., and L. E. Miller, CDMA Systems Engineering Handbook, Norwood, MA: Artech

House, 1998.[8] Lee, W., and N. P. Secord, “Performance of Closed-Loop Power Control for a Multiple-

Channel Mobile Station in the cdma2000 System,” Proceedings of Wireless Communica-tions and Networking Conference, New Orleans, LA, September 21–24, 1999,pp. 908–912.

[9] Chulajata, T., and H. M. Kwon, “Combinations of Power Controls for cdma2000 WirelessCommunications System,” Proceedings of Vehicular Technology Conference, Boston, MA,September 24–28, 2000, pp. 638–645.

7.4 Power Control of the Reverse Link: Closed Loop 121

Page 142: 3G CDMA200 Wireless System Engineering

.

Page 143: 3G CDMA200 Wireless System Engineering

C H A P T E R 8

Handoff

8.1 Introduction

The IS-2000 standard has some enhanced features for handoff1 all aimed at improv-ing system performance, and in the case of soft handoff system capacity as well. Interms of soft handoff, the speed and accuracy with which it is executed have directconsequences on capacity and quality [2]. Fast and accurate soft handoffs decreasethe number of dropped calls and conserve transmit power resources. Fewer droppedcalls translate into improved system performance, and conserving transmit powerreduces unnecessary interference to other receivers and enables the redirection ofpower resources to where they are needed.

In terms of idle, access entry, access, and access probe handoffs, they all serve toincrease a mobile’s chance of successfully receiving or sending a message, and thusto improve system performance. This chapter will focus on those handoff featuresthat are important to the operation of an IS-2000 system. Specifically, Section 8.2describes soft handoff. Section 8.3 describes idle handoff, which can occur when amobile is in the mobile station idle state. Sections 8.4 then discusses access entryhandoff, which can occur right before a mobile enters the system access state, andSections 8.5 and 8.6 describe access handoff and access probe handoff, respectively,which can occur in the system access state.

8.2 Soft Handoff

Soft handoff is a process in which the mobile actively exchanges traffic channelinformation with two or more base stations, hence by definition soft handoff canonly occur when a mobile is in the mobile station control on the traffic channelstate. Readers are no doubt already familiar with the advantage of soft handoff [i.e.,it enables diversity combining when a mobile transitions between coverage areas oftwo base stations (see Figure 8.1)]. In addition, soft handoff can only occur betweentwo base stations transmitting forward traffic channels that are on the same CDMAcarrier and at the same frame offset [3].

In managing the soft handoff process, the mobile maintains in its memoryfour exclusive lists of sectors of base stations. These lists are exclusive in that their

123

1. All of the handoff features discussed in this chapter were available in IS-95-B [1], and IS-2000 has more orless adopted them with minimal modifications.

Page 144: 3G CDMA200 Wireless System Engineering

contents do not overlap. In these lists, the sectors are stored in the form of pilot PNoffsets of the sectors. The lists are also called sets. Similar to IS-95, the mobile (ormore specifically, Layer 3 at the mobile) maintains the active set, candidate set,neighbor set, and remaining set.

Although the mobile is the one that maintains these sets, the base station (ormore specifically, Layer 3 at the base station) can also influence the makeup of thesesets. In general, both the mobile and the base station follow a set of rules whenadministering the contents of these sets.

8.2.1 Active Set

The active set contains the pilots of those sectors that are actively exchanging trafficchannel information with the mobile. If the active set has only one pilot in it, thenthe mobile is not in soft handoff. If the active set has two or more pilots in it, then themobile is maintaining connections with those sectors specified by their pilots in thelist. When the base station first assigns the forward traffic channel to the mobile, thebase station specifies the pilots in the active set through the use of extended channelassignment message or channel assignment message. Subsequent updates to the con-tents of the active set are done by using the extended handoff direction message, gen-eral handoff direction message, or universal handoff direction message. The activeset can have a maximum of six pilots.

8.2.1.1 Removing Pilots from the Active Set

Each pilot in the active set has a handoff drop timer associated with that pilot. InIS-95-A, the mobile starts the handoff drop timer for that pilot when its Ec/I0 goesbelow T_DROP. If the pilot’s Ec/I0 comes back above T_DROP before the handoffdrop timer expires (i.e., reaches T_TDROP), then the pilot remains in the active set

124 Handoff

Sourcecell (X)

Targetcell (Y)

Mobile

Base stationcontroller(BSC)

Figure 8.1 Soft handoff.

Page 145: 3G CDMA200 Wireless System Engineering

and the timer is reinitialized. On the other hand, if the pilot remains below T_DROPuntil the handoff drop timer expires, then a pilot strength measurement message(PSMM) is sent to the base station, and that pilot is moved from the active set to theneighbor set.

As we can see, the administration of the pilots in the active set and therefore ofthe soft handoff process itself is dependent on the drop threshold parameterT_DROP. T_DROP is static in nature and does not change. In IS-2000, the systemhas a handoff algorithm that uses a pilot drop threshold that is dynamic in nature. Inother words, this new drop threshold (which we shall designate as T_DROP*) is afunction of time while the mobile is contemplating on removing a pilot from theactive set. T_DROP* is given by the larger of T_DROP or

18

1012

+

∑SOFT_SLOPE p DROP_INj

j

log TERCEPT (8.1)

where pj is the received pilot strength of pilot j, and the summation is over thosepilots in the active set that have strengths greater than the strength of the pilot underconsideration. Expression (8.1) is called the handoff drop criterion for dropping apilot [3]. Note that two new parameters are used for the calculation of the handoffdrop criterion: SOFT_SLOPE and DROP_INTERCEPT. They are basically theslope and the intercept (in dB) of the handoff drop criterion. Note that given (8.1),the overall T_DROP* is given by

T_DROP*SOFT_SLOPE

pDROP_INTERC

jj

= ⋅

+∑max log

810

EPT,T_DROP

2

(8.2)

What (8.2) tells us is that in assessing whether or not to drop a pilot (e.g.,pilot i), the mobile would sum up the strengths of all those pilots that have strengthsgreater than that of pilot i. The mobile would then convert this sum of pilotstrengths into a T_DROP-like variable (i.e., handoff drop criterion) by usingSOFT_SLOPE and DROP_INTERCEPT. It would then compare the handoff dropcriterion and the original T_DROP. If the original T_DROP is larger than the hand-off drop criterion, then the mobile still uses the old T_DROP as the drop threshold.If the handoff drop criterion is larger than T_DROP, then the mobile would use thevalue given by the handoff drop criterion as the new drop threshold. Note that bychoosing the larger of the two (i.e., the handoff drop criterion or the old T_DROP),the mobile essentially implements an overall stricter drop threshold. This has theeffect of dropping the pilot more quickly whenever possible. In other words, themobile will request that the base station drops a pilot that is not value-added rela-tive to the other (stronger) pilots in the active set2. Also note that since the pilot

8.2 Soft Handoff 125

2. This request is done implicitly through the PSMM or the EPSMM that is transmitted after the handoff droptimer expires.

Page 146: 3G CDMA200 Wireless System Engineering

strengths in the handoff drop criterion (8.1) change as a function of time, T_DROP*(8.2) itself also changes as a function of time.

8.2.1.2 Adding Pilots to the Active Set

Adding an additional pilot to the active set means that the mobile is to commencecommunication with the new sector represented by that pilot. The base stationalways specifies the contents of a mobile’s active set by using various handoff direc-tion messages (e.g., extended handoff direction message) and thereby directs softhandoff performed by the mobile. A pilot to be added to the active set always comesfrom the candidate set.

In IS-95-A, if the strength of a pilot in the candidate set exceeds the strength of apilot in the active set by the threshold T_COMP × 0.5 dB, then a PSMM transmis-sion is triggered. Upon receiving the PSMM, the base station would most likelycommand the mobile to move that pilot from the candidate set to the active set.

In IS-2000, the system uses a new pilot detection threshold that is dynamic innature. This detection threshold (which we shall designate as T_ADD*) consists ofthe handoff add criterion for adding a pilot [3]. This criterion is given as

18

1012

+

∑SOFT_SLOPE p ADD_INTk

k

log ERCEPT (8.3)

where pk is the received pilot strength of pilot k. In this case, the summation is overall the pilots in the active set regardless of their strengths. SOFT_SLOPE andADD_INTERCEPT are the slope and intercept of the handoff add criterion equa-tion. Note that SOFT_SLOPE is identical to that shown in (8.1). Since the pilotstrengths in (8.3) change as a function of time, the overall handoff add criterion isdynamic and also changes as a function of time.

Expression (8.3) states that the criterion depends on the current sum of strengthsof all pilots in the active set. The sum is then linearly transformed into the handoffadd criterion by using SOFT_SLOPE and ADD_INTERCEPT. In assessing whetheror not to add pilot i, the mobile would compare the handoff add criterion with thestrength of pilot i. If the strength of pilot i is less than the handoff add criterion, thenthe mobile does nothing and pilot i remains in the candidate set. On the other hand,if the strength of pilot i exceeds the handoff add criterion, then the mobile sends aPSMM or an EPSMM. Then the base station may command the mobile to movepilot i from the candidate set to the active set. In essence, the strength of a pilot in thecandidate set is compared with (a linear transformation of) the sum of strengths ofall pilots in the active set (i.e., the handoff add criterion). If the strength of the candi-date set pilot exceeds the criterion, then it may be moved from the candidate set tothe active set.

One last note in this section, the system can also use both the T_COMP criterionand the handoff add criterion in deciding whether or not to move a pilot from thecandidate set to the active set. In doing so, the mobile would send a PSMM or anEPSMM if both of the following conditions are met:

126 Handoff

Page 147: 3G CDMA200 Wireless System Engineering

• The strength of a pilot in the candidate set exceeds the strength of a pilot in theactive set by the threshold T_COMP × 0.5 dB;

• The strength of a pilot in the candidate set exceeds the handoff add criterionshown in (8.3).

By demanding that the candidate set pilot meets both conditions, the system onbalance enforces a stricter standard for elevating a pilot from the candidate set tothe active set.

8.2.2 Candidate Set

The candidate set contains the pilots of those sectors whose Ec/I0 are sufficient tomake them handoff candidates. In other words, the signals of those sectors in thecandidate set can be successfully demodulated by the mobile if necessary. When thebase station first assigns the forward traffic channel to the mobile, the mobile’s can-didate set is empty. The candidate set can contain a maximum of 10 pilots.

8.2.2.1 Adding Pilots to the Candidate Set

Adding an additional pilot to the candidate set means that the mobile decides thatthe pilot is a good candidate for soft handoff. In IS-2000, if the strength of a remain-ing set pilot or a neighbor set pilot exceeds T_ADD, then the mobile autonomouslymoves that pilot from the remaining set or the neighbor set to the candidate set.Note that the T_ADD used here is the static pilot detection threshold. The dynamichandoff add criterion discussed previously is only applicable when adding a pilot tothe active set.

The base station can also move pilots to the candidate set via one of the handoffdirection messages (e.g., general handoff direction message). More specifically, thebase station can implicitly direct the mobile to move a pilot from the active set to thecandidate set. The base station does so by not specifying a current active set pilotin its handoff direction message. Upon receiving the message, the mobile willmove that pilot from the active set to the candidate set if one of the following twoconditions is met:

• That pilot’s handoff drop timer has not expired (i.e., has not reachedT_TDROP);

• That pilot’s handoff drop timer has expired, but the strength of that pilot isgreater than T_DROP.

8.2.2.2 Removing Pilots from the Candidate Set

Each pilot in the candidate set has a handoff drop timer associated with that pilot. Inboth IS-95-A and IS-2000, the mobile starts the handoff drop timer for that pilotwhen its Ec/I0 goes below T_DROP. If the pilot’s Ec/I0 comes back above T_DROPbefore the handoff drop timer expires, then the pilot remains in the candidate setand the timer is reinitialized. On the other hand, if the pilot remains below T_DROPuntil the handoff drop timer expires (i.e., reaches T_TDROP), then the mobile

8.2 Soft Handoff 127

Page 148: 3G CDMA200 Wireless System Engineering

autonomously removes that pilot from the candidate set. Note that the T_DROPused here is the static drop threshold. The dynamic drop threshold discussed previ-ously is only applicable when dropping a pilot from the active set.

Similar to the case of adding pilots, the base station can also remove pilots fromthe candidate set via a handoff direction message (e.g., general handoff directionmessage). More specifically, the base station can implicitly direct the mobile toremove a pilot from the candidate set. The base station does so by specifying acurrent candidate set pilot in its handoff direction message. Upon receiving the mes-sage, the mobile will then remove that pilot from the candidate set and add it to theactive set.

In a situation where the candidate set already has 10 pilots in it and the mobilewishes to add one more, the mobile would prioritize the 10 pilots first according tothe statuses of their handoff drop timers and second according to their strengths [3].The mobile then would delete the pilot that has the lowest priority to make room forthe new one, and this pilot is then moved to the neighbor set. Ideally, the mobilewould never run into this overflow situation in the candidate set. An overflowingcandidate set means that there are 10 usable pilots at the mobile’s location in addi-tion to the pilots in the active set! The system designer should minimize the numberof usable pilots in a geographical area to avoid pilot pollution.

8.2.3 Neighbor Set

The neighbor set contains the pilots of those sectors that are likely contenders towhich to handoff. Initially, the neighbor set contains those pilots that are sent to themobile in the general neighbor list message, extended neighbor list message, orneighbor list message. Subsequent updates to the contents of the neighbor set aredone by using the extended neighbor list update message or the neighbor list updatemessage. The neighbor set can contain a maximum of 40 pilots.

8.2.3.1 Adding Pilots to the Neighbor Set

In many ways, the neighbor set serves as the reservoir of pilots that havebeen demoted from the candidate set or from the active set. As discussed inSection 8.2.2.2, the mobile station autonomously moves a candidate set pilot to theneighbor set when that pilot’s handoff drop timer has expired (i.e., has reachedT_TDROP) or that pilot is bumped from an overflowing candidate set because of itslow priority.

In moving a pilot from the active set to the neighbor set, the base station can doso by using one of the handoff direction messages (e.g., general handoff directionmessage). The base station can implicitly direct the mobile to move a pilot from theactive set to the neighbor set. This is done by not specifying a current active set pilotin its handoff direction message. Upon receiving the message, the mobile will movethat pilot from the active set to the neighbor set if the following occurs:

• That pilot’s handoff drop timer has expired (i.e., has reached T_TDROP), andthe strength of that pilot is less than T_DROP.

128 Handoff

Page 149: 3G CDMA200 Wireless System Engineering

8.2.3.2 Removing Pilots from the Neighbor Set

In order to keep current all the pilots in the neighbor set, the mobile keeps anaging counter for each pilot in the neighbor set. The counter is initialized to zerowhen that pilot is moved from the active set or candidate set to the neighbor set.Whenever an extended neighbor list update message or a neighbor list update mes-sage is received, that pilot’s counter is incremented. If the counter of a pilot exceedsNGHBR_MAX_AGE, then the mobile autonomously moves that pilot from theneighbor set to the remaining set.

There are other ways by which the mobile can autonomously remove a pilotfrom the neighbor list. As discussed previously in Section 8.2.2.1, if the strength of aneighbor set pilot becomes greater than T_ADD, then the mobile moves that pilotfrom the neighbor set to the candidate set. In addition, if the neighbor set alreadyhas 40 pilots in it and the mobile wishes to add one more, the mobile would priori-tize the 40 pilots first according to the statuses of their aging counters, and secondaccording to their strengths [3]. The mobile then would remove the pilot that hasthe lowest priority to make room for the new one, and the lowest priority pilot isthen moved to the remaining set.

Of course, the base station can affect the content of the neighbor set by usingone of the handoff direction messages (e.g., general handoff direction message). Thebase station can implicitly direct the mobile to move a pilot from the neighbor set tothe active set. This is done by specifying a current neighbor set pilot in its handoffdirection message. Upon receiving the message, the mobile will move that pilot fromthe neighbor set to the active set.

8.2.4 Remaining Set

The remaining set contains all possible pilots in the system for the current CDMAcarrier frequency, not including those that are in active, candidate, and neighborsets. The pilot PN offsets in the remaining set are defined by the parameter pilotincrement PILOT_INC. For example, if PILOT_INC is 4, then individual sectors inthe system can only transmit pilots with offsets of 0, 4, 8, 12, and so forth.

In terms of adding pilots to the remaining set, the mobile moves a pilot fromthe neighbor set to the remaining set when the pilot’s aging counter exceedsNGHBR_MAX_AGE. A pilot can also enter the remaining set from an overflowingneighbor set if it is one of low priority. In terms of removing pilots from the remain-ing set, if the strength of a remaining set pilot exceeds T_ADD, then the mobileautonomously moves that pilot from the remaining set to the candidate set.

8.2.5 Set Transitions

Figure 8.2 gives a pictorial representation of the events that trigger and can trigger apilot’s transitions between the different sets. Note that (Ec/I0)A denotes the pilotstrength of an active set pilot.

8.2.6 Example: Soft Handoff

8.2 Soft Handoff 129

Page 150: 3G CDMA200 Wireless System Engineering

130 Handoff

Activeset(max=6)

Initially filled byBS in a channelassignment msg

Later updated byBS in a HOdirection msg

Candidateset(max=10)

Ec/Io>

Ec/Io>Ec/Io Ec/Io

T_ADD*(PSMM or EPSMMtransmission)OR

T_ADD* and–( )A>

T_COMP x 0.5 dB(PSMM or EPSMMtransmission)

Pilot not in a HOdirection msgandHO drop timernot expiredORPilot not in a HOdirection msgandHO drop timerexpired but

/ >T_DROPEc Io

Neighborset(max=40)

Remainingset

Pilot not in a HOdirection msgandHO drop timerexpired and

<T_DROPEc/Io

HO drop timer expired(PSMM or EPSMMtransmission)

OverflowOverflow

HO droptimerexpired

Agingcounterexpired

Ec /Io>T_ADD

Ec /Io>T_ADD

Later updated byBS in a neighborlist updatemsg

Initially filled byBS in a neighborlist msg

Figure 8.2 Set transitions. Note that not all transitions are shown here.

Table 8.1 Pilot Strengths and Dynamic Thresholds at Different Times

Time(Ec/I0)for X

(Ec/I0)for Y

T_DROP*for X

T_DROP*for Y T_ADD* Pilot X Pilot Y

1 −3.70 −17.00 — — −10.74 Active Neighbor

2 −3.80 −16.00 — — −10.83 Active Neighbor

3 −3.90 −15.00 — — −10.91 Active Neighbor

4 −4.00 −14.00 — — −11.00 Active Neighbor

5 −4.25 −13.00 — — −11.22 Active Candidate

6 −4.50 −12.00 — — −11.44 Active Candidate

7 −4.75 −11.00 — — −11.66 Active Candidate

8 −5.00 −10.00 — −10.38 −10.83 Active Active

9 −5.50 −9.00 — −10.81 −10.91 Active Active

10 −6.00 −8.00 — −11.25 −10.89 Active Active

11 −7.00 −7.00 — — −10.99 Active Active

12 −8.00 −6.00 −11.25 — −10.89 Active Active

13 −9.00 −5.50 −10.81 — −10.91 Active Active

14 −10.00 −5.00 −10.38 — −10.83 Active Active

15 −11.00 −4.75 −10.16 — −10.85 Active Active

16 −12.00 −4.50 −9.94 — −10.82 Active Active

17 −13.00 −4.25 — — −11.22 Candidate Active

18 −14.00 −4.00 — — −11.00 Candidate Active

19 −15.00 −3.90 — — −10.91 Candidate Active

20 −16.00 −3.80 — — −10.83 Neighbor Active

21 −17.00 −3.70 — — −10.74 Neighbor Active

Page 151: 3G CDMA200 Wireless System Engineering

Table 8.1 shows an example of soft handoff between two base stations X and Y (seeFigure 8.1). The example is meant to show how the dynamic pilot detection thresh-old (T_ADD*) and pilot drop threshold (T_DROP*) work. Here the mobile is mov-ing from base station X to base station Y at a constant velocity. When t = 1, themobile is very close to base station X; at t = 21, the mobile is very close to base sta-tion Y. Table 8.1 shows, for each time stamp, the pilot strengths of X and Y at themobile. It also shows the values of T_DROP* (for pilot X and pilot Y) and T_ADD*at different time stamps. The T_DROP* and T_ADD* values are calculated usingSOFT_SLOPE = 7 dB, DROP_INTERCEPT = −12 dB, and ADD_INTERCEPT =−15 dB. In this soft handoff example, T_DROP = −15 dB and T_ADD = −13 dB.

Table 8.1 also shows in which sets the pilots are at each time stamp. The bold-faced time stamps denote the interval when the mobile is in soft handoff betweenbase station X and base station Y.

Figure 8.3 gives a pictorial representation of this handoff example. The verticalaxis denotes the pilot strength in dB, and the horizontal axis denotes the time(stamp) from 1 to 21. Figure 8.3 also shows the time-varying levels of T_DROP*(for pilots X and Y) and T_ADD*.

As the mobile gradually leaves base station X and goes toward base station Y,its received Ec/I0 from base station X (i.e., (Ec/I0)X) gradually decreases while thereceived Ec/I0 from base station Y (i.e., (Ec/I0)Y) increases. The following describesevents that occur at some key time stamps. For the purpose of this example, assumethat T_TDROP is one time-stamp long.

8.2 Soft Handoff 131

−17.00

−15.00

−13.00

−11.00

−9.00

−7.00

−5.00

−3.00

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Time (time stamp)

Pilo

tst

reng

th(d

B)

( ) for XEc/Io( ) for YEc/IoT_DROP* for XT_DROP* for YT_ADD*

Figure 8.3 Soft handoff example. The mobile is moving from base station X to base station Y at aconstant velocity.

Page 152: 3G CDMA200 Wireless System Engineering

1. At t = 5, (Ec/I0)Y first goes above T_ADD (−13 dB). The mobile moves pilot Yfrom the neighbor set to the candidate set.

2. At t = 7, (Ec/I0)Y now goes above T_ADD*. This event triggers a PSMM orEPSMM transmission from the mobile.

3. At t = 8, the mobile receives a handoff direction message (i.e., extendedhandoff direction message, general handoff direction message, or universalhandoff direction message). The mobile moves pilot Y from the candidate setto the active set. It is now in soft handoff with both base station X and basestation Y.

4. At t = 15, (Ec/I0)X first goes below T_DROP* for pilot X. The mobile startsthe handoff drop timer for pilot X.

5. At t = 16, the handoff drop timer for pilot X reaches T_TDROP and expires.This triggers a PSMM or EPSMM transmission from the mobile [3].

6. At t = 17, the mobile receives a handoff direction message (i.e., extendedhandoff direction message, general handoff direction message, or universalhandoff direction message). The mobile moves pilot X from the active set tothe candidate set. It is now communicating only with base station Y.

7. At t = 19, (Ec/I0)X now goes below T_DROP (−15 dB). The mobile starts thehandoff drop timer for pilot X.

8. At t = 20, the handoff drop timer for pilot X reaches T_TDROP and expires.The mobile moves pilot X from the candidate set to the neighbor set.

Note that in Figure 8.3, T_DROP* for pilot X is not defined from t = 1 throught = 7. This is so because since pilot X is the only pilot in the active set, there is noother active set pilot that has a strength that is greater than that of pilot X, hence thehandoff drop criterion cannot be calculated for pilot X. See (8.1). This also makessense because if there is only one pilot in the active set, there is no other pilot withwhich to compare and there is no use calculating a dynamic pilot drop threshold forthe lone pilot.

T_DROP* for pilot X is also not defined from t = 8 through t = 11, but here for aslightly different reason. Starting at t = 8, the mobile is in soft handoff with both basestation X and base station Y. But from t = 8 through t =11, (Ec/I0)X is still greaterthan (Ec/I0)Y, and since there is still no other active set pilot that has a strengthgreater than that of pilot X, the handoff drop criterion cannot be calculated forpilot X.

From t = 17 to t = 21, T_DROP* for pilot X is not defined for the reason thatpilot X is no longer in the active set during this interval, and handoff drop criterion isnot defined for pilots that are not in the active set.

For the sake of completeness, T_DROP* values for pilot Y are shown in Table8.1. For similar reasons, T_DROP* is only defined for pilot Y from t = 8 through t =10. This is because from t =1 through t = 7, pilot Y is not in the active set; from t = 11through t = 16, no other pilot in the active set has a strength greater than that of pilotY, and from t = 17 through t = 21, pilot Y is the only pilot in the active set.

Note that T_ADD* jumps to slightly above −11 dB from t = 8 through t = 16(i.e., during soft handoff). This is because during soft handoff, there are two pilots(X and Y) in the active set, and the summation in the handoff add criterion (8.3)

132 Handoff

Page 153: 3G CDMA200 Wireless System Engineering

adds the pilot strengths of all pilots in the active set. Therefore, when a pilot is addedto the active set the dynamic pilot detection threshold steps up; when a pilot isremoved from the active set, the same threshold steps down. Again, this makes sensebecause when there are already more than one pilot in the active set, the standard ofentry into the active set for an additional pilot should be higher. This has the neteffect of not allowing mediocre pilots to enter the active set.

The SOFT_SLOPE, ADD_INTERCEPT, and DROP_INTERCEPT values usedto generate the previous handoff example (see Table 8.1) are for illustrative pur-poses only. It is obvious that system designers can adjust these parameters to changethe dynamics of T_ADD* and of the different T_DROP*s. By adjusting how andhow quickly T_ADD* and the different T_DROP*s change in response to receivedstrengths of different pilots, a system designer can attempt to obtain the desiredhandoff performance between multiple base stations.

8.3 Idle Handoff

Idle handoff occurs when a mobile, while in the mobile station idle state, stopsmonitoring the F-PCH or F-CCCH/F-BCCH of one base station and starts monitor-ing the corresponding channel of another base station. Unlike soft handoff, whichcan only occur in the mobile station control on the traffic channel state, idle handoffcan only occur in the mobile station idle state (see Figure 8.4).

In order to perform idle handoff, the mobile maintains in its memory four exclu-sive lists of sectors of base stations. These lists, or sets, are exclusive in that theircontents do not overlap one another. Although these sets are similarly named asthose used in soft handoff, they are logically different sets. One characteristic thatdifferentiates these idle handoff sets from those used in soft handoff is that they areonly defined in the mobile station idle state. They are the active set, neighbor set,remaining set, and private neighbor set [3].

8.3 Idle Handoff 133

Power upMSinitializationstate

MSidlestate

Systemaccessstate

MS controlon the trafficchannelstate

Power down

Soft HOoccurs here

Idle HOoccurs here

Access entryHO occurs here

Figure 8.4 Mobile station states in which idle handoff, access entry handoff, and soft handoff cantake place.

Page 154: 3G CDMA200 Wireless System Engineering

8.3.1 Active Set

The mobile monitors only the F-PCH or F-CCCH of the sector of the base stationthat is in the active set. Unlike the active set used in soft handoff, this active set canonly have one pilot in it. This means that at any given time, the mobile can onlymonitor the F-PCH or F-CCCH of one single sector.

8.3.2 Neighbor Set

The neighbor set contains those pilots that are potential contenders for idle handoff.The neighbor set contains the pilots of those sectors that have been specified by theuniversal neighbor list message, general neighbor list message, extended neighborlist message, or neighbor list message. Similar to the neighbor set used in soft hand-off, this neighbor set can have a maximum of 40 pilots.

8.3.3 Private Neighbor Set

The private neighbor set contains the pilots of those sectors that are potential candi-dates to which to handoff in the private system. This set is analogous to the neighborset, except here the private neighbor set contains only likely handoff candidates in aprevious-defined private system. A private system (as perceived by the mobile) canbe implemented if the system supports tiered services and has user zones defined. Forexample, a user zone can be defined in the business district of a city that has a par-ticular set of services available (e.g., high-speed data). This “private system” canthen be made available only to selected mobiles that travel in the area.

The contents of the private neighbor set are specified by the private neighbor listmessage. It can also contain a maximum of 40 pilots.

8.3.4 Remaining Set

The remaining set contains all possible pilots in the system for the current CDMAcarrier frequency that are not already in the active, neighbor, and private neighborsets. The contents of this remaining set may be similar (but are not necessarily identi-cal) to the remaining set used in soft handoff. This is so because the pilot PN offsetsin this remaining set are also defined by the pilot increment PILOT_INC.

8.3.5 Idle Handoff Process

While in the mobile station idle state, the mobile continues to measure the strengthsof pilots that are in its active, neighbor, private neighbor, and remaining sets. In theslotted mode, if the Ec/I0 of a pilot in the neighbor, private neighbor, or remaining setexceeds the Ec/I0 of the active set pilot by 3 dB, then the mobile removes the weakerpilot from the active set and moves the stronger pilot into the active set. In thenonslotted mode, the Ec/I0 of a pilot needs to exceed the Ec/I0 of the active set pilot by3 dB for a period longer than one second [4]; if this occurs, then the mobile removesthe weaker pilot from and moves the stronger pilot into the active set.

134 Handoff

Page 155: 3G CDMA200 Wireless System Engineering

8.4 Access Entry Handoff

Similar to idle handoff, an access entry handoff occurs when a mobile stops moni-toring the F-PCH or F-CCCH/F-BCCH of one base station and starts monitoringthe corresponding channel of another base station. But unlike idle handoff (whichcan only occur in the mobile station idle state), access entry handoff occurs when themobile is transitioning into the system access state from the mobile station idle state(see Figure 8.4).

The mobile can only perform an access entry handoff if it has received a page oran order/message to which the mobile needs to respond. If it has received such apage or an order/message, then the mobile can determine whether or not it shouldperform an access entry handoff. The IS-2000 standard actually does not specifywhat criteria a mobile should use to make that determination, but it would bereasonable to assume that the mobile should not perform an access entry handoffto a neighbor having a pilot strength that is too weak.

Once a mobile determines that it should perform an access entry handoff, themobile actually follows the same procedure as idle handoff to switch the monitoringof F-PCH or F-CCCH/F-BCCH from the current base station to the new base sta-tion. If the mobile does perform an access entry handoff, it should do so beforeentering the update overhead information substate of the system access state [3].

8.5 Access Handoff

8.4 Access Entry Handoff 135

Power-upMSinitializationstate

MSidlestate

Systemaccessstate

MS controlon the trafficchannelstate

Power down

Soft

HO

occu

rshe

re

Idle

HO

occu

rshe

re

Acc

ess

entr

yH

Ooc

curs

here

Acc

ess

HO

occ

urs

her

e

Access probe HOoccurs here

Figure 8.5 Mobile station states in which access handoff, access probe handoff, idle handoff,access entry handoff, and soft handoff can take place.

Page 156: 3G CDMA200 Wireless System Engineering

Access handoff occurs when a mobile, after an access attempt, stops monitoring theF-PCH or F-CCCH/F-BCCH of one base station and starts monitoring the corre-sponding channel of another base station. Since an access handoff occurs after anaccess attempt, the mobile is in the system access state while performing an accesshandoff (see Figure 8.5).

In the system access state, the mobile maintains in its memory three exclusivelists of sectors of base stations. These lists, or sets, are exclusive in that their contentsdo not overlap one another. These sets are similarly named but different from thosesets used in idle handoff and soft handoff. They are the active set, neighbor set, andremaining set [3].

8.5.1 Active Set

While in the system access state, the mobile monitors only the F-PCH or F-CCCH ofthe sector of the base station that is in the active set. Similar to the active set used inidle handoff, this active set can only have one pilot in it. Thus the mobile can onlymonitor the F-PCH or F-CCCH of one single sector while in the system access state.

8.5.2 Neighbor Set

The neighbor set contains the pilots of those sectors that have been specified by theuniversal neighbor list message, general neighbor list message, extended neighborlist message, or neighbor list message. The neighbor set pilots are those that arepotential contenders for access handoff or access probe handoff.

8.5.3 Remaining Set

The remaining set contains all possible pilots in the system for the current CDMAcarrier frequency that are not already in the active and neighbor sets. The contents ofthis remaining set are generated in a way similar to the generation of the remainingset used in soft handoff (i.e., the pilot PN offsets in this remaining set are also definedby the pilot increment PILOT_INC).

8.5.4 Access Handoff Process

As mentioned above, the mobile can only perform access handoff when it is in thesystem access state. Recall from Chapter 6 that the mobile enters the system accessstate typically after some action has been taken, either by the mobile or by the basestation. Figure 8.6 shows the substates within the system access state. It turns outthat the mobile can only perform access handoff when it is in two of the substates:page response substate and mobile station origination attempt substate.

As Figure 8.6 shows, the mobile enters the page response substate after receivinga general page message. While it is in the page response substate, the mobileresponds by transmitting a page response message. The page response message maybe transmitted on either an R-ACH which is associated with an F-PCH, or anR-EACH which is associated with an F-CCCH. On the other hand, the mobile entersthe mobile station origination attempt substate after originating a call. While it is in

136 Handoff

Page 157: 3G CDMA200 Wireless System Engineering

the mobile station origination attempt substate, the mobile transmits an originationmessage, and the origination message may be transmitted on either an R-ACHwhich is associated with an F-PCH or an R-EACH which is associated with anF-CCCH.

The standard specifies that the mobile must perform an access handoff in thepage response substate or in the mobile station origination attempt substate if one ofthe following occurs [3]:

• The mobile loses the F-PCH or F-CCCH while waiting for a response from thebase station, and the mobile is not already in the middle of an access attempt.

• The mobile loses the F-PCH or F-CCCH after receiving a message but beforeresponding to that message, and the mobile is not already in the middle of anaccess attempt.

Recall that an access attempt is the process of sending a message to the base sta-tion and receiving an acknowledgment for the message [5]. In performing an access

8.5 Access Handoff 137

IS

Updateoverheadinformationsubstate

MS idlestate

MS controlon the trafficchannel state

Pageresponsesubstate

MSmessagetransmissionsubstate

PACAcancelsubstate

Registrationaccesssubstate

MSoriginationattemptsubstate

MS order/messageresponsesubstate

IS

IS

IS

IS

IS

Receives generalpage message

Originates call

Receives generalpage message

Receivesgeneralpagemessage

Originates callor reoriginatesPACA call

Receivesgeneralpagemessage

IS: Idle state

Figure 8.6 Substates in which access handoff and access probe handoff can take place.

Page 158: 3G CDMA200 Wireless System Engineering

handoff, the mobile chooses as its target sector one with the best pilot strength. Inaddition, the chosen target sector should have a pilot strength that is greater thanT_ADD as well [3].

How a mobile determines whether or not it has lost the F-PCH or F-CCCH isdescribed in Chapter 9.

8.6 Access Probe Handoff

Access probe handoff occurs when a mobile, during an access attempt, stops sendingaccess probes to the current base station and starts sending access probes to a newbase station. Since an access probe handoff occurs during an access attempt, themobile is in the system access state while performing an access probe handoff (seeFigure 8.5). Similar to access handoff, access probe handoff can only take place inthe page response substate or the mobile station origination attempt substate (seeFigure 8.6).

Typically, a mobile may perform an access probe handoff in the pageresponse substate or in the mobile station origination attempt substate if the follow-ing occurs:

• The mobile loses the F_PCH or F-CCCH, and the mobile has not performedmore than MAX_NUM_PROBE_HO access probe handoffs during the cur-rent access attempt.

The parameter MAX_NUM_PROBE_HO is the maximum number of timesthat a mobile can perform an access probe handoff. The parameter is meant to pre-vent the mobile from performing an excessive number of access probe handoffs dur-ing an access attempt.

In performing an access probe handoff, the mobile first completes the transmis-sion of the current access subattempt to the current base station, and then it beginsto transmit the next access subattempt to the new base station [3]. An access subat-tempt in IS-2000 is equivalent to a complete access attempt in IS-95-A. As Figure 8.7shows, several access subattempts make up one complete access attempt, and amobile can transmit one complete access subattempt to one and only one base sta-tion. At the end of the current access subattempt, the mobile either performs anaccess probe handoff (and thereby starts to transmit another access subattempt to anew base station) or terminates the access attempt. Therefore, if the mobile does notperform any access probe handoff, then an access attempt consists of only one accesssubattempt [6].

Figure 8.7 shows that an access attempt can contain up to (1 +MAX_NUM_PROBE_HO) access subattempts since the mobile cannot performmore than MAX_NUM_PROBE_HO access probe handoffs during an accessattempt. Within each access subattempt, there can be up to MAX_RSP_SEQ accessprobe sequences if the mobile is transmitting a response message, or up toMAX_REQ_SEQ access sequences if the mobile is transmitting a request message.

138 Handoff

3. In basic access mode or reservation access mode.

Page 159: 3G CDMA200 Wireless System Engineering

And of course within each access sequence, there can be up to (1 + NUM_STEP)access probes. Each access probe is basically a single R-ACH or R-EACH transmis-sion3 described previously in Chapter 4.

8.7 Concluding Remarks

Readers should recognize now that the different handoff features described in thischapter are meant to improve system performance, and in the case of soft handoffsystem capacity as well. In terms of soft handoff, using the new drop threshold andadd threshold enables a mobile to drop pilots that are not and add pilots that arevalue-added relative to the other pilots in the active set.

In terms of idle, access entry, and access handoffs, they afford the mobile anopportunity to switch the monitoring of overhead channels from one base station toanother at different points of the state transitions. This serves to minimize the prob-

8.7 Concluding Remarks 139

Access attempt

Accesssubattempt 1

Accesssubattempt M

Accessprobesequence1

Accessprobesequence2

AccessprobesequenceN

(M = 1+MAX_NUM_PROBE_HO)

( = MAX_REQ_SEQ)N

( = MAX_RSP_SEQ)N

or

Accessprobe 1 (P = 1+NUM_STEP)

Accessprobe 2

Accessprobe P

time

time

time

Figure 8.7 Access attempt. (After: [5].)

Page 160: 3G CDMA200 Wireless System Engineering

ability of missing a message from the base station. In terms of access probe handoff,this feature gives the mobile, in the midst of an access attempt, the ability to transmitan additional set of access subattempt to a different base station having perhaps astronger pilot; this helps improves the probability of achieving a successful access bythe mobile.

References

[1] ANSI/TIA/EIA-95-B, Mobile Station-Base Station Compatibility Standard for WidebandSpread Spectrum Cellular Systems, Telecommunications Industry Association, March1999.

[2] Yang, S. C., CDMA RF System Engineering, Norwood, MA: Artech House, 1998.[3] TIA/EIA/IS-2000.5-A, Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread

Spectrum Systems, Telecommunications Industry Association, March 2000.[4] TIA/EIA-98-C, Recommended Minimum Performance Standards for Dual-Mode Spread

Spectrum Mobile Stations, Telecommunications Industry Association, December 1999.[5] TIA/EIA/IS-2000.3-A, Medium Access Control (MAC) Standard for cdma2000 Spread

Spectrum Systems, Telecommunications Industry Association, March 2000.[6] TIA/EIA/IS-2000.4-A, Signaling Link Access Control (LAC) Standard for cdma2000

Spread Spectrum Systems, Telecommunications Industry Association, March 2000.

140 Handoff

Page 161: 3G CDMA200 Wireless System Engineering

C H A P T E R 9

System Performance

9.1 Introduction

This chapter addresses several topics related to system performance, and it willfocus on those topics that are specific to the operation of an IS-2000 system. Section9.2 describes how the system supervises a channel and makes decisions regardingwhether or not to continue transmitting and receiving the channel. In additionbecause IS-2000 has added a host of new physical channels that can operate at dif-ferent data rates, the administration of orthogonal codes becomes an importantissue, and Section 9.3 explains how the different orthogonal codes are allocated todifferent physical channels. Lastly, Sections 9.4 and 9.5 discuss the codes and trans-mit diversity used by IS-2000.

9.2 Channel Supervision

9.2.1 Forward Link: Traffic Channel

In Chapter 7 (Section 7.4.2.3), we first mentioned the parameter FPC_PRI_CHAN;this parameter specifies the traffic channel (F-DCCH or F-FCH) that carries the for-ward power control subchannel. It turns out that FPC_PRI_CHAN is also the traf-fic channel (F-DCCH or F-FCH) that the mobile monitors in performing forwardtraffic channel supervision. The mobile performs forward traffic channel supervi-sion in the mobile station control on the traffic channel state because it is in thisstate that the forward traffic channel is active.

While in the mobile station control on the traffic channel state, the mobilemonitors each received frame on the traffic channel (F-DCCH or F-FCH). If themobile decides that the received frame has insufficient frame quality, then it declaresthat the received frame is a bad frame. Otherwise, the received frame is a good frame[1]. For each frame, the mobile checks the frame quality indicator (also known asCRC) bits in making its decision. If the mobile receives consecutive bad frames for aperiod of 240 ms (or 12 × 20 ms), then it must shut off its transmitter. The mobilecan only turn on its transmitter again if, after receiving consecutive bad frames for aperiod of 240 ms, it receives consecutive good frames for a period of 40 ms (or2 × 20 ms).

141

Page 162: 3G CDMA200 Wireless System Engineering

In addition, the mobile keeps a fade timer for the forward traffic channel(F-DCCH or F-FCH) being monitored. The timer is initialized when the mobile firstturns on its transmitter while in the traffic channel initialization substate of themobile station control on the traffic channel state. The fade timer is set to 5 secondsand then counts down. It is reset to 5 seconds every time the mobile receives consecu-tive good frames for a period of 40 ms (or 2 × 20 ms). If the timer expires, thenthe mobile must shut off its transmitter and declare a loss of the forward trafficchannel [2].

The mobile performs forward traffic channel supervision while in all the sub-states (i.e., traffic channel initialization substate, traffic channel substate, andrelease substate) of the mobile station control on the traffic channel state. If themobile declares a loss of the forward traffic channel, then the mobile returns to thesystem determination substate of the mobile station initialization state [2].

9.2.2 Forward Link: Common Channel

The mobile performs forward common channel supervision in the mobile stationidle state and system access state by monitoring the F-PCH, F-CCCH, or F-BCCH.So how does a mobile determine whether or not it has lost the F-PCH, F-CCCH, orF-BCCH? It does so by keeping a timer whenever it starts to monitor the F-PCH,F-CCCH, or F-BCCH. The timer is kept as follows: it is initially set for 3 seconds;the timer is reset to 3 seconds whenever the mobile receives a valid message on theF-PCH, F-CCCH, or F-BCCH; the timer is stopped when the mobile is not monitor-ing the F-PCH, F-CCCH, or F-BCCH. The mobile decides that it has lost the F-PCH,F-CCCH, or F-BCCH if the timer expires [2]. Note that different equipment vendorscan also have their own algorithms for determining whether or not a mobile still hasa usable F-PCH, F-CCCH, or F-BCCH.

9.2.3 Reverse Link

The same kind of channel supervision also occurs on the reverse link (i.e., the basestation also supervises the reverse traffic channels [e.g., R-DCCH and/or R-FCH]and reverse common channels [e.g., R-EACH and/or R-ACH]). Although theIS-2000 standard specifies that the base station has to supervise the channels, it doesnot specify how the base station should do so. Each equipment vendor may have dif-ferent ways of performing reverse traffic and common channel supervisions.

9.3 Code Management

Readers will recall that, in a DS-CDMA system, orthogonal (or near-orthogonal)sequences are used to channelize the different users that are in the same RF band. InIS-95, the system uses Walsh codes for channelization on the forward link and pseu-dorandom noise (PN) codes for channelization on the reverse link. In IS-2000, thesystem mostly uses Walsh codes for channelization on both the forward link and thereverse link. Therefore, this section focuses on how IS-2000 manages the assignmentof Walsh codes.

142 System Performance

Page 163: 3G CDMA200 Wireless System Engineering

9.3.1 Generation of Walsh Codes

A group of orthogonal Walsh codes is a set of N binary orthogonal sequences,w k

N , where k denotes the kth sequence in the set. Walsh codes can be derived usingthe Hadamard matrix in that higher order matrixes can be recursively generatedfrom lower order ones [3],

HH H

H H2 NN N

N N

=

(9.1)

where H N contains the inverted elements of H N , and the seed matrix is

H 2

0 0

0 1=

(9.2)

To generate a set of four Walsh codes w 04 , w1

4 , w 24 , and w 3

4 , we need to generatea Hadamard matrix of order 4, or

HH H

H H42 2

2 2

0 0 0 0

0 1 0 1

0 0 1 1

0 1 1 0

=

=

The four Walsh codes in this Walsh code set are taken from the rows of thematrix H4, and each Walsh code has a length of 4,

[ ][ ][ ][ ]

w

w

w

w

04

14

24

34

0 0 0 0

0 1 0 1

0 0 1 1

0 1 1 0

====

Another way to generate Walsh codes is using a recursive tree shown inFigure 9.1. Each node at each level of the tree has two branches below it, resulting intwo nodes at the next level. The left node at the next level consists of two instancesof the node above it. The right node at the next level consists of one instance of thenode above it and one inverted instance. The root node of the tree is 0.

Figure 9.2 shows an example of generating Walsh codes using a recursivetree. The root of the tree is 0 (at level 0). This results in 0, 0, 0, and 1 at the nextlevel (level 1). When one repeats this procedure, the Walsh code set of order 4 is

9.3 Code Management 143

Level j

Level +1j

C

C C C C

Figure 9.1 Recursive tree.

Page 164: 3G CDMA200 Wireless System Engineering

generated at level 2. This set of Walsh codes contains the codes [0 0 0 0], [0 0 1 1], [01 0 1], and [0 1 1 0]. At level 3, the Walsh code set of order 8 (or 23) is generated. Ingeneral, a Walsh code set of order N = 2j is generated at level j of the recursive tree.

9.3.2 Assignment of Walsh Codes: Forward Link

To have effective channelization, the system needs to ensure that all channelizationcodes in use are orthogonal to each another. In IS-2000, this task is complicated bythe fact that at any given time, there may be more than one type of channel operatingon the link, and these channels may be operating at different data rates. For exam-ple, on the forward link, both the F-DCCH and the F-SCH may be simultaneouslyactive for a user. For Spreading Rate (SR) 1, the final chip rate is fixed at 1.2288Mcps in order to fit the RF carrier in a 1.25-MHz band. If Radio Configuration (RC)3 is used, then the F-DCCH can operate at a data rate of 9.6 Kbps, and the F-SCHcan operate at 153.6 Kbps (see Chapter 2). To obtain a final chip rate of 1.2288Mcps, the system needs a processing gain of 128 (= 1.2288 Mcps / 9.6 Kbps) for theF-DCCH, and a processing gain of 8 (= 1.2288 Mcps / 153.6 Kbps) for the F-SCH.Because the processing gain of the F-DCCH is greater than that of the F-SCH, thelength of the Walsh code used by the F-DCCH must be longer than that used bythe F-SCH. In fact, in this case the F-DCCH uses a Walsh code of length 64, and theF-SCH uses a Walsh code of length 4. Although the above example deals withthe forward link, similar situations also exist on the reverse link.

Because IS-2000 supports different data rates simultaneously and the final chiprate is fixed at 1.2288 Mcps (at least for SR1), the system must be able to use Walshcodes of different lengths simultaneously (i.e., a lower data-rate channel requires alonger Walsh code, and a higher data-rate channel requires a shorter Walsh code).Therefore, an IS-2000 system employs Walsh codes of different lengths for differentchannels. Table 9.1 shows the different Walsh code lengths that different forwardlink channels support.

To prevent mutual interference, the system needs to ensure that all Walsh codesin use are orthogonal to each another. Because IS-2000 can use Walsh codes of dif-ferent lengths simultaneously, the system needs to make sure that active Walsh codes

144 System Performance

Level 0

Level 1

0

0 0 0 1

0000 0011 0101 0110

00000000 00001111 00110011 00111100 01010101 01011010 01100110 01101001

Level 2

Level 3

W 4

W 8

W 2

Figure 9.2 An example of generating Walsh codes using a recursive tree.

Page 165: 3G CDMA200 Wireless System Engineering

of different lengths are also orthogonal. This requirement places constraints onwhich specific Walsh codes can be used when one or more Walsh codes are alreadyin use. For example, let’s say that F-SCH 1 is currently active and operating at 307.2Kbps1. The Walsh code being used by F-SCH 1 is of length 4. This results in a finalchip rate of 1.2288 Mcps (= 614.4 Kbps × 4).

Now the mobile requests a second F-SCH (or F-SCH 2) to be operated simulta-neously with F-SCH 1. F-SCH 2 operates at a lower rate of 153.6 Kbps1, and theWalsh code to be used by F-SCH 2 needs to be of length 8 in order to keep the finalchip rate at 1.2288 Mcps (= 153.6 Kbps × 8). Figure 9.3 shows the bit streams andchip streams for F-SCH 1 and F-SCH 2.

If a channel uses a Walsh code, then a simultaneous channel cannot use anyWalsh code that is related directly or indirectly by branching on the recursive tree.For example, if an active channel is using Walsh code [0101] for channelization,then another channel cannot use [01], [01010101], [01011010], and so on (seeFigure 9.2). The reason is that, based on the way a recursive tree is constructed, atleast a part of a given Walsh code is always identical to a Walsh code above it; whenthe two Walsh codes are aligned in the transmission, it is possible that some bits ofone of the channels would be multiplied by identical Walsh chips, thus rendering thecorresponding bits unrecoverable later on. Figure 9.4 shows an example of thissituation. R-SCH 1 is channelized using Walsh code [0101]. R-SCH 2 is channelizedusing Walsh code [01011010] (which is below [0101] on the recursive tree).

One can see in Figure 9.4 that the Walsh chips multiplying the first and fourthbits of F-SCH 1 are identical to the corresponding Walsh chips on F-SCH 2. Thiswill make it impossible to recover the first and fourth bits of F-SCH 1 later on at thereceiver. To guarantee orthogonality for all corresponding bit positions amongsimultaneously active channels, we can only use Walsh codes that are not relateddirectly or indirectly by branching. In our example, if Walsh code [0101] is

9.3 Code Management 145

Table 9.1 Lengths of Walsh Codes Used on the Forward Link

Channel SR1 (RC1, 2, 3, 4, and 5) SR3 (RC6, 7, 8, and 9)

F-SCH 128, 64, 32, 16, 8, or 4 256, 128, 64, 32, 16, 8, or 4

F-FCH 128, 64, 32, 16, 8, or 4 256, 128, 64, 32, 16, 8, or 4

F-DCCH 128 or 64 256 or 128

F-CCCH 128, 64, 32, or 16 256, 128, or 64

F-BCCH 64 or 32 128

F-CACH 128 or 64 256

F-CPCCH 128 or 64 128

F-QPCH 128 256

F-SCCH 64 —

F-PCH 64 —

F-SYNCH 64 64

1. This rate would be the modulation symbol rate in either the I path or the Q path right before Walsh codespreading, not the baseband data rate.

Page 166: 3G CDMA200 Wireless System Engineering

already in use, then we can assign Walsh code (length 8) [00001111], [00110011],[00111100], [01100110], or [01101001].

Readers should recognize now that, to guarantee orthogonality among all bitpositions in all bit streams, the system needs to dynamically assign Walsh codes sub-jected to the constraints described above. Furthermore, the IS-2000 standard haspreassigned Walsh codes to some channels. For example, the F-PCH uses Walsh

146 System Performance

F-SCH 1

1 bit

1 chip307.2 Kbps

1.2288 Mcps

F-SCH 2

1 bit

1 chip153.6 Kbps

1.2288 Mcps

use w

use w

4k

8k

Figure 9.3 Example: F-SCH 1 operating at 307.2 Kbps and F-SCH 2 operating at 153.6 Kbps.

F-SCH 1307.2 Kbps

1.2288 Mcps

F-SCH 2153.6 Kbps

1.2288 Mcps

0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

0 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0

1stbit

4thbit

Figure 9.4 An example of nonorthogonal anomaly when two Walsh codes related by direct andindirect branching are used simultaneously.

Page 167: 3G CDMA200 Wireless System Engineering

code w164 . The existence of these preassigned Walsh codes further reduces the

number of freely available Walsh codes on the recursive tree.

9.3.3 Quasi-Orthogonal Functions

Even with these Walsh codes made available by IS-2000, it is still possible to run outof Walsh codes. Exhausting Walsh codes could happen when interference is rela-tively low and the forward link can sustain more channels than there are availableWalsh codes. In this case, the forward link is limited by the number of availableWalsh codes (Walsh code limited) instead of limited by interference (interferencelimited).

When the forward link is Walsh code limited, more channelization codes can begenerated by multiplying a set of Walsh codes by a specific masking function. Inother words, a new set of channelization codes can be derived by the multiplicationof a set of Walsh codes and a masking function. This new set of channelizationcodes (or “masked” Walsh codes) is called a set of quasi-orthogonal functions(QOFs).

The derivation of specific masking functions is beyond the scope of this book. Itsuffices to say that for a set of Walsh codes, there are more than one masking func-tions. For example, given a set of Walsh codes one can generate two sets of QOFs:one set by multiplying the set of Walsh codes with one masking function, andanother set by multiplying the set of Walsh codes with another masking function.Quasi-orthogonal functions drawn from the same set of QOFs are orthogonal, butquasi-orthogonal functions drawn from different sets of QOFs are not completelyorthogonal (hence the term quasi-orthogonal functions). In addition, quasi-orthogonal functions have constant (hence predictable) and minimal mini-maxcross correlation with the set of Walsh codes. Note that if the original set of Walshcodes contains 256 Walsh codes, then the above process has generated 512 addi-tional channelization codes or quasi-orthogonal functions.

The base station will use Walsh codes for channelization until they areexhausted. Then the base station will generate a set of QOFs and use quasi-orthogonal functions drawn from that set. If that set of QOFs is exhausted, then thebase station will use quasi-orthogonal functions from a different set of QOFs.

The IS-2000 standard specifies three masking functions. These three maskingfunctions are defined such that quasi-orthogonal functions drawn from differentsets of QOFs have minimal cross correlation with each other and with the set ofWalsh codes. In addition, the cross correlation of any two quasi-orthogonal func-tions drawn from different sets of QOFs has constant magnitude [4]. Quasi-orthogonal functions are used by the forward dedicated control channel, forwardfundamental channel, and forward supplemental channel.

9.3.4 Assignment of Walsh Codes: Reverse Link

The IS-2000 reverse link (for RC3, RC4, RC5, and RC6) is fundamentally differentfrom that of IS-95. On the IS-95 reverse link, only one channel is active at a time(i.e., either the access channel or the traffic channel). Therefore, there is no need todistinguish individual channels transmitted by a mobile since each mobile can only

9.3 Code Management 147

Page 168: 3G CDMA200 Wireless System Engineering

transmit one channel at a time. In IS-95, a mobile is distinguished from othermobiles by its long PN code.

In IS-2000, a mobile can transmit multiple channels simultaneously. So the basestation not only has to distinguish among different mobiles, but also has to distin-guish among different channels transmitted by a specific mobile. In IS-2000, thebase station still discriminates the mobiles by their individual long PN codes, butafter a mobile is identified using its long PN code, the base station demodulates thechannels (transmitted by that mobile) using their assigned Walsh codes2. Note thatthis arrangement is analogous to the forward link where, to a mobile, different basestations are first identified by their short PN codes. After a mobile identifies a spe-cific base station, the mobile then demodulates the channels (transmitted by thatbase station) using their assigned Walsh codes. What enables the operation of theIS-2000 reverse link is that the mobile now transmits an R-PICH, which allows thebase station to perform coherent detection of the mobile’s signal and to lock onto amobile’s identifying PN code.

In IS-2000, the base station does not dynamically assign Walsh codes for amobile to use. Rather, the IS-2000 standard defines the Walsh code each reverse linkchannel must use. Table 9.2 shows these predefined Walsh codes and their lengthson the reverse link [1].

To ensure orthogonality, the preassignment of these Walsh codes also meet theconstraints described in the previous section. For example, a mobile would some-times transmit both the R-FCH and the R-DCCH simultaneously. As shown inFigure 9.5, the Walsh code preassigned to the R-FCH ([0000111100001111]) isnot directly or indirectly related to the Walsh code preassigned to the R-DCCH([0000000011111111]). In addition, if the system chooses [01] to channelizeR-SCH 1, then it can choose either [0011] or [00111100] to channelize R-SCH 2. Ifit chooses [0011] to channelize R-SCH 1, then it cannot choose [00111100] to chan-nelize R-SCH 2; in fact, in this case the mobile cannot have an additional R-SCH(i.e., R-SCH 2) because the standard does not have preassigned any usable Walshcode. Figure 9.5 shows the location of these Walsh codes on the recursive tree.

148 System Performance

Table 9.2 Walsh Codes Used on the Reverse Link for Both SR1 (RC3 and RC4)3 andSR3 (RC5 and RC6)

Channel Walsh Code Walsh Code Length

R-SCH 1 w24 =[0011] or w1

2 =[01] 4, or 2

R-SCH 2 w68 =[00111100] or w2

4 =[0011] 8 or 4

R-FCH w416 =[0000111100001111] 16

R-DCCH w816 =[0000000011111111] 16

R-EACH w28 =[00110011] 8

R-CCCH w28 =[00110011] 8

2. IS-2000 calls Walsh codes used on the reverse link Walsh covers.3. Walsh code lengths for RC1 and RC2 are not shown because Walsh codes are not used for channelization in

these radio configurations.

Page 169: 3G CDMA200 Wireless System Engineering

At this point, readers may ask that given a predefined Walsh code, how does thesystem vary the transmission rate on the reverse link. To change the transmissionrate, the mobile uses the same Walsh code but repeats it in a given bit. Figure 9.6illustrates this operation. Suppose that an R-SCH is operating at 614.4 Kbps1 and isusing Walsh code [01]. This gives a final chip rate of 1.2288 Mcps (= 614.4 Kbps ×2). Now the system would like to change the rate from 614.4 Kbps down to 153.6Kbps1 (by a factor of four). What the mobile would do then is to repeat Walsh code[01] four times during a bit, thus still attaining a final chip rate 1.2288 Mcps. Notethat repeating a Walsh code does not cause any orthogonality problems because the

9.3 Code Management 149

Level 0

Level 1

0

0 0 0 1

0000 0011 0101 0110

00000000 00001111 00110011 00111100 01010101 01011010 01100110 01101001

Level 2

Level 3

W 4

W 8

W 2

Level 4 W 160000000011111111

0000111100001111

R-SCH1orR-SCH2

R-SCH1

R-SCH2R-EACHorR-CCCH

R-DCCH

R-FCH

Figure 9.5 Location of reverse link Walsh codes on the recursive tree.

614.4 Kbps

1.2288 Mcps

153.6 Kbps

1.2288 Mcps

0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 chip

1 bit

1 bit

0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 chip

use 21w

repeat 21w four times

Figure 9.6 Example: Changing transmission rate on the R-SCH.

Page 170: 3G CDMA200 Wireless System Engineering

standard has already predefined the Walsh codes in such a way that they are notrelated directly and indirectly (by branches), and repeating a Walsh code is equiva-lent to traversing down the recursive tree along the branches.

9.4 Turbo Codes

Turbo codes are relatively new in the family of error-correcting codes. They werefirst proposed in 1993 [5, 6] and constitute a new way of implementing concate-nated codes. IS-2000 makes use of turbo codes because of their ability to achieve lowerror rates at very-small signal-to-noise ratios (SNR) or Eb/N0. Recall that

MW R

E Nb

∝ ( / )( / )0

(9.3)

where M is the number of simultaneous users [3]. Equation (9.3) states that, in gen-eral, the capacity of a CDMA system is directly proportional to the processing gain(W/R) and inversely proportional to the required Eb/N0. Therefore, to the extent thatthe required Eb/N0 can be reduced, the capacity of a CDMA system can be increased(subject to the availability of orthogonal codes, of course).

A turbo encoder has some important and distinguishing characteristics:

• A turbo encoder typically contains two convolutional encoders. These convo-lutional encoders are sometimes referred to as constituent encoders. The con-stituent encoders are usually identical to each other.

• Each constituent encoder operates as a recursive systematic convolutional(RSC) encoder. In producing coded bits, an RSC encoder not only linearlycombines shifted bits at different stages in the register, but also feeds backthese shifted bits to the beginning of the register.

• Whereas the first constituent encoder codes the message bits as they enter theturbo encoder, the second constituent encoder codes a permuted version of themessage bits.

Figure 9.7 shows an example of a turbo encoder with its two constituent encod-ers arranged in a parallel fashion. In this example, each constituent encoder operatesat rate 1/2 and produces two coded bits for every input bit. Turbo codes imple-mented by turbo encoders shown in Figure 9.7 are also known as parallel concate-nated convolutional codes (PCCC) because they are generated by concatenating twoconvolutional codes in parallel.

Figure 9.7 shows that the message bits mi (to be encoded) also form parts of theoutput bits. Because each constituent encoder is of rate 1/2, Encoder 1 operates onmi and produces coded bits x′ i and x″ i. Encoder 2 operates on a permuted version ofmi, or mi, and produces coded bits y′ i and y″ i. The interleaver rearranges the bits mi toproduce mi in such a way that mi appear completely different from mi. The inter-leaver typically operates on a block of input bits at a time. In addition, a puncturingfunction selectively deletes the coded bits (produced by constituent encoders) toarrive at a desired rate for the whole turbo encoder. In the example shown in Figure

150 System Performance

Page 171: 3G CDMA200 Wireless System Engineering

9.7, each constituent encoder operates at rate 1/2 and produces two coded bits forevery input bit. If there is no puncturing, then the entire turbo encoder operates atrate 1/5 because a total of five bits (including the input bit itself) are produced forevery input bit.

The turbo encoder shown in Figure 9.7 happens to be the one used by IS-2000.In fact, both the forward link and the reverse link use the same turbo encoder. Byusing puncturing, the turbo encoder used in IS-2000 can operate at rates 1/2, 1/3,and 1/4. For example, to achieve rate 1/3, the turbo encoder only outputs mi, x′ i, andy′ i and lets the puncturing function completely punctures out x″ i and y″ i. In terms ofthe interleaver, the interleaver permutes one frame of bits at a time.

The interleaver is a key to turbo codes’ good error-correcting performance.Because of the interleaver, the two constituent encoders essentially operate on thesame set of bits but in different order. Therefore, at the receiver, erroneous bitsequences that appear correct to one decoder would more likely be rejected by theother decoder [7]. As the previous sentence implies, at the receiver the turbo decoderconsists of two convolutional decoders. The decoding of turbo codes is beyond thescope of this book. It suffices to say that the two convolutional decoders worktogether by exchanging soft decisions between themselves and iteratively arrive atthe (hard) decisions on what the correct message bits should be. See [8, 9] for gooddiscussions of turbo decoding.

The reason why turbo codes are used in 3G systems is their ability to correcterrors at a low SNR. They have been shown to achieve very-low error rates (i.e.,around 10–5) but require only an SNR of less than 1 dB above the Shannon’s limit.The cost of such a superior error performance is equally obvious. Turbo coding anddecoding are computationally more intensive than conventional convolutional cod-ing and decoding. Delays resulting from such computations render turbo codesunusable in voice applications. This is the reason why, in IS-2000, turbo codes areonly used for supplemental channels (forward and reverse) for data applications

9.4 Turbo Codes 151

Constituentencoder 1(rate 1/2)

Puncture

mi

Interleaver

xi'

xi''

Constituentencoder 2(rate 1/2)

Puncture

yi'

yi''

mi

(

Turboencodedbits

Figure 9.7 A turbo encoder.

Page 172: 3G CDMA200 Wireless System Engineering

where delays can be tolerated. Research has shown that in IS-2000 turbo codes canachieve gains of 1.3 to 1.5 dB at an FER of 1% [10].

9.5 Transmit Diversity

IS-2000 has made much effort to improve the forward link. One reason is that fieldexperience with IS-95 has shown that in many instances the system is forwardlink limited [11]. Another reason is that many high-rate data applications sup-ported by 3G require higher throughput on the forward link. One enhancementmade to improve the forward link is the enhanced forward link power control (seeChapter 7); IS-2000 can now power control the forward link at a rate of 800-times-per-second.

Another enhancement IS-2000 made is transmit diversity, which typically usestwo transmit antennas. Transmission through two antennas achieves spatial diver-sity when antennas are spaced sufficiently apart (by several wavelengths). This waytwo transmitted signals undergo independent fading and are uncorrelated, and theprobability that both signals undergo fading at the same time is small. IS-2000 pro-visions two transmit diversity schemes: orthogonal transmit diversity (OTD) andspace time spreading (STS). In OTD, the base station splits the symbol stream intomultiple streams and transmits them through multiple antennas. In STS, the basestation duplicates multiple copies of the symbol stream and transmits them throughmultiple antennas.

9.5.1 Orthogonal Transmit Diversity

OTD is a technique by which the base station splits the symbol stream into multiplestreams and transmits them through multiple antennas. A common configuration isto split the symbol stream into two streams (odd and even) and to transmit themthrough two antennas. OTD is a transmit diversity scheme that was proposed in [12]and later adopted by the IS-2000 standard [13]. Figure 9.8 shows the concept ofOTD.

As shown in Figure 9.8, the interleaved symbol stream is split into two streams:odd and even. The odd symbol stream is channelized by one Walsh code, and theeven symbol stream is channelized by another (different) Walsh code to maintainorthogonality between the two streams. Quasi-orthogonal functions can also beused. Both channelized streams are spread by the same short PN code4 and thentransmitted by two different antennas.

Figure 9.9 shows the implementation of OTD in IS-2000. Here the channelstructure is for the forward dedicated control channel, forward fundamentalchannel, and forward supplemental channel5 (same as that shown in Figure 2.14 ofChapter 2) except that the symbol stream is split into four different streams: Iodd,Ieven, Qodd, and Qeven. The odd streams are fed into a complex modulator which

152 System Performance

4. In actuality there are two short PN codes: pI and pQ. See Chapter 2.5. Forward supplemental channel does not have punctured power control bits.

Page 173: 3G CDMA200 Wireless System Engineering

9.5 Transmit Diversity 153

Demux

odd

even

wi or QOF

w’i or QOF’

p

Y todd( ) Y teven( )

Figure 9.8 Othogonal transmit diversity.

Iodd

Blockinterleaving

Long codescrambling

Channelgain

Modulationsymbols

Powercontrolpuncturing

Power control bits

Dem

ux

Long code mask

Qeven

Ieven

Qodd

Iodd

Qodd

Ieven

Qeven

wi or QOF pI

Y todd( )

Y teven( )

Complexmodulator

Complexmodulator

w’i or QOF’

pQ

Figure 9.9 Implementation of OTD in IS-2000. For brevity, symbol repetition is not shown.

Page 174: 3G CDMA200 Wireless System Engineering

generates the transmit signal Yodd(t) for one antenna. The even streams are fed intoanother complex modulator which generates the transmit signal Yeven(t) for anotherantenna.

Each complex modulator uses a different Walsh code but the same short PNcodes. The internal structure of the complex modulator is identical to that used byIS-2000 forward link (see Figure 2.15 in Chapter 2).

To support transmit diversity, the base station sector transmits two pilot chan-nels, one for each of the two transmit antennas. One antenna transmits the originalF-PICH, and the other antenna transmits the F-TDPICH (see Chapter 2). These twopilots are used to perform estimation for the two (independent) propagation chan-nels and to aid coherent detection of the two signals. At the receiver, the two signalsare despread using the same two Walsh codes (used at the transmitter) and multi-plexed and combined to recover the original symbol stream [14].

Studies have shown that OTD outperforms no transmit diversity. Typical gainsare between about 1 to 4 dB (e.g., [14]) depending on the mobile’s speed (transmitdiversity performs best when the mobile is stationary).

9.5.2 Space Time Spreading

STS is a technique by which the base station duplicates multiple copies of the symbolstream and transmits them through multiple antennas. A common configuration isto duplicate two copies (1 and 2) and to transmit them through two antennas. STS isa transmit diversity scheme that was proposed in [15] and later adopted by theIS-2000 standard [13]. Figure 9.10 shows the concept of STS.

As shown in Figure 9.10, the interleaved symbol stream is split into two streams:odd and even. The odd and even streams are combined to form two identical paths 1

154 System Performance

Demux

odd

even

wi or QOF

p

wi or QOF

Y t1( ) Y t2( )

Σ

Σ1

2

Figure 9.10 Space time spreading.

Page 175: 3G CDMA200 Wireless System Engineering

and 2. Path 1 is channelized by one Walsh code, and path 2 is channelized byanother (complementary) Walsh code to maintain orthogonality between the twopaths. Quasi-orthogonal functions can also be used. Both channelized paths arespread by a short PN code6 and then transmitted by two different antennas.

Figure 9.11 shows the implementation of OTD in IS-2000. Here the channelstructure is for the forward dedicated control channel, forward fundamental chan-nel, and forward supplemental channel7 (same as that shown in Figure 2.14 ofChapter 2) except that the symbol stream is split into four different streams: Iodd,Ieven, Qodd, and Qeven. For path 1 (top complex modulator), the combination of Iodd

and Ieven streams forms the in-phase input, and the combination of Qodd and Qeven

streams forms the quadrature input. For path 2 (bottom complex modulator), thecombination of Iodd and Ieven streams forms the in-phase input, and the combinationof Qodd and Qeven streams forms the quadrature input. The top complex modulatorgenerates the path 1 transmit signal Y1(t) for one antenna. The bottom complexmodulator generates the path 2 transmit signal Y2(t) for another antenna. This way,each path effectively transmits all symbol streams.

Each complex modulator uses a complementary Walsh code but the same shortPN codes. The internal structure of the complex modulator is identical to that usedby IS-2000 forward link (see Figure 2.15 in Chapter 2).

9.5 Transmit Diversity 155

Iodd

Blockinterleaving

Long codescrambling

Channelgain

Modulationsymbols

Powercontrolpuncturing

Power control bits

Dem

ux

Long code mask

Qeven

Ieven

Qodd

Iodd

Iodd

Qodd

Qodd

Qeven

Qeven

Ieven

Ieven

wi or QOF

wi or QOF

pI

Y t1( )

Y t2( )

Complexmodulator

Σ

Σ

Σ

Σ

Complexmodulator

pQ

Figure 9.11 Implementation of STS in IS-2000. For brevity, symbol repetition is not shown.

6. In actuality there are two short PN codes: pI and pQ. See Chapter 2.7. Forward supplemental channel does not have punctured power control bits.

Page 176: 3G CDMA200 Wireless System Engineering

To support transmit diversity, the base station sector also transmits two pilotchannels (F-PICH and F-TDPICH), one for each transmit antenna, to perform chan-nel estimation for and coherent detection of the two signals. At the receiver, the twosignals are despread using the same two Walsh codes (used at the transmitter) andcombined to recover the original symbol stream [14].

Studies have shown that STS outperforms OTD by about 0.3 to 2.4 dB (e.g.,[13]) depending on the speed of the mobile (transmit diversity performs best whenthe mobile is stationary).

9.5.3 Concluding Remarks

Based on transmitter structures shown in Figures 9.9 and 9.11, it is clear that bothOTD and STS require modifications of the receiver to support these transmit diver-sity schemes. Therefore, the mobile needs to inform the base station whether or notthe mobile’s receiver is capable of supporting transmit diversity. The mobile doesso by using OTD_SUPPORTED and STS_SUPPORTED fields in messages such asregistration message, origination message, and page response message.

References

[1] TIA/EIA/IS-2000.2-A, Physical Layer Standard for cdma2000 Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

[2] TIA/EIA/IS-2000.5-A, Upper Layer (Layer 3) Signaling Standard for cdma2000 SpreadSpectrum Systems, Telecommunications Industry Association, March 2000.

[3] Yang, S. C., CDMA RF System Engineering, Norwood, MA: Artech House, 1998.[4] Jalloul, L. M. A., and A. Shanbhag, “Enhancing Data Throughput Using Quasi-Orthogonal

Functions Aggregation for 3G CDMA Systems,” Proceedings of Vehicular TechnologyConference, 2002, pp. 2008–2012.

[5] Berrou, C., A. Glavieux, and P. Thitimajshima, “Near Shannon Limit Error-CorrectingCoding and Decoding: Turbo Codes,” Proceedings of IEEE International Conference onCommunication, 1993, pp. 1064–1070.

[6] Berrou, C., and A. Glavieux, “Near Optimum Error Correcting Coding and Decoding:Turbo-Codes,” IEEE Trans. Comm., October 1996, pp. 1261–1271.

[7] Rothweiler, J., “Turbo Codes,” IEEE Potentials, February/March 1999, pp. 23–25.[8] Sklar, B., “A Primer on Turbo Code Concepts,” IEEE Communications, December 1997,

pp. 94–102.[9] Ryan, W. E., “Concatenated Convolutional Codes and Iterative Decoding,” In J. G. Proakis

(Ed.), Wiley Encyclopedia of Telecommunications, Hoboken, NJ: Wiley, 2002.[10] Zhang, P., and P. Luukkanen, “Performance of Turbo Codes in 3rd Generation cdma2000

Mobile System,” Proceedings of Vehicular Technology Conference, 1999, pp. 1674–1677.[11] Walton, R., M. Wallace, and S. Howard, “CDMA Downlink Performance Issues,” Pro-

ceedings of the Ninth IEEE International Symposium on Personal, Indoor and MobileRadio Communications, 1998, pp. 308–312.

[12] Weerackody, V., “Diversity for Direct-Sequence Spread Spectrum System Using MultipleTransmit Antennas,” Proceedings of IEEE International Conference on Communication,1993, pp. 1775–1779.

[13] Wu, G., et al., “Performance Evaluation of Space-Time Spreading and Orthogonal TransmitDiversity in CDMA2000,” Proceeding of IEEE Seventh International Symposium onSpread Spectrum Techniques and Applications, 2002, pp. 323–327.

156 System Performance

Page 177: 3G CDMA200 Wireless System Engineering

[14] Derryberry, R. T., et al., “Transmit Diversity in 3G CDMA Systems,” IEEE Communica-tions, Vol. 40, No. 4, 2002, pp. 68–75.

[15] Papadias, C., et al., “Space-Time Spreading for CDMA Systems,” Proceeding of SixthWorkshop Smart Antennas Wireless Mobile Communications, July 22–23, 1999, Stanford,CA.

Selected Bibliography

Hanzo, L., T. H. Liew, and B. L. Yeap, Turbo Coding, Turbo Equalisation and Space-Time Cod-ing for Transmission over Fading Channels, New York: John Wiley & Sons, 2002.

9.5 Transmit Diversity 157

Page 178: 3G CDMA200 Wireless System Engineering

.

Page 179: 3G CDMA200 Wireless System Engineering

C H A P T E R 1 0

System Design: Coverage

10.1 Introduction

The purpose of system design is to ascertain whether or not a given model of the sys-tem will meet some predetermined requirement. For a wireless system, the require-ment is often that a user should perceive his or her radio connection to be one ofhigh quality (i.e., the user is well within the coverage area of a cell or sector).

Since coverage has to do with the quality of the radio link, this chapter empha-sizes on the analysis of RF part of the system. In performing such an analysis, we areconcerned with the classical figures of merit of a CDMA system (i.e., Ec/I0 andEb/N0). Specifically, we will examine the following more important parameters [1]:

• Ec/I0 of the forward pilot channel;• Eb/N0 of the forward fundamental channel;• Eb/N0 of the reverse fundamental channel;• Eb/N0 of the forward supplemental channel;• Eb/N0 of the reverse supplemental channel.

Calculating the actual Eb/N0 and Ec/I0 ratios essentially involves the accountingof signal and interference terms. Note that throughout this chapter, we refer to themobile of interest as the probe mobile, and link equations are derived from the per-spective of this probe mobile both on the forward link and on the reverse link.

Before we proceed, it is instructive to first examine the analytic definitions ofEb/N0 and Ec/I0 as these terms are used often in CDMA. In fact, we are especiallyinterested in the relationship between Eb/N0 and Ec/I0, if any. In terms of Eb/N0,Eb/N0 is the energy-per-bit (Eb) per noise-power density (N0). It can be treated as aproxy of SNR when one recognizes that energy-per-bit is equal to the average signalpower allocated to each bit duration,

E S Tb b b= (10.1)

where Sb is the average signal power and Tb is the time duration of each bit. Noticethat (10.1) is consistent with dimensional analysis, which states that energy isequivalent to power multiplied by time. Substituting bit rate Rb (which is the inverseof bit duration Tb) into the above equation produces

159

Page 180: 3G CDMA200 Wireless System Engineering

ES

Rbb

b

= (10.2)

Eb/N0 is thus

E

N

S

R Nb b

b0 0

= (10.3)

Given that noise power density N0 is just the noise power N divided by the band-width W, Eb/N0 becomes

E

N

S

NWR

b b

b0

= (10.4)

Equation (10.4) states that Eb/N0 is the same as the SNR (Sb/N) enhanced by (ormultiplied by) the processing gain (W/Rb).

In terms of Ec/I0, Ec/I0 is the pilot energy-per-chip (Ec) per total power density(I0). Ec can be written as

E S Tc c c= (10.5)

where Sc is the average pilot power and Tc is the time duration of each chip. Substi-tuting chip rate Rc (which is the inverse of chip duration Tc) into the above equationproduces

ES

Rcc

c

= (10.6)

Ec/I0 then is

E

I

S

R Ic c

c0 0

= (10.7)

Given that total power density I0 is just the total power I divided by the band-width W, Ec/I0 becomes

E

I

S

IWR

c c

c0

= (10.8)

If we make the assumption that Rc (e.g., 1.2288 Mcps in 1x) is approximatelythe same as W (e.g., 1.25 MHz in 1x), then Ec/I0 is essentially the pilot power (Sc)divided by the total power (I),

E

I

S

Ic c

0

≈ (10.9)

160 System Design: Coverage

Page 181: 3G CDMA200 Wireless System Engineering

Lastly, we are interested in deriving a relationship between Eb/N0 and Ec/I0.Solving the above equation for I and assuming that N is approximately the same as Iyield

N IS

E Ic

c

≈ =/ 0

(10.10)

Substituting (10.10) into (10.4) produces

E

N

S

SWR

E

Ib b

c b

c

0 0

≈ (10.11)

Therefore,

E N

E I

S

SWR

b

c

b

c b

/

/0

0

≈ (10.12)

Equation (10.12) shows that the ratio between Eb/N0 and Ec/I0 is approximatelythe product of the ratio of average signal power to average pilot power and the proc-essing gain. If average signal power is the same as average pilot power, then the ratiobetween Eb/N0 and Ec/I0 is simply the processing gain,

E N

E IWR

if S Sb

c bb c

/

/0

0

≈ = (10.13)

10.2 Forward Pilot Channel

The Ec/I0 is the pilot energy summed over the period of one chip divided by the totalpower density in the RF band. The Ec/I0 is the figure of merit of the forward pilotchannel; it is important in system design because the Ec/I0 effectively determines thecoverage area of a sector. It does so in two ways. First, the forward pilot channelserves as a coherent carrier phase reference for the demodulation of other forwardphysical channels. If a mobile is too far away from the base station, the receivedEc/I0 would not be sufficient for the successful demodulation of other forwardphysical channels. Second, the Ec/I0 is an important parameter in deciding whetheror not a handoff should occur. This is especially so for the enhanced algorithms thatare now available in IS-2000 (see Chapter 8).

The Ec/I0 of the forward pilot channel is given by

E

I

A ( )L ( ,d )G

rNc

0

0 0 0 0 0 0=α θ θ

(10.14)

where

• A0 0( )θ is the total effective radiated power (ERP) of all available amplifierpower of the home sector (sector 0). Because ERP depends on the antenna pat-tern, which is a function of direction θ 0 , ERP is also a function of direction θ 0 .

10.2 Forward Pilot Channel 161

Page 182: 3G CDMA200 Wireless System Engineering

• α 0 is the fraction of the total ERP of all available amplifier power of the homesector (sector 0) that is allocated to the F-PICH.

• L d0 0 0( , )θ is the path loss from the home base station in the direction θ 0 to theprobe mobile a distance d0 away.

• G is the receive antenna gain of the probe mobile;• N is the thermal noise power;• r is the ratio of total interference power received at the probe mobile (on the

forward link) to thermal noise power.

Note that the ERP of the forward pilot channel (α θ0 0 0A ( )) is deterministic anddoes not change.

As defined above, the term rN is then the total interference received on the for-ward link at the mobile and has three components,

rN r N r N Nh a= + + (10.15)

where

• rh is the ratio of interference power received at the probe mobile (from thehome sector) to thermal noise power.

• ra is the ratio of interference power received at the probe mobile (from otheradjacent sectors) to thermal noise power.

For the sake of brevity, (10.14) (and all subsequent link equations in this chap-ter) does not include those received interference from other sources of non-CDMAorigins (e.g., intentional or unintentional jammers). For the same reason, we also donot include those margins that are typically found in link budgets (e.g., lognormalshadow fading).

10.3 Forward Fundamental Channel

In IS-2000, the forward fundamental channel is more frequently used for voiceapplications. To ascertain whether or not the forward fundamental channel can ade-quately support voice applications, a system designer must assess the quality of theradio link associated that channel. Eb/N0 is perhaps the most popular figure of meritfor assessing the quality of the radio link. This is so because Eb/N0 determines the biterror rate (BER) of the link and ultimately affects the frame error rate (FER) of thechannel. In assessing the quality of the link, one ensures that the actual Eb/N0 is atleast equal to the required Eb/N0.

The Eb/N0 of the forward fundamental channel is given by

E

N

F L d G

r N r N NWR

b

h a F0

0 0 0 0 0

1=

− + +

( ) ( , )

( )

θ θ

ε(10.16)

where

162 System Design: Coverage

Page 183: 3G CDMA200 Wireless System Engineering

• F0 0( )θ is ERP of the F-FCH of the home sector (sector 0). Because ERPdepends on the antenna pattern, which is a function of direction θ 0 , ERP isalso a function of direction θ 0 .

• L d0 0 0( , )θ is the path loss from the home base station in the direction θ 0 to theprobe mobile a distance d0 away.

• G is the receive antenna gain of the probe mobile.• N is the thermal noise power.• W is the final spread bandwidth, which for Radio Configurations 1 through 5

is 1.25 MHz.• RF is the data rate of the forward fundamental channel.

The factor (W/RF) is also known as the processing gain. Regarding the interfer-ence terms in the denominator,

• ε is the orthogonality factor1;• rh is the ratio of interference power received at the probe mobile (from the

home sector) to thermal noise power;• ra is the ratio of interference power received at the probe mobile (from other

adjacent sectors) to thermal noise power.

Equation (10.16) states that the interference contributions consist of those fromthermal noise (N), interference received from other adjacent sectors (raN), and inter-ference received from the home sector (( )1 − ε r Nh ). Interference received from thehome sector is essentially the interference power received from the home sector (i.e.,rhN) suppressed by the orthogonality factor (i.e.,1 − ε). In other words, interferencereceived from the home sector that is intended for other users is suppressed becauseof the orthogonal property of channelization codes.

Due to power control, F0 0( )θ is not deterministic. Rather, F0 0( )θ is constantlychanging due to adjustments made by the base station to maintain an acceptableEb/N0. In that regard, F0 0( )θ can be treated as a random variable. In addition, for thesake of brevity (10.16) does not include the effects of diversity gain in soft/softerhandoffs.

10.4 Forward Supplemental Channel

In IS-2000, the forward supplemental channel is only used for data applications. Tofind out if the forward supplemental channel can adequately support the trans-mission of data, a system designer evaluates the quality of the radio link associatedwith the forward supplemental channel. Similar to the forward fundamental chan-nel, Eb/N0 is used as the figure of merit because it determines the BER of the link andultimately the FER of the channel. The actual Eb/N0 should at least be equal to therequired Eb/N0.

The Eb/N0 of the forward supplemental channel is given by

10.4 Forward Supplemental Channel 163

1. Orthogonality factor indicates how much interfering signal power a receiver can reject due to the orthogo-nal property of channelization codes. Ideally, orthogonality factor is 1 (or 100%) if codes are orthogonaland perfectly aligned.

Page 184: 3G CDMA200 Wireless System Engineering

E

N

S L d G

r N r N NWR

b

h a S0

0 0 0 0 0

1=

− + +

( ) ( , )

( )

θ θ

ε(10.17)

where

• S 0 0( )θ is ERP of the F-SCH of the home sector (sector 0). Note that ERP is afunction of direction θ 0 .

• L d0 0 0( , )θ is the path loss from the home base station in the direction θ 0 to theprobe mobile a distance d 0 away.

• G is the receive antenna gain of the probe mobile.• N is the thermal noise power.• W is the final spread bandwidth, which for Radio Configurations 1 through 5

is 1.25 MHz.• RS is the data rate of the forward supplemental channel.

The factor (W/RS) is also known as the processing gain. Because the data rateof the forward supplemental channel (RS) is often greater than that of the for-ward fundamental channel (RF), the processing gain of the forward supplementalchannel is typically less than that of the forward fundamental channel. This is sobecause W is fixed. The effect of this lower processing gain is described later in thissection.

Regarding the interference terms in the denominator,

• ε is the orthogonality factor.• rh is the ratio of interference power received at the probe mobile (from the

home sector) to thermal noise power.• ra is the ratio of interference power received at the probe mobile (from other

adjacent sectors) to thermal noise power.

Equation (10.17) states that the interference contributions consist of those fromthree sources. The first two are similar to those shown for the forward fundamentalchannel [i.e., thermal noise (N) and interference received from other adjacent sectors(raN)]. The third source (( )1 − ε r Nh ) consists of interference received from the homesector. It is essentially the interference power received from the home sector (i.e.,r Nh ) suppressed further by the orthogonality factor (i.e., 1 − ε). Again in this case,interference received from the home sector that is intended for other users is sup-pressed because of the orthogonal property of channelization codes.

Due to power control, S 0 0( )θ is constantly changing due to adjustments madeby the base station to maintain an acceptable Eb/N0. In that sense, S 0 0( )θ is random.In addition, as mentioned before, the forward supplemental channel typically has alower processing gain than the forward fundamental channel. This results in a lowerlink Eb/N0 if all other parameters remain the same. What this means is that, for agiven required Eb/N0, the forward supplemental channel has to transmit at a higherpower S 0 0( )θ to compensate for the lower processing gain (W/RS).

Figure 10.1 shows the signal and interference components of the forward link.

164 System Design: Coverage

Page 185: 3G CDMA200 Wireless System Engineering

10.5 Upper Bounds of Interference: Forward Link

Although rh and ra (and hence r) are typically calculated using system simulations,we can nevertheless derive useful upper bounds for these ratios. For the interferencereceived from the home sector (sector 0),

rA F L d G

Nh ≤−[ ( ) ( )] ( , )0 0 0 0 0 0 0θ θ θ

(10.18a)

or

rA S L d G

Nh ≤−[ ( ) ( )] ( , )0 0 0 0 0 0 0θ θ θ

(10.18b)

where A0 0( )θ is the total ERP of all available amplifier power of the home sector(sector 0). Equation (10.18) effectively states that the interference received from thehome sector can never be greater than what can be radiated by the available ampli-fier power of the home sector.

For the interference received from other sectors

rG A L d

Na

k k k k kk

K

≤ =

∑ ( ) ( , )θ θ1

1

(10.19)

where Ak k( )θ is the total ERP of all available amplifier power of the kth sector, andL dk k k( , )θ is the path loss from the kth sector in the direction θ k to the probe mobilea distance dk away. Note that there are a total of K sectors in the system.

10.6 Reverse Fundamental Channel

In IS-2000, the reverse fundamental channel is more frequently used for voice appli-cations. In a similar manner, the system designer determines whether or not thereverse fundamental channel can adequately support voice applications. In doing

10.5 Upper Bounds of Interference: Forward Link 165

HomeBS

ProbeMS

F S0, 0 L0 G

(1 )−ε r Nh

Other BS

Other BS

r Na

Signal

Interference

Figure 10.1 Forward link: Signal and interference components where the base station (BS) is thetransmitter and the mobile station (MS) is the receiver.

Page 186: 3G CDMA200 Wireless System Engineering

so, he or she calculates the actual Eb/N0 and ensures that it is at least equal to therequired Eb/N0.

The Eb/N0 of the reverse fundamental channel is given by

E

N

F L d G

r NWR

b

F0

0 0 0 0=′ ′ ′

( , ) ( )θ θ(10.20)

where

• ′F0 is ERP of the R-FCH of the probe mobile (mobile 0); the transmit pattern isassumed to be omnidirectional.

• ′L d( , )θ 0 0 is the path loss from the probe mobile (mobile 0) in the directionθ 0 back to the home base station a distance d0 away.

• ′G ( )θ 0 is the receive antenna gain of the home sector in the direction θ 0 to theprobe mobile (mobile 0).

• N is the thermal noise power.• W is the final spread bandwidth, which for Radio Configurations 3 and 4 is

1.25 MHz.• RF′ is the data rate of the reverse fundamental channel.• r′ is the ratio of total interference power received at the home sector (on the

reverse link) to thermal noise power.

r′ is sometimes known as the reverse link rise. As defined above, the term r′N isthe total interference power received on the reverse link at the home sector and hasthree components,

′ = ′ + ′ +r N r N r N Nh a (10.21)

where

• ′rh is the ratio of interference power received at the home sector (from thosemobiles in the home sector) to thermal noise power.

• ′ra is the ratio of interference power received at the home sector (from thosemobiles in other adjacent sectors) to thermal noise power.

Even though IS-2000 has a reverse pilot channel, (10.20) and (10.21) neverthe-less do not contain the orthogonality factor. This is because each mobile is free totransmit its own reverse pilot channel, and no attempt is made at the base station toalign all the channelization codes used by the mobiles in a particular sector. Never-theless, the reverse pilot channel provides an important benefit as it is used as a refer-ence signal to facilitate the coherent detection and demodulation of other reversephysical channels (e.g., reverse fundamental channel). This benefit shows up as thelower required Eb/N0 for IS-2000 reverse fundamental channels.

Due to power control, F′ is not deterministic. Rather, F′ is constantly changingdue to adjustments made by the mobile to maintain an acceptable Eb/N0. In thatregard, F′ can be treated as a random variable. Similarly, for the sake of brevity(10.20) does not include the effects of diversity gain in soft/softer handoffs.

166 System Design: Coverage

Page 187: 3G CDMA200 Wireless System Engineering

10.7 Reverse Supplemental Channel

The reverse supplemental channel is solely used for data applications. To determinewhether or not the reverse supplemental channel can support data transmission, onecalculates its actual Eb/N0 and ensures that it meets the required Eb/N0.

The Eb/N0 of the reverse supplemental channel is given by

E

N

S L d G

r NWR

b

S0

0 0 0 0=′ ′ ′

( , ) ( )θ θ(10.22)

where

• ′S 0 is ERP of the R-SCH of the probe mobile (mobile 0); the transmit pattern isassumed to be omnidirectional;

• ′L d( , )θ 0 0 is the path loss from the probe mobile (mobile 0) in the directionback to the home base station a distance d0 away;

• ′G ( )θ 0 is the receive antenna gain of the home sector in the direction θ 0 to theprobe mobile (mobile 0);

• N is the thermal noise power;• W is the final spread bandwidth, which for Radio Configurations 3 and 4 is

1.25 MHz;• RS′ is the data rate of the reverse supplemental channel;• r′ is the ratio of total interference power received at the home sector (on the

reverse link) to thermal noise power.

Similar to the Eb/N0 expression of the reverse fundamental channel, the term r′Nis the total interference power received on the reverse link at the home sector and isdefined in (10.21).

Due to power control, S′ is not fixed but constantly changing due to reverse linkpower control. Also, to simplify the expression, (10.22) does not include the effectsof diversity gain in soft/softer handoffs.

Figure 10.2 shows the signal and interference components of the reverse link.

10.7 Reverse Supplemental Channel 167

HomeBS

ProbeMS

F’ , S’0 0L’G’

SignalInterference

r’ Nh MSs servedby home BS

r’ Na

MSs servedby other BSs

Figure 10.2 Reverse link: Signal and interference components where the mobile station (MS) isthe transmitter and the base station (BS) is the receiver.

Page 188: 3G CDMA200 Wireless System Engineering

10.8 Upper Bounds of Interference: Reverse Link

Similar to their forward link counterparts, ′rh and ′ra (and hence r′) can be determined

using system simulations and actual measurements. We can also derive upperbounds for these ratios. For the interference received at the home sector from thosemobiles in the home sector,

′ ≤− ′ ′ ′

=

∑r

J A L d G

Nh

j j jj

J

( ) ( , ) ( )11

1

θ θ

(10.23)

where

• A′ is the maximum ERP of the available amplifier power of a single mobile; thetransmit pattern is assumed to be omnidirectional.

• ′L dj j( , )θ is the path loss from the jth mobile in the direction θ j back to thehome base station a distance dj away.

• ′G j( )θ is the receive antenna gain of the home sector in the direction θ j to thejth mobile (mobile j).

Note that there are a total of J mobiles in the home sector, including the probemobile itself. Equation (10.23) effectively states that the interference received at thehome sector can never be greater than what can be radiated by the available ampli-fier power of all the mobiles in the sector.

For the interference received from other mobiles in other sectors,

′ ≤ =

∑r

V

Na

kk

K

1

1

(10.24)

where Vk is the total possible interference that can be received (at the home sector)from those mobiles in the kth sector. Note that the summation is from 1 to K−1,excluding the home sector 0. This means that there are a total of K sectors in the sys-tem. Vk can be derived by summing the interference received from those mobilesserved by sector k, (i.e., for sector k,)

V J A L d Gk k k j k j k jj

J k

= ′ ′ ′=∑ ( , ) ( ), , ,θ θ

1

(10.25)

where

• Jk is the number of mobiles in the kth sector.• ′L dk j k j( , ), ,θ is the path loss from the jth mobile (in the kth sector) in the direc-

tion θ k j, back to the home base station a distance dk,j away.• ′G k j( ),θ is the receive antenna gain of the home sector in the direction θ k j, to

the jth mobile (in the kth sector).

The summation is over those Jk mobiles in the kth sector.

168 System Design: Coverage

Page 189: 3G CDMA200 Wireless System Engineering

10.9 Eb/N0 and Receiver Sensitivity

In the analysis of Eb/N0, it is necessary to distinguish between the actual Eb/N0 andthe required Eb/N0. The actual Eb/N0 can be calculated if all the parameters on theright-hand side of the Eb/N0 equation (e.g., ERP of the channel, path loss, interfer-ence contributions) are given. On the other hand, the required Eb/N0 is the minimumEb/N0 that a channel has to attain in order for a successful demodulation to occur atthe receiver.

Note that we do not have to confine our calculations to only the actual Eb/N0.For example, for a given required Eb/N0 one can use these equations to solve forpath loss. In this case, the resulting path loss would represent the maximum pathloss that is tolerable given all the parameters entered, including the required Eb/N0.This maximum path loss can then be translated into a maximum distance to the celledge within which the stated service (and its data rate) can be supported.

Sometimes, another parameter called receiver sensitivity is used in the linkanalysis. Receiver sensitivity is the minimum received power that a channel has tohave at the receiver in order for a successful demodulation to occur. For example,for the forward fundamental channel, solving (10.16) for the received power gives

F L d G

E

N

WR

r N r N N

b

F

h a0 0 0 0 00 1( ) ( , ) ( )θ θ ε=

− + + (10.26)

If the Eb/N0 shown is the required Eb/N0, then receiver sensitivity RSF for theforward fundamental channel is

RS

E

N

WR

r N r N NF

b

F

h a=

− + +0 1( )ε (10.27)

Similarly, for the reverse fundamental channel, receiver sensitivity RSF’ can bederived using (10.20):

RS

E

N

WR

r NF

b

F

=

′0 (10.28)

where the Eb/N0 shown is also the required Eb/N0.

10.10 Concluding Remarks

The Eb/N0 equations developed in this chapter are the foundations of the linkanalysis. So far we have focused our analysis on the coverage aspects of the link.

10.9 Eb/N0 and Receiver Sensitivity 169

Page 190: 3G CDMA200 Wireless System Engineering

However, coverage and capacity are related to each other in a direct-sequenceCDMA system. In the next chapter, these same Eb/N0 equations will be used todevelop mathematical expressions that are useful in the analysis of RF capacity.

Reference

[1] Yang, S. C., CDMA RF System Engineering, Norwood, MA: Artech House, 1998.

170 System Design: Coverage

Page 191: 3G CDMA200 Wireless System Engineering

C H A P T E R 1 1

System Design: Capacity

11.1 Introduction

In addition to assessing the coverage area of a cell, a system designer should alsoevaluate the capacity of the mobile wireless network. The goal of a system designershould always be to maximize the capacity of the network while meeting all otherrequirements.

In a CDMA system, the air link often is the bottleneck in terms of the end-to-endcapacity of a network. This is so because given a particular arrangement of cells andsectors, one cannot increase RF capacity (i.e., soft capacity) by simply adding physi-cal channels (i.e., hard capacity) at the base station. Because the air link is often thebottleneck, this chapter again emphasizes on the RF part of the system.

In performing capacity analysis, we use as our dependent variable the numberof simultaneous users that a sector can support. In the case of data applications,“throughput” admittedly may be a better definition of end-to-end capacity. How-ever, since this chapter focuses on the RF part of the system, we will focus on thenumber of simultaneous users, or the number of simultaneously active channels. Inaddition, rather than overwhelming readers with many independent variables, thischapter identifies a subset of those variables that are important to RF capacity andsystem design. After identifying those independent variables, the relevant sectionsclose with a discussion of some ways of increasing RF capacity.

11.2 Mathematical Definitions

Before we begin, it is useful to define some additional variables that will facilitatethe subsequent analysis. This section describes two new sets of variables. The firstset deals with the received signal power. The second set deals with the loading fromother adjacent sectors.

11.2.1 Received Signal Power

Recall from the last chapter that for the reverse fundamental channel,

• ′F0 is ERP of the R-FCH of the probe mobile (mobile 0); the transmit pattern isassumed to be omnidirectional.

171

Page 192: 3G CDMA200 Wireless System Engineering

• ′L d( , )θ 0 0 is the path loss from the probe mobile (mobile 0) in the direc-tion θ 0 back to the home base station a distance d0 away.

• ′G ( )θ 0 is the receive antenna gain of the home sector in the direction θ 0 to theprobe mobile (mobile 0).

It turns out that the signal power received at the home sector (from the probemobile or mobile 0) is

′ = ′ ′ ′f F L d G0 0 0 0 0( , ) ( )θ θ (11.1)

where ′f0 is the signal power received from mobile 0 for the reverse fundamentalchannel. In general, ′f is defined for any mobile (mobile j) in the home sector, notjust the probe mobile (mobile 0). Hence,

′ = ′ ′ ′f F L d Gj j j j j( , ) ( )θ θ (11.2)

For the reverse supplemental channel,

• ′S 0 is ERP of the R-SCH of the probe mobile (mobile 0); the transmit pattern isassumed to be omnidirectional.

The signal power received at the home sector (from the probe mobile or mobile0) is

′ = ′ ′ ′s S L d G0 0 0 0 0( , ) ( )θ θ (11.3)

where ′s0 is the signal power received from mobile 0 for the reverse supplementalchannel. ′s can be defined for any mobile (mobile j) in the home sector, not just theprobe mobile (mobile 0). Hence,

′ = ′ ′ ′s S L d Gj j j j j( , ) ( )θ θ (11.4)

Having defined the variables for received signal power on the reverse link, wecan also define those similar variables on the forward link. Recall from the last chap-ter that:

• F0 0( )θ is ERP of the F-FCH of the home sector (sector 0). Because ERPdepends on the antenna pattern, which is a function of direction θ 0 , ERP isalso a function of direction θ 0 .

• S 0 0( )θ is ERP of the F-SCH of the home sector (sector 0). Note that ERP is afunction of direction θ 0 .

• L d0 0 0( , )θ is the path loss from the home base station in the direction θ 0 to theprobe mobile a distance d0 away.

• G is the receive antenna gain of the probe mobile.

The signal power received at the probe mobile (from the home sector or sector 0)is

f F L d G0 0 0 0= ( ) ( , )θ θ0 0 (11.5)

172 System Design: Capacity

Page 193: 3G CDMA200 Wireless System Engineering

where f0 is the signal power received from sector 0 for the forward fundamentalchannel. In general, f is defined for any sector (sector j), not just the home sector(sector 0). Hence,

f F L d Gj j j j j j= ( ) ( , )θ θ (11.6)

For the forward supplemental channel, the signal power received at the probemobile (from the home sector or sector 0) is

s S L d G0 0 0 0= ( ) ( , )θ θ0 0 (11.7)

where s0 is the signal power received from sector 0 for the forward supplementalchannel. s can be defined for any sector (sector j), not just the home sector (sector0). Hence,

s S L d Gj j j j j j= ( ) ( , )θ θ (11.8)

11.2.2 Loading Factor

Recall from the last chapter that for the reverse link,

• ′rh is the ratio of interference power received at the home sector (from thosemobiles in the home sector) to thermal noise power.

• ′ra is the ratio of interference power received at the home sector (from thosemobiles in other adjacent sectors) to thermal noise power.

We can define a reverse link loading factor ′η to be the ratio of interferencepower received from those mobiles in other adjacent sectors to interference powerreceived from those mobiles in the home sector. Here the interference power is thatreceived at the home sector. Effectively then,

′ =′′

ηr

ra

h

(11.9)

Note that ′η is defined at the home sector.

For the forward link, we have the following:

• rh is the ratio of interference power received at the probe mobile (from thehome sector) to thermal noise power.

• ra is the ratio of interference power received at the probe mobile (from otheradjacent sectors) to thermal noise power.

A forward link loading factor η is defined as the ratio of interference powerreceived from other adjacent sectors to interference power received from the homesector. The interference power here is that received at the probe mobile. Effectivelythen,

11.2 Mathematical Definitions 173

Page 194: 3G CDMA200 Wireless System Engineering

η =r

ra

h

(11.10)

Note that η is defined at the probe mobile, and it changes depending on the loca-tion of the mobile in the cell. If the mobile is well inside the cell near the home basestation, then it is receiving more power from the home base station and less powerfrom other adjacent base stations. In this case, η would be low. If the mobile is at theedge of the cell far away from the home base station, then η would be high because itis receiving more power from other adjacent base stations.

11.3 Reverse Link

In the capacity analysis that follows, we will treat the number of simultaneouslyactive fundamental channels as the dependent variable. Then the improvement ofIS-2000 over that of IS-95 is briefly discussed. Finally this section closes with a dis-cussion of some ways that one can adopt to increase reverse link capacity.

11.3.1 Capacity

Recall from the last chapter that the Eb/N0 of the reverse fundamental channel isgiven by (10.7) and (10.8). Substituting (11.1) and (10.8) into (10.7) yields

E

N

f

r N r N NWR

b

h a F0

0=′

′ + ′ +

(11.11)

Substituting (11.9) into (11.11) then yields

E

N

f

r N r N NWR

f

r N NWR

b

h h F h0

0 0

1=

′′ + ′ ′ +

=

′+ ′ ′ +′ ′η η( ) F

(11.12)

But the interference power received at the home sector ( )′r Nh from those mobilesin the home sector is simply the summation of all the signal powers received at thehome sector (from all the mobiles in the home sector excluding the probe mobileitself),

′ = ′=

∑r N fh jj

J

1

1

(11.13)

Note that there are a total of J mobiles in the home sector, including the probemobile (mobile 0) itself. Now, substituting (11.13) into (11.12) results in

E

N

f

f N

WR

b

jj

JF0

0

1

1

1

=′

+ ′ ′ +=

−′∑( )η

(11.14)

Solving for the summation yields

174 System Design: Capacity

Page 195: 3G CDMA200 Wireless System Engineering

′ =′

+ ′

−+ ′=

−′∑ f

fWR

E

N

Nj

j

JF

b1

1 0

0

11

( )( )

ηη

(11.15)

which can be approximated as follows if we assume that the second term (the con-tribution from thermal noise power divided by( )1 + ′η ) is small when compared withthe first term,

′ ≈′

+ ′

=

−′∑ f

fWR

E

N

jj

JF

b1

1 0

0

1( )η

(11.16)

Given that there is power control, all the signal powers received at the home sec-tor (from all the mobiles in the home sector) must be equal [1]. If this is true, thenthe summation reduces to

( )

( )

J f

fWR

E

N

jF

b

− ′ =′

+ ′

′1

1

0

0

η

(11.17)

Since ′f j is also equal to ′f0 , (11.17) becomes

J

fWR

E

N

F

b

=′

+ ′

+′0

0

1

1

( )η

(11.18)

where J is the number of simultaneously active reverse fundamental channels,(Eb/N0) is the (Eb/N0) required for the reverse fundamental channel, and RF’ is thedata rate of the reverse fundamental channel.

Figure 11.1 shows the relationship between J and ′η (i.e., the ratio of interfer-ence power received from other adjacent sectors to interference power receivedfrom the home sector). The figure shows that as the home sector becomes increas-ingly loaded by the transmissions of mobiles in other adjacent sectors, the numberof reverse fundamental channels that can be supported by the home sectordecreases.

For a generalized case where the reverse link contains multiple traffic channels(e.g., reverse fundamental channel, reverse dedicated control channel, and reversesupplemental channel) each operating at different data rates and requiring differenttarget Eb/N0, the computation of the number of simultaneously active channels rap-idly becomes analytically intractable. In general, however, the relationship shown in(11.18) holds true (i.e., capacity is directly proportional to the processing gain and

11.3 Reverse Link 175

Page 196: 3G CDMA200 Wireless System Engineering

inversely proportional to the required Eb/N0 and to the loading factor). In practice,system designers often resort to numerical or simulation methods to numericallyconverge to or simulate a solution.

11.3.2 Capacity Improvements in IS-2000

The capacity improvements afforded by the IS-2000 standard typically deals withthe required Eb/N0 of the different channels. Improvements in the IS-2000 physicallayer have in general decreased the required Eb/N0 and hence increased capacity.

In terms of the reverse fundamental channel, this physical channel is frequentlyused to transmit voice. For the reverse fundamental channel, the Eb/N0 valuerequired to achieve a target FER (e.g., 1% FER) for Radio Configurations 3 and 4(i.e., IS-2000) is lower than that for Radio Configurations 1 and 2 (i.e., IS-95). Thisis because the reverse fundamental channel for Radio Configurations 3 and 4 cannow use better convolutional coding (rate 1/4 instead of rate 1/3 or rate 1/2) whichreduces the required Eb/N0. In addition, the reverse pilot channel enables the coher-ent detection and demodulation of the reverse fundamental channel and also lowersthe required Eb/N0.

The reverse supplemental channel, on the other hand, is used to transmit data.For data applications, the data rate RS’ of the reverse supplemental channel is typi-cally higher than that of the reverse fundamental channel. As such, for a fixed RFbandwidth W, the processing gain ( / )W RS ′ is lower for the reverse supplementalchannel. Hence, all else being equal, the resulting actual Eb/N0 is lower for thereverse supplemental channel.

But fortunately, the required Eb/N0 value is also lower for the reverse supple-mental channel. This is so because of two reasons. First, the reverse supplementalchannel can use turbo coding which has higher coding gain than its convolutionalcoding counterpart. This results in a lower required Eb/N0. Second, the target FER ofthe reverse supplemental channel can be set higher than the typical 1% (e.g., 5%),and a higher target FER would then result in a lower required Eb/N0.

176 System Design: Capacity

η'

0

5

10

15

20

25

30

35

Num

ber

ofac

tive

R-FC

H

40

45

0 0.2 0.4 0.6 0.8 1

Figure 11.1 The relationship between J and ′η . The assumptions are that the (Eb/N0) required forthe reverse fundamental channel is 5 dB, and RF ′ is 9.6 Kbps. This graph is for illustrative purposesonly.

Page 197: 3G CDMA200 Wireless System Engineering

For data applications, a higher FER (e.g., 5%) at the physical layer is acceptablebecause an application can rely on error-control mechanisms at higher layers toensure the delivery of user data (if such a quality of service is required). Relying onhigher layers for error control means that some retransmissions are necessary andhence delays are inevitable. However, these retransmissions are acceptable becausesome delays in data reception are tolerable in data applications.

11.3.3 Capacity Improvements in a System

In a live or modeled IS-2000 system the physical layer is already fixed, so a systemdesigner cannot readily reduce the required Eb/N0. Although at times, an equipmentvendor may release a new chip set with a lower required Eb/N0, the option of reduc-ing required Eb/N0 is not generally available to a system designer. However, what asystem designer can influence is ′η , or the ratio of interference power received fromthose mobiles in other adjacent sectors to interference power received from thosemobiles in the home sector.

Many capacity-enhancing methods used in a live or modeled system have to dowith ways of minimizing ′η . In general, these methods can be classified along twodimensions: spatial and power1. Recall (11.9) where:

• ′rh is the ratio of interference power received at the home sector (from thosemobiles in the home sector) to thermal noise power.

• ′ra is the ratio of interference power received at the home sector (from thosemobiles in other adjacent sectors) to thermal noise power.

On the reverse link, the spatial dimension consists of those methods thatattempt to spatially isolate the reverse coverage area of a sector. As shown in Figure11.2, going from an omnidirectional coverage area to a sectorized coverage area hasthe effect of reducing the amount of interference power received at the home sectorfrom those mobiles in other adjacent sectors. This effectively reduces ′ra which inturn reduces ′η .

Other examples of the spatial method include six-sectors and microcells. Ofcourse, various smart antenna schemes represent an extreme case of the spatialmethod. Here, a dedicated beam is directed at a mobile or a group of mobiles. Onthe reverse link, this (narrow) beam increases the antenna gain in the direction of themobile(s) and rejects the transmissions of other unwanted mobiles.

On the reverse link, the power dimension consists of those methods thatattempt to reduce the transmission power of the mobile. Because the transmissionpattern of a mobile is (typically) omnidirectional, a mobile in a neighboring cell doesnot focus its transmission toward its own base station. As a result, its transmissioncan be received by the home base station in question. This has the effect of increas-ing the home base station’s ′ra . Therefore, the goal of the various capacity-enhancingmethods in this category is to minimize the transmission power of those mobiles inother adjacent cells.

11.3 Reverse Link 177

1. There is actually a third category: frequency. Adding additional RF carriers of course always increases RFcapacity. But since this chapter primarily deals with increasing RF capacity using existing air interfaceresources, adding RF carriers is not considered here.

Page 198: 3G CDMA200 Wireless System Engineering

Some popular methods in this category include various receive diversityschemes, such as receive antenna diversity, receive polarization diversity, andsoft/softer handoff diversity2. These diversity methods all have the net effect ofreducing the unnecessary transmit power of a mobile.

Another method that can reduce the transmission power of mobiles in neighbor-ing sectors is installing low-noise amplifiers (LNAs). The mobile transmit powertypically decreases when LNAs are installed at the serving base station. This reduc-tion in mobile transmit power is due to reverse link power control. LNAs decreasethe noise figure of the receiver (at the base station) so that the mobile can transmitat a lower power level and still close the link. The reverse link power control directsthe mobile to transmit at a power level just low enough to meet the requiredEb/N0 [1, 2].

Figures 11.3 and 11.4 illustrate the concept. In Figure 11.3, the mobiles (servedby base station 2) transmit at nominal power levels, and base station 1 is loaded bythe transmit powers of these mobiles. In Figure 11.4, base station 2 now has LNAsinstalled. As a result, the transmit powers of the mobiles (served by base station 2)are reduced. Consequently, base station 1 experiences a smaller ′ra and hence asmaller ′η .

Although one study [2] has suggested deploying LNAs in a specific pattern in thenetwork to increase overall system capacity, another study [3] has shown thatdeploying LNAs ubiquitously can also have beneficial effects on system capacity.

11.4 Forward Link

In this section, we will again treat the number of simultaneously active fundamentalchannels as the dependent variable, then discuss the improvement of IS-2000 over

178 System Design: Capacity

BS MS

Before

BS MS

After

Figure 11.2 Through sectorization, the amount of interference power received at the home sec-tor from those mobiles in other adjacent sectors is reduced. BS stands for base station, and MSstands for mobile station.

2. The implementations of soft and softer handoffs are specified in the IS-2000 standard.

Page 199: 3G CDMA200 Wireless System Engineering

that of IS-95. This section concludes with a discussion of some ways that a systemdesigner can adopt to increase forward link capacity.

11.4.1 Capacity

From the last chapter, the Eb/N0 of the forward fundamental channel is given by(10.3). Substituting (11.5) and (11.10) into (10.3) yields

E

N

f

r N r N NWR

f

r N NWR

b

h h F

h F

0

0

0

1

1

=− + +

=

− + +

( )

[( ) ]

ε

ε η

(11.19)

11.4 Forward Link 179

BS 1 BS 2

MS

MS

Figure 11.3 Base station 2 has no LNAs. The mobiles (served by the neighboring base station 2)transmit at nominal power levels.

BS 1 BS 2

(LNA)

MS

MS

Figure 11.4 Base station 2 has LNAs. The mobiles (served by the neighboring base station 2)transmit at reduced power levels.

Page 200: 3G CDMA200 Wireless System Engineering

Now, let γ 0 be the fraction of the total ERP of the home sector (sector 0) that isallocated to the forward fundamental channel in question, then

f f r Nh0 0 0= +γ ( ) (11.20)

where ( )f r Nh0 + is effectively the total power (signal power + interference power)

received at the probe mobile from the home sector. Substituting (11.20) into (11.19)results in

E

N

f r N

r N NWR

b h

h F0

0 0

1=

+− + +

γ

ε η

( )

[( ) ](11.21)

Solving for γ 0 yields

γε η

00

0

1=

− + ++

E

N

WR

r N N

f r N

b

F

h

h

[( ) ]

( )(11.22)

If we assume that the received interference power is a lot greater than thereceived signal power (i.e., r N fh >> 0 ) and orthogonality is perfect [i.e., ( )1 0− =ε ],then the above equation reduces to

γη

00 0≈

+=

E

N

WR

r N N

r N

E

N

WR

b

F

h

h

b

F

+=

+

ηη

r

r

E

N

WR

rh

h

b

F

h

1 10 (11.23)

In general, γ 0 can be defined for any channel (channel k) transmitted by thehome sector (sector 0) (i.e., γ 0,k ). In order not to exceed the upper limit of the avail-able amplifier power of the home sector, the following inequality must hold true:

β γ0 01

1+ ≤=∑ ,kk

K

(11.24)

where

• β 0 is the fraction of the total ERP of all available amplifier power of the homesector (sector 0) that is allocated to forward overhead channels. Note that β 0

is deterministic and does not change.

The above inequality must hold true when the home sector’s amplifier is operat-ing at its maximum. Of course, K reaches a maximum when

β γ0 01

1+ ==∑ ,kk

K

(11.25)

180 System Design: Capacity

Page 201: 3G CDMA200 Wireless System Engineering

where K is the number of simultaneously active forward fundamental channels [4].As readers can clearly see, to maximize K one must minimize γ 0,k . This is

because as the individual fractions (allocated to individual channels) decrease, anamplifier with a fixed maximum power can support more channels.

When the forward link contains multiple traffic channels each operating at dif-ferent data rates and targeting different required Eb/N0, the computation of thenumber of simultaneously active channels rapidly becomes complex. In general,however, the relationship shown in (11.25) holds true (i.e., to the extent that thefraction allocated to a channel can be reduced, the power amplifier can accommo-date more forward channels). And the fraction of allocation can be reduced byreducing the required Eb/N0 and by reducing η [see (11.23)]. In practice, to computeK a system designer needs to first calculate the individual fractions γ 0,k (for each k),then numerically compute K such that the condition shown in (11.25) is met.

Although the computation of K often requires the use of simulation or numeri-cal methods, one can make some assumptions to reduce the calculation of K to ananalytically closed form. Assume a static situation where all mobiles are equidistantfrom the base station on a flat terrain. This may be the case where mobiles arearranged in a circular fashion around the base station (see Figure 11.5). In this case,identical path losses would cause all mobiles’ perceived rh to be the same.

Furthermore, assume neighboring cells are arranged in a perfectly hexagonalpattern and these neighboring base stations are transmitting identical forward linkpowers. In this case, mobiles in the home sector would be equally loaded by neigh-boring cells, hence these mobiles’ perceived η would be identical.

Making the above assumptions would cause all mobiles’ γ 0,k to be identical(i.e., γ γ0 0,k = ). See (11.23). Hence (11.25) reduces to

β γ0 0 1+ =K (11.26)

Substituting (11.23) into (11.26) and rearranging yield

11.4 Forward Link 181

BS

MS

Figure 11.5 An idealized situation to simplify the calculation of K.

Page 202: 3G CDMA200 Wireless System Engineering

K

WR

r

E

N

F

h

b

=−

=−

+

11

10

0

0

0

β

γ

β

η

( )

(11.27)

where K is the number of simultaneously active forward fundamental channels.Figure 11.6 shows the relationship between K and η. As expected, K decreases as themobile becomes increasingly loaded by the transmissions of other adjacent sectors(i.e., as η increases).

11.4.2 Capacity Improvements in IS-2000

Similar to the reverse link, the forward link capacity improvements made by theIS-2000 standard generally has to do with the required Eb/N0. Improvements in theIS-2000 physical layer have in general decreased the required Eb/N0 and henceincreased capacity.

In terms of the forward fundamental channel, this physical channel is frequentlyused to transmit voice. For the forward fundamental channel, the Eb/N0 valuerequired to achieve a target FER (e.g., 1% FER) for Radio Configurations 3 through5 (i.e., IS-2000) is typically lower than that for Radio Configurations 1 and 2 (i.e.,IS-95). This is because Radio Configurations 3 through 5 now support fast powercontrol of the forward link. In addition, the forward fundamental channel for RadioConfigurations 3 through 5 now have better convolutional coding (rate 1/4 insteadof rate 1/2) which further reduces the required Eb/N0.

In terms of the forward supplemental channel, this physical channel is used totransmit data. For the forward supplemental channel, the required Eb/N0 can be low-ered somewhat because the forward supplemental channel can use turbo codingwith a higher coding gain; this results in a lower power required to achieve a givenFER. Furthermore, the target FER of the forward supplemental channel is often set

182 System Design: Capacity

η

0

5

10

15

20

25

30

35

40

45

0 0.2

Num

ber

ofac

tive

F-FC

H

0.4 0.6 0.8 1

Figure 11.6 The relationship between K and η. The assumptions are that the (Eb/N0) required forthe forward fundamental channel is 5 dB, RF is 9.6 Kbps, rh = 1, and β0 is 10%. This graph is forillustrative purposes only.

Page 203: 3G CDMA200 Wireless System Engineering

higher than the 1% value typical for voice applications. A higher target FER (e.g.,5%) is acceptable for data applications because data frames, unlike voice frames,can be retransmitted if they are received in error.

11.4.3 Capacity Improvements in a System

On the forward link, many capacity-enhancing methods used in the field also haveto do with ways of minimizing η for the various mobiles. Note that η is definedfor each mobile. These methods can be similarly classified along two dimensions:spatial and power3. Recall (11.10), where:

• rh is the ratio of interference power received at the probe mobile (from thehome sector) to thermal noise power.

• ra is the ratio of interference power received at the probe mobile (from otheradjacent sectors) to thermal noise power.

On the forward link, the spatial dimension consists of those methods thatattempt to spatially isolate the forward coverage area of a base station. Because thereceive antenna pattern of the mobile is (typically) omnidirectional, the transmitantenna pattern of the sector is manipulated to isolate its forward coverage area.This way, a base station reduces unwanted transmissions to other mobiles in otheradjacent cells.

As shown in Figures 11.7 and 11.8, going from omnidirectional coverage to sec-torized coverage has the effect of reducing the amount of interference power

11.4 Forward Link 183

3. The category of frequency is similarly omitted for the reason cited earlier.

1

2

3

4

5

6

7

Base station Mobile station

Figure 11.7 The probe mobile in a system consisting of omnidirectional cells.

Page 204: 3G CDMA200 Wireless System Engineering

received at the mobile from other adjacent cells. Figure 11.7 shows that the (probe)mobile is in cell 1 near its center. The mobile is receiving full interference power fromsix surrounding cells (cells 2, 3, 4, 5, 6, and 7). After sectorizing the cells in Figure11.8, the same mobile in cell 1 near its center now receives full interference powerfrom only three surrounding sectors (3C, 5A, and 7B)4. All else being equal, themobile in Figure 11.8 now has a lower ra and hence a lower η.

Other examples of spatial methods include six-sectors, microcells, and varioussmart antenna schemes. In smart antenna, for example, a dedicated beam is directedat a mobile or a group of mobiles. On the forward link, this narrow beam directs thetransmission power to the intended mobile(s) and minimizes the transmission powerto other unintended mobiles.

On the forward link, the power dimension consists of those methods thatattempt to minimize the transmit power of the base station. Because the receive pat-tern of a mobile is (typically) omnidirectional, a mobile can receive forward linktransmissions from all directions. The goal of the various capacity-enhancing

184 System Design: Capacity

Base station Mobile station

2A

BC

7A

6A

5A

4A

3A

B

B

B

B

B

B

1A

C

C

C

C

C

C

Figure 11.8 The probe mobile in a system consisting of three-sector cells.

4. The mobile in Figure 11.8 would receive the same amount of interference power as it does in Figure 11.7if the sectors use antennas that are 120 degrees wide. But narrower antennas are more commonly usedtoday.

Page 205: 3G CDMA200 Wireless System Engineering

methods in this category is, then, to minimize the transmission power of the adja-cent sectors.

Soft and softer handoffs certainly qualify as ways reducing forward link trans-mission power. Other methods in this category include various transmit diversityschemes, such as transmit polarization diversity, OTD, and STS5. These diversitymethods all have the net effect of reducing the unnecessary transmit power of thebase station. See Chapter 9 for more details on OTD and STS.

References

[1] Yang, S. C., CDMA RF System Engineering, Norwood, MA: Artech House, 1998.[2] Yang, S. C., “The Application of Low Noise Amplifiers in CDMA Cellular and PCS Sys-

tems for Coverage and Capacity Enhancements,” Proceedings of IEEE Radio and WirelessConference, Colorado Springs, CO, August 9–12, 1998, pp. 181–184.

[3] Salkola, M. I., “CDMA Capacity—Can You Supersize That?” Proceedings of IEEE Wire-less Communications and Networking Conference, Vol. 2, Orlando, FL, March 18–21,2002, pp. 768–773.

[4] Yang, S. C., “Increasing RF Capacity of 2G and 3G CDMA Systems: Theory and Meth-ods,” Proceedings of the 15th International Conference on Wireless Communications, Cal-gary, Alberta, July 7–9, 2003, pp. 405–410.

11.4 Forward Link 185

5. The implementations of soft and softer handoffs, OTD, and STS are specified in the IS-2000 standard.

Page 206: 3G CDMA200 Wireless System Engineering

.

Page 207: 3G CDMA200 Wireless System Engineering

C H A P T E R 1 2

Network Architecture

12.1 Introduction

Thus far this book has focused on the different aspects of the IS-2000 standard, spe-cifically its protocol layers, functions, performance, and design. We purposely waituntil now to introduce the architecture of a wireless network that supports IS-2000.The reason is that, in an end-to-end wireless network, there are other protocols andprotocol layers that are operative in addition to those in IS-2000. We also wouldlike to show the relationship between protocol layers and elements of an end-to-endwireless network; although IS-2000 governs the communication between themobile station and the base station, other protocols and protocol layers govern thecommunication among other network elements in the network.

This chapter starts with a typical 2G network and expands it to include thoseelements that make up a typical 3G network. Protocols used in different parts of thenetwork are also cited. The goal of this chapter is not to cover exhaustively the wire-less network, but to provide a framework of network architecture associated withan IS-2000 system. Although a complete description of all network elements andprotocols are outside the scope of this book, this chapter will cite salient referencesand documents so that readers can explore further those specific areas that interestthem.

12.2 2G Network

A 2G wireless network provides both circuit-switched voice service and circuit-switched data service. Figure 12.1 depicts the architecture of a typical 2G wirelessnetwork. The figure is partly based on the reference models provided by [1, 2].

12.2.1 Network Elements

Readers are undoubtedly already familiar with both the mobile station (MS) and thebase transceiver system (BTS). Other elements of a 2G wireless network are:

• Base station controller (BSC): This element controls a group of BTSs that areattached to it.

187

Page 208: 3G CDMA200 Wireless System Engineering

• Mobile switching center (MSC): The MSC switches user traffic that goesbetween the MS and the public switched telephone network (PSTN) orbetween the MS and another MSC.

• Home location register (HLR): This is a database that contains subscriberinformation.

• Visitor location register (VLR): This is a database that contains subscriberinformation of those users who are “active” on a particular MSC.

• Authentication center (AC): The AC verifies the identity of a user before grant-ing permission to provide service to that user. It does so by processing theauthentication response sent by the user.

• Interworking function (IWF): In a 2G wireless network, the IWF is the elementthat enables circuit-switched data service.

One important function carried out by the BSC is mobility management, whichdirects the handoff that occurs when a mobile transitions from one BTS to the nextBTS. Another important function of the BSC is transcoding. Transcoding convertsbetween the voice format used in the air interface (e.g., enhanced variable rate codec

188 Network Architecture

IS-41

MSC

AC

PSTN

VLR

IWF

Internet

ISP

IS-634(IOS)

IS-41

BSCBSC

BTS BTSBTSBTS

MS

MSCVLR

IS-95

HLR

Figure 12.1 A typical 2G wireless network. The boldfaced parts are those that provide circuit-switched data service.

Page 209: 3G CDMA200 Wireless System Engineering

or EVRC) and the voice format used in the PSTN (e.g., pulse code modulationor PCM).

As mentioned before, the HLR is a database that contains subscriber informa-tion. For each subscriber, the HLR holds his or her subscriber information such asthe international mobile subscriber identity (IMSI) and the selected long-distancecarrier. To avoid the problem associated with data duplication, there is typicallyonly one HLR for a wireless network.

On the other hand, the VLR is a database that contains subscriber informationof those users who are active on a particular MSC; these users include both visitorsfrom other networks and mobiles in home networks. As such, a VLR is typicallycolocated with an MSC. A subscriber is removed from an MSC’s VLR if, for exam-ple, he or she moves to another MSC. The use of a VLR is preferred because if thereis no VLR, then the MSC would have to query the HLR every time an access requestis made.

To provide circuit-switch data service, the 2G wireless network uses the IWF.The IWF converts from one transmission format to another, and vice versa. Forexample, low-rate data originated from the MS is (circuit) switched by the MSC tothe IWF. The IWF converts the PCM data stream (used by the MSC) into modemtones that can be transmitted over the PSTN. Then a dedicated circuit on the PSTNtransmits the modem tones to an Internet service provider (ISP), which ultimatelyprovides connectivity to the Internet.

12.2.2 Protocols

As readers can see in Figure 12.1, a 2G wireless network contains different inter-faces among different network elements. The exchange of information across theseinterfaces is typically governed by some standards, the use of which may be volun-tary. The salient standards are:

• IS-95 [3, 4]: These standards govern the (air) interface between the MS andthe BSC in a 2G CDMA wireless network.

• IS-634 [5]: It is the 2G version of the interoperability specification (IOS)which defines the interface between the BSC and the MSC. It also defines howBSCs can cooperate amongst themselves to support mobility management andhandoff of MS from one BSC to another BSC.

• IS-41 [1]: This standard defines the interfaces among the MSC, HLR, VLR,and AC. It also defines how MSCs of different equipment vendors can be con-nected together so that there is interoperability among these MSCs.

12.3 3G Network

A 3G wireless network is capable of providing circuit-switched voice service,circuit-switched data service, and packet-switched data service. Figure 12.2 depictsthe architecture of a typical 3G wireless network. The figure is partly based on thereference models provided by [1, 2].

12.3 3G Network 189

Page 210: 3G CDMA200 Wireless System Engineering

12.3.1 Network Elements

In addition to possessing similar 2G wireless network elements, a 3G wireless net-work has some important additions that are for the purpose of providing packet-switched data services. These additional elements are:

• Packet data serving node (PDSN): In a 3G wireless network, the PDSN is theelement that enables packet-switched data service.

• Authentication, authorization, and accounting (AAA): The AAA is a serverthat provides authentication, authorization, and accounting services for thePDSN, which in turn renders packet data network connectivity services to themobile users.

The BSC in a 3G wireless network not only supports mobility management andtranscoding, it also directs circuit-switched voice/data traffic to the MSC andpacket-switched data traffic to the PDSN. To provide packet-switch data service, the3G wireless network uses the PDSN which is essentially an Internet Protocol (IP)router that routes user data traffic to a public packet data network (e.g., Internet).In this regard, the PDSN in packet switching is analogous to the MSC in circuit

190 Network Architecture

IS-41

MSC

AC

PSTN

VLR

IWF

Internet

ISP

IS -2001(IOS)

IS-41

BSCBSC

BTS BTSBTSBTS

MS

IS-2000

MSCVLR PDSN

BSC

BTSBTS

IP

AAAHLR

IS-2001(IOS)

Figure 12.2 A typical 3G wireless network. The boldfaced parts are those that provide packet-switched data service.

Page 211: 3G CDMA200 Wireless System Engineering

switching. Whereas the MSC directs circuit-switched traffic between the MS and acircuit-switched network (e.g., PSTN), the PDSN directs packet-switched trafficbetween the MS and a packet-switched network (e.g., Internet).

The AAA carries out an important function of authentication. When an MSrequests packet-switched data service, it has to go through (at least) two levels ofauthentication. First, the MS goes through the usual radio-connection serviceauthentication performed by the AC using subscriber information (e.g., IMSI) con-tained in the HLR. If this authentication is successful, then the MS is assigned aradio connection and proceeds to the packet-data service authentication. Thisauthentication is performed by the AAA and may simply require the user to providean account number and the password. If this authentication is also successful, thenthe MS is granted packet data service.

In addition, the AAA performs the function of accounting. For example, foreach MS the AAA collects information on its usage of packet data service. The AAAthen passes this information to a downstream billing application so that the user canbe properly billed for the service. Note that the use of the AAA is not exclusive to a3G wireless network. The AAA is actually an off-the-shelf component commonlyused by providers of packet network services (e.g., ISPs).

12.3.2 Protocols

The 3G wireless network shown in Figure 12.2 contains interfaces among networkelements added to provide packet-switched data service. The definitions of theseinterfaces are typically governed by some standards, the use of which may be volun-tary. The salient standards are:

• IS-2000 [6–11]: These standards govern the (air) interface between the MSand the BSC in a 3G CDMA wireless network.

• IS-2001 [12–18]: It is the 3G version of the interoperability specification(IOS), which defines the interface between the BSC and the PDSN [17, 18]. Italso defines the interface between the BSC and the MSC [15], as well as theinterface between BSCs [16] for mobility management.

• IS-41 [1]: This standard, which is used in 2G wireless networks, is also used in3G wireless networks. It defines the interfaces among the MSC, HLR, VLR,and AC, as well as the interface between MSCs.

Figure 12.3 gives another view of the different protocols used in a 3G wirelessnetwork. The protocols are shown according to the layers at which they operate1.For the sake of clarity, only the portion relating to packet-switched data service isshown. One additional standard shown in Figure 12.3 is:

• IS-707 [19]: This standard specifies the radio link protocol (RLP), which isused to provide delivery and receipt of user packet data. The RLP is a Layer 2protocol designed especially for use over the air interface (see Chapter 4).

Figure 12.3 shows that for a specific packet data session, the PDSN initiates andmaintains a logical session with the MS. This logical session is maintained using the

12.3 3G Network 191

1. Here we adopt the five-layer Internet model rather than the seven-layer OSI model. The five layers are physi-cal, data link, network, transport, and application layers.

Page 212: 3G CDMA200 Wireless System Engineering

point-to-point protocol (PPP). In other words, at a higher level the PDSN and theMS exchange data using the PPP. The PPP [20] is more or less a de facto method oftransporting blocks of data over point-to-point links. For example, the PPP is com-monly used for dial-up connections between a home computer and an ISP becausethe telephone line is a point-to-point link. Incidentally, the capacity of a PDSN issometimes specified as the number of simultaneous PPP connections that it canmaintain.

At the next level up, the PDSN (an IP router) routes IP packets between the MS(a client) and the server; the PDSN does so by using IP. Then at the transport layer,the transmission control protocol (TCP) or user datagram protocol (UDP) is respon-sible for the end-to-end delivery of data (from the MS to the server and vice versa). InTCP, a TCP connection is set up between the MS and the server. The TCP connec-tion is also known as a virtual circuit in that it appears to the application layer as apoint-to-point circuit. On the other hand, the UDP is connectionless in that eachpacket is treated separately and makes its own way through the network [21].

12.4 Simple IP

The 3G wireless network shown previously in Figure 12.2 is capable of supportingsimple IP. Figure 12.4 illustrates how IP packets are exchanged between the MS (cli-ent) and the server on the Internet2. For clarity, only the portion relating to packet-switched data service is shown in Figure 12.4. An MS residing on its home PDSN hasan IP address M3, and the server on the Internet has an IP address S. Given these two

192 Network Architecture

Server

Layer 1(IS-2000)

Layer 2(IS-2000)

RLP(IS-707)

Signaling(IS-2000)

PPP (RFC 1661)

IP

IOS(IS2001)

IP

MS BSC PDSN

TCP/UDP

HTTP or other services

IP

network

Figure 12.3 Protocol layers used for packet-switched data service.

2. The server in this case is also known as a correspondent, which is defined as an entity that wishes to commu-nicate with the MS (or any mobile entity).

3. Figure 12.4 shows that the PDSN has the IP address M of the MS, even though the IP address is assigned tothe MS. In actuality, for each MS the PDSN maintains a logical mapping between MS’ identifier on the BSCand MS’ IP address.

Page 213: 3G CDMA200 Wireless System Engineering

addresses, IP packets can be exchanged between the MS and the server. Specifically,a packet going from the MS to the server would have as its source address M and itsdestination address S, and a packet going from the server to the MS would have asits source address S and its destination address M.

What happens when the MS moves from its home PDSN to a foreign PDSNwhile the service is still active? Well, the radio connection would still be up becausethe IOS or IS-2001 specifies how handoffs across BSCs or across MSCs are handled.But the service connection would be broken. A packet going from the MS to theserver would still reach its destination (because the packet has the correct destina-tion address S), but a packet going from the server to the MS would not reach theMS (because the packet has the incorrect destination address M). This is so becausesince the MS is no longer at the home PDSN, the home PDSN cannot deliver thepacket to the MS. See Figure 12.5.

The goal is, then, to keep the service connection up when the MS travels fromone PDSN to another. The solution is mobile IP.

12.5 Mobile IP

In order to support mobile IP [22, 23], two additional network elements are needed:

• Home agent (HA): This is a router that, together with the foreign agent (FA),provides mobile IP functionality. From the perspective of the MS, the HA is arouter that resides on that MS’ home IP network (served by that MS’ homePDSN). When the MS travels away from its home PDSN, the MS’ HA

12.5 Mobile IP 193

Internet

PDSN

BSC

BTSBTS

AAA

IP

Server

PDSN

BSC

AAA

IP

BSCBSC

BTSBTS

(Home) (Foreign)

MS

M

S

Figure 12.4 IP packets are exchanged between the MS and the server. The bold line depicts thepath taken by IP packets.

Page 214: 3G CDMA200 Wireless System Engineering

forwards those packets (destined for the MS) to the MS. In doing so, the MS’HA must know on what PDSN the MS current resides.

• Foreign agent (FA): This is another router that, together with the HA, providesmobile IP functionality. The FA is typically colocated with the PDSN. Whenan MS “visits” a foreign IP network (served by another PDSN), the FA on theforeign network receives packets forwarded from the MS’ HA and deliversthem to the MS (that is currently on the foreign network).

Figure 12.6 shows how mobile IP works. When the MS travels from the homePDSN to the foreign PDSN, a packet sent by the MS would reach the server becausethe packet has the correct destination address S. On the other hand, when the serversends a packet to the MS the server still uses the MS’ IP address M. That packet trav-els to the MS’ home IP network and is intercepted by the MS’ HA. The HA thenreroutes that packet to the FA on the foreign IP network (on which the MS iscurrently). Then the FA on the foreign network receives that packet and routes it tothe MS.

In order for the MS’ HA to forward packets to the correct place, the HA mustknow the MS’ current temporary IP address on the foreign network. This temporaryIP address T, or care-of address, is obtained by the MS when it first gets on the for-eign network. In fact, the mobile IP scheme requires two functionalities:

194 Network Architecture

Internet

PDSN

BSC

BTSBTS

AAA

IP

Server

PDSN

BSC

AAA

IP

BSCBSC

BTSBTS

(Home) (Foreign)

MS

M

S

Figure 12.5 If an MS moves to another PDSN, then the service connection is broken.

Page 215: 3G CDMA200 Wireless System Engineering

• MS’ registration with the FA: When an MS visits a foreign network, it needs toregister with the FA. The FA on the foreign network then creates a care-ofaddress for the MS.

• FA’s registration with the HA: After the FA creates the care-of address for theMS, the FA needs to register the MS’ care-of address with the MS’ HA. Thisway, the HA knows where to reroute the incoming packets for the MS.

Readers at this point may ask why not just let the server know the MS’ currentaddress T. This way the server can send packets directly to T on the visited networkinstead of asking the MS’ HA to forward packets. The answer is that it is necessaryto implement a mobility solution that is transparent to all servers at large on theInternet. The mobile IP scheme, as readers can see, does not require the server toperform any additional tasks, such as changing the MS’ address from M to T in themiddle of a service session. When an MS is able to maintain its IP address as itmoves, mobility then becomes invisible from the perspective of the server. In fact, inthe mobile IP scheme the server is completely unaware of the fact that the MS (or amobile client) has moved. This transparency is very valuable to the server as theserver does not need to be concerned with a potentially changing IP address. Thesame transparency afforded by mobile IP also enables that same server to serve notonly an MS in a wireless network but also a regular stationary client [24].

Figure 12.7 provides the protocol-layer view of mobile IP. This figure is similarto that shown in Figure 12.3. There are two differences, however. First, the HA is

12.5 Mobile IP 195

Internet

PDSN

BSC

BTSBTS

AAA

IP

Server

PDSN

BSC

AAA

IP

BSCBSC

BTSBTS

(Home) (Foreign)

MS

M

S

HA

FA

T

Figure 12.6 In mobile IP, the HA forwards the packet to the MS’ current location.

Page 216: 3G CDMA200 Wireless System Engineering

now responsible for routing packets from the server to the FA on the foreign PDSN,then that FA in turn routes packets to the MS. Second, mobile IP is now usedbetween the MS and the PDSN/FA and between the PDSN/FA and the HA. From theperspective of the server, the server still communicates using standard IP and noth-ing has changed.

Note that in both Figures 12.6 and 12.7, the HA and the FA shown are from theperspective of one particular MS. In this case, this particular MS has moved from itshome PDSN to a foreign PDSN. From the perspective of this MS, the HA is in itshome IP network and the operative FA is in the foreign IP network. In general, anyIP network has both the HA and the FA, where the FA serves those MSs that are vis-iting this network, and the HA serves those MSs that are visiting other networks.Figure 12.8 shows the architecture of a typical 3G wireless network that supportsmobile IP. The figure is partly based on the reference models provided by [1, 2, 12].

It is important to recognize that mobile IP is not used exclusively to support IPmobility in wireless networks. In fact, it can be used to support any network inwhich IP mobility is required (i.e., when a mobile entity such as a notebook com-puter moves from its home IP network to a foreign IP network).

12.6 Concluding Remarks

This chapter provides a general introduction to the architecture of a network thatsupports IS-2000. We have examined network elements and operative protocols inboth 2G and 3G networks, as well as introduced both simple IP and mobile IP. As

196 Network Architecture

Server

Layer 1(IS-2000)

Layer 2(IS-2000)

RLP(IS-707)

Signaling(IS-2000)

PPP (RFC 1661)

Mobile IP(RFC 3344)

IOS(IS-2001)

MS BSC

PDSN/

TCP/UDP

HTTP or other services

IP

network

Mobile IP(RFC 3344)

HA

IP

network

IP

FA

Figure 12.7 Protocol layers used for mobile IP.

Page 217: 3G CDMA200 Wireless System Engineering

mentioned in the beginning of this chapter, the goal is not to cover exhaustively thenetwork, but to introduce a framework of network architecture associated withIS-2000. Readers are advised that there are a lot more details embedded in the net-work, especially in the packet-switched portion of the network and its protocols.For example, the interface between PSTN and BSC in the packet-switched domain(packet control function or PCF and radio resource control or RRC) are not coverednor are the tunneling protocol between the FA and the HA, as such details would betoo distracting in an introductory oriented chapter.

Although a complete description of all network elements and protocols are out-side the scope of this book, this chapter provides some salient references in the refer-ence section, and readers are encouraged to explore further those specific areas ofnetworks that interest them.

References

[1] TIA/EIA-41-D, Cellular Radiotelecommunications Intersystem Operations, Telecommuni-cations Industry Association, December 1997.

12.6 Concluding Remarks 197

IS -41

MSC

AC

PSTN

VLR

IWF

Internet

ISP

IS-2001(IOS)

IS -41

BSCBSC

BTS BTSBTSBTS

MS

IS-2000

MSCVLR PDSN

BSC

BTSBTS

IP

HA

FA

AAAHLR

IS-2001(IOS)

Figure 12.8 A typical 3G wireless network that supports mobile IP. The boldfaced parts are thosethat provide packet-switched data service.

Page 218: 3G CDMA200 Wireless System Engineering

[2] TIA/EIA/TSB 100-A, Wireless Network Reference Model, Telecommunications IndustryAssociation, March 2001.

[3] TIA/EIA/IS-95-A, Mobile Station-Base Station Compatibility Standard for WidebandSpread Spectrum Cellular Systems, Telecommunications Industry Association, May 1995.

[4] ANSI/TIA/EIA-95-B, Mobile Station-Base Station Compatibility Standard for WidebandSpread Spectrum Cellular Systems, Telecommunications Industry Association, March1999.

[5] TIA/EIA/IS-634-A, MSC-BS Interface for Public Wireless Communications Systems, Tele-communications Industry Association, to be published.

[6] TIA/EIA/IS-2000.1-A, Introduction to cdma2000 Standards for Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

[7] TIA/EIA/IS-2000.2-A, Physical Layer Standard for cdma2000 Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

[8] TIA/EIA/IS-2000.3-A, Medium Access Control (MAC) Standard for cdma2000 SpreadSpectrum Systems, Telecommunications Industry Association, March 2000.

[9] TIA/EIA/IS-2000.4-A, Signaling Link Access Control (LAC) Standard for cdma2000Spread Spectrum Systems, Telecommunications Industry Association, March 2000.

[10] TIA/EIA/IS-2000.5-A, Upper Layer (Layer 3) Signaling Standard for cdma2000 SpreadSpectrum Systems, Telecommunications Industry Association, March 2000.

[11] TIA/EIA/IS-2000.6-A, Analog Signaling Standard for cdma2000 Spread Spectrum Systems,Telecommunications Industry Association, March 2000.

[12] TIA/EIA-2001.1-B, Interoperability Specification (IOS) for CDMA 2000 Access NetworkInterfaces—Part 1 Overview, Telecommunications Industry Association, May 2002.

[13] TIA/EIA-2001.2-C, Interoperability Specification (IOS) for CDMA 2000 Access NetworkInterfaces—Part 2 Transport, Telecommunications Industry Association, October 2002.

[14] TIA/EIA-2001.3-C, Interoperability Specification (IOS) for CDMA 2000 Access NetworkInterfaces—Part 3 Features, Telecommunications Industry Association, Telecommunica-tions Industry Association, October 2002.

[15] TIA/EIA-2001.4-C, Interoperability Specification (IOS) for CDMA 2000 Access NetworkInterfaces—Part 4 (A1, A2 and A5 Interfaces), Telecommunications Industry Association,October 2002.

[16] TIA/EIA-2001.5-C, Interoperability Specification (IOS) for CDMA 2000 Access NetworkInterfaces—Part 5 (A3 and A7 Interfaces), Telecommunications Industry Association,October 2002.

[17] TIA/EIA-2001.6-C, Interoperability Specification (IOS) for CDMA 2000 Access NetworkInterfaces—Part 6 (A8 and A9 Interfaces), Telecommunications Industry Association,October 2002.

[18] TIA/EIA-2001.7-C, Interoperability Specification (IOS) for CDMA 2000 Access NetworkInterfaces—Part 7 (A10 and A11 Interfaces), Telecommunications Industry Association,October 2002.

[19] TIA/EIA/IS-707-A, Data Service Options for Wideband Spread Spectrum Systems, Tele-communications Industry Association, February 2003.

[20] RFC 1661, The Point-to-Point Protocol (PPP), W. Simpson (Ed.), IETF, July 1994.[21] Fitzgerald, J., and A. Dennis, Business Data Communications and Networking, New York:

Wiley, 2004.[22] RFC 2794, Mobile IP Network Access Identifier Extension for IPv4, Calhoun, P., and C.

Perkins, IETF, March 2000.[23] RFC 3344, IP Mobility Support for IPv4, C. Perkins (Ed.), IETF, August 2002.[24] Kurose, J. F., and K. W. Ross, Computer Networking, New York: Addison Wesley, 2003.

198 Network Architecture

Page 219: 3G CDMA200 Wireless System Engineering

C H A P T E R 1 3

1xEV-DO Network

13.1 Introduction

The advantages of an IS-2000 system are that it is not only a fully compliant 3G sys-tem, but also a natural evolution from the previous-generation IS-95 system. Thebenefit of implementing an evolutionary system is that it takes into account thoseinfrastructure investments already deployed in the field [1], as well as leverages theexisting body of knowledge and experience already gained from operating thesystem.

Although IS-2000 is already capable of meeting the 3G data rate requirement of2 Mbps, Qualcomm proposed a new standard 1xEV-DO (1x Evolution for DataOptimized) in March of 2000 as another option that supports high-rate data serv-ices. 1xEV-DO is effectively a hybrid CDMA/TDM system and has two advantageswhen supporting high-rate data services.

First, 1xEV-DO can support a data rate of up to 2.4576 Mbps using a band-width of only 1.25 MHz1. This is in contrast with IS-2000, which can support a datarate of up to 2.0736 Mbps using a bandwidth of 3.75 MHz (i.e., Spreading Rate 3)2.

Second, 1xEV-DO takes advantage of the characteristics of some data services,which are:

• Data rates are mostly asymmetrical: Data rate requirements downstream (onthe forward link) are usually higher than those upstream (on the reverse link).

• Latency can be tolerated: Data services, unlike voice services, can withstanddelays of up to seconds.

• Transmissions are bursty in nature: A burst of data transmission is often fol-lowed by a period of inactivity.

1xEV-DO [2] designs its air interface to take advantage of these characteristicsof data services. First, because data rates are asymmetrical, 1xEV-DO provisionshigher data rates on the forward link. It is able to do so because the base stationinherently has more transmit power resources and thus can utilize higher ordermodulation schemes.

199

1. On the forward link.2. On both the forward and reverse links.

Page 220: 3G CDMA200 Wireless System Engineering

Second, because latency can be tolerated, 1xEV-DO can retransmit a packet if itis received in error. In addition, powerful error-correcting codes (i.e., turbo codes)can be applied without worrying about the additional computational time.

Third, because transmissions are bursty in nature, 1xEV-DO time division mul-tiplexes different users to take advantage of inactive periods of transmissions.

In some ways, 1xEV-DO represents a paradigm shift from classical spread spec-trum multiple access systems that employ power control. In a classical spread spec-trum wireless system, the path loss increases as a mobile moves away from the basestation. The base station responds to this increase in path loss by increasing its trans-mit power (via forward link power control). This way, power received at the mobileis kept constant. Figure 13.1 illustrates the concept. The base station controls thepower to maintain a constant data rate and quality of service. Constant data rateand quality of service are especially important in supporting circuit-switched appli-cations such as voice.

However, guaranteeing data rate and quality of service regardless of themobile’s distance from the base station comes at a cost. Increasing the transmitpower to a mobile far away means less forward link power resources for othermobiles in the same cell. Moreover, it is not necessary to guarantee a specific datarate and quality of service if data transmission is bursty and can tolerate latency.Therefore, given that data transmission is heavier on the forward link, 1xEV-DOfocuses its power resources to delivery the highest possible data rate (on the forwardlink) to those mobiles that are closest to the base station. Figure 13.2 illustrates theconcept. A 1xEV-DO base station transmits a fixed amount of power at all times; asa mobile moves away from the base station, the mobile’s receive power decreases. Asthe mobile’s receive power decreases, the base station does not increase the transmitpower. Rather, the base station decreases the data rate delivered to the mobile. Inother words, the base station controls the rate of data transmission given a constanttransmit power.

200 1xEV-DO Network

Mobile received power

Data rate

Pow

erD

ata

rate

Distance from base station

Figure 13.1 In a classical spread spectrum wireless system, the base station controls the power tomaintain a constant data rate and quality of service.

Page 221: 3G CDMA200 Wireless System Engineering

Because 1xEV-DO operates differently than IS-2000, 1xEV-DO necessitates itsown dedicated RF carrier to support data services. This way, system engineers onlyhave to configure parameters that optimize data services in the dedicated RF carrier.Using a bandwidth of 1.25 MHz, 1xEV-DO can support a data rate of up to 2.4576Mbps on the forward link and a data rate of up to 153.6 Kbps on the reverse link. Asthe name 1x Evolution for Data Optimized implies, 1xEV-DO supports data appli-cations and does not support voice.

13.2 1xEV-DO Network

1xEV-DO has a very different physical layer from that of IS-2000. As a result, addi-tional hardware is required to overlay 1xEV-DO on an existing IS-2000 system. Butas we will see, 1xEV-DO does leverage existing network elements. Figure 13.3shows a typical wireless network using 1xEV-DO. The boldfaced parts denote theadditional hardware that supports 1xEV-DO.

An access terminal (AT) is equivalent to a mobile station, and it is defined as theequipment that provides data connectivity to the mobile user. The access network(AN) is defined as the equipment that provides data connectivity between a packet-switched data network and the access terminal [2]. So in the context of Figure 13.3,the access network comprises of both the BTS and the BSC. In this case, the bold-faced BTS and the BSC shown are 1xEV-DO BTS and BSC that support the IS-856standard.

Note that from the perspective of the PDSN, the PDSN is providing the sameservice and connectivity regardless of whether or not the BSC is one that supportsIS-2000 or 1xEV-DO. Therefore, a wireless network that supports 1xEV-DO usesthe same IOS that defines the interface between the BSC and the PDSN [3, 4].

13.2 1xEV-DO Network 201

Mobile received power

Data rate

Pow

erD

ata

rate

Distance from base station

Figure 13.2 In an 1xEV-DO system, the base station controls the rate of data transmission givena constant transmit power.

Page 222: 3G CDMA200 Wireless System Engineering

In addition, note that Figure 13.3 shows that an IS-2000 BSC and a 1xEV-DOBSC are distinct entities and that there is no connection between the two. They aredistinct and different because they support two different sets of protocols (IS-2000vs. IS-856). Although there is no connection logically between an IS-2000 BSC and a1xEV-DO BSC, the two could be physically colocated.

13.3 Protocol Architecture

In supporting the connectivity between the mobile and the packet-switched data net-work, 1xEV-DO uses a seven-layer protocol architecture. Figure 13.4 shows thatprotocol architecture [2].

202 1xEV-DO Network

IS-41

MSC

AC

PSTN

VLR

IWF

Internet

ISP

IS -2001(IOS)

IS-41

BSCBSC

BTS BTSBTSBTS

MS

IS -2000

MSCVLR PDSN

BSC

BTSBTS

HA

FA

AAAHLR

IP

IS-2001(IOS)

MS

AN

AT

IS-856

Figure 13.3 A typical wireless network using 1xEV-DO. The boldfaced parts are those that enable1xEV-DO service.

Page 223: 3G CDMA200 Wireless System Engineering

Each layer contains a number of protocols that implement some specified func-tions. At the transmitting end, a message generated at the application layer is succes-sively processed by the layers below (or more specifically the protocols in the layersbelow). Each layer may encapsulate the message with its own header and/or trailerand pass the message to the layer below. At the physical layer, the message is trans-mitted over the physical medium.

At the receiving end, the message received by the physical layer is successivelyprocessed by the layers above (or more specifically the protocols in the layersabove). Each layer processes the message, strips off the header when appropriate,and passes the message to the layer above. This process continues until the messageis finally delivered to the application layer.

Note that, given the previous descriptions, each layer effectively performs aservice for the layer above. At the transmitter, the layer below performs a transmis-sion service for the layer above, whereas at the receiver, the layer below performs adelivery service for the layer above.

In describing the protocol architecture of 1xEV-DO, we will use an actualexample that illustrates the functions of the different layers. Figures 13.5(a) and13.5(b) show that example. The example entails how a message is successivelypassed from one layer to the next and how each layer performs its functions. In

13.3 Protocol Architecture 203

Applicationlayer

Signaling link protocolSignaling network protocol

Flow control protocolLocation update protocolRadio link protocol

Streamlayer

Sessionlayer

Connectionlayer

Securitylayer

MAClayer

Physicallayer

Stream protocol

Sessionmanagementprotocol

Addressmanagementprotocol

Sessionconfigurationprotocol

Air linkmanagementprotocol

Connectedstate protocol

Idle stateprotocol

Initializationstate protocol

Overheadmessagesprotocol

Routeupdate protocol

Packetconsolidationprotocol

Authentication protocolEncryption protocol

Key exchange protocolSecurity protocol

Accesschannel MACprotocol

ControlchannelMACprotocol

ForwardtrafficchannelMAC protocol

Reversetraffic channelMAC protocol

Physical layer protocol

Figure 13.4 Protocol layers used by 1xEV-DO. Protocols in each layer are listed alphabetically.

Page 224: 3G CDMA200 Wireless System Engineering

following this example, the functions of each layer are in turn explained in Sections13.3.1 to 13.3.5.

To simplify the example, we only focus on how user data is processed by the dif-ferent layers and ignore the transmission and processing of signaling data. In otherwords, we examine how a message generated by the upper layer will be ultimatelytransported by the forward traffic channel in the physical layer. In addition, thisexample focuses only on the forward direction (i.e., how a packet is passed down thelayers at the transmitter) with the assumption that at the receiver the reverse processmerely takes place.

To start our example: At the transmitter, a message generated by the upper layerfirst goes to the application layer.

13.3.1 Application Layer

The RLP residing in the application layer processes the message sent by the upperlayer. After the message is passed from the upper layer to the RLP, the message itselfbecomes the payload. In processing the message, the RLP attaches a header to thepayload to form a packet.

204 1xEV-DO Network

Encryptionprotocolpacket

Connectionlayerpacket

Encryptionprotocoltrailer

Encryptionprotocolpayload**

Encryptionprotocolheader

* Format A** Format A*** Traffic channel only

Authen. protocolpayload

Authenprotocolpacket

.

Security protocolpayload

Securityprotocolpacket

Authen.protocolheader

Securityprotocolheader

Encryptionprotocol

Secu

rity

laye

r

MA

Cla

yer

Phys

ical

laye

r

Up

per

laye

rsA

pp

licat

ion

laye

rSe

ssio

nla

yer

Stre

amla

yer

Con

nect

ion

laye

r

Con

nect

ion

laye

rSe

curit

yla

yer

Authen.protocol

Securityprotocol

(Securitylayerpacket)

MAClayertrailer

MAClayerpacket

MAC layerpayload***

Physical layerpayload

Message

RLPpayload

RLPheader

Stream layerpayload

Stream layerheader

Session layerpayload

Connectionlayer payload*

RLPpacket

Streamlayerpacket

Sessionlayerpacket

Connectionlayer packet

* Format A

(b)(a)

Figure 13.5 At the transmitter, a message generated by the upper layer is successively processed by thelayers below. At the receiver, a message received by the physical layer is successively processed by the layersabove. This figure shows layer processing between: (a) the application layer and the connection layer, and(b) the security layer and the physical layer.

Page 225: 3G CDMA200 Wireless System Engineering

Recall from Chapter 4 that the RLP is used for the delivery of user data packet[5], and it is designed especially for use over an air interface. Since the air link isinherently error-prone, the RLP does not attempt to provide a guaranteed deliveryof packets over the air link because doing so would cost too many retransmissions.Instead, the RLP provides a best effort delivery in that it will attempt to deliver apacket up to a point, then give up.

Note that in adopting the best effort strategy, the RLP (and the system) isimplicitly relying on error-control mechanisms at the upper layer to guarantee deliv-ery of user data, if such a QoS is required. To further minimize the transmission ofcontrol packets (e.g., ACK and NAK) over the air link, the RLP uses only negativeacknowledgment (NAK) and retransmission mechanisms.

In performing the functions described above, the RLP attaches the header to thepayload and forms an RLP packet. Then the RLP passes the RLP packet to thestream layer below.

13.3.2 Stream Layer

The function of the stream layer is to multiplex streams of data coming from theapplication layer. Since the stream protocol is the only protocol residing in thestream layer (see Figure 13.4), the stream protocol is the protocol that performs thisfunction. The stream protocol can multiplex streams of data for up to four differentapplications. Of the four streams (00, 01, 10, 11), stream 00 is reserved for signalingmessages.

In performing the multiplexing function, the stream protocol attaches a headerto the payload and forms a stream layer packet. In this case, the header is only 2-bitslong and is a 2-bit number indicating one of the four streams to which the payloadcorresponds. The stream protocol then passes the stream layer packet to the sessionlayer below.

13.3.3 Session Layer

The function of the session layer is to manage the logical session used for communi-cation between the AN and the AT. In order for a session to exist, the AN and theAT have to agree on the following:

• The logical address assigned to the AT;• The actual protocols to be used;• The configuration parameters for the protocols.

In managing the logical session between the AN and the AT, the session layermakes use of three different protocols (see Figure 13.4):

• Session management protocol;• Address management protocol;• Session configuration protocol.

In particular, the address management protocol maintains the logical addressassigned to the AT, and the session configuration protocol negotiates the actual

13.3 Protocol Architecture 205

Page 226: 3G CDMA200 Wireless System Engineering

protocols used during the session and the configuration parameters for these proto-cols [2]. The session management protocol has the overall management responsibil-ity for opening and closing a session. See Figure 13.4.

Because the session layer mostly carries out the signaling functions of sessionmaintenance and management, the session layer does not modify the packet that isused to transport user data. Therefore, in this case the session layer merely relays thepacket received from the stream layer to the connection layer [see Figure 13.5(a)].

13.3.4 Connection Layer

Whereas the session layer manages the logical session, the connection layer managesthe actual air link connection between the AN and the AT. As such, a session lastslonger than the connections that support it. The connection layer contains a total ofseven protocols. They are [2]:

• Air link management protocol;• Route update protocol;• Initialization protocol;• Idle state protocol;• Connected state protocol;• Overhead messages protocol;• Packet consolidation protocol.

See Figure 13.4. Of these protocols, the air link management protocol has theoverall management responsibility for opening and closing a connection. In addi-tion, the route update protocol maintains the air link as the AT moves among differ-ent cells and sectors. In fact, in examining the connection layer we will look moreclosely at these two protocols in the connection layer: air link management protocoland route update protocol.

13.3.4.1 Air Link Management Protocol

The air link management protocol has the overall management responsibility foropening and closing a connection. The air link management protocol in the connec-tion layer is analogous to the session management protocol (which has the overallmanagement responsibility of opening and closing a session) in the session layer.

The reason why we want to actively open and close connections is to conserveair link resources. When data transmission is temporary idle, it is desirable to releasethe precious air link resources so that other users can use them. In particular, the airlink management protocol can transition among three different states to manage theconnection [2]:

• In the initialization state, the AT acquires the AN.• In the idle state, the connection is closed. The bulk of the air link resources is

released, but the AT and the AN can still communicate signaling messagesusing the (forward) control channel and the (reverse) access channel.

206 1xEV-DO Network

Page 227: 3G CDMA200 Wireless System Engineering

• In the connected state, the connection is open. Here the AT and the AN canexchange user data using forward traffic channel and reverse traffic channel.Signaling messages can be exchanged using the (forward) control channel andthe reverse power control channel.

Figure 13.6 shows the possible transitions among these states. The states of theair link management protocol are especially important because the activity of theother six protocols (in the connection layer) depends on what state the air link man-agement protocol is in. For example, the idle state protocol is only active when theair link management protocol is in the idle state, while the connected state protocolis only active when the air link management protocol is in the connected state. Onthe other hand, the route update protocol is active when the air link managementprotocol is in both the idle state and the connected state.

Typically, when a connection is closed, the session remains open. While the sys-tem wants to actively open and close connections for the purpose of air link conser-vation, it does not necessarily want to open and close sessions at will. The reason isthat, when opening a session, it does take some time for the session layer to negoti-ate protocols to be used during the session and configuration parameters for theseprotocols. The system does not want to redo negotiations each time a connection isclosed and opened again. In fact, sessions are rarely closed except, for example,when an AT leaves the coverage area [2].

13.3 Protocol Architecture 207

Connectedstate

Openconnection

Closeconnection

Idlestate

Initializationstate

Connectedstate

Openconnection

Closeconnection

Idlestate

Initializationstate

Acquirenetwork

Networkredirection

Networkredirection

AN AT

Figure 13.6 State transitions of the air link management protocol. (After: [2].)

Page 228: 3G CDMA200 Wireless System Engineering

13.3.4.2 Route Update Protocol

The route update protocol maintains the air link as the AT moves among differentcells and sectors. As such, the route update protocol is only active when the air linkmanagement protocol is in either the connected state or the idle state.

As the AT moves among different cells and sectors, the AT receives the forwardpilot channels of these cells and sectors. Since each sector has its own pilot, the routeupdate protocol in maintaining the air link has to track the different pilots. In doingso, the route update protocol (at the AT) maintains four pilot sets specified by thepilot’s PN offset. Similar to the pilot sets that exist in an IS-2000 system, the fourpilot sets here are [2]:

• Active set. The active set contains the pilots of those sectors that are exchang-ing data with the mobile on a forward traffic channel, reverse traffic channeland reverse power control channel, or control channel.

• Candidate set. The candidate set contains the pilots of those sectors whosestrengths are sufficient to include them in the active set.

• Neighbor set. The neighbor set contains the pilots of those sectors that are alsolikely candidates for the active set, but are not in the active set or the candidateset.

• Remaining set. The remaining set contains all possible pilots in the system forthe current 1xEV-DO carrier frequency, not including those that are in active,candidate, and neighbor sets.

Similar to IS-2000 where Layer 3 manages the pilot sets, in 1xEV-DO the con-nection layer (or more specifically the route update protocol) manages the pilot sets.As such, at the AT the route update protocol measures the strength of the forwardpilot channel, searches for pilots, maintains the pilot drop timer, and in general man-ages the membership of the four pilot sets per a set of rules similar to ones used inIS-2000.

The route update protocol processes two important signaling messages: theRouteUpdate message and the TrafficChannelAssignment message. On the reverselink, the AT transmits the RouteUpdate message to inform the AN of the AT’s localradio conditions (e.g., the number of pilots the AT sees). On the forward link, theAN transmits the TrafficChannelAssignment message to manage the AT’s active set,especially when the AT (and the AN) is in the connected state [2].

13.3.4.3 Other Protocols

The other five protocols (besides the air link management protocol and the routeupdate protocol) in the connection layer carry out other connection-related activi-ties. For examples, the initialization protocol is responsible for the initial radioacquisition of the AN. In performing the initial acquisition, the initialization proto-col goes through a set of states (e.g., network determination state, pilot acquisitionstate, and synchronization state). Understandably, the initialization protocol is onlyactive when the air link management protocol is in the initialization state.

Readers may recognize that the initialization protocol’s states are similar tothose used in IS-2000. In fact, they are. The initialization protocol’s states are similar

208 1xEV-DO Network

Page 229: 3G CDMA200 Wireless System Engineering

to an IS-2000 mobile’s substates of the IS-2000 initialization state (e.g., systemdetermination substate, pilot channel acquisition substate, and sync channel acqui-sition substate). See Chapter 6 for more details on the IS-2000 initialization state.Again, whereas in IS-2000 Layer 3 manages the (sub)state transitions to acquire thenetwork, in 1xEV-DO the initialization protocol manages the state transitions toacquire the AN.

The idle state protocol carries out functions of an AT after it has acquired theAN but is idle in the idle state when the connection is not open. Therefore, the idlestate protocol is only active when the air link management protocol is in the idlestate. On the other hand, the connected state protocol carries out functions of an ATthat is in the connected state when the connection is open. Thus, the connected stateis only active when the air link management protocol is in the connected state.

The overhead messages protocol differs from all the other protocols in the con-nection layer in that it is the only protocol active in all three states of the air linkmanagement protocol (i.e., initialization state, idle state, and connected state). Thismakes sense because the overhead messages protocol is responsible for processingoverhead parameters sent over the control channel. Specifically, the overhead mes-sages protocol processes two messages: the SectorParameters message and theQuickConfig message. The AN uses the (long) SectorParameters message to informthe AT of all relevant overhead parameters pertaining to the transmitting sector. Onthe other hand, the AN uses the (short) QuickConfig message to quickly notify theAT of any change in the overhead parameters, so naturally the QuickConfig mes-sage is used for those parameters that change most often. These two messages arecalled overhead messages because parameters contained in these messages are usedby more than one protocol in the connection layer.

13.3.4.4 Packet Consolidation Protocol

The packet consolidation protocol in the connection layer performs the functions ofpacket consolidation and prioritization. Every message generated by the applicationlayer has a priority number that ranges between 0 and 255. The lower the number,the higher the priority. The packet consolidation protocol makes use of this infor-mation to prioritize packets for transmission. In other words, transmission andprocessing of higher priority packets will always take place before transmission andprocessing of lower priority packets.

Because the connection layer mostly carries out the signaling functions of airlink maintenance and management, the connection layer does not substantivelymodify the packet that is used to transport user data. Many times, the packet con-solidation protocol merely relays the packet received from the session layer to thesecurity layer3. This is the case in the ensuing example: As far as the user datapacket is concerned, the packet consolidation protocol in the connection layerreceives the packet from the session layer and passes it on to the security layer [seeFigure 13.5(b)].

13.3 Protocol Architecture 209

3. This is true for format A connection layer packets that are at the maximum size. For format B, the connec-tion layer may add more than one header and a padding.

Page 230: 3G CDMA200 Wireless System Engineering

13.3.5 Security Layer

The functions of the security layer are to encrypt and authenticate packets and tomanage the key exchange necessary for the functions of encryption and authentica-tion. The security layer contains four different protocols (see Figure 13.4):

• Key exchange protocol;• Encryption protocol;• Authentication protocol;• Security protocol.

The key exchange protocol actually does not perform any packet processing.Instead, its function is to exchange keys (between the AN and the AT) that are neces-sary for encryption and authentication. In exchanging keys, the key exchange proto-col originates and receives messages such as the KeyRequest message and theKeyResponse message.

As shown in Figure 13.5(b), the encryption protocol is the protocol thatfirst processes the connection layer packet received from the connection layer. Inencrypting the packet, the encryption protocol may add a header and/or a trailer tothe packet4. One way that the encryption protocol may encrypt the packet is to add atrailer in order to hide the actual length of the packet [2].

After being processed by the encryption protocol, the encryption protocolpacket goes to the authentication protocol. In authenticating the packet, the authen-tication protocol may add a header to the packet5. Note that placing the authentica-tion protocol below the encryption protocol means the security layer (in thereceiver) has to authenticate before it decrypts. This arrangement avoids the need todecrypt if authentication is unsuccessful [2].

After being processed by the authentication protocol, the authentication proto-col packet is passed on to the security protocol. The security protocol performshousekeeping functions such as providing parameters that are needed by other pro-tocols in the security layer; these parameters may be incorporated in the securityprotocol header6. After being processed by the security protocol, the security proto-col packet (also the security layer packet) then goes to the MAC layer.

13.3.6 Concluding Remarks

In Section 13.3, we have described the protocol architecture of 1xEV-DO by usingan actual example [in Figures 13.5(a) and 13.5(b)] that illustrates the functions ofdifferent layers. This example shows how a message is successively passed from onelayer to the next, as well as what functions each layer performs. To simplify the

210 1xEV-DO Network

4 In the initial versions of IS-856, the encryption protocol actually does not add any header or trailer anddefers the encryption function to the application layer.

5. In the initial versions of IS-856, the authentication protocol only authenticates packets for the access chan-nel. This makes sense because authenticating a user is most needed when that user is first attempting toaccess the network.

6. Obviously, if the security layer does not perform any encryption or authentication then there is no need forthe security protocol to provide any encryption- or authentication-related parameters. In that case, the secu-rity protocol header is null.

Page 231: 3G CDMA200 Wireless System Engineering

example, we focused on the layer processing done at the transmitter, knowing thatat the receiver the reverse process takes place. In addition, we illustrated how userdata is processed by different layers and did not go into transmission and processingof signaling data (i.e., we examine how a message generated by the upper layer willbe ultimately transported by the forward traffic channel in the physical layer).

Although this section has casually used the terms such as traffic channel, controlchannel, and access channel, it has thus far not formally defined these channels. Infact, it will not be possible to describe the last two layers (i.e., MAC layer and physi-cal layer) without defining these channels. We defer the formal definition of thechannels and the descriptions of the MAC layer and the physical layer to the nexttwo chapters. Specifically, Chapter 14 will be on the MAC and physical layers ofthe forward link, and Chapter 15 will be on the MAC and physical layers of thereverse link.

References

[1] Prasad, R., W. Mohr, and W. Konhauser (Eds.), Third Generation Mobile CommunicationSystems, Norwood, MA: Artech House, 2000, p. 2.

[2] TIA/EIA/IS-856, cdma2000 High Rate Packet Data Air Interface Specification, Telecom-munications Industry Association, January 2002.

[3] TIA/EIA-2001.6-C, Interoperability Specification (IOS) for CDMA 2000 Access NetworkInterfaces—Part 6 (A8 and A9 Interfaces), Telecommunications Industry Association,October 2002.

[4] TIA/EIA-2001.7-C, Interoperability Specification (IOS) for CDMA 2000 Access NetworkInterfaces—Part 7 (A10 and A11 Interfaces), Telecommunications Industry Association,October 2002.

[5] TIA/EIA/IS-707-A, Data Service Options for Wideband Spread Spectrum Systems, Tele-communications Industry Association, February 2003.

13.3 Protocol Architecture 211

Page 232: 3G CDMA200 Wireless System Engineering

.

Page 233: 3G CDMA200 Wireless System Engineering

C H A P T E R 1 4

1xEV-DO Radio Interface: Forward Link

14.1 Introduction

This chapter describes 1xEV-DO’s radio interface on the forward link. Specifically,the MAC layer and the physical layer of the forward link will be examined. In1xEV-DO, the MAC layer serves as an interface between the physical layer below itand the higher layers above it. Therefore, the MAC layer controls higher layers’access to the physical medium (i.e., physical layer), which is shared among manyusers. The goal of this chapter is to describe the salient points of the MAC andphysical layers so readers can have a solid foundation from which to explore thedetails of the standard. To that end, Section 14.2 concerns the MAC layer of the for-ward link, and Section 14.3 describes the physical layer of the forward link.

Before we start, it is useful to emphasize some important characteristics of theforward link of 1xEV-DO:

• There is no power control of the forward link. As mentioned in the beginningof Chapter 13, the AN transmits at constant power. So instead of requestingvariable power on the forward link, the AT requests variable rates on the for-ward link. The AT makes such requests using the data rate control channel onthe reverse link. In other words, the AN can deliver different data rates on theforward link based on feedback received from the ATs.

• The forward link uses time division multiplexing (TDM) to multiplex differ-ent channels (in addition to CDMA). This is done to take advantage of thebursty nature of data transmissions. Because in TDM different users maytransmit at different times, it is difficult to diversity combine transmissionsfrom different base stations that are destined to a single user. Therefore, thereis no soft handoff (hence no diversity combining) on the forward link, andeach AT is served by only one base station.

14.2 MAC Layer

The function of the MAC layer is to regulate higher layers’ access to the physicallayer. There are two types of messages originating from higher layers that are trans-ported across the physical layer: user data messages and signaling messages. In regu-lating the transmission and reception of these two types of messages on the forwardlink, the MAC layer makes use of two protocols [1]:

213

Page 234: 3G CDMA200 Wireless System Engineering

• Forward traffic channel MAC protocol;• Control channel MAC protocol.

14.2.1 Forward Traffic Channel MAC Protocol

The functions of the forward traffic channel MAC protocol are not only to controlthe transmission and reception of packets on the forward traffic channel, but also tocontrol their rate of transmission. As mentioned in Chapter 13, 1xEV-DO focusesits power resources to deliver the highest possible data rate (on the forward link) tothose ATs that are closest to the base station.

In order to manage the transmission rate of the forward traffic channel, the for-ward traffic channel MAC protocol operates in two active states. In the variable ratestate, the forward traffic channel transmits at a rate that can change in real time. Inthis case, the transmission rate is requested by the AT using the data rate control(DRC) channel on the reverse link. In the variable rate state, the transmission ratecan vary from 38.4 Kbps to 2.4576 Mbps. When the AN first starts transmittingto the AT, the forward traffic channel MAC protocol always starts in the variablerate state.

Nevertheless, the AT can request that the transmission rate be fixed. It does soby transmitting a FixedModeRequest message to the AN. If the AN approves therequest, it acknowledges the request message by sending a FixedModeResponsemessage back to the AT. Then the forward traffic channel MAC protocol transitionsto the fixed rate state in which the forward traffic channel can be transmitted andreceived at a fixed rate. Note that although the AT is free to request fixed rates thatcan also range from 38.4 Kbps to 2.4576 Mbps, the AN does not have to approve(and acknowledge) the request.

To continue with the forward link example that began in the last chapter,Figure 14.1 shows the packet encapsulation in the MAC and physical layers. At theAN, after receiving a security layer packet (containing user data) from the security

214 1xEV-DO Radio Interface: Forward Link

Forwardtraffic channelphysical layerpacket

Securitylayerpacket

MAClayertrailer

Physicallayertrailer

Forwardtraffic channelMAC layerpacket

MAClayerpayload

Physicallayerpayload

1,024 bits

Secu

rity

laye

rM

AC

laye

rPh

ysic

alla

yer

Figure 14.1 Packet encapsulation at the MAC and physical layers. Note that the forward trafficchannel MAC layer packet shown contains user data and is for the forward traffic channel. In thiscase, the physical layer packet contains one MAC layer packet.

Page 235: 3G CDMA200 Wireless System Engineering

layer, the forward traffic channel MAC protocol attaches a MAC layer trailer andforms a forward traffic channel MAC layer packet. The protocol then passes theMAC layer packet to the physical layer below.

14.2.2 Control Channel MAC Protocol

The control channel MAC protocol has the responsibility of managing the transmis-sion and reception of signaling packets on the control channel. At the AN, after asecurity layer packet (containing signaling data) is passed to the control channelMAC protocol in the MAC layer, the control channel MAC protocol formats thepacket (by adding more headers and trailers) and generates a control channel MAClayer packet. The control channel MAC layer packets are then sequenced to betransmitted on the control channel.

The control channel is a signaling channel that is shared among many users (i.e.,ATs). As such, the receiver (i.e., the AT) needs some way of distinguishing amongthe different packets and finding out which packet is destined for it. The methodused is that when an AT receives a control channel MAC packet, it checks the accessterminal identifier record field of the MAC layer header and performs addressmatching. The access terminal identifier record specifies the AT’s address. If theaddress matches that maintained by the address management protocol (in the ses-sion layer), then the AT continues processing the packet. If not, then the AT rejectsthe packet.

14.3 Physical Layer

The following are the different channels that are used on the forward link of a1xEV-DO system:

• Pilot channel;• Forward traffic channel/control channel;• MAC channel.

The pilot channel provides ATs with timing and phase reference. The forwardtraffic channel/control channel transports both forward traffic channel MAC layerpackets and control channel MAC layer packets. The MAC channel consists of thefollowing channels:

• Reverse activity (RA) channel;• Reverse power control (RPC) channel;• DRCLock channel.

Figure 14.2 shows the organization of channels on the forward link.

14.3.1 Pilot Channel

The pilot channel serves a similar function as its IS-95 and IS-2000 counterpartsin that it provides ATs with timing and phase reference. It is a stream of 1s and

14.3 Physical Layer 215

Page 236: 3G CDMA200 Wireless System Engineering

contains no baseband information. The pilot is multiplexed into the transmittedchip stream by the time division multiplexer. See Section 14.3.4 later for moredetails on time division multiplexing of different forward channels.

14.3.2 Forward Traffic Channel/Control Channel

14.3.2.1 Formats

For the forward traffic channel, after receiving a forward traffic channel MAC layerpacket the physical layer constructs a forward traffic channel physical layer packet(by adding CRC bits, for example). Figure 14.1 shows the case where the physicallayer packet contains only one MAC layer packet, and in this case the physical layerpacket is 1,024 bits long. Nevertheless, a forward traffic channel physical layerpacket can contain up to four forward traffic channel MAC layer packets. Ofcourse, the size of the physical layer packet gets longer when it contains more MAClayer packets. Table 14.1 shows the size of the physical layer packet verses thenumber of MAC layer packets it can carry.

For the control channel, after receiving a control channel MAC layer packet thephysical layer constructs a control channel physical layer packet (by adding CRCbits, for example). In the case of the control channel, a control channel physical layerpacket can only carry one control channel MAC layer packet. Therefore, a controlchannel physical layer packet is always 1,024 bits long (see Table 14.1).

In transmitting a forward traffic channel physical layer packet, the physicallayer can use different modulation schemes based on the amount of data to be trans-mitted. The physical layer can use three successively higher orders of modulation asthe size of the physical layer packet increases: QPSK (or 4-PSK), 8-PSK, and16-QAM. In fact, it is the use of the highest order modulation 16-QAM thatenables 1xEV-DO to transmit at a rate of 2.4576 Mbps using only 1.25 MHz of RF

216 1xEV-DO Radio Interface: Forward Link

Forward traffic channel/control channel

MAC channel Reverse activity (RA) channelReverse power control (RPC) channelDRCLock channel

Forward traffic channelControl channel

Pilot channel Pilot channel

Figure 14.2 Forward link channels.

Table 14.1 Length of a Physical Layer Packet

Length of a PhysicalLayer Packet (Bits)

Number of CarriedMAC Layer Packets

Type of PhysicalLayer Packet

1,024 1 Forward traffic channel or control channel

2,048 2 Forward traffic channel

3,072 3 Forward traffic channel

4,096 4 Forward traffic channel

Page 237: 3G CDMA200 Wireless System Engineering

bandwidth1. Table 14.2 shows the modulation scheme as a function of the size ofthe physical layer packet. Note in Table 14.2 that the modulation scheme alsodepends on the data rate chosen for transmission (i.e., as data rate increases, ahigher-order modulation scheme is used).

In transmitting a control channel physical layer packet, the physical layer canonly use QPSK (as shown in Table 14.2). In fact, the physical layer can use a datarate of either 76.8 or 38.4 Kbps when sending a control channel physical layerpacket.

Table 14.2 also shows the code rate used for each length of physical layerpacket. Since 1xEV-DO is used exclusively for data applications, processing delay isnot an issue. Thus computationally intensive turbo codes are used for all forwarderror corrections on the forward link.

14.3.2.2 Channel Structure

Figure 14.3 shows the conceptual block diagram for the forward traffic channel andcontrol channel. After a physical layer packet (forward traffic channel or controlchannel) is generated, then the physical layer performs the usual functions such as:

• Encoding the bits for correcting bit errors;• Scrambling2;• Interleaving for combating fades.

After interleaving, the symbols go into the modulator (QPSK/8-PSK/16-QAM)which produces one output symbol (I,Q) for every two input symbols. After repeti-tion and puncture, the I symbol stream is demultiplexed into 16 substreams, and theQ symbol stream is demultiplexed into 16 substreams. Each substream is multipliedby a Walsh code (of length 16) and scaled by 1/4. Then summers add the substreamsto yield an I chip stream and a Q chip stream. The I and Q chip streams are fed intothe respective time division multiplexers [1].

14.3 Physical Layer 217

1. Although higher order modulations tend to have greater spectral efficiency, the distance between the originand the outermost constellation point (on the constellation diagram) is also greater. So higher order modu-lations require higher powers to maintain the same probability of bit error. This means that only ATs thatare close to the base station can receive at 2.4576 Mbps.

2. Scrambling the data reduces the peak-to-average ratio of the RF waveform [2].

Table 14.2 Forward Traffic Channel Modulation Schemes and Data Rates

Length of a PhysicalLayer Packet (Bits) Data Rates (Kbps) Code Rate

ModulationScheme

1,024 38.4*, 76.8*, 153.6, 307.2, or 614.4 1/5** QPSK

2,048 307.2, 614.4, or 1,228.8 1/3 QPSK

3,072 921.6 or 1,843.2 1/3 8-PSK

4,096 1,228.8 or 2,457.6 1/3 16-QAM

* Also used for control channel.** For data rate of 614.4 Kbps and physical layer packet length of 1,024, the code rate used is 1/3.

Page 238: 3G CDMA200 Wireless System Engineering

In demultiplexing into 16 substreams and multiplying by 16 Walsh codes, tokeep the power constant at the summer output the physical layer multiplies eachsubstream by1 16 or 1/4. Note that the symbol rate of each substream is 76.8 Kspsat the output of the 1-to-16 demultiplexer [1]. After Walsh code multiplication(×16), the chip rate of each substream becomes 1.2288 Mcps. Since the summer doesnot alter the chip rate, the chip rate at the input to the time division multiplexerremains at 1.2288 Mcps.

In Figure 14.3, both forward traffic channel physical layer packets and controlchannel physical layer packets share the same QPSK/8-PSK/16-QAM modulator. Sohow can the AT tell the difference between a forward traffic channel transmissionand a control channel transmission? It turns out that the AT distinguishes a forwardtraffic channel transmission from a control channel transmission by examining thepreamble that precedes the data transmission in the (time division multiplexed) chipstream. There are specific patterns of the preamble that tell the AT whether or notthe subsequent data transmission is of forward traffic channel or control channel3.Figure 14.4 shows the preamble before time division multiplexing.

See Section 14.3.4 later for more details on time division multiplexing of differ-ent forward channels.

218 1xEV-DO Radio Interface: Forward Link

I

QScrambling

1to

16de

mux

1to

16de

mux

Interleaving

Modulator(QPSK/8-PSK/16-QAM)

Repetition/puncture

Physicallayerpacket

I

Q

16 substreams

Encoding

x 1/4

x 1/4

160w

16w15

+

x 1/4

x 1/4

160w

16w15

+

To TDM ( )I

To TDM ( )Q

Figure 14.3 Conceptual block diagram: Forward traffic channel and control channel.

3. The IS-856 standard defines 64 possible patterns of the preamble (the preamble patterns themselves are bior-thogonal functions). Each preamble pattern is indexed by the parameter MACIndex (which ranges from 0 to63). For example, if MACIndex = 3 then the subsequent data transmission is a 38.4-Kbps control channel.

Page 239: 3G CDMA200 Wireless System Engineering

14.3.3 MAC Channel

The MAC channel consists of the following channels:

• RA channel;• RPC channel;• DRCLock channel.

14.3.3.1 Reverse Activity (RA) Channel

The AN uses the reverse activity channel to inform all ATs (in its coverage area) ofthe current traffic activity on the reverse link. ATs incorporate this information inmaking decisions to decrease their data rates because of high traffic load, or toincrease their data rates because of nominal traffic load on the reverse link [2]. Thereverse activity channel carries reverse activity bits.

In time division multiplexing reverse activity bits onto the forward link, thephysical layer transmits each reverse activity bit once every specified numberof slots. The number of slots over which a single reverse activity bit is transmittedis specified by the parameter RABLength. Since each slot lasts 1.67 ms (seeFigure 14.7), the reverse activity bits are sent at a rate of 1 / (RABLength × 1.67 ms)[1]. For example, if RABLength = 2 then the reverse activity bits are sent at a rate of300 bps (= 1 / (2 × 1.67 ms)).

Note that the reverse activity channel and the reverse power control channel dif-fer in their intended recipient. Whereas the reverse activity channel broadcasts to allATs, the reverse power control channel targets individual ATs who are transmittingon the reverse link.

See Section 14.3.4 later for more details on time division multiplexing of differ-ent forward channels.

14.3.3.2 Reverse Power Control (RPC) Channel

The AN uses the reverse power control channel to power control ATs’ reverse linktransmission. Although there is no power control on the forward link, there ispower control on the reverse link, and the reverse power control channel is used tosend power control bits for that purpose.

In time division multiplexing power control bits onto the forward link, thephysical layer transmits each power control bit effectively once every slot. Sinceeach slot lasts 1.67 ms (see Figure 14.7), power control bits are sent at a rate of 600

14.3 Physical Layer 219

RepetitionPreambledefined byMacIndex i

To TDM ( )I

To TDM ( )Q0

Figure 14.4 Preamble.

Page 240: 3G CDMA200 Wireless System Engineering

bps (= 1 / 1.67 ms). In later versions of the 1xEV-DO standard, a new MAC channelDRCLock channel is introduced (see next section), so the reverse power controlchannel now has to share its time slot resources with the DRCLock channel. Specifi-cally, the parameter DRCLockPeriod specifies that one out of every DRCLockPe-riod slots is taken away from the reverse power control channel and given to theDRCLock channel. So now power control bits are transmitted not once every 1.66ms, but effectively once very 1.67 × DRCLockPeriod / (DRCLockPeriod – 1) ms [1].For example, if DRCLockPeriod = 8 (slots) then power control bits are transmittedonce every 1.67 × (8/7) ms or 1.905 ms. By inverting this number, we arrive at therate at which power control bits are transmitted which is 525 bps (= 1 / 1.905 ms).

As readers know already, the quality of the reverse link depends on the qualityof the reverse power control channel. To ensure the quality of the reverse link, thesystem needs to make sure that the reverse power control channel is received cor-rectly by the AT. But this is difficult because, similar to IS-2000, the power controlbits (sent on the reverse power control channel) are not error protected.

One way that 1xEV-DO ensures the quality of the reverse power control chan-nel is that the AT can diversity combine the same power control bit received fromtwo different sectors (on two separate reverse power control channels). The ANspecifies whether or not the AT should diversity combine reverse power controlchannels through the SofterHandoff field in the TrafficChannelAssignment mes-sage. Of course, if the AN specifies that an AT should diversity combine, then theAN needs to transmit the same power control information through those sectors.

See Section 14.3.4 later for more details on time division multiplexing of differ-ent forward channels.

14.3.3.3 DRCLock Channel

The AN uses the DRCLock channel to tell the AT if the AN is successfully receiv-ing the DRC information sent by the AT. The DRC information consists of thefollowing:

• Data rate/packet lengths. There are 12 different possible combinations of datarates versus packet lengths (see Table 14.2). Each combination is specified by aDRC value. An AT requests a forward link data rate by transmitting a DRCvalue on the data rate control channel on the reverse link.

• AT’s current home sector. This sector is one that the AT selects as the bestserving sector. The AT specifies this best serving sector by using a DRCCover.Each DRCCover is a three-bit symbol k (0 ≤ k ≤ 7) which in turn defines aWalsh code of length eight (i.e.,w i

8 ). The AT specifies its best serving sector bymultiplying (covering) its data rate control channel with the correspondingWalsh code.

Using the DRCLock channel, the AN tells the AT if the AN is successfully receiv-ing the DRC information sent by the AT. More specifically, DRCLock bits (indicat-ing “yes” or “no”) are sent over the DRCLock channel.

In time division multiplexing DRCLock bits onto the forward link, theDRCLock channel and the reverse power control channel share the same MACchannel slot resources (see Figure 14.5). The parameters DRCLockPeriod and

220 1xEV-DO Radio Interface: Forward Link

Page 241: 3G CDMA200 Wireless System Engineering

DRCLockLength specify how DRCLock bits are transmitted. As mentioned before,DRCLockPeriod specifies the fact that one out of every DRCLockPeriod slots isused for the DRCLock channel. DRCLockLength, on the other hand, specifies howmany slots are used to repeat a single DRCLock bit. Therefore, given these twoparameters, a single DRCLock bit is transmitted effectively once every (DRCLock-Period x DRCLockLength) slots. Since each slot lasts 1.66 ms (see Figure 14.7),DRCLock bits are sent at a rate of 1 / (1.66 x DRCLockPeriod x DRCLockLength)ms [1]. For example, if DRCLockPeriod = 8 and DRCLockLength = 4 thenDRCLock bits are sent once every 32 slots, or at a rate of 18.75 bps.

To ensure the quality of the DRCLock channel, the AT can also diversitycombine the same DRCLock bit received from two different sectors (on two differ-ent DRCLock channels). The AN specifies whether or not the AT should diver-sity combine DRCLock channels also through the SofterHandoff field in theTrafficChannelAssignment message. So if an AT diversity combines two DRCLockchannels it also diversity combines two reverse power control channels.

See Section 14.3.4 later for more details on time division multiplexing of differ-ent forward channels.

14.3.3.4 Channel Structure

Figure 14.5 shows a conceptual block diagram of the reverse power control chan-nel, DRCLock channel, and reverse activity channel. In terms of the reverse power

14.3 Physical Layer 221

4. MACIndex is also used to refer to and tag specific ATs. MACIndex ranges from 0 to 63.

Repetition

I

64iw

forMACIndex j

+ToTDM( )I

RepetitionToTDM( )Q

TDM

Repetition

I

QGain

DRCLockbits forMACIndex j

GainRPCbits forMACIndex j

642w

for4MACIndex

Repetition GainRAbits forMACIndex j

If = even thenj IIf = odd thenj Q

Figure 14.5 Conceptual block diagram: reverse power control channel, DRCLock channel, andreverse activity channel.

Page 242: 3G CDMA200 Wireless System Engineering

control channel and DRCLock channel, both power control bits and DRCLock bitsare applied their respective gains (except for DRCLock bits which are first repeatedby a factor of DRCLockLength). Then the two streams are combined using TDM,and the combined stream is channelized by the Walsh code (of length 64) defined bythe MACIndex4. The resulting chip stream is transmitted on the I path if the MAC-Index is even or on the Q path if the MACIndex is odd. Finally, both paths undergorepetition before time division multiplexing with other forward channels [1].

In terms of the reverse activity channel, reverse activity bits are first repeated bya factor of RABLength and applied a gain. Then the stream is channelized by theWalsh code assigned to the reverse activity channel (i.e., w 2

64 corresponding toMACIndex 4). Because reverse activity channel uses MACIndex 4 which is even, theresulting chip stream is transmitted on the I path.

Recall from Section 14.3.3.1 that the AN uses the reverse activity channel toinform all ATs about the current traffic activity on the reverse link. The reason thatthe reverse activity channel’s Walsh code is fixed (i.e., w 2

64 ) is because all ATs can usethis fixed Walsh code to receive the reverse activity channel and know the currenttraffic condition on the reverse link, at all times.

See the next section for more details on time division multiplexing of differentforward channels.

14.3.4 Time Division Multiplexing

As mentioned before, the chip streams of all forward channels are time division mul-tiplexed together to be transmitted to the ATs. Note that this combination ofCDMA/TDM is not foreign to those readers who are familiar with IS-95, asIS-95 also effectively uses CDMA/TDM in its paging channel (in the slotted mode).Figure 14.6 shows the block diagram of the time division multiplexer. As shown inthe figure, the chip streams of the pilot channel, forward traffic channel/controlchannel, preamble, reverse power control channel, DRCLock channel, and reverseactivity channel are multiplexed together prior to complex modulation.

On the forward link, the TDM chip stream generated by the time division multi-plexer is organized into slots. Each slot lasts 1.67 ms and contains 2,048 chips. Thisresults in a final chip rate of 1.2288 Mcps (= 2,048 chips / 1.67 ms). Figure 14.7shows the slot structure of the time division multiplexed chip stream.

All forward link channels are time division multiplexed onto a chip stream andthen transmitted. In that regard, individual channels occur in “bursts” on that chipstream. Figure 14.8 shows an example of that time division multiplexed chip streamused to transport a forward traffic channel physical layer packet. The stream runs at1.2288 Mcps. The following parameters are used in the example:

• Length of physical layer packet = 1,024 bits;• Data rate = 307.2 Kbps;• Code rate = 1/5;• Modulation scheme = QPSK;• Length of preamble = 128 chips (defined by IS-856 for this case);• Number of slots required = 2 slots (defined by IS-856 for this case).

222 1xEV-DO Radio Interface: Forward Link

Page 243: 3G CDMA200 Wireless System Engineering

The turbo encoder (R = 1/5) encodes 1,024 data bits of the forward traffic chan-nel physical layer packet and outputs 5,120 code symbols. The QPSK modulator inturn outputs one data modulation symbol for every two code symbols, resulting in

14.3 Physical Layer 223

TDM

( )ITomodulation

I

IFrom forward traffic channel/control channel

IFrompreamble

IFrom RA channel/RPC channel, andDRCLock channel

TDM

( )QTomodulation

QFrompilot channel

QFrom forward traffic channel/control channel

QFrompreamble

QFrom RPC channel andDRCLock channel

0

0

Frompilot channel

w0

Figure 14.6 Time division multiplexing.

Slot i Slot + 1i Slot + 15i

1.67 ms

2,048 chips1.2288 Mcps

Figure 14.7 Slot structure of the time division multiplexed chip stream.

Page 244: 3G CDMA200 Wireless System Engineering

2,560 data modulation symbols. After 1-to-16 demultiplexing and Walsh multipli-cation, these 2,560 data modulation symbols are assigned to the data-burst portionsof the time division multiplexed chip stream. As shown in Figure 14.8, in eachslot the forward traffic channel data (modulation symbols) are transmitted in threeseparate bursts. The preamble preceding the first data burst identifies whether ornot the subsequent data bursts are of forward traffic channel or control channel (seeSection 14.3.2).

224 1xEV-DO Radio Interface: Forward Link

1 slot 1 slot

2,048 chips 2,048 chips

400chips

400chips

400chips

400chips

800chips

800chips

Preamble128 chips

MAC64 chips

Pilot96 chips

Physicallayerpacket

1,024bits

5,120symbols

2,560symbols

Code symbols

Data modulation symbols

Encoder ( = 1/5)R

Modulator (QPSK)

Figure 14.8 Example of a time division multiplexed chip stream used to transport a forward traf-fic channel physical layer packet. Note that only those functions relevant to the calculation of thefinal number of data modulation symbols are shown (i.e., encoder and QPSK modulator). Otherfunctions of the physical layer such as interleaving and puncturing are not shown.

Page 245: 3G CDMA200 Wireless System Engineering

In addition, the pilot channel is transmitted in two separate bursts in each slot,each burst lasting 96 chips. The MAC channel, which can be used for reverse powercontrol channel or reverse activity channel, is transmitted in four separate bursts ineach slot, each burst lasting 64 chips. For example, if the MAC channel is used forreverse power control channel, then all four 64-chip bursts in a slot are used totransmit a single power control bit.

In this example, the physical layer packet requires two slots to transmit. If morethan one slot is required to transmit a physical layer packet, then the system usesfour-slot interlacing. Four-slot interlacing means that successive slots used to trans-mit a physical layer packet are four slots apart (i.e., separated by three slots inbetween) [1]. The three slots in between are used to transmit other physical layerpackets.

Figure 14.8 shows one possible format of the time division multiplexed streamand gives readers an idea of how the time division multiplexed stream is organized.Other time division multiplexed formats are possible for different data rates andlengths of physical layer packets. Consult [1] for the details of other specifiedformats.

14.3.5 Modulation

The output of the time division multiplexer is spread by the short PN code in a com-plex manner similar to IS-2000. Figure 14.9 shows that the I and Q outputs of thetime division multiplexer are multiplied by a pair of short PN codes (pI and pQ).After complex spreading, the spread chip streams are modulated onto in-phase andquadrature carriers and transmitted.

14.3 Physical Layer 225

pI

pQ

pQ

pI

BF

BF

cos(2 )πf tc

sin(2 )πf tc

Y t( )

+

+

+

I

Q

IpI

QpQ

IpQ

QpI

Ip QpI Q−

Ip + QpQ I

FromTDM ( )I

FromTDM ( )Q

Figure 14.9 Modulation: Forward link.

Page 246: 3G CDMA200 Wireless System Engineering

Note that since the pilot channel is w0 (all 1s), through complex spreading thepilot channel (burst) effectively carries the short PN code, which identifies the basestation sector.

14.4 Concluding Remarks

1xEV-DO forward link does not control the power to guarantee a constant data rateand grade of service. Rather, it controls the rate of data transmission given a con-stant transmit power. In doing so, 1xEV-DO forward link allocates each user a frac-tion of total base station power and adapts the data rate, code rate, and modulationscheme based on link conditions. In fact, the scheduler constantly optimizes thepower allocated to each user. The scheduler does so by looking at the current linkconditions experienced by ATs, as well as the current data rate, coding, and modula-tion scheme. Ultimately, the goal of the scheduler is to maximize total throughputwhile submitting to some constraint of fairness (to users) [3]. A discussion of thecritical role of the scheduler is outside the scope of this book. Readers may wish toconsult references such as [3] for a more detailed treatment of the scheduler.

References

[1] TIA/EIA/IS-856, cdma2000 High Rate Packet Data Air Interface Specification, Telecom-munications Industry Association, January 2002.

[2] Mandyam, G., and J. Lai, Third-Generation CDMA Systems for Enhanced Data Services,San Diego, CA: Academic Press, 2002.

[3] Wu, Q., and E. Esteves, “CDMA2000 High-Rate Packet Data System,” In Advances in 3GEnhanced Technologies for Wireless Communications, J. Wang, and T. Ng (eds.), Nor-wood, MA: Artech House, 2002, pp. 149–226.

Selected Bibliography

Bender, P., et al., “CDMA/HDR: A Bandwidth Efficient High Speed Wireless Data Service forNomadic Users,” IEEE Communications, Vol. 38, No. 7, July 2000, pp. 70–77.

TIA-864, Recommended Minimum Performance Standards for cdma2000 High Rate Packet DataAccess Network Equipment, Telecommunications Industry Association, February 2002.

TIA-866, Recommended Minimum Performance Standards for cdma2000 High Rate Packet DataAccess Terminal, Telecommunications Industry Association, February 2002.

226 1xEV-DO Radio Interface: Forward Link

Page 247: 3G CDMA200 Wireless System Engineering

C H A P T E R 1 5

1xEV-DO Radio Interface: Reverse Link

15.1 Introduction

This chapter covers the MAC and physical layers of 1xEV-DO reverse link. To start,it would be appropriate to emphasize some important characteristics of the reverselink and contrast them to the forward link:

• There is power control on the reverse link. The AN can power control thereverse link by using the reverse power control channel. An AT can change itstransmit power on the reverse link based on feedback received from the AN.

• There is soft handoff on the reverse link. In other words, more than one basestation can receive one AT’s transmission.

• There is no TDM on the reverse link. The reverse link channels are separatedusing CDMA. This is in contrast to the forward link which usesCDMA/TDM.

In this chapter, Sections 15.2 and 15.3 cover the MAC layer and the physicallayer of the reverse link, respectively. Then Section 15.4 describes reverse powercontrol that is present on the 1xEV-DO reverse link.

15.2 MAC Layer

The MAC layer regulates the transmission and reception of two types of messages:user data messages and signaling messages. In doing so, the MAC layer uses twoprotocols [1]:

• Reverse traffic channel MAC protocol;• Access channel MAC protocol.

15.2.1 Reverse Traffic Channel MAC Protocol

In addition to controlling the transmission and reception of packets on the reversetraffic channel, the reverse traffic channel MAC protocol also negotiates the reversetransmission rate and oversees reverse power control. To perform these functions,the reverse traffic channel MAC protocol operates in two active states.

In the setup state, the reverse traffic channel is not being used. However, in thisstate the AT prepares (“sets up”) for the eventual data transmission on the reverse

227

Page 248: 3G CDMA200 Wireless System Engineering

traffic channel. In doing so the AT starts to comply with power control bits (receivedon the reverse power control channel) sent by the AN. When the AT first beginstransmitting to the AN, the reverse traffic channel MAC protocol always starts inthe setup state first.

In the open state, the reverse traffic channel is being used. At the same time, theAT may set different transmission rates on the reverse traffic channel. In setting thetransmission rate, the AT cannot exceed a maximum transmission rate. Here the ATmakes use of the following information to set the parameter MaxRate (maximumtransmission rate the AT can use on the reverse traffic channel):

• Reverse activity bit. Recall from Chapter 14 that the AN sends the AT reverseactivity bits using the reverse activity channel; the reverse activity channel isused to inform the ATs the current traffic activity on the reverse link. The ATwould tend to decrease its MaxRate if there is high traffic load, or to increaseits MaxRate if there is nominal traffic load on the reverse link.

• Current transmission rate. The AT considers its current transmission rate indetermining the maximum transmission rate.

• Probability parameter. The AN exercises some control over the distribution oftransmission rates of ATs in its coverage area by specifying the probability anAT uses to increase or decrease its transmission rate. These probabilities arealso known as RateParameters and are sent to the AT by the AN as part of theconfiguration parameters.

The AT makes use of these three pieces of information in determining themaximum transmission rate that can be used on the reverse traffic channel. In addi-tion, the AN can also directly determine the maximum transmission rate. The ANdoes so by communicating the parameter RateLimit to the AT. The RateLimitparameter also specifies the maximum transmission rate the AT can use on thereverse traffic channel. Whereas MaxRate is indirectly determined by the AT usingseveral inputs, RateLimit is directly decreed by the AN. The AN sends the parameterRateLimit to the AT using the BroadcastReverseRateLimit message or the Unicast-ReverseRateLimit message1. In the open state, the transmission rate can vary from9.6 to 153.6 Kbps.

Figure 15.1 shows the packet encapsulation in the MAC and physical layers onthe reverse link. At the AT, after receiving a security layer packet (containing userdata) from the security layer, the reverse traffic channel MAC protocol attaches aMAC layer trailer and forms a reverse traffic channel MAC layer packet. The proto-col then passes the MAC layer packet to the physical layer below.

15.2.2 Access Channel MAC Protocol

The access channel MAC protocol has the responsibility of managing the transmis-sion and reception of signaling packets on the access channel. At the AT, after asecurity layer packet is passed to the access channel MAC protocol in the MAClayer, the access channel MAC protocol formats the packet and generates an access

228 1xEV-DO Radio Interface: Reverse Link

1. The BroadcastReverseRateLimit message is sent to a group of ATs, whereas the UnicastReverseRateLimitmessage is sent to a single AT.

Page 249: 3G CDMA200 Wireless System Engineering

channel MAC layer packet. The access channel MAC layer packets then are passedto the physical layer to be transmitted on the access channel (using a series of accessprobes).

The access procedure performed by the access channel MAC protocol is similarto that used in basic access mode of IS-2000 (see Chapter 4). Namely, the AT keepstransmitting access probes at increasing power levels until it gets an acknowledge-ment back from the AN. Also, ATs transmit pseudorandomly in their attempts togain access. As shown in Figure 15.2, each access probe contains a preamble and acapsule. The preamble is actually a pilot channel transmission, which is used tofacilitate the acquisition of the access channel by the AN. The capsule is a data chan-nel transmission that carries the access data. Note that in an access probe, the pilotchannel is also active during the transmission of the data channel.

The access channel is a signaling channel that is shared among many users (i.e.,ATs). As such, the AN needs someway of distinguishing among the different packetsand finding out which packet is from which AT. The method used is that when anAN receives an access channel MAC packet, it checks the access terminal identifierrecord field of the MAC layer header and performs address matching. The accessterminal identifier record specifies the AT’s address and is maintained by theaddress management protocol in the session layer.

15.3 Physical Layer

The following are the two channels used on the reverse link of a 1xEV-DO system.They are the:

• Reverse traffic channel;• Access channel.

Specifically, the reverse traffic channel consists of the:

15.3 Physical Layer 229

Reversetraffic channelphysical layerpacket

Securitylayerpacket

MAClayertrailer

Physicallayertrailer

Reversetraffic channelMAC layerpacket

Phys

ical

laye

rM

AC

laye

rSe

curit

yla

yer

Physicallayerpayload

Figure 15.1 Packet encapsulation at the MAC and the physical layers. Note that the reverse traf-fic channel MAC layer packet shown contains user data and is for the reverse traffic channel. Thereverse traffic channel physical layer packet always contains one reverse traffic channel MAC layerpacket.

Page 250: 3G CDMA200 Wireless System Engineering

• Data channel;• Pilot channel;• Reverse rate indicator (RRI) channel;• Data rate control (DRC) channel;• ACK channel.

The reverse rate indicator channel and the data rate control channel are also col-lectively known as the MAC channel.

The access channel consists of the:

• Pilot channel;• Data channel.

As briefly mentioned in the last section, an access channel actually consists of apilot channel transmission (preamble) followed by the data channel transmission(capsule). Figure 15.3 shows the organization of channels on the reverse link. On1xEV-DO reverse link, channels are channelized by their assigned Walsh codes.

At this point, it would be instructive to contrast and compare 1xEV-DO reverselink with 1xEV-DO forward link. Because in 1xEV-DO reverse link channels are

230 1xEV-DO Radio Interface: Reverse Link

Preamble Capsule

Pilot channel

Data channel

Access probe

Figure 15.2 An access probe. Note that the total power has to be the same during both pream-ble and capsule portions. This means that the pilot channel power is necessarily less during thecapsule portion. See also Figure 15.9.

Reverse traffic channel

Access channel Data channel

Pilot channel

Data channel

Pilot channel

Reverse rate indicator (RRI) channel

Data rate control (DRC) channel

ACK channel

Figure 15.3 Reverse link channels.

Page 251: 3G CDMA200 Wireless System Engineering

channelized using Walsh codes and ATs are separated from each other using longPN codes, 1xEV-DO reverse link is a CDMA system whereas 1xEV-DO forwardlink uses a combination of CDMA and TDM.

Another difference between 1xEV-DO reverse link and 1xEV-DO forward linkis that the reverse link uses only one modulation scheme of BPSK whereas the for-ward link can use one of three modulation schemes: QPSK, 8-PSK, and 16-QAM.The reason for using only BPSK on the reverse link is simple: power. While provid-ing greater spectral efficiencies, higher order modulations such as 8-PSK and16-QAM consume more power. This is not practical at the AT that has limitedbattery power. Consequently, using BPSK enables the reverse link to provide up to153.6 Kbps.

In terms of similarity, the reverse link slot structure is similar to that of the for-ward link. Each slot lasts 1.67 ms and contains 2,048 chips. This results in a finalchip rate of 1.2288 Mcps (= 2,048 chips / 1.67 ms). Figure 15.4 shows the slot struc-ture of the reverse link.

15.3.1 Reverse Traffic Channel

The reverse traffic channel is used to transport both user data messages and signal-ing messages and consists of the:

• Data channel;• Pilot channel;• Reverse rate indicator (RRI) channel;• Data rate indicator (DRC) channel;• ACK channel.

After receiving a reverse traffic channel MAC layer packet the physical layerconstructs a reverse traffic channel physical layer packet (by adding CRC bits, forexample). The reverse traffic channel physical layer packet always contains justone reverse traffic channel MAC layer packet. However, the size of the physicallayer packet gets larger when the MAC layer packet carried gets longer. Table 15.1shows the size of the physical layer packet versus the size of the MAC layer packetcarried.

On the reverse link, the size of the physical layer packet is directly related to thedata rate. Table 15.2 shows the size of the reverse traffic channel physical layerpacket versus the data rate. Note that the size of the physical layer packet depends

15.3 Physical Layer 231

Slot i Slot + 1i Slot + 15i

1.67 ms2,048 chips 1.2288 Mcps

Figure 15.4 Slot structure of the reverse link.

Page 252: 3G CDMA200 Wireless System Engineering

on the data rate chosen for transmission (i.e., as data rate increases, a longer physicallayer packet is used).

If you examine Table 15.2 closely, you will discover something interesting. Rec-ognize that dividing the size of a physical layer packet by the data rate yields the timeduration of a physical layer packet. If you divide 256 bits by 9.6 Kbps, you get 26.67ms. If you divide 4,096 bits by 153.6 Kbps, you also get 26.67 ms. In fact, all physi-cal layer packets used on the reverse link last the same amount of time—26.67 msregardless of the size. This makes sense because the larger the physical layer packet,the higher the data rate if the duration of a packet is constant. Given that each slotlasts 1.67 ms, each physical layer packet then always occupies 16 slots.

Table 15.2 also shows the code rate used for each data rate. Since 1xEV-DO isused exclusively for data applications, processing delay is not an issue. Thus compu-tationally intensive turbo codes are used for all forward error corrections on thereverse link.

15.3.1.1 Data Channel

In transmitting a reverse traffic channel physical layer packet, the physical layer usesthe data channel. The data channel is separated from all other channels (e.g., ACKchannel and data rate control channel) through the use of Walsh codes. In fact, thedata channel uses Walsh code w 2

4 for channelization prior to quadrature spreading.Figure 15.5 shows a conceptual block diagram of the data channel (boldfaced).

After the physical layer packet is generated, the physical layer performs the usualfunctions such as:

232 1xEV-DO Radio Interface: Reverse Link

Table 15.1 Length of a Physical Layer Packet

Length of aPhysical LayerPacket (Bits)

Length of theCarried MACLayer Packet

Type ofPhysical Layer Packet

256 234 Reverse traffic channel or access channel

512 490 Reverse traffic channel

1,024 1,002 Reverse traffic channel

2,048 2,026 Reverse traffic channel

4,096 4,074 Reverse traffic channel

Table 15.2 Lengths of Physical Layer Packets and Data Rates

Length of a PhysicalLayer Packet (Bits) Data Rates (Kbps) Code Rate Modulation Scheme

256 9.6 1/4 BPSK

512 19.2 1/4 BPSK

1,024 38.4 1/4 BPSK

2,048 76.8 1/4 BPSK

4,096 153.6 1/2 BPSK

Page 253: 3G CDMA200 Wireless System Engineering

• Encoding the bits for correcting bit errors;• Interleaving for combating fades.

After repetition, the symbols are channelized by Walsh code w 24 and applied a

gain. Then the chip stream is summed with that of the data rate control channelprior to quadrature spreading and modulation [1].

When the data channel (carrying reverse traffic channel physical layer packets)is active, the pilot channel and the reverse rate indicator channel are also active. Thisis because the AN needs the pilot for timing and reference, and needs the reverse rateindicator to know what data rate the data channel is using. Section 15.3.1.3 exam-ines these two channels.

15.3.1.2 Data Rate Control (DRC) Channel

As mentioned in Chapter 14, an AT can request different data rates on the forwardlink, and an AT makes such requests using the data rate control channel on thereverse link. In addition, the AT uses the data rate control channel to notify the ANof the AT’s current home sector.

Since on the forward link there are 12 possible combinations of data rates ver-sus packet lengths (see Table 14.2)2, the AT needs four bits to request these datarate/ packet length combinations. In fact, the data rate control channel is a series of

15.3 Physical Layer 233

2. For example, in Table 14.2 a packet length of 1,024 bits and 38.4 Kbps is one combination. A packet lengthof 1,024 bits and 76.8 Kbps is another combination.

3. Each of these 4-bit symbols or data rate/packet length combinations is also known as the DRC value. TheDRC value (which is the forward link data rate/packet length requested by the AT) is generated by the for-ward traffic channel MAC protocol. See Chapter 14.

Repetition

+Tomodulation( )Q

w24

Encoding InterleavingPhysicallayerpacket

Gain

Bi-orthogonalfunctionmapping

DRCsymbols(4 bits/symbol) forDRC value

Repetition Gain

Walshcodemapping

DRCCoversymbols(3 bits/symbol)

wi8 w8

16

Figure 15.5 Conceptual block diagram: Data channel (boldfaced) and data rate control channel.

Page 254: 3G CDMA200 Wireless System Engineering

logical four-bit symbols3. Each four-bit symbol is sent once every specified numberof slots. The number of slots over which a single four-bit symbol is sent is specifiedby the parameter DRCLength. Since each slot lasts 1.67 ms (see Figure 15.4),the four-bit symbols are sent at a rate of 1 / (DRCLength × 1.67 ms). For example,if DRCLength = 2 then the four-bit symbols are sent at a rate of 300 bps (= 1 /(2 × 1.67 ms)).

The criterion that the AT uses to request different forward traffic channel datarates is primarily the SNR of the forward link. One implementation uses the Ec/I0 ofthe forward pilot channel [2]. The AT continuously measures the Ec/I0 of the for-ward pilot channel. If the Ec/I0 is high, then the forward link can support highermodulation schemes and hence higher data rates. Figure 15.6 shows the relationshipbetween data rates and Ec/I0 for a 1% packet error rate based on link simulation andlaboratory measurements of a complete RF link [2].

In addition to requesting different forward link data rates, an AT also uses thedata rate control channel to notify the AN of the AT’s current best serving sector (onthe forward link). Recall that there is no soft handoff on the forward link; an AT canonly have one home sector, and this sector is the one that the AT selects as the bestserving sector [3]. The AT specifies this best serving sector by using a three-bit sym-bol4. Each three-bit symbol k (0 ≤ k ≤ 7) in turn defines a Walsh code of length eight(i.e.,w i

8 ). The AT specifies its best serving sector by multiplying (covering) its datarate control channel with the corresponding Walsh code.

Figure 15.5 also shows the conceptual block diagram of the data rate controlchannel (nonboldfaced). Data rate control symbols are first mapped to specificbiorthogonal functions. After repetition, the symbols are multiplied by a Walshcode w i

8 (used to index a best serving sector). Then the data rate control channel ischannelized by Walsh code w 8

16 and applied a gain. The resulting chip streamis summed with that of the data channel prior to quadrature spreading andmodulation [1].

234 1xEV-DO Radio Interface: Reverse Link

4. Each one of these indexed sectors is also known as the DRCCover. The DRCCover (which specifies the AT’sbest serving sector) is generated by the forward traffic channel MAC protocol.

−15

−10

−5

0

5

10

15

0 500

Eclo/

(dB)

1,000 1,500 2,000 2,500

Data rate (Kbps)

Figure 15.6 The relationship between forward traffic channel data rates and forward pilot chan-nel Ec/I0 for a 1% packet error rate. (After: [2].)

Page 255: 3G CDMA200 Wireless System Engineering

15.3.1.3 Pilot Channel and Reverse Rate Indicator (RRI) Channel

The pilot channel serves a similar function as its counterpart in IS-2000 in that itprovides the AN with timing and phase reference. It is a stream of 1s and containsno baseband information.

The reverse rate indicator channel tells the AN what data rate is currently beingused by the data channel. Since there are six possible data rates (including 0 Kbps)on the reverse link (see Table 15.2), one needs 3 bits to represent these data rates. Infact, the reverse rate indicator channel is a series of logical 3-bit symbols. The 3-bitsymbols are sent once every physical layer packet.

Figure 15.7 shows the conceptual block diagram of the pilot channel andreverse rate indicator channel (boldfaced). Reverse rate indicator symbols are firstencoded, then they undergo repetition and puncture. In preparation for transmis-sion, the reverse rate indicator channel and the pilot channel are time division multi-plexed together (in a 7-to-1 ratio favoring reverse rate indicator symbols) onto asingle symbol stream. Then the symbol stream is channelized by Walsh code w 0

16 ,and the resulting chip stream is summed with that of the ACK channel prior toquadrature spreading and modulation [1]. As readers can see, the pilot chan-nel/reverse rate indicator channel is distinguished from the ACK channel throughdifferent Walsh codes.

15.3.1.4 ACK Channel

The ACK channel is used by the AT to acknowledge the receipt of a forward trafficchannel physical layer packet. An ACK bit of “0” means that the CRC check of thereceived packet succeeded (positive acknowledgment). An ACK bit of “1” means

15.3 Physical Layer 235

Repetition+

Tomodulation( )I

TDM

(7:1

)

w016

Encoding

RRIsymbols(3 bits/symbol)

Gain

Puncture

Pilot(1s)

w48

RepetitionACKbits

Figure 15.7 Conceptual block diagram: Pilot channel/reverse rate indicator channel (boldfaced)and ACK channel.

Page 256: 3G CDMA200 Wireless System Engineering

that the CRC check of the received packet failed (negative acknowledgment). If apacket has not been received successfully, the AN typically retransmits the packet.

Figure 15.8 shows an example of how forward link and reverse link slots aretimed in the context of the ACK channel. Here the forward traffic channel is trans-mitting at 614.4 Kbps, and there is one forward traffic channel physical layer packetper slot5. As one can see in this figure, after a physical layer packet is received a cor-responding ACK bit is sent three slots later.

Figure 15.7 also shows the conceptual block diagram of the ACK channel (non-boldfaced). Before channelization by the Walsh code, a baseband ACK bit is firstrepeated 128 times. Then this group of 128 bits is channelized by Walsh codew 4

8 and applied a gain. The resulting chip stream is summed with that of thepilot channel/reverse rate indicator channel prior to quadrature spreading andmodulation [1].

Note that after multiplying by Walsh code w 48 , the group of 128 bits is expanded

to 1,024 chips (= 128 bits × 8 chips/bit) which occupy half a slot (each slot lasts2,048 chips). In fact, as shown in Figure 15.8 each ACK bit is represented by 1,024chips in the first half of the slot in the ACK channel.

15.3.2 Access Channel

The access channel is used by the AT to first contact the AN and to respond to a mes-sage from the AN. After receiving an access channel MAC layer packet, the physicallayer constructs an access channel physical layer packet (by adding CRC bits, forexample). An access channel physical layer packet can only carry one access channelMAC layer packet. Because access channel data rate is fixed at 9.6 Kbps, an accesschannel physical layer packet is always 256 bits long (see Table 15.2).

236 1xEV-DO Radio Interface: Reverse Link

5. In general, a forward traffic channel physical layer packet may occupy more than one slot (depending on thedata rate).

Slot

Receivedforwardtrafficchannel

0 1 2 3 15

Slot

TransmittedACKchannel

0 1 2 3 154

4

ACK bit

Figure 15.8 Forward traffic channel and ACK channel at the AT. (After: [1].)

Page 257: 3G CDMA200 Wireless System Engineering

An access channel physical layer packet is transported using the access probe.An access probe is transmitted on the access channel; the access channel actuallyuses two channels that are also used by the reverse traffic channel: pilot channel anddata channel.

Figure 15.9 shows an example of an access probe. As mentioned previously,each access probe contains a preamble and a capsule. The preamble is a pilot chan-nel transmission whose length is specified by the parameter PreambleLength. Pre-ambleLength is in the units of 16 slots. On the other hand, the capsule is a datachannel transmission whose maximum length is specified by the parameter Cap-suleLengthMax. CapsuleLengthMax is also in the units of 16 slots. In this example,the following is assumed:

• PreambleLength = 2;• CapsuleLengthMax = 2.

In this case, the AT only sends one access channel physical layer packet; it lasts16 slots which is less than that specified by CapsuleLengthMax. Note that in anaccess probe, the pilot channel is also active during the transmission of the datachannel.

Figure 15.10 shows the conceptual block diagram of the access channel (bold-faced) and the pilot channel. After the physical layer packet is generated, the physi-cal layer performs the usual functions such as:

• Encoding the bits for correcting bit errors;• Interleaving for combating fades.

After repetition, the symbols are channelized by Walsh code w 24 and applied a

gain prior to quadrature spreading and modulation [1]. Note that when the accesschannel is active, the pilot channel also needs to be active.

15.3 Physical Layer 237

Pilot channel

Data channel

Preamble32 slots

(= x 16 slots)PreambleLength

( x 16 slots)≤CapsuleLengthMax

Capsule16 slots

Figure 15.9 An example of an access probe.

Page 258: 3G CDMA200 Wireless System Engineering

15.3.3 Modulation

Figure 15.11 shows quadrature spreading and modulation functions of the reverselink. If the reverse traffic channel is active, then the summation of chip streams of thepilot channel/reverse rate indicator channel and the ACK channel goes into the Iinput, and the summation of chip streams of the data channel and the data rate con-trol channel goes into the Q input. If the access channel is active, then the chipstream of the pilot channel goes into the I input, and the chip stream of the datachannel goes into the Q input.

I and Q inputs undergo quadrature spreading by a pair of spreading codes sI

and sQ. These two spreading codes are derived from the long PN code, which inturn is derived from the AT’s unique identity. After quadrature spreading, thespread chip streams are modulated onto in-phase and quadrature carriers andtransmitted [1].

The long PN code used (to derive sI and sQ) may be different depending onwhether the access channel is active or the reverse traffic channel is active.

238 1xEV-DO Radio Interface: Reverse Link

Tomodulation( )Q

Pilot(1s)

Repetition

w24

Encoding InterleavingPhysicallayerpacket

Gain

Tomodulation( )I

w016

Figure 15.10 Conceptual block diagram: Access channel (boldfaced) and pilot channel.

sI

sQ

sQ

sI

BF

BF

cos(2 )πf tc

sin(2 )πf tc

Y t( )

+

+

+

I

Q

IsI

QsQ

IsQ

QsI

Is QsI Q−

Is QsQ I+

Pilot ch/RRI ch/ACK chorpilot ch

Data ch/DRC chordata ch

Figure 15.11 Modulation: Reverse link.

Page 259: 3G CDMA200 Wireless System Engineering

15.4 Reverse Power Control

In 1xEV-DO, there is power control on the reverse link for the following channels:• Pilot channel;• Data channel;• Data rate control (DRC) channel;• ACK channel.

We have already mentioned in a previous section that when transmitting theaccess channel, the AT transmits access probes at successively higher power levelsuntil it gets an acknowledgement back from the AN. In this section, we will focus onthe power control of the reverse traffic channel. More specifically, when the ATtransmits the reverse traffic channel using the pilot channel, data channel, data ratecontrol channel, and ACK channel, it uses both open-loop power control andclosed-loop power control. Both open-loop and closed-loop power controls aresimilar to those used in IS-2000.

One note before we go into open- and closed-loop power controls: A character-istic of 1xEV-DO reverse power control is that everything is referenced to thereverse pilot channel. This means that when the reverse pilot channel powerchanges, the powers of other reverse channels also change.

15.4.1 Open-Loop Power Control

For the open loop, the AT receives the forward pilot channel and uses its power tocompute the open loop mean output power of the reverse pilot channel. The equa-tion used for this computation is linear (in decibels) and is similar to that used inIS-2000. The lower the mean received power of the forward pilot channel, thehigher the open loop mean output power of the reverse pilot channel. Therefore, asthe received power of the forward pilot channel changes, the open-loop outputpower of the reverse pilot channel also changes.

In turn, this open-loop output power of the reverse pilot channel determinesthe power of the following channels:

• Data channel;• Data rate control (DRC) channel;• ACK channel.

The powers of these three channels are determined by using a number of “off-set” factors (i.e., gain relative to pilot). For the data channel, the actual offset factorsused depend on the data rate. For example, if the data rate is 9.6 Kbps then the offsetfactor is (DataOffsetNom + DataOffset9k6 + 3.75); if the data rate is 153.6 Kbpsthen the offset factor is (DataOffsetNom + DataOffset153k6 + 18.5) [1]. In general,the higher the data rate, the higher the offset factor (i.e., gain relative to pilot). Thisis because that since the modulation scheme is fixed (i.e., BPSK), the AT needshigher powers to transmit at higher data rates.

The parameters (e.g., DataOffsetNom and DataOffset9k6) that determine thedifferent offset factors are known as the PowerParameters. They are sent by the ANto the AT as part of the configuration parameters.

15.4 Reverse Power Control 239

Page 260: 3G CDMA200 Wireless System Engineering

For the data rate control channel, the offset factor used is specified by theparameter DRCChannelGain. For the ACK channel, the offset factor used is speci-fied by the parameter ACKChannelGain. These two parameters are sent by the ANto the AT in the TrafficChannelAssignment message.

15.4.2 Closed-Loop Power Control

In addition to performing open-loop power control, the AT also performs closed-loop power control of the reverse traffic channel. Here the AT receives power con-trol bits on the reverse power control channel; based on those power control bits, theAT changes the mean output power of the reverse pilot channel.

The AN transmits power control bits to the AT based on AN’s reception of thereverse link signal. This process is similar to that of IS-2000. Typically, the AN hasan Eb/N0 threshold. If the received Eb/N0 is below the Eb/N0 threshold, then the ANtransmits a power-up power control bit. If the received Eb/N0 is above the Eb/N0

threshold, then the AN transmits a power-down power control bit (i.e., inner loop).Furthermore, the AN dynamically computes the Eb/N0 threshold in response tochanging link conditions (i.e., outer loop).

References

[1] TIA/EIA/IS-856, cdma2000 High Rate Packet Data Air Interface Specification, Telecom-munications Industry Association, January 2002.

[2] Bender, P., et al., “CDMA/HDR: A Bandwidth Efficient High Speed Wireless Data Servicefor Nomadic Users,” IEEE Communications, Vol. 38, No. 7, July 2000, pp. 70–77.

[3] Mandyam, G., and J. Lai, Third-Generation CDMA Systems for Enhanced Data Services,San Diego, CA: Academic Press, 2002.

Selected Bibliography

TIA-864, Recommended Minimum Performance Standards for cdma2000 High Rate Packet DataAccess Network Equipment, Telecommunications Industry Association, February 2002.

TIA-866, Recommended Minimum Performance Standards for cdma2000 High Rate Packet DataAccess Terminal, Telecommunications Industry Association, February 2002.

240 1xEV-DO Radio Interface: Reverse Link

Page 261: 3G CDMA200 Wireless System Engineering

About the Author

Samuel C. Yang is currently a professor at California State University, Fullerton,where he conducts research and consults in the area of wireless networks. He is alsoa registered professional engineer in the state of California. Dr. Yang holds anundergraduate degree from Cornell University and two graduate degrees from Stan-ford University, all in electrical engineering. He also holds a Ph.D. in informationscience from Claremont Graduate University.

Dr. Yang has over 15 years of managerial and professional experience in wire-less and satellite industries. Before entering academia, he was with Verizon Wire-less, where he led the planning and design of its 2G and 3G wireless networks in thewestern United States. In 1995, he played a key role in the design and commerciali-zation of the first large-scale CDMA network in North America. Prior to VerizonWireless, Dr. Yang was with Hughes Space and Communications (now Boeing Sat-ellite Systems), where he served as a technical lead on several international commu-nication satellite programs for China, Japan, and Thailand. While at Hughes, healso conducted research in channel simulation and advanced multiple-access tech-niques, as well as served as a system engineer on NASA’s Magellan radar-mappingmission to Venus.

Dr. Yang has published papers in the area of wireless communications and is theauthor of the Artech book CDMA RF System Engineering. His current interests arein design and management of mobile and fixed wireless networks and how organi-zations can best benefit from the use of wireless technologies.

241

Page 262: 3G CDMA200 Wireless System Engineering

.

Page 263: 3G CDMA200 Wireless System Engineering

Index

1xEV-DO, 7air interface, 199application layer, 204–5base station control, 201base stations, 200BSC, 202connection layer, 206–9data application support, 201data rate provisions, 199dedicated RF carrier, 201defined, 199latency tolerance, 200layer transmission service, 203network, 201–2as paradigm shift, 200physical layer, 201, 215–26, 229–38power resource focus, 200protocol architecture, 202–11protocol layers, 203radio interface (forward link), 213–26radio interface (reverse link), 227–40security layer, 210session layer, 205–6stream layer, 205wireless network support, 201–2

2G networks, 187–89illustrated, 188network elements, 187–89protocols, 189See also Network architecture

3G networks, 189–92illustrated, 190network elements, 190–91protocols, 191–92supporting mobile IP, 197See also Network architecture

AAccess

attempt, 139subattempt, 138

Access channel, 236–38access probe, 237block diagram, 238defined, 236elements, 230physical layer packet, 236, 237See also Reverse link (1xEV-DO)

Access channel MAC protocol, 228–29access probes, 229, 230capsule, 229defined, 228packet generation, 228–29preamble, 229See also MAC layer (1xEV-DO reverse link)

Access channel (R-ACH), 42, 45, 65Access entry handoff, 134–35Access handoff, 135–38

active set, 136defined, 135mobile station states, 135neighbor set, 136process, 136–38remaining set, 136substates, 137See also Handoffs

Access network (AN), 201, 205, 206Access probe handoff, 138Access terminal (AT), 201, 205, 206ACK channel, 235–36

at AT, 236block diagram, 235defined, 235See also Reverse traffic channel

Active mode, 96, 97Active set, 124–27

access handoff, 136adding pilots to, 126–27defined, 124idle handoff, 133removing pilots from, 124–25See also Handoff

243

Page 264: 3G CDMA200 Wireless System Engineering

Addressing sublayeractive, 73address parameters, 74common signaling: reverse link, 77defined, 71See also Link access control (LAC)

Air link capacity, 8Air link management protocol, 206–7

defined, 206states, 206–7transitions, 207See also Connection layer (1xEV-DO)

Application layer (1xEV-DO), 204–5Assured delivery, 73Asymmetric data rates, 1Authentication, authorization, and accounting

(AAA), 190, 191Authentication center (AC), 188Authentication sublayer

active, 73in common signaling, 74common signaling: reverse link, 77defined, 71See also Link access control (LAC)

Automatic repeat request (ARQ) sublayeracknowledgment fields, 74common signaling: reverse link, 77dedicated signaling: forward link, 77dedicated signaling: reverse link, 80defined, 73delivery modes, 73PDU delivery, 73See also Link access control (LAC)

Auxiliary pilot channel (F-APICH), 25Auxiliary transmit diversity pilot channel

(F-ATDPICH), 25–26Average pilot power, 161

BBase station controller (BSC), 187, 188

1xEV-DO, 202defined, 187

Base transceiver system (BTS), 187, 188Basic access mode, 44, 65

R-EACH probe, 65R-EACH transmission, 46

Binary phase-shift keying (BPSK), 34coherent, 52modulators, 52signals, 52

Bit error rate (BER), 162Broadcast control channel (F-BCCH), 7, 20–21

conceptual block diagram, 31data rate, 21defined, 19frame, 21monitoring, 90–91purpose, 20slot, 21structure, 20, 21

Broadcast slots, 91

CCall processing, 87–95Candidate set, 127–28

adding pilots to, 127defined, 127removing pilots from, 127–28See also Soft handoff

Capacity, 171–85forward link, 178–85introduction, 171mathematical definitions, 171–74reverse link, 174–78

Capacity gainforward link, 34reverse link, 52–53

Channelization, 32, 51, 52codes, 164defined, 11

Channel setup, 97–104base station-originated voice call, 98–99mobile station-originated packet data call,

100–101mobile station-originated voice call, 99–100supplemental channel request during packet

data call, 101–4Channel structure, 31–32, 217–18Channel supervision, 141–42

forward link: common channel, 142forward link: traffic channel, 141–42reverse link, 142

Closed-loop power control, 8, 108reverse link, 117–21reverse link (1xEV-DO), 240See also Power control

Code channel calculation, 113Code management, 142–50

quasi-orthogonal functions (QOFs), 147Walsh code assignment: forward link,

144–47Walsh code assignment: reverse link,

147–50Walsh code generation, 143–44

244 Index

Page 265: 3G CDMA200 Wireless System Engineering

See also System performanceCoding, 11, 31Common assignment channel (F-CACH),

7, 21–22block diagram, 31data rate, 22frames, 22function, 21

Common channel multiplex sublayer, 5Common power control channel (F-CPCCH),

7, 22–24format, 23frames, 22function, 22power control bits, 22, 24power control groups, 23

Common signaling: forward link, 74–76addressing sublayer, 74ARQ sublayer, 74authentication sublayer, 74base station, 75MAC sublayer, 74mobile station, 75SAR sublayer, 74, 76utility sublayer, 74, 76

Common signaling: reverse link, 76–77addressing sublayer, 77ARQ sublayer, 77authentication sublayer, 77base station, 78MAC sublayer, 77mobile station, 76SAR sublayer, 77utility sublayer, 77

Connected state protocol, 209Connection layer (1xEV-DO), 206–9

air link management protocol, 206–7connected state protocol, 209defined, 206idle state protocol, 209initialization protocol, 208–9overhead messages protocol, 209packet consolidation protocol, 209protocols, 206route update protocol, 208

Constituent encoders, 150Control channel MAC protocol, 215Control hold mode, 96, 97Coverage, 159–70

F-FCH, 162–63F-PICH, 161–62F-SCH, 163–65

interference; forward link, 165interference: reverse link, 168introduction, 159–61receiver sensitivity and, 169R-FCH, 165–66R-SCH, 167

Cyclic redundancy check (CRC), 18, 19,31, 51

for receipt verification, 74striping, 76, 78

DData channel, 232–33

active, 233block diagram, 233defined, 232See also Reverse traffic channel

Data rate control channel, 233–34block diagram, 233defined, 233symbols, 234See also Reverse traffic channel

Data rate control (DRC), 214Data rates

1xEV-DO, 199asymmetric, 1F-BCCH, 21F-CACH, 22F-CCCH, 19F-DCCH, 15F-FCH, 27forward traffic channel (1xEV-DO), 217F-SCH, 28–29R-CCCH, 42reverse traffic channel (1xEV-DO), 232R-FCH, 50R-SCH, 50symmetric, 1

Data units, 4–5Dedicated channel multiplex sublayer, 5Dedicated signaling: forward layer, 77–80

ARQ sublayer, 77base station, 79MAC sublayer, 78mobile station, 79SAR sublayer, 78utility sublayer, 77–78

Dedicated signaling: reverse link, 80ARQ sublayer, 80base station, 81mobile station, 80SAR sublayer, 80

Index 245

Page 266: 3G CDMA200 Wireless System Engineering

Dedicated signaling: reverse link (continued)utility layer, 80

Demultiplexers, 32Designated access mode, 68Direct spread (DS), 5Dormant mode, 96, 97DRCLock channel, 220–21

bits, multiplexing, 220–21block diagram, 222defined, 220elements, 220quality, 221See also MAC channel (1xEV-DO)

EEarly acknowledgment channel assignment

message (EACAM), 66–67fields, 67length, 67transmission, 66–67verification, 67

Effective radiated power (ERP), 161–62, 163antenna pattern dependence, 161total, 165, 180

Electronic serial number (ESN), 71Enhanced access channel (R-EACH), 8, 24,

42–45basic access mode, 44, 46block diagram, 51closed-loop power control, 119defined, 42frames, 43, 45gated transmission, 44header frame, 43, 45power control, 114–15power controlled access mode, 44, 47preamble, 44probes, 44reservation access mode, 44, 46transmission, 42

Erasure indicator bits (EIBs), 112, 113Extended supplemental channel assignment

message (ESCAM), 101assignment fields, 103field specification, 101SCCL update, 103successful reception of, 102

FForeign agent (FA), 194, 195, 196Forward common control channel (F-CCCH),

7, 19–20, 24

base station acknowledgment order, 99block diagram, 31data rate, 19defined, 19for fast acknowledgment, 67with F-QPCH, 20frames, 20function, 19monitoring, 90–91signaling data on, 57slots, 19in slotted mode, 90SRBP processing, 63–64status request message, 68

Forward common signaling channel (f-csch),58, 74

Forward dedicated control channel (F-DCCH),8, 15–16, 26

block diagram, 32data rate, 15defined, 15frames, 16power control bits, 16

Forward dedicated signaling channel (f-dsch),58, 80

Forward dedicated traffic channel (f-dtch), 58Forward fundamental channel (F-FCH), 26–27

base station acknowledgment order, 99block diagram, 32coverage, 162–63data rate, 27frames, 27, 28functions, 26–27radio configurations, 27

Forward linkcapacity, 178–85capacity gain, 34capacity improvements (IS-2000), 182–83capacity improvements (system), 183–85channel structure, 31–32channel supervision, 141–42common signaling, 74–76dedicated signaling, 77–80loading factor, 173–74modulation, 32–34physical layer, 11–34power dimension, 184–85radio configurations, 14–15signaling channels, 15–26spatial dimension, 183upper bounds interference, 165user channels, 26–31

246 Index

Page 267: 3G CDMA200 Wireless System Engineering

Walsh code lengths, 145Walsh codes assignment, 144–47See also Reverse link

Forward link (1xEV-DO), 213–26channels, 215characteristics, 213forward traffic channel/control channel,

216–19introduction, 213MAC channel, 219–21MAC layer, 213–15modulation, 225–26physical layer, 215–26pilot channel, 215–16TDM, 213, 221–25See also 1xEV-DO

Forward link power control, 107–13base station functions, 109closed-loop, 108inner loop/outer loop, 107–10mobile functions, 109multiple forward channels, 110–13operating modes, 111See also Power control

Forward pilot channel (F-PICH), 24coverage, 161–62defined, 24

Forward power control subchannel, 121Forward supplemental channel assignment

mini message (FSCAMM), 102Forward supplemental channel (F-SCH),

8, 27–31block diagram, 32characteristics, 27data rate, 28–29error protection, 31with F-DCCH, 27with F-FCH, 27frame duration, 29frames, 28–31functions, 27–28radio configurations, 28–29

Forward traffic channel/control channel(1xEV-DO), 216–19

block diagram, 218channel structure, 217–18data rates, 217formats, 216–17modulation schemes, 217preamble, 218, 219See also Physical layer (1xEV-DO)

Forward traffic channel MAC protocol,214–15

Four-slot interlacing, 225Frame error rate (FER), 162

HHadamard matrix, 143Handoffs, 123–39

access, 135–38access entry, 134–35access probe, 138add criteria, 126, 132drop criteria, 125idle, 133–34introduction, 123in private system, 134soft, 123–33

Home agent (HA), 193–94, 195, 196Home location register (HLR), 188

IIdle handoff, 133–34

active set, 133defined, 133mobile station states, 133neighbor set, 134private neighbor set, 134process, 134remaining set, 134See also Handoff

Idle state protocol, 209IEEE 802 standards, 60Initialization protocol, 208–9Initialization state, 88–89

pilot channel acquisition substate, 88–89sync channel acquisition substate, 89system determination substate, 88timing change substate, 89See also State transitions

Interferencecomponents, 165contribution, 164received power, 180upper bounds: forward link, 165

Interleaving, 31, 51International mobile subscriber identity

(IMSI), 189International Mobile Telecommunications-

2000 (IMT-2000), 1, 2International Telecommunications Union

(ITU), 1

Index 247

Page 268: 3G CDMA200 Wireless System Engineering

Interworking function (IWF), 188IP packets, 193IS-41 standard, 189, 191IS-95 standard, 1, 2, 189

defined, 189F-PCH, 16IS-2000 vs., 7–9power control, 107

IS-634 standard, 189IS-707 standard, 191IS-2000

backward compatibility, 1defined, 191forward link capacity improvements,

182–83IS-95 vs., 7–9power control, 8, 107primitives, 55protocol architecture, 2–3, 56, 85reverse link capacity improvements, 176–77signaling, 7–8traffic channels, 14transmission, 8

IS-2001, 191

LLayer 2 protocols, 60Link access control (LAC), 59, 71–83

addressing sublayer, 71, 73ARQ sublayer, 73authentication sublayer, 71, 73defined, 2interaction with layer/sublayers, 80–83receive side, 82–83SAR sublayer, 74in SRBP, 63sublayer processing, 74–80sublayers, 71–74sublayer structure, 72transmit side, 81–82in unassured delivery, 73utility sublayer, 73

Loading factor, 173–74forward link, 173–74reverse link, 173

Local area networks (LANs), 55Logical channels, 55

defined, 4designations, 5mapping, 58

Logical link control (LLC) protocol, 60Low-noise amplifiers (LNAs), 178

deploying, 178use illustration, 179

MMac channel (1xEV-DO), 219–21

channel structure, 221DRCLock channel, 220–21reverse activity channel, 219reverse power control channel, 219–20See also Physical layer (1xEV-DO)

MAC layer (1xEV-DO forward link), 213–15control channel MAC protocol, 215forward traffic channel MAC protocol,

214–15function, 213packet encapsulation, 214protocols, 213–14signaling messages, 213user data messages, 213

MAC layer (1xEV-DO reverse link), 227–29access channel MAC protocol, 228–29packet encapsulation, 229protocols, 227reverse traffic channel MAC protocol,

227–28Medium access control (MAC) sublayer,

55–68common signaling: forward link, 74common signaling: reverse link, 77dedicated signaling: forward link, 78defined, 2entities, 5introduction, 55multiplex sublayers, 57–60primary function, 55primitives, 55–57RLP, 60–63SDUs, 60SRBP, 63–64system access, 64–68

Messages, 55alert with information, 99BroadcastReverseRateLimit, 228channel assignment, 92, 98, 100, 101, 110data burst, 93enhanced origination, 104extended channel assignment, 92, 93, 98,

101, 121, 124extended global service redirection, 88extended handoff direction, 124, 126,

131, 132extended neighbor list, 128, 134, 136

248 Index

Page 269: 3G CDMA200 Wireless System Engineering

extended release, 97extended release response, 95extended supplemental channel assignment,

97, 101, 121FixedModeRequest, 214FixedModeResponse, 214forward supplemental channel assignment

mini (FSCAMM), 102general handoff direction, 110, 121, 124,

127, 131, 132general neighbor list, 128, 134, 136general page, 91, 92, 98global service redirection, 88KeyResponse, 210neighbor list, 128, 134, 136neighbor list update, 128origination, 86, 94, 99, 156PACA cancel, 94page response, 98, 156pilot strength measurement (PSMM), 125power control, 110, 121private neighbor list, 134QuickConfig, 209registration, 93, 156resource release request, 95reverse supplemental channel assignment

mini (RSCAMM), 102SectorParameters, 209service connect, 101, 110, 121service connect completion, 101service redirection, 88service request, 95supplemental channel request mini

(SCRMM), 104sync channel, 89system parameters, 89TrafficChannelAssignment, 220, 221UnicastReverseRateLimit, 228universal handoff direction, 110, 121, 124,

131–32universal neighbor list, 134, 136universal page, 91

Mobile identification number (MIN), 71Mobile IP, 193–96

3G wireless network support, 197foreign agent (FA), 194, 195, 196functionalities, 194–95home agent (HA), 193–94, 195, 196illustrated, 195protocol layers, 196See also Network architecture

Mobile station idle state, 89–91

functions, 91monitoring F-BCCH, 90–91monitoring F-CCCH, 90–91monitoring paging channel, 89monitoring quick paging channel, 90See also State transitions

Mobile station message transmission substate,93

Mobile station (MS), 187Mobile station order/message response

substate, 93Mobile station origination attempt substate, 93Mobile switching center (MSC), 188Mode transitions, 96–97

active mode, 96control hold mode, 96dormant mode, 96transitions, 97

Modulation, 1164-ary orthogonal, 52complex, 33, 34forward link, 32–34forward link (1xEV-DO), 225–26forward traffic channel (1xEV-DO), 217reverse link, 51–52reverse link (1xEV-DO), 238

Multicarrier (MC), 5Multiplex sublayers, 57–60

common channel, 57data block reception, 59dedicated channel, 57defined, 57entity interaction, 58inputs/outputs, 59

NNegative acknowledgment (NAK)

defined, 60RLP use of, 61use example, 61

Neighbor set, 128–29access handoff, 136adding pilots to, 128idle handoff, 134private, 134removing pilots from, 128–29See also Handoffs

Network architecture, 187–972G, 187–893G, 189–92mobile IP, 193–96simple IP, 192–93

Index 249

Page 270: 3G CDMA200 Wireless System Engineering

Noise power density, 160Nonslotted mode, 89

OOmnidirectional cells, 183Open-loop power control, 113–17

R-CCCH, 115R-EACH, 114reverse link (1xEV-DO), 239–40of reverse physical channels, 114reverse traffic channels, 116

Open Systems Interconnection (OSI) ReferenceModel, 3

Origination messages, 86, 94, 99, 156Orthogonal transmit diversity (OTD), 152–54

defined, 152illustrated, 153implementation, 153performance, 154See also Transmit diversity

Overhead messages protocol, 209

PPACA cancel substate, 94Packet consolidation protocol, 209Packet data calls

mobile station-originated, 100–101setup, 100supplemental channel request during, 101–4

Packet data serving mode (PDSN), 190, 192defined, 190foreign, 193, 194home, 193

Packet data transmission, 96–97Packets, 204

access channel MAC layer, 228–29control channel MAC layer, 215encapsulation, 214, 229forward channel MAC layer, 215forward traffic channel physical layer, 216guaranteed delivery of, 61IP, 193physical layer, 231, 232, 236, 237

Paging channel (F-PCH), 16, 17base station acknowledgment order on, 101monitoring, 89

Paging indicators, 17–18Parallel concatenated convolutional codes

(PCCC), 150Payload data units (PDUs), 4, 5Physical channels, 55

categories, 11

defined, 3–4designations, 4list of, 12–14mapping, 58signaling, 11, 15–26user, 11, 26–31

Physical layer1xEV-DO, 201capacity gain, 34channelization function, 11channel structure, 31–32coding functions, 11defined, 2forward link, 11–34introduction, 11–14modulation, 32–34radio configurations, 14–15reverse link, 37–53signaling channels, 15–26user channels, 26–31

Physical layer (1xEV-DO forward link),215–26

packet encapsulation, 214pilot channel, 215–16

Physical layer (1xEV-DO reverse link), 229–38access channel, 236–38channels, 229–30packet encapsulation, 229reverse traffic channel, 231–36

Pilot channel (1xEV-DO forward link),215–16

defined, 215multiplexing, 216

Pilot channel (1xEV-DO reverse link), 235Pilot channels, 24–26

acquisition substate, 88–89F-APICH, 25F-PICH, 24F-TDPICH, 25types of, 24

Pilotsadding, to active set, 126–27adding, to candidate set, 127adding, to neighbor set, 128adding, to remaining set, 129average power, 161dynamic detection threshold, 132energy, 161removing, from active set, 124–25removing, from candidate set, 127–28removing, from neighbor set, 128–29removing, from remaining set, 129

250 Index

Page 271: 3G CDMA200 Wireless System Engineering

strengths and dynamic thresholds, 130transitions between sets, 129

Pilot strength measurement message(PSMM), 125

PN codes, 32, 51for channelization, 142long, 51, 238short, 33

Point-to-point protocol (PPP), 192Positive acknowledgment (ACK), 60Power control, 107–21

closed loop, 8, 108forward link, 107–13F-QPCH, 19introduction, 107IS-95, 107of multiple forward traffic channels,

110–13open loop, 113–17reverse, 239–40reverse link: closed loop, 117–21reverse link: open loop, 113–17subchannel, 22

Power control bits, 16, 19, 22, 31, 67, 108fast Rayleigh fading and, 108multiplexed, 121reverse power control channel and, 219R-PICH, 48, 49

Power control groups, 16, 23, 24forward traffic channel in, 121for primary subchannel, 111R-PICH, 48for secondary subchannel, 111

Power controlled access mode, 44, 67–68base station, 67R-EACH problem, 68R-EACH transmission, 47

Power control subchannels, 110–13primary, 111secondary, 111structure, 110–11

Primitives, 55–57defined, 55form, 56indication, 56, 57interaction of, 83parts, 56–57request, 56

Priority access and channel assignment (PACA)cancel substate, 91, 94

Private neighbor set, 134Probe mobile, 159

omnidirectional cells and, 183three-sector cells and, 184

Processing gain, 164Protocol architecture, 2–3

1xEV-DO, 202–11illustrated, 3layers, 2other elements, 3–5

Protocol data units (PDUs)assured delivery, 73fragments, 74, 78fragments, reassembly, 74Layer 3, 74, 77padding, 73unassured delivery, 73

Pseudorandom noise codes. See PN codes

QQuadrature phase-shift keying (QPSK), 8, 22,33, 34, 223Quality indicator bits (QIBs), 112, 113Quality of service (QoS), 61Quasi-orthogonal functions (QOFs), 25, 147

defined, 147sets of, 147

Quick paging channel (F-QPCH), 7, 16–19broadcast/configuration change indicators,

18characteristics, 18–19defined, 16, 17format, 17monitoring, 90non-slotted mode, 17paging indicators, 17–18slotted mode, 17

RRadio configurations, 14–15

F-FCH, 27on forward link, 14F-SCH, 28–29reverse link, 39–40R-SCH, 50

Radio environment report, 73Radio Link Protocol (RLP), 4, 5, 55, 60–63

best effort transport, 71, 205defined, 55, 60illustration, 61–62as Layer 2 protocol, 60, 191specification, 191standards family, 62

Receive diversity, 178

Index 251

Page 272: 3G CDMA200 Wireless System Engineering

Received signal power, 171–73R-FCH, 171R-SCH, 172

Receiver sensitivity, 169Recursive systematic convolutional (RSC)

encoder, 150Recursive tree, 143, 144Registration access substate, 93Registration request order, 93Release substate, 95Remaining set

access handoff, 136idle handoff, 134soft handoff, 129See also Handoffs

Reservation access mode, 44, 65–67access header, 66header fields, 66R-EACH probe, 66R-EACH transmission, 46

Retransmissiondefined, 60RLP use of, 61use example, 61

Reverse activity channel, 219block diagram, 222defined, 219reverse activity bits, 219See also MAC channel (1xEV-DO)

Reverse common control channel (R-CCCH),8, 21, 24, 41–42

block diagram, 51closed-loop power control, 119data rate, 42defined, 42frames, 42, 43gated transmission, 42power control, 115preamble, 42transmission illustration, 44

Reverse common signaling channel (r-csch),58, 77

Reverse dedicated control channel (R-DCCH),8, 21, 40–41

block diagram, 51defined, 40frames, 40–41power control, 116SDU assembly, 59, 60

Reverse dedicated signaling channel (r-dsch),58, 80

Reverse dedicated traffic channel (r-dtch), 58

Reverse fundamental channel (R-FCH), 50block diagram, 51coverage, 165–66frames, 50functions, 50power control, 116received signal power, 171–72

Reverse linkcapacity, 174–78capacity gain, 52–53capacity improvements (IS-2000), 176–77capacity improvements (system), 177–78channel supervision, 142common signaling, 76–77dedicated signaling, 80loading factor, 173logical/physical channel mapping, 58modulation, 51–52multiple traffic channels, 175power dimension, 177radio configuration, 39–40rise, 166spatial dimension, 177upper bounds interference, 168Walsh code assignment, 147–50See also Forward link

Reverse link (1xEV-DO), 227–40access channel, 236–38channelization, 230channels, 229–30characteristics, 227introduction, 227MAC layer, 227–29modulation, 238physical layer, 229–38power control, 239–40reverse power control, 239–40reverse traffic channel, 231–36slot structure, 231See also 1xEV-DO

Reverse link physical channelscategories, 37common, 37dedicated, 37list of, 38–39R-CCCH, 41–42R-DCCH, 40–41R-EACH, 42–45R-FCH, 50R-PICH, 45–49R-SCCH, 49R-SCH, 50

252 Index

Page 273: 3G CDMA200 Wireless System Engineering

signaling, 37, 40–49structure, 50–51user, 37, 49–50

Reverse link power control, 113–21base station functions, 119closed-loop, 117–21illustrated, 117inner loop, 118mobile functions, 120multiple reverse channels, 113–16, 119–21open loop, 113–17outer loop, 118R-CCCH, 115, 119R-EACH, 114–15, 119reverse traffic channel, 116, 120–21See also Power control

Reverse pilot channel (R-PICH), 8, 45–49defined, 45format illustration, 48gated transmission, 47gating, 48–49gating illustration, 49gating rate, 48power control, 47power control bits, 48, 49power control groups, 48power control subchannel, 47–48power measurement report messages, 47transmit power, 116uses, 45

Reverse power control (1xEV-DO), 239–40closed-loop, 240open-loop, 239–40

Reverse power control channel, 219–20block diagram, 222defined, 219quality, 220for sending power control bits, 219See also MAC channel (1xEV-DO)

Reverse rate indicator channel, 235Reverse supplemental channel assignment mini

message (RSCAMM), 102Reverse supplemental channel (R-SCH), 8, 50

block diagram, 51changing transmission rate on, 149characteristics, 50coverage, 167frame, 50power control, 116received signal power, 172use, 167, 176

Reverse traffic channel, 231–36

ACK channel, 235–36data channel, 232–33data rate control channel, 233–34data rates, 232elements, 229–30physical layer packet, 231, 232pilot channel, 235reverse rate indicator channel, 235See also Reverse link (1xEV-DO)

Reverse traffic channel MAC protocol, 227–28defined, 227open state, 228setup state, 227–28See also MAC layer (1xEV-DO reverse link)

Route update protocol, 208

SSectorization, 178Security layer (1xEV-DO), 210Segmentation and reassembly (SAR) sublayer,

74common signaling: forward link, 74common signaling: reverse link, 77dedicated signaling: forward link, 78dedicated signaling: reverse link, 80defined, 74

Service data units (SDUs), 4, 5Layer 3, 77MAC sublayer passing, 60R-DCCH, 59, 60

Service option connection, 95Session layer (1xEV-DO), 205–6Shared secret data (SSD), 93Signaling, 7–8

channel setup, 97–104dimensions, 86entity, 86, 87functions, 86mode transitions, 96–97state transitions, 87–95upper layers, 85–104

Signaling channelsdefined, 11F-APICH, 25F-ATDPICH, 25–26F-BCCH, 20–21F-CACH, 21–22F-CCCH, 19–20F-CPCCH, 22–24F-DCCH, 15–16forward link, 15–26F-QPCH, 16–19

Index 253

Page 274: 3G CDMA200 Wireless System Engineering

Signaling channels (continued)F-TDPICH, 25R-DCCH, 40–41reverse link, 37, 40–49See also Physical layer

Signaling LAC, 71–83Signaling Radio Burst Protocol (SRBP), 3, 4, 5,

63–64access probes, 63channels controlled by, 63function, 55processing at base station, 64SDUs, 63

Slotted mode, 89, 90Smart antenna schemes, 177Soft handoff, 123–33

active set, 124–27candidate set, 127–28defined, 123example, 129–33example illustration, 131illustrated, 124neighbor set, 128–29process management, 123remaining set, 129set transitions, 129See also Handoffs

Space time spreading (STS), 152, 154–56defined, 154illustrated, 154implementation, 155performance, 156See also Transmit diversity

Spot beams, 25Spreading, 51

codes, 51space time, 154–55

Spreading Rate 1, 144defined, 5illustrated, 6, 7on reverse link, 7

Spreading Rate 3defined, 5on forward link, 7illustrated, 6, 7implementation options, 5

State transitions, 87–95air link management protocol, 207initialization state, 88–89at the mobile, 87mobile station idle state, 89–91system access state, 91–94

top-level, 87traffic channel state, 94–95

Stream layer (1xEV-DO), 205Supplemental channel assignment

base station initiation, 102mobile station initiation, 103

Supplemental channel code list (SCCL),101, 103

Supplemental channel request mini message(SCRMM), 104Symmetric data rates, 1Sync channel acquisition substate, 89Sync channel messages, 89System access, 64–68

access mode types, 64basic access mode, 65designated access mode, 68PACA cancel substate, 94power controlled access mode, 67–68reservation access mode, 65–67See also Medium access control (MAC)

sublayerSystem access state, 91–94

mobile station message transmissionsubstate, 93

mobile station order/message responsesubstate, 93

mobile station origination attempt substate,93

normal transitions, 92page response substate, 92–93registration access substate, 93update overhead information substate,

91–92See also State transitions

System designcapacity, 171–85coverage, 159–70purpose, 159

System determination substate, 88System performance, 141–56

channel supervision, 141–42code management, 142–50transmit diversity, 152–56turbo codes, 150–52

TThird generation (3G) systems, 1

turbo codes in, 151See also 3G networks

Three-sector cells, 184

254 Index

Page 275: 3G CDMA200 Wireless System Engineering

Time division multiplexing (TDM), 213,221–25

chip stream, 222, 223chip stream example, 224illustrated, 223output, 225slot structure, 223

Timing change substate, 89Total power density, 160Traffic channels

IS-2000, 14reverse link, 175supervision, 141–42

Traffic channel state, 94–95initialization substate, 94release substate, 95substate, 94–95See also State transitions

Transcoding, 188Transitions, 97Transmission control protocol (TCP), 192Transmit diversity, 25, 26, 152–56

orthogonal, 152–54space time spreading, 154–56

Transmit diversity pilot channel(F-TDPICH), 25

Turbo codes, 8, 150–52in 3G systems, 151characteristics, 150defined, 150for supplemental channels, 151–52

UUnassured delivery, 73Universal Mobile Telephone System (UMTS), 1Update overhead information substate, 91–92Upper layer

defined, 2signaling, 85–104

User channelsdefined, 11

F-FCH, 26–27forward link, 26–31F-SCH, 27–31reverse link, 37, 49–50R-FCH, 50R-SCCH, 49R-SCH, 50See also Physical layer

User datagram protocol (UDP), 192Utility sublayer

in common signaling, 74common signaling: reverse link, 77dedicated signaling: forward link, 77–78dedicated signaling: reverse link, 80defined, 73functions, 73See also Link access control (LAC)

VVisitor location register (VLR), 188Voice calls

base station-originated, 98–99mobile station-originated, 99–100

WWalsh codes, 24, 25, 26, 32, 234, 236

assignment of, 144–47for channelization, 52, 53chip rate, 51deriving, 143generation of, 143–44lengths of, 145multiplying with, 33predefined, 149, 150short, 34simultaneous use, 146

XX.25 standard, 60

Index 255

Page 276: 3G CDMA200 Wireless System Engineering

.

Page 277: 3G CDMA200 Wireless System Engineering

Recent Titles in the Artech HouseMobile Communications Series

John Walker, Series Editor

3G CDMA2000 Wireless System Engineering, Samuel C. Yang

3G Multimedia Network Services, Accounting, and User Profiles, Freddy Ghys,Marcel Mampaey, Michel Smouts, and Arto Vaaraniemi

Advances in 3G Enhanced Technologies for Wireless Communications,Jiangzhou Wang and Tung-Sang Ng, editors

Advances in Mobile Information Systems, John Walker, editor

CDMA for Wireless Personal Communications, Ramjee Prasad

CDMA Mobile Radio Design, John B. Groe and Lawrence E. Larson

CDMA RF System Engineering, Samuel C. Yang

CDMA Systems Engineering Handbook, Jhong S. Lee andLeonard E. Miller

Cell Planning for Wireless Communications, Manuel F. Cátedra andJesús Pérez-Arriaga

Cellular Communications: Worldwide Market Development,Garry A. Garrard

Cellular Mobile Systems Engineering, Saleh Faruque

The Complete Wireless Communications Professional: A Guide for Engineers andManagers, William Webb

EDGE for Mobile Internet, Emmanuel Seurre, Patrick Savelli, and Pierre-Jean Pietri

Emerging Public Safety Wireless Communication Systems,Robert I. Desourdis, Jr., et al.

The Future of Wireless Communications, William Webb

GPRS for Mobile Internet, Emmanuel Seurre, Patrick Savelli, and Pierre-Jean Pietri

GPRS: Gateway to Third Generation Mobile Networks,Gunnar Heine and Holger Sagkob

GSM and Personal Communications Handbook, Siegmund M. Redl,Matthias K. Weber, and Malcolm W. Oliphant

GSM Networks: Protocols, Terminology, and Implementation, Gunnar Heine

GSM System Engineering, Asha Mehrotra

Handbook of Land-Mobile Radio System Coverage, Garry C. Hess

Handbook of Mobile Radio Networks, Sami Tabbane

Page 278: 3G CDMA200 Wireless System Engineering

High-Speed Wireless ATM and LANs, Benny Bing

Interference Analysis and Reduction for Wireless Systems,Peter Stavroulakis

Introduction to Digital Professional Mobile Radio, Hans-Peter A. Ketterling

Introduction to 3G Mobile Communications, Second Edition,Juha Korhonen

Introduction to GPS: The Global Positioning System, Ahmed El-Rabbany

An Introduction to GSM, Siegmund M. Redl, Matthias K. Weber,and Malcolm W. Oliphant

Introduction to Mobile Communications Engineering, José M. Hernando andF. Pérez-Fontán

Introduction to Radio Propagation for Fixed and Mobile Communications,John Doble

Introduction to Wireless Local Loop, Second Edition: Broadband and NarrowbandSystems, William Webb

IS-136 TDMA Technology, Economics, and Services, Lawrence Harte, Adrian Smith,and Charles A. Jacobs

Location Management and Routing in Mobile Wireless Networks,Amitava Mukherjee, Somprakash Bandyopadhyay, and Debashis Saha

Mobile Data Communications Systems, Peter Wong and David Britland

Mobile IP Technology for M-Business, Mark Norris

Mobile Satellite Communications, Shingo Ohmori, Hiromitsu Wakana, andSeiichiro Kawase

Mobile Telecommunications Standards: GSM, UMTS, TETRA, and ERMES,Rudi Bekkers

Mobile Telecommunications: Standards, Regulation, and Applications,Rudi Bekkers and Jan Smits

Multiantenna Digital Radio Transmission, Massimiliano “Max” Martone

Multipath Phenomena in Cellular Networks, Nathan Blaunstein andJørgen Bach Andersen

Multiuser Detection in CDMA Mobile Terminals, Piero Castoldi

Personal Wireless Communication with DECT and PWT, John Phillips andGerard Mac Namee

Practical Wireless Data Modem Design, Jonathon Y. C. Cheah

Prime Codes with Applications to CDMA Optical and Wireless Networks,Guu-Chang Yang and Wing C. Kwong

QoS in Integrated 3G Networks, Robert Lloyd-Evans

Page 279: 3G CDMA200 Wireless System Engineering

Radio Engineering for Wireless Communication and Sensor Applications,Antti V. Räisänen and Arto Lehto

Radio Propagation in Cellular Networks, Nathan Blaunstein

Radio Resource Management for Wireless Networks, Jens Zander andSeong-Lyun Kim

RDS: The Radio Data System, Dietmar Kopitz and Bev Marks

Resource Allocation in Hierarchical Cellular Systems, Lauro Ortigoza-Guerrero andA. Hamid Aghvami

RF and Microwave Circuit Design for Wireless Communications, Lawrence E.Larson, editor

Sample Rate Conversion in Software Configurable Radios, Tim Hentschel

Signal Processing Applications in CDMA Communications, Hui Liu

Software Defined Radio for 3G, Paul Burns

Spread Spectrum CDMA Systems for Wireless Communications, Savo G. Glisic andBranka Vucetic

Third Generation Wireless Systems, Volume 1: Post-Shannon Signal Architectures,George M. Calhoun

Traffic Analysis and Design of Wireless IP Networks, Toni Janevski

Transmission Systems Design Handbook for Wireless Networks,Harvey Lehpamer

UMTS and Mobile Computing, Alexander Joseph Huber andJosef Franz Huber

Understanding Cellular Radio, William Webb

Understanding Digital PCS: The TDMA Standard, Cameron Kelly Coursey

Understanding GPS: Principles and Applications, Elliott D. Kaplan, editor

Understanding WAP: Wireless Applications, Devices, and Services, Marcel van derHeijden and Marcus Taylor, editors

Universal Wireless Personal Communications, Ramjee Prasad

WCDMA: Towards IP Mobility and Mobile Internet, Tero Ojanperä andRamjee Prasad, editors

Wireless Communications in Developing Countries: Cellular and Satellite Systems,Rachael E. Schwartz

Wireless Intelligent Networking, Gerry Christensen, Paul G. Florack, andRobert Duncan

Wireless LAN Standards and Applications, Asunción Santamaríaand Francisco J. López-Hernández, editors

Page 280: 3G CDMA200 Wireless System Engineering

Wireless Technician’s Handbook, Second Edition, Andrew Miceli

For further information on these and other Artech House titles,

including previously considered out-of-print books now available through our

In-Print-Forever® (IPF®) program, contact:

Artech House Artech House

685 Canton Street 46 Gillingham Street

Norwood, MA 02062 London SW1V 1AH UK

Phone: 781-769-9750 Phone: +44 (0)20 7596-8750

Fax: 781-769-6334 Fax: +44 (0)20 7630-0166

e-mail: [email protected] e-mail: [email protected]

Find us on the World Wide Web at:www.artechhouse.com