CDMA3G-1X RF Engineering

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Flexent /AUTOPLEX Wireless NetworksCDMA 3G-1X RF Engineering Guidelines

401-614-040Issue 2

February 2003


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Contents

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About

Purpose iReason for reissue iiRelated information products iiiRelated training iii

To obtain technical support, documentation, and training orsend feedback ivNotations used iv

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1 Discussion of CDMA 3G-1X RF engineering 1-1

Introduction 1-2

Capacity and coverage for voice applications 1-4

Spectrum requirements 1-4Link budget 1-4Voice capacity 1-5

RF engineering for data 1-6

Introduction 1-6Overview of traffic theory 1-7Data link budget 1-8Resource management 1-9Deployment 1-9

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2 Voice coverage, capacity and link budget 2-1

Introduction 2-2

Analysis 2-4

Reverse link 2-4Forward link 2-20

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3 RF engineering for data 3-1

Introduction 3-3

Traffic theory 3-4

Introduction 3-4


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General Erlang model 3-5Special cases: Erlang B and Erlang C 3-7Applications of Erlang C to 3G-1X data 3-10

Data capacity 3-13

Introduction 3-13Data link budgets 3-19

Reverse link 3-19Forward link 3-22

Resource management: RF scheduling 3-36

Introduction 3-36Scheduling algorithm 3-36Conclusions 3-43

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4 System deployment 4-1

Introduction 4-2

Spectrum use: Carrier assignments and guard band 4-4

Cellular band 4-4PCS band 4-8Preferred channels 4-10

2G/3G-1X spatial and frequency design 4-11

Coverage (spatial) design: overlay and greenfield 4-11Frequency design 4-13

Mixed 3G-1X voice/data capacity and coverage 4-19............................................................................................................................................................................................................................................................

5 Handoff 5-1

Introduction 5-3

Soft handoff definition 5-3Procedure 5-3IS-95B soft handoff algorithm 5-6Signal combining 5-8Coverage contour 5-8

Discussion 5-12

Soft handoff costs on channel elements and packet pipe 5-12Soft handoff cost on forward link 5-12Soft handoff advantages 5-13Qualitative description of forward link soft handoff benefit 5-22IS-95B parameters 5-25

SOFT_SLOPE, DROP_INTERCEPT, ADD_INTERCEPT 5-30SCH anchor transfer vs. SHO 5-31Hard handoffs 5-36

References 5-37............................................................................................................................................................................................................................................................

6 Power control 6-1

Introduction 6-2


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Reverse power control 6-4

Reverse power control for voice traffic 6-5RPC for packet data traffic 6-8Reverse SARA for 3G-1X packet data calls 6-9

Forward power control 6-11

Forward power control for voice traffic 6-12Forward power control for packet data traffic 6-15............................................................................................................................................................................................................................................................

7 Extended carrier 7-1

Introduction 7-3

Single extended carrier 7-6

Reverse link 7-6Forward link 7-8Forward Data Capacity 7-14Growth strategies 7-15Applications 7-18

Concentric carriers 7-19Core carrier reverse link 7-20Core carrier forward link 7-23Traffic density 7-25Determining mobile location 7-25Growth strategies 7-26Applications 7-26

Amplifier sharing - Quasi omni 7-28

Growth strategies 7-29Amplifier sharing - Asymmetric cell 7-31

Growth strategies 7-32Summary 7-33

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8 Fixed wireless voice networks 8-1

Introduction 8-2

Parameters for fixed wireless analysis 8-3

Reverse link interference ratio (br) 8-3Required reverse link Eb/Nt for 3G 8-4Walsh code overhead 8-6Recommended loading factor 8-8Channel activity factor 8-8

Reverse link coverage 8-9System capacity calculation 8-10

Capacity calculation methodology 8-10Reverse link based capacity calculations 8-11

Power requirements of forward link 8-17

3G-1X RC3 8-173G-1X RC4 8-21


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3G-1X with SMV 8-21Conclusions 8-23

References 8-24


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About this information product

Purpose This document, CDMA 3G-1X RF Engineering Guidelines , addressesselected radio frequency engineering topics for the Lucentimplementation of CDMA2000-1X, also known as CDMA 3G-1X, orsimply 3G-1X.

3G-1X is a first-phase implementation of an IS-95 based, third

generation CDMA network that complies with the recommendationsfor third generation wireless systems advanced by the ITU. Inparticular, 3G-1X offers both voice and data capabilities that aresignificantly improved with respect to IS-95 (second generation or 2G)offerings. Voice capacity is increased, offering up to twice the Erlangcapacity per Hz achieved by IS-95. Features allowing burst speeds of up to 153.6 kbps for packet-switched data are also provided, in contrastto the maximum 14.4 kbps circuit-switched capability provided inIS-95. Furthermore, voice and data users can coexist within the samewideband carrier.

In spite of the differences, many RF engineering principles of 3G-1Xremain comparable to those of IS-95, particularly for voiceapplications. For example, the frequency reuse remains at 1. Voice link budget and voice capacity analyses are similar. Management of cochannel interference remains key for both voice and data users, and


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is accomplished through application of familiar IS-95 principles suchas fast power control, variable-rate voice coding, and careful network optimization.

Accordingly, this document does not offer extensive discussions of

topics with strong IS-95 counterparts; rather, in such cases, thedifferences relative to 3G-1X implementation are emphasized. Moredetailed information on IS-95 can be found in Lucent documents401-614-012, AUTOPLEX Cellular CDMA RF EngineeringGuidelines , 401-703-201, PCS CDMA RF Engineering Guidelines , aswell as TIA/EIA/IS-2000A standards. In contrast, much attention isdevoted to topics without clear IS-95 analogues, such as the RFengineering issues associated with the advent of wireless packet data.These include packet data coverage, coexistence of voice and datausers within the same carrier, and allocation of communicationresources such as power amongst competing data users.

Reason for reissue Starting from Issue 2, the information in this document is divided intotwo parts. Part I includes the updated information for Issue 1 of thisdocument. Part 2 introduces the following new chapters.

Chapter 5: Handoff

Chapter 6: Power Control

Chapter 7: Extended Carrier

Chapter 8: Fixed Wireless Voice Networks

Intended audience This document is intended for engineers who will be responsible forsystem design and performance analysis of a Lucent Technologies3G-1X system.

How to use this informationproduct

This document is organized as follows:

Part I, which consists of Chapters 1 through 4, provides a system-level picture of 3G-1X RF engineering.

Chapter 1, Overview, provides a brief overview of Part I Chapter 2, Voice Coverage/Capacity/Link Budget,

discusses the essential coverage and capacity issues for voiceapplications

Chapter 3, RF Engineering for Data, offers a discussion of RF data issues for 3G-1X, including a contrast between theErlang B (voice) and Erlang C (data) models, analysis of capacity and coverage, and an examination of resourcemanagement


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Chapter 4, System Deployment, describes deploymentissues, with focus on transition from 2G to 3G-1X

Part II, which consists Chapters 5 through 8, provides morespecialized discussions on individual topics such as power controland soft handoff.

Chapter 5, Handoff, discusses the soft handoff procedures,algorithms, coverage, cost and benefit for the CDMA 3G-1Xvoice and packet data calls

Chapter 6, Power Control, describes the power controlfunctions for both the forward link and reverse links for theCDMA 3G-1X voice and packet data calls

Chapter 7, Extended Carrier, provides guidelines for RFplanning for extended carrier deployment

Chapter 8, Fixed Wireless Voice Networks, provides a

detailed analysis of the system performance of 2G and 3G-1X CDMA fixed wireless voice networks.

Related informationproducts

The Lucent document 401-610-000, Flexent /AUTOPLEX Wireless Networks Documentation Guide , provides a brief overview of eachinformation product that supports Flexent /AUTOPLEX wirelessnetworks systems, products, and features.

The following Flexent /AUTOPLEX wireless networks informationproducts are either referenced in this information product or provideadditional information that relates to the Prepaid Services feature:

401-614-012, AUTOPLEX Cellular CDMA RF EngineeringGuidelines

401-703-201, PCS CDMA RF Engineering Guidelines

TIA/EIA/IS-2000A, family of standards for CDMA2000Standards for spread Spectrum SystemsGlobal Engineering Documents1-800-854-71791-303-397-7956

Related training Lucent Technologies offers the following training products that relateto CDMA RF design and operation:

CL3715, Understanding CDMA

CL8301, CDMA IS-95 and 3G-1X RF Design and Growth Engineering for Cellular System

CL8302, CDMA IS-95 and 3G-1X RF Design and Growth Engineering for PCS System


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CL8303, CDMA IS-95 and 3G-1X Base Station Call Processing

CL8304, 3G-1X RF Design Engineering and Base Station CallProcessing .

To obtain technical

support, documentation,and training or send

feedback

The current release of the Flexent /AUTOPLEX wireless networks

documentation is provided on the Lucent Technologies wirelessnetworks customer technical support web site to all customers free of charge. To access the site, please visit:

https://wireless.support.lucent.com

To provide the most current, complete, and technically accuratedocumentation to customers as quickly as possible, revisions andupdates of information products on the current release of the401-010-001 Flexent /AUTOPLEX Wireless Networks Electronic Documentation CD-ROM are also provided on the site for allcustomers free of charge.

For details on obtaining technical support, documentation, and trainingor sending feedback, refer to document To Obtain Technical Support, Documentation, and Training or Send Feedback .

Notations used Notations used in this document are listed below.

AG = Cell site antenna gain in dBi BL/VL = Building or vehicle penetration loss in dB, whichever is applicableCL = Cell site cable loss in dB

d = The Eb/Nt required for acceptable qualityEb/Nt = The ratio of channel bit energy to spectral density of total channelimpairmentF = The receiver noise figureF mobile = The mobile receiver noise figureF cell = The base station receiver noise figureFade = Fade (in dB) at mobile locationg = The spread spectrum processing gaingnet = The net gain consisting of the product of mobile antenna gains, body

(head) loss, building/vehicle penetration loss, cell site antenna gain, and cellsite cable loss HL = Head (body) loss in dBint = The dB path loss at a 1 km reference pointk = The multiplier used in a Gaussian distribution to achieve a certain percen-tile; for example, k =1.3 corresponds to a 1.3 choice which yields a 90 th per-centileM = The length of queue for the general Erlang model N = The number of active channels
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N max = pole capacity N o = Thermal noise density N sect = The total number of sectors N k = The total number of mobiles in sector k

N total = The total number of mobiles within the network N links = The number of links per sector N suppl = The number of supplemental links N fund = The number of fundamental linksP host = The mobile received power from its host or serving sectorP other = The mobile received power from surrounding non-serving sectorsPL = Point to point (average) path loss in dB between mobile antenna and cellsite antennaQ total = The current (steady-state) average power radiated at the J4 portQmax = The maximum average power allowed at the J4 port before overload

(blocking) occursQover = The constant overhead powerr i = The random position of the ith mobile within the cell R = The cell radius Ri = The channel bit rate of the ith mobileSi = The base station received power from the ith mobileSmin = The minimum receiver sensitivitysij = The distance from the jth surrounding cell to the ith mobileu = Loading factorW = The carrier bandwidth

wmax = The maximum mobile power into the mobile antenna xij = Link (traffic channel) power as measured at the J4 port for the jth mobile

in the ith sector X max = Maximum mobile transmit power (in dBm) out of mobile antenna xi = A sample drawn from a Gaussian (0,8) distribution, thus corresponding to

a dB fade drawn from lognormal fading statistics with a 0 dB mean and 8 dBstandard deviationY = A random number defined in Equation 2-19 i = The channel activity factor for the ith mobile ij = The channel activity of the jth mobile in the ith sector

a k ;ij = The attenuation from the k th sector to the jth mobile in the ith sector , reverse = The ratio of other cell interference to serving cell interference forthe reverse link

i = The ratio of other cell interference to serving cell interference plusreceiver noise floor for the forward link

omni = The ratio of other cell interference to serving cell interference for theforward link and omni antenna configuration


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i = The fraction of the mobile received host power dedicated to the ith trafficchannel = r/R

= The orthogonality factor = The average arrival rate for the general Erlang model a = The mean of b = The mean of a = The standard deviation of b = The standard deviation of = The fixed fraction of the maximum average power dedicated to the over-head channels

= s/R = The average server completion (of service) rate for the general Erlangmodel

d id d i / =

gig gi / =


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1 Discussion of CDMA 3G-1X RF

engineering

............................................................................................................................................................................................................................................................Overview

Objectives This chapter provides a brief overview of Part I of this document,which consists of Chapters 1 through 4.

Contents Introduction 1-2

Capacity and coverage for voice applications 1-5

Spectrum requirements 1-5Link budget 1-5Voice capacity 1-6

RF engineering for data 1-7

Introduction 1-7Overview of traffic theory 1-8Data link budget 1-9Resource management 1-10Deployment 1-10


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Discussion of CDMA 3G-1X RF engineeringIntroduction

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............................................................................................................................................................................................................................................................Introduction

The ITU-2000 recommendation calls for third generation wirelesscommunication systems with a number of features. These includeenhanced voice capacity as well as wireless packet data features, withthe latter offering rates of up to 144 kbps for outdoor mobilesubscribers.

CDMA2000 (also known as CDMA3G) is an IS-95 based standard thatsatisfies ITU recommendations. This standard allows for a phasedimplementation of 3G capabilities. CDMA 3G-1X RF EngineeringGuidelines summarizes the radio frequency engineering aspects of theLucent implementation of the first phase, known as CDMA2000-1X, orCDMA3G-1X. This implementation offers enhanced voice capacity as

well as wireless packet data at burst speeds of up to 153.6 kbps. Voiceand data users can coexist within the same 3G-1X carrier.

The Lucent implementation of 3G-1X will support existing IS-95 (2G)services of voice and circuit-switched data as well as 3G-1X voice andpacket switched data. The 3G-1X voice will provide improvedcapacity, expected to be greater by up to a factor of two in terms of supported Erlangs. The 3G-1X packet data service supports access tothe Internet via the IP protocol.

The 3G-1X and IOS (Inter-Operability Specification) Packet Data

services feature(s) provides a subscriber the ability to transmit andreceive data with raw rates of up to 153.6 kbps over a packet datanetwork via the 3G-1X IS-2000 air interface.

The 3G-1X Packet Data feature(s) enable mobile users with laptopcomputers or other data devices conforming to the IS-2000 andIS-707A1 standards to access various data applications, such asInternet access, Intranet access, Database access, e-mail, and filetransfer at higher speed.

The 3G-1X physical layer incorporates a number of majorenhancements that provide for higher data rates and better spectralefficiencies compared to second generation CDMA systems. A burst-mode capability is defined to allow better interference management andcapacity utilization. An active high-speed packet data mobile alwayshas a traffic channel using a Fundamental Cod e. This channel is calledthe Fundamental Channel (FCH). An active Packet Data call with theneed for higher bandwidth, either in the forward or reverse direction,


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could be allocated an additional channel for the duration of a data burst ,whose duration can be up to a few seconds. The additional channelduring this state is called the Supplemental Channel (SCH). A widerange of data rates (raw data rates of 9.6 to 153.6 kbps) is supportedover each SCH. One SCH is assigned per data service. An SCH with a

data rate of 19.2 kbps or higher is equivalent to multiple voice callsfrom the consideration of air interface capacity.

The assignment of the SCH, along with its data rate, is controlled bythe infrastructure based on system load and interference conditions.Static allocation of multiple codes to a small number of users can resultin inefficient use of CDMA air interface capacity. Dynamicinfrastructure-controlled burst allocation makes it possible toefficiently share the bandwidth among several high-speed packet datamobiles. Efficient algorithms to support dynamic burst allocation havebeen developed by Lucent. The burst allocation scheme is designed tomaximize utilization of CDMA channel bandwidth and systemresources. As has been determined during the extensive design processfor Lucent Technologies HSPD (High Speed Packet Data) Service, thepotential risks and issues that arise in designing the packet data service(especially risks of voice quality impact) are minimal, and are easilymanageable with minimal impact on voice or data capacity.

The data rate and duration of the burst (i.e., the supplemental channel)will be dynamically determined by the infrastructure, depending onload, interference, and resource availability conditions. Therefore, the

supplemental channel does not offer any guaranteed bit rate. However,the data rate offered by the fundamental channel with raw data rate of 9.6 kbps is always guaranteed to the 3G-1X data user. For the forwarddirection, the burst allocation is triggered when data gets backlogged inthe network side of the system. For the reverse direction, data builds upat the mobile, which in turn sends a supplemental channel requestmessage to the system, triggering the burst allocation procedure.

The new service can be asymmetri c, i.e., the high speed packet datamobile, at any given instant, may be assigned different bandwidths onthe forward and reverse link s. This helps to maximize the efficient useof bandwidth in both directions, still meeting the bandwidth demand of the end-user in each direction. The 3G-1X CDMA HSPD product isbuilt on the 2G/3G CDMA Low Speed Packet Data (LSPD) softwaresince the operation of the fundamental channel and packet data callsetup and tear-down procedures are almost identical to the LSPDservice when there is no data burst in progress. To end users, the mostvisible advantage of HSPD over LSPD releases is speed.


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Discussion of CDMA 3G-1X RF engineeringCapacity and coverage for voice applications


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............................................................................................................................................................................................................................................................Capacity and coverage for voice applications

Spectrum requirements Spectrum requirements for 3G-1X are modest and identical to those foran IS-95 carrier. 3G-1X requires a 1.23 MHz carrier in the cellular bandor a 1.25 MHz carrier in the PCS band, with a recommended guardband of 270 kHz between the CDMA and AMPS carriers in the cellularband, and a guard band of 625 kHz (~ carrier) on either side of thePCS block. The guard band recommended is typical, and may berelaxed or expanded depending upon the specific wireless applicationsin contiguous spectrum. In most cases, it is anticipated that the 270 kHzfor the cellular band or 625 kHz for the PCS band should be sufficient.

As in IS-95 engineering, no guard band is required between contiguous3G-1X carriers. Additionally, no guard band is required between an IS-

95 carrier and an adjacent 3G-1X carrier. 3G-1X and IS-95 subscribersmay, in fact, share the same carrier frequency with concomitant effectson each technology's capacity. This strategy is discussed further inChapter 4, "System deployment" .

Link budget 3G-1X voice coverage is essentially determined via link budgetanalysis, which follows a strategy comparable to that pursued in IS-95applications. The cell footprint is first sized using the reverse link,which properly takes into account the impact of limited mobile transmitpower. Forward link budget analysis focuses on ensuring that sufficientforward power is available to support operations within the footprintdictated by the reverse link.

The link budgets used for voice coverage follow a format similar to thatfor IS-95; however, key parameters differ in value and meaning. Forexample, the receiver Eb/Nt requirement used to determine cell sitereceiver sensitivity is based on the total mobile transmit power, ratherthan the fraction of mobile power dedicated to the traffic channel(unlike IS-95, the uplink consists of both a traffic channel and a pilotchannel). In addition, a more aggressive loading with respect to thepole point is allowed due to the inherently greater number of users

within a single carrier. These topics are discussed in greater detail inChapter 2, "Voice coverage, capacity and link budget" , which derivesboth forward and reverse link budgets. A comparison is also drawnbetween 3G-1X and IS-95 coverage. The slight improvement offeredby 3G coverage is key to a 2G to 3G (i.e., IS-95 to 3G-1X) migrationstrategy, as discussed in Chapter 4, "System deployment" .


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Voice capacity The analysis of 3G-1X voice capacity is also similar to that of IS-95,albeit with different values of key parameters. In particular, relaxed Eb/ Nt requirements on both links drive Erlang capacity/Hz up to twice thevalue available for IS-95, i.e., up to 26.4 Erlangs per 1.23 MHz carrierfor an 8 kbps vocoder. The improved Eb/Nt requirements derive from a

number of air interface features, such as enhanced convolutionalcoding, faster power control, and a reverse link pilot channel thatprovides a reference signal to aid in signal demodulation. The analysisof 3G-1X capacity is coupled to that of 3G-1X coverage, since both areultimately driven by Eb/Nt requirements on each link. This analysis ispresented in some detail in Chapter 2, "Voice coverage, capacity andlink budget" .


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Discussion of CDMA 3G-1X RF engineeringRF engineering for data


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............................................................................................................................................................................................................................................................RF engineering for data

Introduction Unlike voice applications, the analysis of RF engineering issues forwireless packet data has no ready analogue in IS-95. This discussiontherefore occupies a major portion of these guidelines. Key differencesinclude the use of packet-switched rather than circuit-switched dataprinciples, subscriber time-sharing of the same data channel, and newmeasures of capacity that vary widely with subscriber usage statistics.

From a simple overall perspective, a collection of 3G-1X data userswithin the cell footprint are subscribers engaging in data sessions (e.g.,web-browsing) that are inherently bursty in nature. Each user maintainsa constant low-rate data connection (fundamental channel) to the cell inorder to maintain the call, provide infrequent signaling frames, and

occasionally aid in data transmission. For example, in an 8 kbpssystem, the fundamental channel operates at 1/8 rate on a 9.6 kbpschannel, powering to full-rate when signaling information is present.

In addition, each subscriber intermittently transmits bursts of data at amuch higher rate. This rate is negotiated for each burst between themobile and base station in a process that takes into account a number of factors including the current interference background, the mobiles RFconditions, the amount of data that needs to be sent, and the history of the data session (i.e., when the user was last served). These bursts takeplace over supplemental channels that are set up and torn down asnecessary, with raw data rates ranging up to 153.6 kbps.

Since the system can simultaneously support only a limited number of supplemental channels due to the higher data rate, this dynamic processof allocating and removing supplemental channels to each user can beviewed as time-sharing a small number of high-speed data pipesamongst the users. In this model, the user transmissions queue up forservice until one of the high-speed pipes is available. Since the traffic isbursty in nature (i.e., user need for the supplemental channels is brief and not simultaneous across users), the time-sharing of resources is not

readily apparent to the end user. For example, wait time in the queue ismodest.

In this sense, the air interface is packet-switched rather than circuit-switched , since channels are time-shared throughout the user session(packet-switched) rather than completely dedicated to a user (circuit-switched) for this time. Accordingly, performance criteria distinct fromthose employed in voice networks (circuit-switched) must be used.


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These include data throughput, average wait time, probability of beingdelayed, and average length of the queue. The performance may alsovary considerably with user statistics, which are necessarily a functionof the data applications employed (e.g., e-mail, web-browsing, etc.)and of user behavior (e.g., think or idle time between the download of

each web page). Accordingly, performance predictions obtained byemploying user statistics that are significantly different from thoseobserved in commercial systems may not match the commercialperformance.

Overview of traffic theory IS-95 has typically employed a circuit-switched analysis of traffic,since this body of theory is based on a dedicated resource (channel) peruser. The resource is held exclusively by the user for the duration of service (i.e., for the duration of the call) and released upon callcompletion.

The performance of this system approximates that of an Erlang Bmodel, which dictates the probability of blocking for a traffic loadincident upon a fixed number of servers. The probability of blockingrepresents the probability that a user will be turned away because allchannels are occupied. Although IS-95 principles deviate in someimportant ways from Erlang B assumptions, the use of circuit-switchedprinciples is correct in that each user occupies a channel resource that isdedicated to its application for the duration of the user session.

In contrast, the packet-switched data feature of 3G-1X is not as readily

captured by Erlang B principles, since subscriber transmissions (datamessages waiting to be burst) can wait or queue up for service ratherthan be blocked when all resources are busy. In packet-switched data,high-speed data users are serviced by a small number of supplementalchannels capable of supporting a high data rate. These channels aretime-shared by a fairly large number of data users that transmit burstsof data in turn when cued to do so by the network.

This situation is better (although still not precisely) described by anErlang C model, which relates the probability of delay and average wait time for an incident traffic load funneled through an infinite queue to afixed number of servers. Since the queue is infinite, no blocking canoccur; however, arrivals wait in the queue for service when all channelsare busy. In this model, the supplemental channels are viewed as thefixed number of servers. The arrivals are message bursts that are eitherimmediately transmitted (if a channel is idle), or wait in memory at themobile (reverse link) or cell site (forward link) for their chance attransmission.


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The Erlang C model can be readily applied to estimate suchperformance parameters such as wait time and throughput provided that the number and data transmission rate of the servers are known.For the 3G-1X air interface, these values must be determined from RFanalysis. This determination is complicated by the fact that the Erlang

C model requires a fixed number of servers each with a fixed data rate;however, the number and rate of supplemental channels within the airinterface vary dynamically with factors such as user number, speed,multipath, fade, and transmission history. Accordingly, numericalanalysis must be employed to obtain probability distributions of thenumber and type of supplemental channels available within the cellfootprint. This information is then employed to drive an Erlang Cmodel in a manner that reflects the varying, statistical nature of theservers.

The process described is computationally intensive, and must berepeated for every design scenario where key input aspects such asperformance requirements (e.g., average delay, minimal data ratesupported at cell edge) are changed. Some baseline results (see Chapter3, "RF engineering for data" ) have been established for a Lucent trafficmodel, and may be used in planning in the absence of more specificinformation regarding subscriber behavior and performancerequirements. If baseline results are employed, design scenarios can beaddressed by using link budget analysis to verify that the air interfacecan support the total number of fundamental and average number of supplemental channels required within the cell footprint.

Data link budget The data link budget serves two primary purposes. First, the analysisdictates coverage by establishing a minimum data rate available at thecell edge. Second, the analysis verifies that the system has sufficientpower to support the mix of fundamental and supplemental channelsthat are required within this design footprint in order to achieveperformance (e.g., data throughput).

The reverse link budget for data applications is relativelystraightforward in that only the coverage of the supplemental channel

need be considered to establish a footprint. This strategy follows fromthe fact that the high data rate of the supplemental channel renders itscoverage the limiting factor. The necessary coverage requirements aretypically expressed by requiring a minimum data rate at the cell edgewith a specified level of probability (e.g., 90%). For a high data rate,the coverage is naturally limited, and is usually less than that of thelower rate 3G-1X voice or fundamental channel. In these instances,service providers may choose to locally or globally augment cell count


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engineered simply by restricting carrier access to 3G mobiles only.Restricted access is achieved via messages that can be read by 3Gmobiles only; i.e., the 3G carrier is invisible to 2G mobiles.

The overlay ratio for upgrade of an existing IS-95 system to 3G-1X is

recommended to be at least 1:1 (i.e., one 3G-1X cell for every existingIS-95 cell) since the 3G-1X voice coverage is slightly better than theIS-95 voice coverage. The improvement is not enough to recommendan overlay consisting of fewer 3G-1X cells than IS-95 cells, such as1:1.5. Overlays that exceed 1:1 (e.g., such as two 3G-1X cells for everyIS-95 cell, or 2:1) are not generally recommended unless the serviceprovider desires to obtain a high-speed data coverage that entirelymatches the underlying (low-speed) voice coverage. A 1:1 overlay willsupply a low-rate data channel across the entire voice coverage area,while confining higher-rate users to the interior of the cell.

Channel element provisioning, i.e., the determination of the number of channel elements required at the cell site to support a traffic load thatcan consist of 3G-1X voice users, 3G-1X data users, and IS-95 voiceusers, is not straightforward, but facilitated by the fact that the dual-mode 3G-1X channel element can support both 3G and IS-95 (2G)calls. This feature reduces the problem difficulty somewhat, as theexact proportion of 2G and 3G users need not be known in order toproduce a channel element number that is operationally sufficient.


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Voice coverage, capacity and link budget Introduction


401-614-040Issue 2, February 2003

............................................................................................................................................................................................................................................................Introduction

The 3G-1X principles of voice coverage and capacity are similar tothose of IS-95. This similarity is to be expected, as 3G-1X is a spreadspectrum system based upon IS-95. In the following sections, webriefly review these principles. A more detailed discussion can befound in Lucent documents 401-614-012, AUTOPLEX Cellular CDMA RF Engineering Guidelines , and 401-703-201, PCS CDMA RF Engineering Guidelines , as well as TIA/EIA/IS-2000A standards.

In 3G-1X, all users share the same wideband carrier; i.e., the frequencyreuse is 1. Transmissions within this channel are distinguished bycoding. This approach stands in contrast to other approaches such asfrequency division multiple access (each user occupies a distinct

narrowband channel) or time division multiple access (each useroccupies a distinct time slot).

The simultaneous use of the same wideband carrier means that all usersinterfere with one another. On both forward and reverse links, thisinterference is tolerated but mitigated through means such asprocessing gain, fast power control, variable-rate coding, and softhandoff. Interference from other users is suppressed by the processinggain (typically about 20 dB), which derives from the manner in whicheach traffic channel is uniquely coded to allow ready identification.Power control dynamically adjusts each traffic channel power to theminimum required to maintain performance. Variable-rate codingfurther suppresses the background interference level by powering downthe link (i.e., reducing the voice coding rate) whenever the user is notspeaking. Finally, soft handoff reduces overall interference levels byallowing the call to be simultaneously supported by multiple basestations, thereby introducing a diversity gain that lowers the net trafficpower required per mobile.

Soft handoff is also important in mitigating interference to the forwardlink receiver (mobile) from a nearby base station that is not supporting

the call. Once the mobile enters into a soft handoff state with this basestation, this cell becomes a source of signal rather than of interference.This effect of soft handoff is important in real-time applications such asvoice, but is less significant in data applications where real-timedecoding is not as critical since messages received in error areretransmitted.


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Voice coverage, capacity and link budget Analysis


401-614-040Issue 2, February 2003

............................................................................................................................................................................................................................................................Analysis

In the following sections, we outline the coverage and capacity analysisfor both the reverse and forward links. In each case, the governingperformance equations are presented and discussed.

Although exact solution of the equations via numerical simulation isoutlined, the focus of the discussion is directed towards simplificationsor approximations that can be used in planning processes such asdesign. The exact solution is discussed only in order to illustrate thecomplexity underlying accurate performance predictions, and to aid inunderstanding some of the simulation results presented throughout thedocument. The latter include offline simulation values employed as lineitems in planning approximations such as the link budget, as well as

key performance results that are based upon numerical analysis outsidethe scope of this document.

Note that in all cases, warrantable performance predictions must beobtained via a mixture of numerical simulation as well as trial (field)results.

Reverse link The key to reverse link analysis lies in assessing the receiversensitivity; i.e., the minimum power (usually expressed in dBm)required per receive diversity branch at the cell site receiver input. Thisinput (the J4 port) lies at the end of the cable connecting receiver toantenna; i.e., at the point where the incoming signal has alreadysuffered cable loss.

Consider a collection of mobiles within a sector. For the moment, wepresume a steady-state condition; i.e., one where all mobile positionsare fixed and the mobile conditions of voice activity factor, multipath,and fade are unchanging. At the J4 port, each mobile must satisfy itsparticular Eb/Nt (ratio of channel bit energy to spectral density of totalchannel impairment) requirement, which is a function of mobile speed,multipath, and required channel Frame Erasure Rate (FER).

For all mobiles within the sector:

Equation 2-1: Eb/Nt requirement

i

it

b d N E


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In this equation, the letter i is the index of the mobile in question. Theleft-hand side is the achieved Eb/Nt at the cell site receiver (J4 port);the right-hand side is the required median Eb/Nt corresponding to theparticular mobiles condition (speed, multipath) at the design FER(e.g., 1%).

For the sake of simplicity, we presume an isolated sector with N mobiles. Expanding the above, we obtain:

Equation 2-2: Expanded Eb/Nt definition

This expression is the heart of system analysis for reverse link coverageand capacity; accordingly, we consider it in some detail.

In the above, the energy per bit (numerator) is determined by the ratioof received power Si to channel bit rate Ri. The spectral density of receiver interference plus receiver noise (denominator) is determinedby the sum of receiver noise density (the thermal noise density N oscaled by the receiver noise figure F ) and the sum of power receivedfrom the other N -1 mobiles.

In voice applications, the channel bit rate is constant for all usersprovided that a single vocoder, either 8 or 13 kbps speech, is employedwithin the mobile population; hence Ri= R. This is not the case in dataapplications, where the channel bit rate can vary per user. Additionally,a voice network may contain a mixed population of 8 and 13 kbpsvocoders. These points are explored later on in this document.

W is the channel (carrier) bandwidth. The quantity W / R = g is thespread spectrum processing gain. Equation 2-2 shows that the ratio of signal power to impairment (noise plus interference) power, whenmultiplied by the processing gain, must equal or exceed the Eb/Ntrequirement.

( )ii N

i J j

j jo

ii N

i J j

j jo

ii N

i J j

j jo

iii

it

bi d

SW FN

Sg

SW FN

S RW

SW

FN

RS N E

=

+=

+=

+=

=

=

= 111

/ 1

/


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The variable is the mobile voice or channel activity factor withpossible values ranging from 0 to 1 in discrete steps of 1/8, , , and1.0. 1 The last value applies when the user is speaking; the first applieswhen the user is listening. Intermediate values are transitional ratesinserted to avoid a clipped sound to speech when the channel is

changing between the speak/listen states. The probability (relativedwell time) of each value has been determined from analysis of vocoder speech and is known. The statistics of alpha are thereforecompletely characterized.

The d i is the median full-rate (i.e., =1) Eb/Nt requirement. In theabove, we have explicitly made the assumption that the Eb/Ntrequirement is scaled by the voice activity; e.g., the Eb/Nt requirementfor a user in the 1/8 state (listen) is 1/8 of the full-rate Eb/Ntrequirement. The Eb/Nt requirement as a function of multipath, speed,and Frame Erasure Rate (FER) is determined via a combination of link level simulations and receiver tests.

Equation 2-2 represents a set of linear equations in the variables S1,S2,S N . These equations express the coupling between mobiles; i.e.,the fact that each users signal is interference to all other users.

Solution--Exact

We presume an ideal power control, which would without error ensurethat all mobiles just achieve (rather than exceed) their Eb/Ntrequirement. Accordingly, we change the inequality in Equation 2-2 toan equality. This expression can then be expanded to the matrixequation:

Equation 2-3: Reverse link Eb/Nt matrix

...........................................................................................................................

1 The and are transitional rates (from speak to listen), and are not always employed.

=

1

.

.

1

1

.

.

/ ..

.....

.....

.. /

.. /

2

1

21

21

21

W FN

S

S

S

d g

d g

d g

o

N N

N

N


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Each value of Si can be replaced by a i xi, where a i is the total attenuation(loss) from the transmit antenna of the ith mobile to the J4 port and xi isthe transmit power out of the ith mobile. Note that the former includestotal loss, and therefore could be computed by the dB sum of body(head) loss, building/vehicle loss, (random) fade, point-to-point

(distance-dependent) path loss, receiver antenna gain, and receivercable loss. The latter constitutes the total mobile transmit power,including the 3G-1X pilot signal that accompanies traffic power inorder to aid demodulation at the cell site receiver. The Equation 2-3becomes:

Equation 2-4: Reverse link expanded matrix form

Note that the matrix containing the attenuations ( a) is diagonal, with 0sin all nondiagonal entries.

The importance of Equation 2-4 cannot be overemphasized, since itrepresents the key to analysis of system performance via numerical

simulation. In this Monte Carlo process, the performance limits of capacity and coverage are established by computing performance for arange of possible values of sector coverage and capacity.

In this process, a sector perimeter (footprint) and number of mobiles N are first selected. A trial is conducted by randomly placing N mobileswithin the footprint, and assigning them random values of voiceactivity, fade, and multipath. The multipath value and 0 velocity (fixedposition) dictate the full-rate requirement d for each mobile. Theexpression Equation 2-4 is then solved for the transmit powers x. This

process is repeated over many trials until the statistics of the mobiletransmit powers can be determined for the selected perimeter andcapacity.

One or both of these values (perimeter, capacity) is then altered. Theprocess of determining mobile transmit power distributions byconducting multiple trials is then repeated, thereby characterizingperformance for this new selection.

=

1

.

.

1

1

.

.

.

.

/ ..

.....

.....

.. /

.. /

2

1

2

1

21

21

21

W FN

x

x

x

a

a

a

d g

d g

d g

o

N N N

N

N


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particular, the size of the matrix increases from N N to N total N total ,where N total is the number of mobiles in all sectors. The analysisproceeds similarly but with considerably more computationalcomplexity, since for each trial the N total 1 vector of transmitstrengths, representing the transmit strengths of all mobiles within the

network, must be solved for.

The techniques described have been used to simulate the performanceof IS-95 (2G) systems, achieving results that are supported by fielddata. For example, the capacity of a fully mobile system within anominal cell footprint (i.e., a footprint dictated by the reverse link budget analysis outlined in "Solution--Approximate" section on Page2-9 and "Link budget" section on Page 2-14 ) is the equivalent of 13channels (7.4 Erlangs at 2% block) and the equivalent of 20 channels(13.2 Erlangs at 2% block) for 13 kbps and 8 kbps coding, respectively.These values apply to the early version of the ASIC receiver chip (1.0),and rise to 9.0 Erlangs and 16.6 Erlangs, respectively, with use of theASIC 1.1 chip in the cell site receiver.

The same techniques have been employed in predicting 3G-1Xcapacity for nominal (link budget) footprint, indicating 26.4 Erlangs at2% block (35 channels) for 8 kbps coding. This value is as yetunsupported by extensive field data, since no 3G-1X commercialsystems have been deployed.

Table 2-1 Air interface capacity

Solution--Approximate

We now consider means of obtaining solutions to Equation 2-2 that areapproximate. Although any final performance prediction should relyupon a mixture of exact solution (see "Solution--Exact" section above)as well as trial results, the approximate solutions are useful for planningas well as lending insight into performance trends.

We seek an approximate solution to Equation 2-2 , repeated here forconvenience.

Air interface IS-95 at 13 kbps IS-95 at 8 kbps 3G/1X at 8 kbps

Capacity @ 2% block 7.4 Erlangs 13.2 Erlangs 26.4 Erlangs


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2 - 1 1Lucent Technologies - ProprietarySee Notice on first page

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Equation 2-6: Reverse link Eb/Nt assuming worst case required Eb/Nt

This expression is readily solved for the single value of the keyparameter S, the required signal strength per diversity branch at the J4port of the cell site receiver:

Equation 2-7: Required received reverse link power

The value S is a random variable, since the summation in thedenominator is a sum of the independent but identically distributedvalues of channel (voice) activity. For planning purposes, we seek theexpected value of S for use as the minimum receiver sensitivity Smin.This value is conveniently expressed as:

Equation 2-8: Reverse link receiver sensitivity

Here, E denotes the expectation operator; also, the represents theexpected value of the channel activity.

The expectation on the far right of Equation 2-8 can be computedanalytically since the distribution of the random value of voice activityis known. This value is close to 1. For large g/d max , this result can beobtained by inspection; moreover, regardless of the value of g/d max , theexpected value is always 1 for very large N since the sum over ( N -1)voice activity values is equal to ( N -1) times the mean voice activity. Wetherefore approximate the mean receiver sensitivity as:

max

1

)1(d

SW FN

gS N

i J j

jo

=++

=

=+

= N

i J

j j

o

d g

W FN S

1max

)1(

{ }+

+

+==

=

N

i J j

j

o

d g

N d

g

E N

d g

W FN S E S

1max

max

max

min

)1(

)1)(1(

)1)(1(


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401-614-040Issue 2, February 2003

Equation 2-9: Reverse link receiver sensitivity - approximation

This expression shows that the receiver sensitivity is a monotonicallyincreasing function of N , the sector loading. Since increased sensitivityclearly requires decreased cell radius, this expression illustrates thefundamental trade-off between coverage and capacity that can bepursued in CDMA systems. In addition, there is clearly a hard limit tothe loading N , since the denominator must be greater than zero. Thelimit N max can be obtained by setting the denominator equal to zero,obtaining the reference or pole point at which the required receiversensitivity grows without bound:

Equation 2-10: Pole capacity definition

The receiver sensitivity can be recast using N max as:

Equation 2-11: Reverse link receiver sensitivity in terms of loading

where u = N / N max is the loading with respect to the pole point. Equation 2-11 can be used to determine the receiver sensitivity for usein a link budget , as discussed below. For:

Equation 2-12: Receiver sensitivity simplifying assumption

{ }+

= )1)(1(

max

N

d

gW FN

S E o

1)1(

1

maxmax ++

= d

g N

{}

=+

=+

=maxmaxmax

11

11

11

)1(1

)1(1

N u RdFN

u

W FN

N N N

W FN S E

ooo

)1(max

+>>d g


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Equation 2-11 can be simplified to:

Equation 2-13: Simplified reverse link receiver sensitivity

This approximation allows the receiver sensitivity to be determined bythe dB sum of Eb/Nt requirement, data rate, interference margin 1/(1- u)and receiver noise floor. The reverse link budget format (see "Link budget" section below) is based upon this approximation; however, theunderlying calculations rely upon Equation 2-11 since theapproximation Equation 2-12 may not always be satisfied.

Equation 2-11 suggests that any integer value of N less than N max (i.e.,any value of u less than 1) is permissible provided that one is willing topay the penalty of reduced cell coverage associated with very high poleloadings (e.g., u=0.95). In practice, loadings approaching u=1 areavoided due to the possibility of associated instabilities. Suchinstabilities exist regardless of the nature or form of power control, ascan be demonstrated by a sensitivity analysis that relates relativechanges in loading u to relative changes in required receiver sensitivity.

Differentiating Equation 2-11 with respect to u, we obtain:

Equation 2-14: Sensitivity of receiver sensitivity to loading

This expression indicates that relative changes in required receiversensitivity are related to relative changes in loading u by the sensitivityfactor u /(1-u). This factor indicates to what degree relative changes in uare suppressed or amplified into relative changes in Smin . The sensitivityin Equation 2-14 increases with loading, rising from values


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401-614-040Issue 2, February 2003

Large sensitivities indicate that minor changes in loading can requirelarge changes in Smin . In this region, the finite time and finite accuracyassociated with any power control loop can result in large overshoots(instability) as the system tries to make the necessary large adjustmentsin response to small, fast changes in loading. This effect constrains the

maximum loading that can be tolerated.

These concepts are illustrated in the curve in Figure 2-1 below.

Figure 2-1 The sensitivity factor maps relative changes in loadinginto relative changes in receiver sensitivity. The factor isa function of the design loading . For large values of ,small relative changes in loading are amplified intolarge relative changes in receiver sensitivity. The choiceof design loading factor must avoid this region of thecurve.

Simulation and field results suggest that the maximum tolerableloading falls within the range of u=0.5 to u=0.75. The allowed loadingimproves with better power control and with lower d min (i.e., higherpole point). The latter effect arises since a larger number of usersassociated with any value of u tends to stabilize that value; i.e., the

relative change of u per the addition or deletion of a single user is less.

Link budget

The required receiver sensitivity Smin in Equation 2-11 can be used toobtain a reverse link budget. This budget dictates the maximumallowable path loss between mobile transmit antenna and cell sitereceive antenna. Provided further analysis indicates that the forward

Sensitivity Factor

0

5

10

15

20

0 0.2 0.4 0.6 0.8 1

mu

m u / ( 1

- m u )


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link can support performance at the same loss (See "Forward link"section on Page 2-20 ), the loss can be used on a market-by-market basisto perform RF design. This process employs algorithms that map lossinto cell radii via consideration of local variables such as tower height,terrain, and clutter.

The allowed point-to-point path loss is determined by considering theterms that dictate net loss from mobile to cell. Components of the netloss are indicated in the following figure (head loss and fading are notshown in the figure, but are included in the link budget equations).

Figure 2-2 Components of net path loss from mobile to base station

The terms characterizing the net loss are captured in the followingrelation, which requires that at maximum mobile transmit power thesignal power achieved at the J4 port must equal or exceed 10log( Smin):

Equation 2-15: Reverse link budget equation

where:

X max= Maximum mobile EIRP (Effective Isotropic Radiated Power) (in dBm) HL = dB head (body) lossFade = dB fade at mobile location BL/VL = dB building or dB vehicle penetration loss, whichever is applicablePL = dB point to point (average) path loss between mobile antenna and cell

site antenna AG = dBi cell site antenna gainCL = dB cell site cable loss.

This expression is readily rewritten for the allowed maximum dB pathloss. This value dictates the edge (boundary) of the cell coverage.

CDMAMobile

CDMA BaseStationMax. Path

MobileEIRP Receiver

Sensitivity

BuildingPenetration

Loss

AntennaGain

CableLoss

)log(10 minmax SCL- AGPL- BL/VL- fade- HL- X +


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Equation 2-16: Reverse link budget equation

Equation 2-16 can be viewed as constructing the allowed maximumpath loss as a dB sum of credits (e.g., mobile transmit power) anddeficits (e.g., cable loss). This dB process is captured in the reverse link voice budget. Several examples are shown in Table 2-2 below. The link budgets serve as examples only and will vary from market to market per the service providers requirements. For instance, the cell siteantenna gain, cable loss, fade margin, and building penetration margincould be modified, substantially altering the (bottom line) allowed pathloss to be used in design.

Table 2-2 shows PCS link budgets for second generation (2G) voicecoded at 13 kbps (total rate with overhead bits is 14,400) and at 8 kbps(total rate with overhead bits is 9600). These are included for reference.The 3G-1X budget for 8 kbps is shown in the right-hand column. The2G budgets are created from parameters (e.g., noise figure) applicableto the IS-95 Minicell and the ASIC 1.0 chip. The 3G-1X budget usesparameters appropriate to the Flexent Modular Cell.

In all cases, the format of the link budget is essentially obtained fromEquation 2-16 , with Equation 2-13 used to create the value of Smin . Asdiscussed above, the approximation Equation 2-13 is not always valid;

hence, in spite of the format the spreadsheet uses an embedded form of Equation 2-11 to obtain the Smin.

max) PL10log(S-CL- AG BL/VL- fade- HL- X PL minmax =+


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Table 2-2 Reverse PCS link budget for IS-95 9.6 kbps, IS-95 14.4 kbps, and 3G-1X 9.6 kbps voice,mobility application

Item Units 2G Voice14.4kbps

2G Voice9.6kbps

3G-1X Voice9.6kbps

Comments

(a) Maximum Transmitted power perchannel

dBm 21 21 21

(b) Transmit Cable, connector, com-biner, and body losses

dB 2 2 2 Body loss

(c) Transmitter Antenna Gain dBi 2 2 2

(d) Transmitter EIRP per channel (a - b + c)

dBm 21 21 21

(e) Receiver Antenna Gain dBi 18 18 18

(f) Receiver Cable and ConnectorLosses

dB 3 3 3

(g) Receiver Noise Figure dB 5 5 4 PCS Minicell for 2G andModcell for 3G-1X

(h) Receiver Noise Density dBm/Hz -174 -174 -174

(i) Receiver Interference Margin dB 3.4 3.6 5.5 72% loading for 3G-1X

(j) Total Effective Noise plus Interfer-ence Density = (g + h + i)

dBm/Hz -165.6 -165.4 -164.5

(k1) Information Rate (10log(Rb)) dB 41.6 39.8 39.8

(l1) Required Eb/Nt dB 7 7 4 Considering 2 spatialreceive diversitybranches

(m) Receiver sensitivity (j + k +l) dBm -117.2 -118.7 -120.7

(n) Hand-off Gain dB 4 4 4 For 90% cell edge cover-age and 8 dB log-normalstandard deviation

(o) Explicit Diversity Gain dB 0 0 0 Diversity gain has beenincluded in required Eb/ Nt

(p) Log-normal Fade Margin dB 10.3 10.3 10.3 For 90% edge coveragewith 8dB log-normal stan-dard deviation

(p') Building/Vehicle Penetration Loss dB 0.0 0.0 0.0 For outdoor coverage

(q) Maximum Path loss {d-m+e-f+o+n-p-p'}

dB 146.9 148.4 150.4


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Note that the link budget creates the fade margin in Equation 2-16 as asum of two terms: The single-link (simplex) fade margin and the softhandoff gain.

The simplex fade margin is obtained conventionally by selecting a dB

value from a normal distribution of possible values. For a simplexconnection, the path loss at the cell edge therefore accommodates allvalues of fade up to and including this value. For example, a selectionof 10.3 dB means that at cell edge all fades up to and including 10.3 dBcan be tolerated without requiring that the mobile exceed its maximumtransmit power. Since the 10.3 dB is the 90 th percentile within thedistribution of fades 3, this choice corresponds to a 90% probability of cell edge coverage. The probability of area coverage is greater, sinceinside the cell boundary the path loss is less and the mobile has moretransmit margin to overcome deeper fades.

The fade margin required for 90% edge coverage is actually less thanthe simplex value, since a CDMA mobile at the cell edge is in a softhandoff state with at least two legs. The full simplex margin wouldonly be required if both legs faded simultaneously and equally. Sincethe leg-to-leg fading is at least partly uncorrelated, the net fade marginrequired to achieve a given probability of coverage is less. The softhandoff gain is the difference between the simplex and actual fademargin. The exact value is a weak function of probability of edgecoverage and is determined by offline calculations that are supportedby field data. Recommended values are tabulated, below. These values

correspond to a 60% correlation between soft handoff legs in alognormal fading environment (8 dB standard deviation).

Table 2-3 Reverse link soft handoff gains

...........................................................................................................................

3 This is true for lognormally distributed fades with 8 dB standard deviation, this distri-bution is common and often observed in path loss measurements

Probability of Edge Coverage Soft Handoff Gain (dB)

75% 3

90% 4


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The differences between the 3G-1X and the IS-95 voice reverse link budgets must be emphasized. They include the following:

For 2G, the mobile transmitted power consists solely of trafficchannel power; however, for 3G-1X, the mobile transmitted thepower includes the traffic channel and reverse pilot channelpower. The analysis described in the "Solution--Exact" and"Solution--Approximate" sections applies in either case since theEb/Nt requirements d i are adjusted appropriately. It is simply amatter of interpretation of the transmit power x.

The required Eb/Nt d (i.e., the traffic channel Eb/Nt requirementsfor the 2G, and the total traffic plus pilot Eb/Nt requirement for the3G-1X) to achieve 1% target Frame Erasure Rate (FER) differ. Forthe 9.6 kbps voice, mobility application and 1% FER target, therequirement for the 3G-1X is 4 dB, less than the 7 dB required forthe IS-95 system (ASIC 1.0 chip).

The pole loading factor for 3G-1X is higher than the pole loadingfactor for IS-95, due to a larger user base and slightly improvedpower control (see the "Solution--Approximate" section). Thisdifference is reflected within the interference margin. Theexample budgets employ the maximum loading recommended forthe scenarios chosen. Lower loadings are allowed, increasingcoverage at the expense of reducing capacity.

The air interface capacity of the 3G-1X 8kbps voice application is26.4 Erlangs per sector per carrier (corresponding to 35 channels

at 2% blocking) while that of the IS-95 8kbps voice is 13.2Erlangs per sector per carrier (corresponding to 20 channels at 2%blocking). This difference arises due to the 3G-1X reduced Eb/Ntrequirement, as well as the increased 3G-1X maximum poleloading.

The base receiver noise floor of the PCS CDMA Minicell is 5 dBwhile that of the PCS CDMA Flexent Modular Cell is 4 dB. Theformer has been extensively deployed within the field, and wastherefore used as a 2G reference in Table 2-2 .

The examples above indicate that 3G-1X can tolerate more path lossthan IS-95 under identical (normalized) conditions; i.e., equal valuesof antenna gain, fade margin, building penetration loss, etc. Thisdifference allows an IS-95 system to be upgraded to 3G-1X on a 1:1basis without loss of coverage performance. Overlay strategies arediscussed in more detail in Chapter 4, "System deployment" .


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401-614-040Issue 2, February 2003

Forward link Reverse link analysis is used to establish the cell footprint. Thisanalysis can be viewed as driven by the limit on mobile transmit power.This limit is a key constraining factor in cell size, driven by marketdemands for more compact subscriber units and longer battery life.

The objective of forward link analysis is to ensure that the forward link has sufficient power to support performance within the footprintdictated by the reverse link. Accordingly, the dB design path lossdetermined by reverse link analysis is an input to the forward link analysis process, which assesses whether the forward link has sufficientresources to deliver adequate power to each mobile receiver within thedesign path loss.

This analysis differs in three important ways from that of the reverselink:

First, the link transmitter power (forward link amplifier power)considered in analysis is shared amongst multiple users. Incontrast, the transmit power employed in reverse link analysis (themobile transmit power) is dedicated to a single subscriber.

Second, the effect of other sectors at the receiver is moreimportant, as a mobile receiver near the cell boundary can besubjected to a significant amount of interference broadcast bynearby neighbor sectors. In contrast, the other-cell interferenceconsidered in reverse link analysis consisted of power frommodest transmitters at a greater distance from the cell site receiver.

Third, the available link level information does not consist(directly) of receiver Eb/Nt requirements; rather, the fractional forward link power (Ec/Ior) as a function of mobile geometry isused in analysis. The geometry is defined as the ratio of the totalpower within the active set to the sum of receiver noise and totalpower received from all sectors not within the active set. A sectoris in the mobiles active set when it is supporting the mobile call;i.e., providing a signal or leg that the mobile is demodulating.

In order to ensure clarity, we provide a few examples of the last point.The fractional forward link power requirement Ec/Ior (or x = Ec/Ior,used here for convenience) is a pure (dimensionless) number and afunction of the mobile geometry G:


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Equation 2-17

For example, x may be 0.05, indicating that 5% of the total forward link power broadcast by a sector is required to maintain forward link FER.Note that this relationship says nothing about the total power broadcastby the sector, but simply indicates what fraction of the power beingbroadcast is required by the mobile in question.

The geometry must be defined with care. For a mobile not in softhandoff, the numerator of the geometry consists only of the powerreceived from its host sector. For a mobile in soft handoff, thenumerator consists of the power received from the host as well as all

other sectors supporting the call. In each case, the denominator consistsof the sum of receiver noise and the received power from all othersectors not supporting the call.

As a specific example, we consider the following. Without loss of generality, we may denote the received host sector power P1 for amobile not in handoff. For a mobile in soft handoff with sectors 1 and2, we denote the received host sectors power P1 and P2 . Then:

Equation 2-18: Geometry calculation example

Note the contrast between the first (no soft handoff) and last (soft

handoff) definition of geometry. In the former case, only sector 1supports the call; accordingly, only th

CDMA3G-1X RF Engineering

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