3G RF Engineering Guidelines

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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 iiiTo 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


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 5-25SOFT_SLOPE, DROP_INTERCEPT, ADD_INTERCEPT 5-30SCH anchor transfer vs. SHO 5-31

Hard 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

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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 7-19

Core 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 8-9

System 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, thirdgeneration 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 ofup 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 linkbudget and voice capacity analyses are similar. Management ofcochannel 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 networkoptimization.

Accordingly, this document does not offer extensive discussions oftopics 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 ofRF data issues for 3G-1X, including a contrast between theErlang B (voice) and Erlang C (data) models, analysis ofcapacity 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 adetailed 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® WirelessNetworks 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 Systems”Global 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 GrowthEngineering for Cellular System

• CL8302, CDMA IS-95 and 3G-1X RF Design and GrowthEngineering 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 technicalsupport, documentation,

and training or sendfeedback

The current release of the Flexent®/AUTOPLEX® wireless networksdocumentation is provided on the Lucent Technologies wirelessnetworks customer technical support web site to all customers free ofcharge. 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 ElectronicDocumentation 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 dBiBL/VL = Building or vehicle penetration loss in dB, whichever is applicableCL = Cell site cable loss in dBd = The Eb/Nt required for acceptable qualityEb/Nt = The ratio of channel bit energy to spectral density of total channelimpairmentF = The receiver noise figureFmobile = The mobile receiver noise figure

Fcell = The base station receiver noise figure

Fade = 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 lossHL = 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×σ choice which yields a 90th per-centileM = The length of queue for the general Erlang modelN = The number of active channels

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Nmax = “pole” capacity

No = Thermal noise density

Nsect = The total number of sectors

Nk = The total number of mobiles in sector k

Ntotal = The total number of mobiles within the network

Nlinks = The number of links per sector

Nsuppl = The number of supplemental links

Nfund = The number of fundamental links

Phost = The mobile received power from its host or serving sector

Pother = The mobile received power from surrounding non-serving sectors

PL = Point to point (average) path loss in dB between mobile antenna and cellsite antennaQtotal = The current (steady-state) average power radiated at the J4 port

Qmax = The maximum average power allowed at the J4 port before overload

(blocking) occursQover = The constant overhead power

ri = The random position of the ith mobile within the cell

R = The cell radiusRi = The channel bit rate of the ith mobile

Si = The base station received power from the ith mobile

Smin = The minimum receiver sensitivity

sij = The distance from the jth surrounding cell to the ith mobile

u = Loading factorW = The carrier bandwidthwmax = 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 sectorXmax = 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

α i = The channel activity factor for the ith mobile

α ij = The channel activity of the jth mobile in the ith sector

ak;ij = The attenuation from the kth sector to the jth mobile in the ith sector

β, βreverse = The ratio of other cell interference to serving cell interference for

the reverse link

βi = The ratio of other cell interference to serving cell interference plus

receiver noise floor for the forward link

βomni = The ratio of other cell interference to serving cell interference for the

forward link and omni antenna configuration

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δi = The fraction of the mobile received host power dedicated to the ith traffic

channel

ε = r/R

ξ = The orthogonality factor

λ = The average arrival rate for the general Erlang model

ηa = The mean of αηb = The mean of βσa = The standard deviation of ασb = The standard deviation of βγ = The fixed fraction of the maximum average power dedicated to the over-head channels

χ = s/R

µ = The average server completion (of service) rate for the general Erlangmodel

didd

iηε /=

gigg

iηε /=

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1 Discussion of CDMA 3G-1X RFengineering

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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 aswell 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 ofsupported Erlangs. The 3G-1X packet data service supports access tothe Internet via the IP protocol.

The 3G-1X and IOS (Inter-Operability Specification) Packet Dataservices 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 Code. This channel is calledthe Fundamental Channel (FCH). An active Packet Data call with theneed for higher bandwidth, either in the forward or reverse direction,

Discussion of CDMA 3G-1X RF engineeringIntroduction

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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 adata 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, thesupplemental channel does not offer any guaranteed bit rate. However,the data rate offered by the fundamental channel with raw data rate of9.6 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 asymmetric, i.e., the high speed packet datamobile, at any given instant, may be assigned different bandwidths onthe forward and reverse links. This helps to maximize the efficient useof bandwidth in both directions, still meeting the bandwidth demand ofthe 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 (~ ½ 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 userswithin 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".

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

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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 anumber 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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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, andoccasionally 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 offactors including the current interference background, the mobile’s RFconditions, the amount of data that needs to be sent, and the history ofthe 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 ofsupplemental 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 briefand not simultaneous across users), the time-sharing of resources is notreadily 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 ofeach 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 ofservice (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 readilycaptured 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 waittime 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 providedthat 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 ErlangC 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 ofsupplemental 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 channelneed 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


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


401-614-040Issue 2, February 2003

in order to achieve a ubiquitous coverage for high-rate users, or mayallow the network to naturally restrict the higher data rates to userswithin the interior of the cell.

The forward link budget analysis is more complex, in the sense thatforward power must be appropriately shared between fundamental(voice and low-speed data) and supplemental (high-speed data)channels in order to provide coverage within the footprint. In addition,the forward link supplemental channel does not enter soft handoff at theboundary. This design strategy limits forward link interference byensuring that only one high-rate burst is simultaneously active to themobile. Supplemental channel performance at the cell edge is enhancedby anchor transfer (essentially a fast hard handoff to the best servingcell), which exploits the fact that the supplemental channel is burstyrather than continuous in nature. The anchor transfer allows the mobileto be served by the best cell for the burst duration.

Resource management The complexity of capacity analysis is a natural consequence ofresource allocation or resource management across data subscribers.This strategy dictates the optimal use of available RF resources such aspower and data rate in light of the demands being made upon thenetwork. For example, each subscriber’s data rate can be adjustedduring the course of a call, and is a function of the subscriber’s reportedRF condition (e.g., interference, fading, multipath) as well as theamount of data waiting (queued) for transmission. Although resourcemanagement might not be properly regarded as an RF engineeringissue per se, the subject is so fundamental to overall performance that itis discussed in detail. The throttling down of the rate of a high-speeddata call as it moves from the interior to the exterior of the cell, or as itmoves from benign RF conditions to poor RF conditions, is astraightforward consequence of resource management.

Deployment Deployment of a 3G-1X system entails considerations such as carrierspectrum assignment, overlay ratios, and 3G-1X channel elementprovisioning. These issues are discussed in detail in Chapter 4, "Systemdeployment".

3G-1X may be deployed in a separate wideband carrier or within anexisting IS-95 carrier. The latter may be preferable in areas wherespectrum resources are constrained or a gentle migration from IS-95 to3G-1X is desired; however, the former will result in somewhat greatercapacity per Hz within the 3G-1X carrier. A dedicated 3G-1X carrier is

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


1 - 1 0 Lucent Technologies - ProprietarySee Notice on first page

401-614-040Issue 2, February 2003

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 isrecommended 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 ofchannel 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.


401-614-040Issue 2, February 2003

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

2 Voice coverage, capacity and linkbudget

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

Overview

Purpose This chapter describes the essential coverage and capacity issues forvoice applications.


Analysis 2-4

Reverse link 2-4Solution--Exact 2-6Solution--Approximate 2-9Link budget 2-14

Forward link 2-20Solution--Exact 2-25Solution--Approximate 2-29

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

Voice coverage, capacity and link budgetIntroduction


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® CellularCDMA RF Engineering Guidelines, and 401-703-201, PCS CDMA RFEngineering 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 distinctnarrowband 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 supportingthe 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.

Voice coverage, capacity and link budgetIntroduction

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401-614-040Issue 2, February 2003

The improvements to the air interface in 3G-1X have improvedcapacity performance to the point where the limiting resource in somecases will be the number of available Walsh codes, as opposed to airinterface resources.

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

Voice coverage, capacity and link budgetAnalysis


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 askey 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 dN

E≥


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


401-614-040Issue 2, February 2003

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 mobile’s condition (speed, multipath) at the design FER(e.g., 1%).

For the sake of simplicity, we presume an isolated sector with Nmobiles. 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 ofreceiver interference plus receiver noise (denominator) is determinedby the sum of receiver noise density (the thermal noise density No

scaled 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 ofsignal power to impairment (noise plus interference) power, whenmultiplied by the processing gain, must equal or exceed the Eb/Ntrequirement.

( )iiN

iJj

jjo

iiN

iJj

jjo

iiN

iJj

jjo

iii

it

bi

dSWFN

Sg

SWFN

SRW

SW

FN

RS

N

Eα

α

α

α

α

α

αα =+

=+

=+

=

∑∑∑≠=

≠=

≠= 111

/

1

/

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



401-614-040Issue 2, February 2003

The variable α is the mobile voice or channel activity factor withpossible values ranging from 0 to 1 in discrete steps of 1/8, ¼, ½, 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 ischanging between the speak/listen states. The probability (relativedwell time) of each value has been determined from analysis ofvocoder speech and is known. The statistics of alpha are thereforecompletely characterized.

The di is the median full-rate (i.e., α =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 linklevel simulations and receiver tests.

Equation 2-2 represents a set of linear equations in the variables S1,S2,…SN. These equations express the coupling between mobiles; i.e.,the fact that each user’s 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 ½ and ¼ are transitional rates (from speak to listen), and are not always employed.

=

−−

−−−−

1

.

.

1

1

.

.

/..

.....

.....

../

../

2

1

21

21

21

WFN

S

S

S

dg

dg

dg

o

NN

N

N

αα

αααα


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


401-614-040Issue 2, February 2003

Each value of Si can be replaced by aixi, where ai 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 0’sin all nondiagonal entries.

The importance of Equation 2-4 cannot be overemphasized, since itrepresents the key to analysis of system performance via numericalsimulation. In this Monte Carlo process, the performance limits ofcapacity 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 Nare 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. Thisprocess 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

WFN

x

x

x

a

a

a

dg

dg

dg

o

NNN

N

N

αα

αααα

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



401-614-040Issue 2, February 2003

This process is repeated for a number of selections (perimeter,capacity). Given a target probability of outage for the mobiles, e.g., nomore than 5% of the transmit powers observed can exceed the mobilemaximum transmit power, this analysis can determine the best valuesof coverage and capacity that can be supported.

For example, the maximum value of N that can be supported within agiven fixed footprint at a 5% outage can be determined by computingthe probability distribution of mobile transmit powers for each value ofN. At a small value of N, the probability distribution is unlikely toexceed the mobile maximum transmit power xmax at all; at a larger valueof N, a significant portion of observed values may be above xmax. Thedesired value of N is that which yields a probability distribution thatdisplays the value xmax for its 95th percentile (i.e., the 95th percentile ofthe mobile transmit power distribution can be no greater than themaximum mobile transmit power).

Although the analysis outlined by Equation 2-4 has been pursued, theresults are generally not applicable to network performance unless themodel is expanded in two ways: The incorporation of the impact ofmoving (non-fixed) mobiles, and the incorporation of the effects ofother sectors. For completeness, these are described below.

In the above, we have presumed that the mobiles are fixed. Thisconcept lends itself readily to the steady-state assumption, whereposition, fade, multipath, and voice activity do not change with time. Ineach trial, the required Eb/Nt, di, for each mobile was obtained solelyas a function of the random choice made for multipath since the speedwas fixed at 0. The situation for moving mobiles is assessed by using arandomly assigned value of speed as well as multipath to determine therequired Eb/Nt, (di) in Equation 2-4. The performance of a system withmoving mobiles is thus determined by applying mobile Eb/Ntrequirements to an otherwise static situation. This approach, whichapproximates the more complex situation where the mobile positionsare changing from instant to instant, is sometimes referred to asanalysis via a series of static snapshots.

The analysis embodied in Equation 2-2 and Equation 2-4 consideredonly an isolated sector; in contrast, an embedded sector, i.e., a sectorsurrounded by a sea of cells, is clearly a better model of real-worldconditions. The effects of other sectors can be included by expandingthe denominator of Equation 2-2 to include the interference at thesector receiver from mobiles transmitting in other surrounding sectors.These expressions expand and alter the matrix in Equation 2-4; in


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


401-614-040Issue 2, February 2003

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

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



401-614-040Issue 2, February 2003

As discussed above, real-world conditions are better modeled byincorporating the effects of other sectors. This can be done by alteringthe summation term in the denominator appropriately. The interferencefrom other (outside) sectors can be viewed as the outer interference.The interference from mobiles within the sector is the innerinterference, represented by the summation term over N-1 users in thedenominator of Equation 2-2. Simulations employing the techniquesdescribed in the "Solution--Exact" section have shown that the ratio ofouter to inner interference can be approximated by a constant β, for anembedded sector in a sea of cells with uniform sector loading. Theimpact of outer cell interference is therefore captured by alteringEquation 2-2 to:

Equation 2-5: Reverse link Eb/Nt with interference ratio

The di represents the per-path median Eb/Nt requirement of the ith

mobile, which is dictated by conditions of multipath, speed, and FER.At 1% FER, the range of possible values is not large; moreover, theexistence of at least two paths is guaranteed in the presence of two-branch spatial diversity2. The analysis can therefore be considerablysimplified by making the conservative assumption that all mobilesachieve the Eb/Nt for the worst-case (maximum) of the 2-pathmultipath cases (di=dmax). The condition that all mobiles achieve thesame d= dmax introduces a symmetry into the above expression thatrequires all received powers be equal as well; i.e., Si=S:

( )iiN

iJj

jjo

iiN

iJj

jjo

iiN

iJj

jjo

iii

io

b dSWFN

Sg

SWFN

SRW

SW

FN

RS

N

E αα

α

α

α

α

α =+

=+

=+

=

∑∑∑≠=

≠=

≠= 111

/1

/

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

2 The two-path existence is also guaranteed in some other diversity schemes such asslant polarized diversity branches; however, these schemes are not applicable at all frequen-cies.

iN

iJj

jjo

i

it

b dSWFN

gS

N

E=

++=

∑≠=1

)1( αβ


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

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

401-614-040Issue 2, February 2003

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 ηα 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/dmax, this result can beobtained by inspection; moreover, regardless of the value of g/dmax, 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

SWFN

gSN

iJj

jo

=++ ∑

≠=

αβ

∑≠=

+−=

N

iJj

j

o

d

gWFN

S

1max

)1( αβ

{ }

+−

−+−

−+−==

∑≠=

N

iJj

j

o

d

g

Nd

g

EN

d

gWFN

SES

1max

max

max

min

)1(

)1)(1(

)1)(1( αβ

ηβ

ηβ

α

α

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



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 Nmax 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 Nmax as:

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

where u = N/ Nmax 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

{ }

−+−=

αηβ )1)(1(max

Nd

gWFN

SE o

1)1(

1

maxmax

++

=βηα d

gN

{ }

−

−=

−+=

−+

=maxmaxmax

11

1

1

1

1

)1(

1

)1(

1

NuRdFN

u

WFN

NNN

WFNSE

ooo

βηβη αα

)1(max

βηα +>>d

g


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


401-614-040Issue 2, February 2003

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 "Linkbudget" 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 Nmax (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 <<1 (whererelative changes are suppressed) to 1 when u reaches u=0.5 (50%loading). Loadings greater than 50% yield sensitivity factors greaterthan 1, indicating that required relative changes in S are amplifiedrelative to changes in u; in particular, the sensitivity factor is greaterthan 3 for loadings exceeding u=0.75 and rises rapidly thereafter.

{} WFNug

dSE

o

−=

1

1max

−=

u

du

u

u

S

dS

1min

min

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



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 themaximum 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 µ. For large values of µ,small relative changes in loading are “amplified” intolarge relative changes in receiver sensitivity. The choiceof design loading factor µ 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 dmin (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., therelative 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

mu

/(1-

mu

)


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


401-614-040Issue 2, February 2003

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:

Xmax= Maximum mobile EIRP (Effective Isotropic Radiated Power) (in dBm)HL = dB head (body) lossFade = dB fade at mobile locationBL/VL = dB building or dB vehicle penetration loss, whichever is applicablePL = dB point to point (average) path loss between mobile antenna and cellsite antennaAG = 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(10minmax

SCL-AGPL-BL/VL-fade-HL-X ≥+

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401-614-040Issue 2, February 2003

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 linkvoice budget. Several examples are shown in Table 2-2 below. The linkbudgets serve as examples only and will vary from market to marketper the service provider’s 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 ofEquation 2-11 to obtain the Smin.

max) PL10log(S-CL-AGBL/VL-fade-HL-XPL

minmax=+≤


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401-614-040Issue 2, February 2003

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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401-614-040Issue 2, February 2003

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 dBvalue 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 90th percentile within thedistribution of fades3, this choice corresponds to a 90% probability ofcell 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 valuescorrespond 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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401-614-040Issue 2, February 2003

The differences between the 3G-1X and the IS-95 voice reverse linkbudgets 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 di 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 channelsat 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 linkhas 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 linkanalysis 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 fractionalforward 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 mobile’s 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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401-614-040Issue 2, February 2003

Equation 2-17

For example, x may be 0.05, indicating that 5% of the total forward linkpower 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 allother 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 ofgenerality, 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 (softhandoff) definition of geometry. In the former case, only sector 1supports the call; accordingly, only the received power from sector 1 isin the numerator. In the latter case, both sectors 1 and 2 support the call.In this case, the received power from sector 2 is removed from the sumin the denominator and placed within the numerator.

)(

1;/

Gfx

xIorEcx

=<=

21sec;

1sec;;

sec;/

sec

3

21

sec

2

1

andtorswithhandoffsoftinmobile

IFN

IIG

istorhosthandoffsoftinnotmobile

IFN

IG

densitypowertorreceivedorWPILet

torsall

iit

torsall

iit

ii

∑

∑

=

=

+

+=

+=

=

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401-614-040Issue 2, February 2003

In all cases, the I represents the received spectral density from allmultipath reaching the mobile receiver from the sector in question. Forclarity, some sample mappings of x = Ec/Ior vs. geometry G are shownbelow. The mapping is from an early study examining the impact ofpower control, which, as expected, improves the link performance bylowering the x required. The study per se will not be discussed furtherhere; the chart is used only to demonstrate the general shape of thecurve x = f(G).

Figure 2-3 Required fractional power versus geometry example

Note that, in general, the required x shrinks as the number of multipathfrom the sector to the mobile increase.

We now consider the system-level analysis of forward link employingthis information. Consider a collection of mobiles within a sector. Weagain presume a steady-state condition; i.e., one where all mobilepositions are fixed and the mobile conditions of voice activity factor,multipath, and fade are unchanging. The sector is embedded,surrounded by a sea of other sectors containing mobiles.

At the sector J4 port, the fractional transmit power allocated to eachmobile must be sufficient to reach or exceed the mobile receiver’sEc/Ior requirement, which is dependent upon its speed and geometry.The geometry is dependent upon the host and other sector powersreceived at the mobile; these, in turn, are dependent upon the mobile


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401-614-040Issue 2, February 2003

position and fading state. In order to support N links (includingprimary, soft, and softer handoff links), the total fractional transmitpower required must not exceed the fraction of amplifier power that isavailable for traffic:

Equation 2-19: Sum of powers less than available traffic power

In the above, αj represents the channel activity of the jth forward link,and xj represents the fractional power required to support this link. Thevalues Qmax and Qover are the maximum average available power andthe average power assigned to overhead channels (e.g., pilot),respectively. This inequality must be satisfied for each sector within thesystem.

For clarity, we write the value xj more completely to show its functionaldependence:

Equation 2-20: Required fractional power dependencies

The fractional transmit power requirement is a function of speed,multipath, and mobile geometry. Geometry, in turn, is a function ofmobile location, powers broadcast by all surrounding sectors, fadesbetween the mobile and all sectors, and the mobile handoff state.

Given the randomness of location, speed, multipath, and fading, it isclear that for fixed N, the sum Y is a random variable with an associatedprobability distribution. As N varies, the distribution retains(approximately) its shape but shifts to the right or left; see Figure 2-4.For a given coverage footprint and given number of links, i.e., givennumber of users, the computation of the associated probabilitydistribution provides the probability that the sum Y satisfies theinequality (Equation 2-19). In particular, for a given footprint, theforward link capacity limit can be obtained by finding the highest valueof N such that the sum Y still satisfies the inequality (Equation 2-19)with acceptable probability. This probability should be high, e.g., 90%,95%, in order to be consistent with the high probability of coveragegenerally provided by the reverse link.

max

max

1 Q

OQxY over

N

jjj

−≤=∑

=

α

]),,,sec[,,( statehandofflocationfadingpowerstorallgeometrymultipathspeedxxjj =

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401-614-040Issue 2, February 2003

Figure 2-4 Various probability distributions as a function of N(number of users)

For fixed footprint, as N increases, the probability distribution associatedwith the sum Y (total fractional transmit power) retains its shape (approxi-mately) but shifts to the right. A maximum amount of fractional transmitpower (“max allowed”) is available for traffic. The maximum capacity Nmaxcan be found by locating the highest value of N for which the probability dis-tribution still has an acceptably small probability of violating the maximumallowed fractional transmit power.

In order to conduct the above analysis, Equation 2-19 must be solvedfor all sectors. This analysis is not straightforward; in particular, themethod of solution is not analogous to that employed in the reverse link(linear algebra). The additional complexity arises from several factors,including:

• The nonlinear mapping x = f(G) in Equation 2-17, which can betabulated but not readily expressed in analytical form

• The dependence of fractional transmit powers x on a number offactors (Equation 2-20), including geometry

• The fact that the computation of geometry for a given locationdepends upon knowledge of the radiated power from allsectors…but the radiated power from all sectors cannot becomputed unless the fractional transmit powers x are known.These, in turn, depend upon geometry. This circularity prevents astraightforward solution; rather, an iterative approach thateventually results in an answer with self-consistent sector powers,fractional transmit powers, and geometries must be employed.

Total fractional power used

. . . . .

. . . .

Increasing links

probability

Max allowed

N links N +1 links N +2 links Nmax links


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401-614-040Issue 2, February 2003

This complexity has resulted in a number of forward link analysistechniques, which vary depending upon the speed, accuracy, and extentof information desired. We describe two examples below.

Solution--Exact

The exact solution of Equation 2-19 is complex, but neverthelessemployed in system performance simulations. We outline the methodof solution here.

The analysis can be done by collecting data from a number ofsimulated snapshots, where within each snapshot a predeterminednumber Ntotal of mobiles are randomly distributed throughout thesectors comprising the network. The snapshot is static in the sense thatthe mobiles do not move; however, motion can be modeled in a limitedsense by randomly selecting a velocity for each mobile, and using thegeometry curves for that velocity to assign fractional transmit powersto the (stationary) mobile. Given a sufficiently large number ofsnapshots, the probability distribution for the sum Y (Equation 2-19)can be obtained. This curve then allows specification of the probabilitythat the total fractional transmit power remains below an allowablelevel.

As discussed above, the geometry associated with a given locationdepends upon the total powers broadcast by the sectors. These totalpowers cannot be determined unless the fractional transmit powers xare known; however, these cannot be specified without knowledge ofthe geometry. This interrelationship dictates an iterative approach to theproblem, which can be generally pursued as follows:

• Construct a nominal (i.e., hexagonal) arrangement of cells, withper-sector footprint dictated by an allowable path loss and a pathloss law (e.g., Hata model). The former is usually dictated by thereverse link budget

• Choose a value of Ntotal users within the network, whichcorresponds to a desired average value of users per sector.

• Choose an initial value (e.g., Qmax) of power broadcast by allsectors

• Create and solve a single static snapshot via the following steps:

1. Randomly place the Ntotal users within the network

2. For each user, randomly select a multipath and velocity value

3. Specify a value of Qmax power broadcast by all sectors

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401-614-040Issue 2, February 2003

4. Using these values, compute each user’s soft handoff state

5. Compute each user’s geometry

6. Using the appropriate curve for each user’s multipath andvelocity, map user geometry into required fractional transmitpower from its host sector

7. Compute actual user (link) power from host sector

8. Compute total power broadcast by all sectors, and comparewith values assumed in Step 3, above. If they do not match,reassign sector broadcast powers in Step 3 to the new valuescomputed in this Step 8.

9. Repeat Steps 3 through 8 until convergence; i.e., until theassigned sector powers in Step 3 match the computed sectorpowers in Step 8.

10. Store the sector power for this value of Ntotal as a single pointwithin the probability distribution of required power (seeFigure 2-4). This point corresponds to a single static snapshotfor Ntotal users.

11. Repeat Steps 1 through 10 (i.e., run additional staticsnapshots) until a sufficient number of points is obtained tocharacterize the probability distribution of required power forNtotal users (see Figure 2-4)

• Assess this distribution to ascertain whether the available power issufficient to support the capacity within the coverage footprint.

The list above summarizes the general steps to be taken in forward linkanalysis. This process can be implemented in several ways; inparticular, it is possible to obtain a set of solutions for a normalizednetwork (e.g., unity power, unity coverage, etc.) and then scale thesesolutions in a simple way to address a wide variety of design scenarios.This strategy obviates the difficulty of running a computationallyintensive model for every design scenario; rather, solutions for anormalized scenario can be scaled to a variety of other scenariosthrough straightforward adjustments of antenna gain, cell radius, fademargin, etc.

For this approach, the normalized results are captured in a set ofcoefficients (Figure 2-5) that are used to reconstruct values relevant tothe design scenario at hand by using scenario-specific parameters suchas uplink coverage footprint, antenna gain, and available forward sectorpower. The coefficients capturing baseline performance are sometimestermed “Hong Yang” coefficients, after their author.


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401-614-040Issue 2, February 2003

Figure 2-5 “Hong Yong” coefficients

A set of coefficients that captures forward link performance for anormalized case (e.g., unity coverage, unity power, etc.) can beobtained via a computationally complex model. These coefficients canthen be used to scale results to a variety of design scenarios, usingdesign-specific parameters such as antenna gain and forward power.

Design scenarios that cannot be scaled from a normalized resultinclude those in which such underlying assumptions as fading andvoice statistics, velocity distribution, and path loss laws differ fromthose employed in the normalized result. In these cases, a different setof normalized results employing the new assumptions is required.

An example of a spreadsheet that functions as a link budget in that itextrapolates normalized results is shown in Table 2-4.

CDMAForward

Link Solver

Distributionof mobileposition

Distributionof shadow

fading

Distributionof soft

handoffs

Ec/Ior vs.Geometry

curves

µµµµ(xN)µµµµ(xI)σσσσ(xN)σσσσ(xI)E(xNxI)

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401-614-040Issue 2, February 2003

Table 2-4 Forward link budget

Forward Link Budget for 3G PCS 3 Sector 8 kbps CDMA with ASIC 1.1 and Mobility Applications (on Street)

B C D E F G

Line # Description Power W Power Comments

Transmit Power calculations

5 Nominal available power at J4 point 10.5 W 40.2 dBm Max power available

6 Pilot Channel Power 1.575 W 32.0 dBm 15% of max. power

7 Sync Channel Power 0.2 W 22.0 dBm 10% pilot power

8 Paging Channel Power 0.6 W 27.4 dBm 35.1% pilot power

9 Power available for the traffic Channel 8.2 W 39.1 dBm 78.2% total power

10 Total Overhead 21.8 % C10 = 100*(1 - (c9/c5))

11 Overhead factor to convert from mobiles to thenumber of active power channels

1.75 2.4 dB IS-95B new handoff

12 Cell site Cable Loss and combiner loss 2.0 3.00 dB

13 Cell site Transmit Antenna Gain 63.1 18.0 dBi

14 Propagation loss

15 Max. mean Propagation Path Loss 1.06E+15 150.2 dB

16 Mobile RX Signal power Calculations

17 Mobile Receive Antenna Gain 1.6 2.0 dBi

18 Mobile Body/Cable/Building Losses 1.6 2.0 dB

19 Thermal Noise Calculations

20 Mobile Noise Figure (F) 7.9 9.0 dB

21 Thermal Noise Density (No = KT) 3.98E-21 -174.0 dBm/Hz

22 Total thermal Noise power per Hz (NoF) 3.16228E-20

-165.0 dBm/Hz

23 Spreading bandwidth (W) 1.23E+06 Hz 60.9 dB

24 Total thermal noise power (NoWF) 3.88581E-14

W -104.1 dBm

25 External (intermod/spectrum clearance)interference

1.58489E-15

W -118.0 dBm

26 Number of Mobiles per Sector 36

27 Power Outage Probability 0.040


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401-614-040Issue 2, February 2003

A “Forward Link Budget” that extrapolates normalized results. Sincethe assessment of forward link performance can be computationallyintensive, a few normalized scenarios (e.g., unity coverage, unitypower, etc.) are assessed and can be later extrapolated in astraightforward way to design scenarios of specific interest. Thenormalized results are captured in the Hong Yang coefficients. Theextrapolation uses design-specific values such as antenna gain, sectorpower, and uplink coverage footprint. New coefficients must begenerated if the design scenario of interest has different fundamentalassumptions (e.g., fading statistics, path loss laws) from thoseemployed in generating the normalized results.

Solution--Approximate

Additional means may be used for forward link analysis. These aresimpler but approximate. Since the time required to obtain a solution byextrapolating from a normalized baseline (see the "Solution--Approximate" section) is usually comparable to the time required toobtain an approximate solution, the former is preferred. Nevertheless,approximate methods can provide useful insight. For completeness, webriefly outline several methods below.

28 Pilot Ec/(No+Io) at cell edge 0.04 -13.7 dB

29 Voice Activity Factor

30 Mean of VAF 0.48

31 Variance of VAF 0.122725

32 Hong Yang's Coefficients

µ(xN) 0.0107

µ(xΙ) 0.0200

E(xNxI) 0.0003

σ(xN) 0.0368

σ(xΙ) 0.0064

µ(Ξ) 0.01025894

σ2(Ξ) 0.00008474

µ(Ψ) 0.64631291

σ2(Ψ) 0.00533881

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401-614-040Issue 2, February 2003

The method outlined in the "Solution--Approximate" section can besimplified by placing all users at cell edge in an identical multipath andhandoff state. Given the specification of user number, cell radius (i.e.,allowed path loss, usually from the reverse link budget), forward sectorpower, and fading statistics, a geometry value for each user can becomputed. The distribution of these values is then examined todetermine whether it is appropriate to deliver performance; forexample, the range of user velocity that can be supported could beassessed.

This approach has the value of reasonable simplicity, particularly sincethe fades of the links from the host cell are assumed independent. Itsdisadvantages are the inaccuracies stemming from several sources,including the following:

• No fading can be assigned to the interference backgroundexperienced by each mobile at cell edge…for simplicity, thisbackground is presumed constant

• The presumption of all users at the cell edge is very conservative

• The presumption of identical multipath for each user is not correct

Although these limitations introduce error, the result is usuallyconservative, particularly if a high value of surrounding interferencebackground is used in computing user geometry. Accordingly, thisapproximate method remains useful.

A simpler approximation may be obtained by analyzing a single mobileat the cell edge, and assessing its performance when assigned themaximum allowed value of single link traffic channel power. Thisapproach renders the forward link very similar to the reverse link, sincethe fundamental issue of power-sharing amongst multiple mobiles isremoved. Although this approach also provides insight, it is less oftenused since it completely decouples coverage from capacity; i.e., it isdifficult to extrapolate from the single-link result how many additionalmobiles may be served within the footprint.


401-614-040Issue 2, February 2003

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3 RF engineering for data

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

Overview

Purpose This chapter offers a discussion of RF data issues for 3G-1X, includinga contrast between the Erlang B (voice) and Erlang C (data) models,analysis of capacity and coverage, and an examination of resourcemanagement.


Traffic theory 3-4

Introduction 3-4General 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


Symmetric forward data link analysis 3-23Example forward link budget 3-31Monte carlo forward link analysis 3-35

Resource management: RF scheduling 3-36

Introduction 3-36Scheduling algorithm 3-36

Fundamental Channel (FCH) assignment and release 3-36Forward link supplemental channel (F-SCH)

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

RF engineering for data


401-614-040Issue 2, February 2003

assignment and release 3-38Reverse link supplemental channel (R-SCH)assignment and release 3-41Load Balancing 3-42

Conclusions 3-43

RF engineering for dataIntroduction

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401-614-040Issue 2, February 2003

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Introduction

The availability of packet data features introduces additionalcomplexity into the air interface. In voice-only applications, channelrates are fixed and known; moreover, network influence on the channelis limited to handoff decisions and power control. In contrast, packetdata features allow variable channel rates dictated by the network. Inaddition, the network exerts further influence on the use of air interfaceresources through instructing channels when to transmit (burst) andwhen to wait. The role of the network in managing resources isdiscussed in some detail in "Resource management: RF scheduling"section on Page 3-36.

The performance impact of these differences must be added to thealready-present random effects of mobile speed, position, and fade. Theadditional parameters of channel rate and network control increase thecomplexity of performance prediction to the point where the situationis best analyzed via detailed end-to-end simulations of the 3G network.Simulators providing this level of detail have been developed to assessthe 3G performance. Approximate analyses via other methods, e.g.,link budget, have also been developed, but are of less utility for packetdata than for voice. The use and limitations of approximate methods arediscussed below.

In the following sections, insight into 3G-1X performance is offeredvia several discussions. In "Traffic theory" section, we overview thedifferences between circuit-switched (voice) and packet-switched(data) transmissions. This information provides a brief but necessaryframework for the performance discussions that follow. such as theidentification and computation of performance metrics applicable to adata network. These are shown to depend upon the number and datarates of channels available, which are obtained from RF analyses thatemploy numerical modeling within an RF footprint. The design of thisfootprint is addressed in the "Data link budgets" section, whichpresents the 3G-1X data link budget for various data rates.

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

RF engineering for dataTraffic theory


401-614-040Issue 2, February 2003

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

Traffic theory

Introduction The 3G-1X air interface is packet-switched in the sense that a limitednumber of high-speed RF data channels are shared across many users.

A packet-switched network may share channels across users for theduration of the calls, or user sessions. In contrast, a circuit-switchednetwork dedicates a channel exclusively to the user for the duration ofthe session. The latter model is frequently used in voice applications,where a dedicated channel is allocated and held for the duration of thevoice call. The former model is used in packet data applications, wheremultiple data sources transmit data intermittently over a group ofshared channels.

The “sharing” on the 3G-1X air interface does not entail the sharing ofa physically tangible resource; rather, the sharing concept derives fromthe fact that users transmit high-speed data bursts only when cued to doso by the network. Since channels at higher data rates produce moreinterference, the network manages these bursts in a way that ensuresonly a limited number of high-speed data bursts are simultaneouslyactive. This process prevents the interference background from risingabove acceptable levels while still allowing users to experience highdata rates. This resource management (see "Resource management: RFscheduling" section on Page 3-36) can be viewed as time-sharing alimited number of high-speed data channels amongst the users, and isthereby characterized as a packet-switching process. The restrictedavailability of the data channel for the duration of the user sessionwould be unacceptable for a real-time application such as voice, but isan efficient means for data support since the user need for transmissionis at most intermittent for many data applications (e.g., web-browsing).

For our purposes, the packet-switched nature of the air interface can becaptured through use of the Erlang model. This model can also be usedto illustrate the differences between the more familiar circuit-switched(voice) and packet-switched approaches, as well as to develop theperformance metrics that are relevant to a data network. Although thismodel is well documented in a number of references,4 it is overviewedbelow in order to establish a framework for the performancediscussions that follow. A variation of this model shall be used toestimate network performance, below (see "Data capacity" section onPage 3-13).

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

4 See for example Mischa Schwartz; “Telecommunication Networks”


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General Erlang model The Erlang model applies to the following general scenario, applicableto either voice or data:

Figure 3-1 General Erlang Model

The assumptions and results associated with this model are absolutelyessential in characterizing data performance. We review these briefly,below.

The model shows service requests (arrivals) entering a waiting area(queue). From the queue, the arrivals are vectored out into one of Npossible servers. Each server can serve only one arrival at a time. Anarrival has immediate access to any non-busy server.

If all servers are busy, the arrivals wait in the queue. The number ofarrivals waiting in the queue is therefore variable. The maximum sizeaccommodated by the queue, or queue length, is M arrivals. If thequeue reaches a size of M, further arrivals are turned away or blockeduntil at least one arrival can exit the queue and enter a non-busy server.

The definition of arrivals is very general. For wireless purposes, weview the arrivals as either voice calls requiring service (voice network)or message bursts requiring transmission (data network). In either case,the server is a transmission channel. In the former case, the server is a

Arrivals λ

Completions µ

Completions µ

Queue (length M)

Nservers

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dedicated channel that holds the voice call for its entire duration; in thelatter case, the server is a transmission channel that transmits the burst.In either case, once service for the arrival is complete, the resource isthen freed up for the next arrival.

The rate of arrivals is characterized by a process in which the time ofarrivals is random and independent; i.e., the probability of an arrival inany one instant is identical to and independent of the probability of anarrival in any other instant. The average rate of arrivals is usuallycharacterized by λ (e.g., calls/minute, messages/hour).

The service process is similarly characterized. For a busy server, thetime of service completions is also random and independent. Theaverage rate of completions for each server is usually characterized byµ (e.g., completed calls/minute, messages transmitted/hour). The per-server completion rate is of course distinct from the system completionrate, since the system rate is dependent upon the number of busyservers. For example, the system average completion rate when Nservers are busy is N×µ .

Knowledge of the parameter µ can be used to compute the probabilitydistribution of the inter-completion time. For voice calls, the inter-completion time is clearly the hold time. Its random distributionreflects the random duration of voice calls. For messages, the inter-completion time is simply the time required for the channel to transmitthe message. Given a fixed channel data rate (e.g., 64 kbps), thisrandom distribution reflects the random length of arriving messages. Inboth cases, the average inter-completion time is computed to be 1/µ.

Within these very general assumptions, the model in Figure 3-1 can besolved analytically for the probability of all possible states, where thestate is determined by the total number of arrivals within the system;i.e., the sum of all arrivals being served as well as any arrivals waitingin the queue. The possible states, therefore, range from 0 to (M+N).The last state is the blocking state, since in this state no more arrivalscan enter the system. The probability of the state (M+N) is therefore theprobability of blocking.

The probability states are found to depend upon the ratio of λ /µ , ratherthan the value of either alone. This ratio is a system load parametermeasured in Erlangs. Since 1/µ is the average inter-completion time,this load measure may be viewed as the arrival rate weighted by theaverage “stress” (average hold or average transmit time) each arrivalplaces on the system.


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The computations described above produce an analytical relationbetween the Erlang load, number of channels, queue length, and stateprobabilities. This relation has been extensively tabulated for thespecial case where the queue length is zero. This Erlang B tabledemonstrates the relation between the Erlang load, the number ofchannels, and the probability of state N. The latter is the probability ofblocking in this case: since there is no queue, the probability of newarrivals being turned away or blocked is simply the probability that allN servers are occupied. The Erlang B model is discussed in more detailbelow, and contrasted to an alternate special case of infinite-lengthqueue (Erlang C).

The above concepts are summarized in the table below.

Table 3-1 Summary of Erlang model

Special cases: Erlang Band Erlang C

In any situation, the collection of state probabilities depends upon theErlang load as well as the values of M (queue length) and N (servers).Two limiting cases are of especial interest.

In the first case, the queue length is set to 0. Arrivals are thereforeblocked as soon as all servers are busy; i.e., the probability of blockingis probability of the state N. The blocking probability is entirelydetermined by the Erlang load and the number of servers N. Therelation between the three is captured in an Erlang B table, whichallows computation of any one (e.g., Erlangs) from specification of anyother two (e.g., probability of block, number of servers).

Average arrival rate λ

Average server completion (of service) rate µ

Average server inter-completion time 1/µ

System load (Erlangs) λ /µ

Number of servers N

Length of queue M

Maximum system occupancy N+M

Probability of block = Probability of state (M+N)

Average system completion (of service) rate nµ , where n = current system state

Special case Erlang B (M = 0 or no queue)

Special case Erlang C (M → infinity or infinite queue)

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The Erlang B table is widely used for voice calls, since its underlyingmodel captures the scenario where voice users make a single callattempt (a single arrival) and are either immediately served or blocked.In the latter case, the user may try again at a later time, but the elapsedtime is sufficient to ensure that the next attempt resembles a new,independent arrival to the system.

In the second case, the queue length is presumed infinite. Arrivals aretherefore never blocked; however, there is a probability of delay. Theprobability of being delayed (i.e., of waiting some nonzero time in thequeue for service) is the probability of the state N, where all servers arebusy. The delay probability is entirely determined by the Erlang loadand the number of servers N. The relation between the three is capturedin an Erlang C table, which allows computation of any one value (e.g.,Erlangs) from specification of any other two (e.g., probability of delay,number of servers). Since the average wait time in the queue can bedetermined from the probability of delay (and vice-versa), an alternate3-way relation of Erlangs, average wait, and number of servers may betabulated.

The Erlang C table may also be used for voice calls, since itsunderlying model captures the scenario where voice users makerepeated, multiple attempts as necessary to be served. In thisinterpretation, each arrival is a single voice user attempting to accessthe system. The user is either served on the first attempt, or not; in thelatter case, the user continues to attempt to access the system untilserved. These continuous reattempts place the user in the system queue,“waiting” for service. Note that the queue in this application isconceptual, representing the collection of users attempting but not yetachieving access.

The use of this model for voice calls is less prevalent than that ofErlang B, since it requires that each user continuously attempt accessuntil finally served; in contrast, Erlang B requires a single accessattempt per user. Neither model can therefore accommodate scenarioswhere each user may execute 1 or 2 immediate re-access attemptsbefore being served or blocked, but Erlang B is frequently consideredto be a better approximation of this situation than Erlang C.

The Erlang C model is more typically used for packet data, since thepresence of a queue lends itself to modeling the management of dataresources over shared channels. In this application, a large number ofdata sources time-share a modest number of transmission channels N.The data sources send brief data transmissions (bursts) as permitted by


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the network, which attempts to share the transmission channelresources in some efficient manner. Bursts (messages) undergoingtransmission are being served by one of the N servers in the Erlang Cmodel (see Figure 3-1). Messages waiting their turn for transmissionare in the queue, regardless of whether these messages are stored ateach data source (a conceptual queue) or stored in a single intermediatephysical buffer between the data sources and the servers (physicalqueue).

The random nature of the arrival process into the queue is driven by thefact that the data source does not require the sending of continuousmessages; rather, the arrival of messages is randomized by the bursty,interactive nature of the data application (e.g., web-browsing). Indeed,this randomness is exploited in order to efficiently serve the data userswith a number of servers that is less than the total number of active datasessions. The random nature of the service process at each serverderives from the random variations in message length. For a server offixed transmission rate, these random variations in length randomizethe service or hold time for each arrival.

In Erlang C, the net rate at which arrivals exit the system after beingserved depends upon the number of busy servers. For n busy servers,the net rate is n×µ , where n can vary from 0 to N. Since the probabilityof all states is known, the average net rate at which arrivals exit thesystem (the throughput) can be computed as:

Equation 3-1: Throughput equation

The units of throughput are messages/second or more conventionallybits/sec. In the above, the average rate is computed by weighing theservice rate at each state by its state probability. For n less than N, theservice rate associated with each state is n×µ , since for these states, thequeue is empty and n servers are busy. For n greater than or equal to N,all servers are busy and the service rate becomes fixed at N×µ. This rateis therefore weighted by the probability of delay, since the probabilityof all servers busy is simply the probability that an arrival will bedelayed (i.e., will need to wait in the queue). The concept of throughputis directly applicable to 3G-1X traffic planning, as described below.

delay

N

n

pNnpnthroughput ⋅⋅+⋅⋅=∑−

=

µµ1

0

)(

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Applications of Erlang C to3G-1X data

We now consider specific use of the Erlang C model for 3G-1X data.Identity of the model components, as well as specific measures ofperformance for planning and analysis, are discussed below.

In 3G-1X data, high-speed or supplemental channels are dynamicallyset up for the users when a burst is cued, and torn down when the burstis complete (see "Resource management: RF scheduling" section onPage 3-36). In order to control interference, only a limited number ofsupplemental channels may be simultaneously active; accordingly, wemay view the process as simply time-sharing a fixed number N of high-speed servers. These high-speed channels are the servers within theErlang C model. (The number of servers is determined via RF analysisin "Data link budgets" section on Page 3-19).

Message bursts requiring transmission are either immediatelytransmitted, or stored awaiting transmission. At the reverse link,storage occurs within the mobile data device. At the forward link,storage occurs at a buffer in the cell site. In both cases, this storagecorresponds to the queue in the Erlang C model where arrivals arewaiting for access to the servers. The forward link queue is physical inthat a single buffer can be identified where messages arrive and awaitservice. The reverse link queue is more conceptual in that it consists ofthe collection of stored messages across the mobile data devices. Inboth cases a large number of arrivals can be stored; hence, the queuelength is approximated as infinite.

For this queue and these servers, a three-way relation between Erlangload, number of servers, and average wait time in the queue is readilydetermined from the Erlang C model. Once these values aredetermined, the throughput can also be calculated (see Equation 3-1).Accordingly, the load that can be accommodated by a sector can beobtained by specifying the number of servers and the average waittime.

In 3G-1X, the determination of the number of servers per sector is aconstraint dictated by the RF interface. The average wait time (e.g., 5seconds) is specified as a requirement and corresponds to the averagetime between actual message transmission and the time at which dataenters the buffer (mobile or cell) to await service. Given these values,the Erlang load that the sector can accommodate follows directly fromthe Erlang C model. This load can then be compared to the load offeredfrom the subscriber population to assess how many sectors arerequired.


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This process is followed in 3G-1X traffic planning with a slightmodification: the offered load is assessed in throughput rather than inErlangs. This approach differs from that employed in Erlang B, since inthe Erlang B model the subscriber load in Erlangs can be determined ina manner independent of the network; i.e., the load depends only uponthe characteristics of the subscriber population. In Erlang C, thesubscriber load in Erlangs depends upon transmission properties of thenetwork as well as upon characteristics of the subscriber population.This difference, which drives the use of throughput as an alternate loadmeasure in planning data networks, is described below.

In a voice network modeled by Erlang B, the load in Erlangs is theproduct of arrival rate and of average hold time (see "General Erlangmodel" section on Page 3-5 and "Special cases: Erlang B and Erlang C"section on Page 3-7). Arrival rates (e.g., calls/minute) are clearly afunction of the subscriber characteristics alone. Hold times (e.g.,minutes/call) are also a function of the subscriber characteristics aloneprovided that any additional network processing time is negligible bycomparison (a very good assumption for hold times that are typicallymeasured in minutes). The Erlang load offered to a sector can thereforebe determined from subscriber characteristics alone; indeed, sinceErlangs from different sources add together to yield net Erlang loads5,the total load offered to an unspecified voice system can be determinedby multiplying the estimated average subscriber contribution (typicallyexpressed as milliErlangs per subscriber) by the estimated subscriberpopulation. In planning, this offered load is readily compared to theaccommodated load per sector in order to determine the number ofsectors needed within any geographic area.

Accordingly, we seek an alternative measure of load that is a functionof subscriber characteristics alone. Since Erlang loads from multipledata sources add, we view the subscriber population as a largecollection of data sources, each contributing a modest Erlang load tothe data network. The arrival rate (e.g., messages/second) for the ithdata user is λi. The average hold time per message is identical at 1/µ,which can be expressed as the average message length in bits dividedby the server capacity of C bits/second:

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

5 This addition property for multiple sources holds provided that each source has iden-tical hold time statistics. This assumption holds well for voice users.

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Equation 3-2: Total Erlang calculation

In the above equation, the expression within the final sum has the unitsof messages/sec * bits/message or bits/sec. This measure represents thetotal data transmission load (usually expressed in kbits/sec) orthroughput offered by the subscriber population. This measure of loadis proportional to the Erlang load via the transmission capacity C asshown above, and is a property of the subscriber population alone.Since the throughput accommodated by the network can be readilycomputed from the Erlang C model (see Equation 3-1), this value canbe compared to the throughput offered by the subscriber population inmuch the same way that the Erlang load possible on a voice networkcan be compared to the Erlangs offered by the subscribers.

Traffic planning for 3G-1X data networks can therefore be done asfollows:

1. Establish the number and rate of servers available on the airinterface per sector via RF analysis

2. Specify average wait time required

3. Compute the throughput that can be accommodated by the sectorby using the Erlang C model

4. Estimate the throughput offered by the subscriber populationthrough estimating the messages/sec and the average messagelength (see Equation 3-2)

5. Compare the accommodated throughput to the offered throughputto determine how many sectors are required.

For example, if a sector can accommodate 100 kbps satisfying the waittime constraint specified, 10 sectors are needed to address an areaoffering a total 1000 kbps. More sectors might be needed to addressother requirements, such as RF coverage throughout the area.

Steps 1 through 3 are addressed in the Lucent modeling describedbelow. This information establishes a throughput per sector for anaverage wait time of 5 seconds and various other assumptions on thedata traffic encountered. The value obtained varies as wait time anddata statistics are altered.

∑∑∑ ====issubscriberdata

iissubscriberdata

iissubscriberdata

itotal LCC

LErlangsTotal λλ

µλ

µλ 1

RF engineering for dataData capacity

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Data capacity

Introduction In this section, we determine the capacity offered by a 3G-1X sector.Although this capacity is best determined by detailed time-dependentsimulations, considerable insight can be gained by less computationallyintensive modeling that exploits the Erlang C model. The essentialdetails of this modeling are overviewed below.

In summary, information obtained from standards is used to developlink level simulations. This data is input to a system simulation. Thissimulation determines the number and rate of channels available fromRF considerations. This information, coupled with end-user trafficmodels and system performance constraints, is used to determinecapacity via an Erlang C model (see Figure 3-1).

We focus our attention on the capacity calculation.

An average wait time for a message is specified as a requirement. Thethroughput for the sector can then be calculated from the Erlang Cmodel provided that the other components within the model arespecified. These include hold time per server, rate of server, andnumber of servers.

To determine this information, we presume a forward-link limitedsituation within a cell coverage area. This presumption divorces theanalysis from specific output powers and specific cell radii. The powerrequired to balance the links is discussed separately in "Data linkbudgets" section on Page 3-19.

Within the coverage area, one of the possible 3G-1X supplemental datarates (e.g., 19.2 kbps) is selected and fixed. Given a presumed averagemessage size, the average supplemental channel hold time required permessage is computed. The number of channels accommodated by theair interface at this rate is a random function depending upon a numberof variables including mobile position, speed, multipath, and fade.Monte Carlo analysis is therefore employed to produce a probabilitydistribution function of the number of channels at this rate.

For each possible number of channels within the distribution, athroughput is calculated from the Erlang C model. The probability ofthis throughput is the probability of the associated number of channels.An overall average throughput for this data rate is computed byweighing each value of throughput by its probability.

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The process is repeated for each 3G-1X data rate of interest, yielding anaverage throughput for each rate. Using estimated average throughputper subscriber (where the averaging interval includes delays betweentransmissions required to read or think about a downloaded message),the number of subscribers accommodated at each rate is calculated.

The results for each data rate are tabulated and then combined in aweighted fashion that reflects the anticipated mix of users at differentdata rates. The thoughputs calculated are then compared to offeredsubscriber loads to determine how many sectors are required.

This process is summarized in Figure 3-2, and described in greaterdetail below.

Figure 3-2 Overview of computation process for capacity

Estimation of data capacity From an air interface perspective, we anticipate that the 3G-1X packetdata capacity and throughput will be governed by several interlockingfactors including:

• The number of users (fundamental and supplemental channels)that can be supported

• The number of users that share the supplemental channels

LINK LEVELSIMULATION

Power Requirementsper Channel

PhysicalLayerSpecs.

User Mobility ChannelStructure

DataProtocols

SYSTEM LEVELSIMULATION

Number of Channels

End UserTraffic Model

QoSRequirements

QUEUING MODEL

CAPACITY

IS-2000 STANDARD


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• The relative position of the users within the cell site coverage area.This information is key since the maximum data rate supported bythe link can clearly increase when the user is closer to cell center.

• The average throughput per data user

• The associated FER target

• The Automatic Repeat Request (ARQ)

• The link channel activity and packet call size.

Several studies have been done to examine aspects of these elements.For example, analysis on the air interface limit of supplementalchannels has been done for each supplemental channel data rate byconducting link level and system level simulations. The air-interfacelimit of supplement channels derived in this analysis is the distributionof the simultaneous active channel number that depends on the targetFrame Error Rate (FER), mobile locations, mobile speeds, propagationenvironments, other user interference and the base station powerallocated to each traffic channel. Once the distribution of the number ofsupplemental channels is determined, the M/M/m queuing model(Poisson arrival, exponential distribution of service time and m servers)is used to compute the average total throughput and data user capacitythat can be supported for a given data traffic model including averagepacket call size, target queuing delay, and supplemental channel rate.More specifically, the link level simulations are performed to obtain therequired base station power fraction for a traffic channel versus thegeometry that is a function of the mobile location and propagationenvironments. The geometry is defined as the ratio of the mobilereceived serving sector power to the mobile received other interferingsector power plus noise power. In the link level simulation, we considerthe following parameters:

• Radio Configuration 3 (RC3)

• 9.6kbps at 1% FER, 19.2kbps at 2% FER, 38.4kbps at 2% FER,76.8kbps at 3% FER, and 153.6kbps at 5% FER

• No handoff on the forward link for supplemental channels.

In order to obtain the Probability Density Function (PDF) ofsupportable supplemental channels from the system level simulator, thefollowing assumptions are made:

• Snapshot simulation technique

• 3-sector configuration, 19 cells and 57 sectors

• Randomly generate data user location within center cell

• ITU vehicular propagation model

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• 8 dB log-normal standard deviation and 0.5 site-to-site correlation

• Mobile speed distribution: 50% for Additive White GaussianNoise (AWGN) and 50% for 1 path Rayleigh fading at 3 kmph(pedestrian speed)

• 5% outage probability

• Turbo code gain is considered for data rates greater than or equalto 19.2 kbps.

Having determined the distribution of the supplemental channelnumber, we employ the M/M/m queuing theory to derive the averagethroughput and data user capacity based on the data traffic model forweb browsing (illustrated in Figure 3-3). In the data traffic model, asession is defined as the interval between the time instant when a datauser logs in the web site and the time instant when the user logs off theweb. A session consists of a number of packet calls (web pages for theweb browsing application), each of which is comprised of severalpackets. For the web browsing application, the total delay per page isdefined as the time interval between a mouse click and the completionof a web page download. In other words, the total delay per page is thesum of the access time, network delay, queuing delay and downloadtime. The average packet call inter-arrival time between two adjacentmouse clicks equals the total delay per page plus the think time.Think time is the duration between the time instant when startingreading a web page and the time instant when clicking a mouse for thenext page. Therefore, the average throughput is obtained by dividingthe average packet call size by the average packet call inter-arrivaltime.

In the following, we will provide the average throughput and data usercapacity in terms of simultaneous data sessions for the case where5 sec is selected as the queuing delay per packet. To characterize thedata session fully, some additional assumptions are made:

• Exponentially distributed packet call (web page) size with a meanof 41.1 kBytes

• Exponentially distributed “think” time between packet calls (pagedownloads) with a mean of 40 sec

• Packet Call Inter-Arrival Time = Access & Network Delay (3 sec)+ Target Queuing Delay (5 sec) + Download Time (dependent onthe channel rate) + Think Time

• Average number of packet calls per session = 20

• “Equal user throughput” scheduling policy


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Figure 3-3 Data traffic model for web browsing application with the3G-1X packet data users

Feeding the system level simulation results into the queuing modelwith the data traffic scenario, we obtain that average throughput peruser for 3G-1X packet data. The packet data capacity is shown inTable 3-2 as a function of supplemental channel data rate. In the table,the average total delay per page is defined as the sum of the accesstime, network delay, queuing delay, and download time. The averagenumber of simultaneous data sessions can be calculated by dividing theaverage sector throughput by the average user throughput. It isobserved that as the supplemental channel data rate decreases, theaverage total delay increases but the average sector throughput and theaverage number of simultaneous data sessions are comparable.

The average data user capacity is determined by several dominantfactors: average packet call size, supplemental channel rate, think time,and Quality of Service (QoS) including the target FER and queuingdelay.

38.4

76.8SCH

153.6SCH

SupplementalChannelBursts

AccessTime

76.8SCH

9.6 kbps FCH

76.8SCH

153.6SCH

153.6SCH

9.6 FCH

Web Browsing Session

Active Dormant Active

MouseClick

MouseClick

NetworkDelay Queuing Delay

( incl. SCH Setup Delay)

FirstData

Arrivedat IWF

"Think" Time

Dormancy TimerDuration

DownloadTime

FundamentalChannels

Dormant

StartReading

Web Page

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Table 3-2 Average data user capacity and throughput with anaverage packet call size of 41.1 kBytes and a targetqueuing delay of 5 seconds

Note that the above values indicate that the throughput per sector isrobust with respect to the data rate. This result indicates that ananticipated throughput of 109 to 112 kbps is robust with respect towhatever weighting is employed to combine the results at individualdata rates into an overall estimate. This observation is useful inplanning, but could change as components of the underlying trafficmodel or requirements (e.g., think time and the average wait in queue)are altered.

ChannelRate(kbps)

Total Delayper Page(sec)

Average UserThroughput(kbps)

Number ofSimultaneous DataSessions

Throughput persector percarrier(kbps)

19.2 25.1 4.9 23 11138.4 16.6 5.7 20 11276.8 12.4 6.1 18 111153.6 10.3 6.4 17 109

Average 16.1 5.8 20 110.8

RF engineering for dataData link budgets

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Data link budgets

Reverse link The reverse link data budget for 3G-1X data is readily obtained byrecognizing that coverage is dictated by the data rate desired at theedge of the data coverage; i.e., the edge of the coverage of the reverselink supplemental channel used to transmit high-speed data bursts. Thisedge may or may not correspond to the physical edge of the cell, whichcould for example be designed to support voice rate at its perimeter andhigher data rates only within its interior. With the data rate desired atthe edge of data coverage specified, the data coverage footprint isdetermined by presuming that all users within this footprint operate atthis data rate when transmitting on a supplemental channel. Theanalysis outlined in Chapter 2, "Reverse link" section on Page 2-4, forvoice therefore applies directly with only a few simple modifications.These are:

• The voice activity for the supplemental channel is presumed to be1. This high usage reflects the assumption that the fewsupplemental channels supported by the air interface will bealmost continuously busy as they are shared from user to user.

• The information rate is higher, corresponding to the data rate (e.g.,19.2 kbps) selected for cell edge

• A voice user certainly requires a body (head) loss; e.g., 2 dB. Adata user employing a data device may encounter little or no loss.In the below, a 0 dB loss for data users is assumed.

• The Eb/Nt requirement is lower for the data application due to therelaxed target FER. The relaxed FER is permissible since the dataapplication is not real time; i.e., frames received in error can beretransmitted.

The PCS Modcell reverse link budget examples for 3G-1X 19.2 kbps to153.6 kbps packet data, mobility applications and 9.6 kbps voiceapplication are shown in Table 3-3. Note that the target FER relaxationfor the data application is used to increase the maximum path loss (orcell coverage). Simulation results indicate that the increased FER doesnot cause significant TCP/IP throughput degradation.

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Table 3-3 Reverse link budget for PCS 3G-1X 9.6 kbps voice, 19.2 kbps to 153.6 kbps packet data,mobility applications

Item Units 3G-1XVoice

9.6kbps

3G-1XData

19.2kbps

3G-1XData

38.4kbps

3G-1X Data76.8kbps

3G-1XData

153.6kbps

Comments

(a) Maximum Transmittedpower per traffic channel

dBm 21 21 21 21 21

(b) Transmit Cable, connec-tor, combiner, and bodylosses

dB 2 0 0 0 0 No body loss for data user

(c) Transmitter AntennaGain

dBi 2 2 2 2 2

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

dBm 21 23 23 23 23

(e) Receiver Antenna Gain dBi 18 18 18 18 18

(f) Receiver Cable and Con-nector Losses

dB 3 3 3 3 3

(g) Receiver Noise Figure dB 4 4 4 4 4 For Modcell

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

(i) Receiver InterferenceMargin

dB 5.5 5.5 5.5 5.5 5.5 72% loading for 3G-1X

(j) Total Effective Noise plusInterference Density= (g + h + i)

dBm/Hz -164.5 -164.5 -164.5 -164.5 -164.5

(k1) Information Rate(10log(Rb))

dB 39.8 42.8 45.8 48.9 51.9

(l1) Required Eb/Nt dB 4 3.4 2.6 1.8 1 With Turbo code gain fordata; 1% target FER for9.6kbps, 2% for 19.2kbps,2% for 38.4 kbps, 3% for76.8kbps and 5% for153.6kbps; considering 2spatial receive diversitybranches

(m) Receiver sensitivity(j + k + l)

dBm -120.7 -118.5 -116.5 -114.5 -112.7

(n) Hand-off Gain dB 4 4 4 4 4 90% cell edge coverage

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

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

(p') Building/Vehicle Pene-tration Loss

dB 0.0 0.0 0.0 0.0 0.0 For outdoor coverage

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

dB 150.4 150.2 148.2 146.2 144.4


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401-614-040Issue 2, February 2003

If the design goal of a newly deployed 3G-1X system is to provide aubiquitous coverage for a high-rate data service, then the link budgetbased on the supplemental channel rate should be used for RF design.In this case, the physical edge of the cell is determined by the edge ofdata coverage. In contrast, if the voice link budget is used, then thehigh-rate data service will be available with the same probability ofcoverage as voice coverage in an inner circle of the cell coverage. Inthis case, the supportable packet data rate, or alternatively theprobability of achieving a higher data rate, will reduce when the mobilemoves close to the cell edge. The maximum allowable path loss for thepacket data can be extended by employing the data terminals withhigher antenna gain and transmitted power and increasing the basestation transmit power.

In the above examples, the interference margin is retained at a constant5.5 dB in spite of the fact that the number of supplemental channelsavailable at each data rate decreases as the data rate increases. Areduced number of supplemental channels could force a reduction inloading in order to ensure system stability; however, the interferencebackground is stabilized by the constant (1) value of voice activity forthe few channels present (see Chapter 2, "Solution--Approximate"section on Page 2-9).

The link budgets shown above can be applied to the situation ofubiquitous coverage at a given data rate. For example, if 76.8 kbps isdesired throughout the coverage area, the cell footprint would bedesigned by employing the 76.8 kbps budget: since this cell spacingextends the 76.8 kbps to the cell edge, this rate is by extension availablethroughout the interior of the cell. Since each data rate has equalinterference margin, the budgets shown can also be used to map out therelative coverage areas for a mix of supplemental channels within alarger footprint. For example, the outer physical perimeter of the cellcould be established using the 9.6 kbps link budget. Within thisperimeter, the restricted dB losses shown for the link budgets at higherrates establish the inner coverage areas where the higher rates areavailable as shown in the following figure:

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401-614-040Issue 2, February 2003

Figure 3-4 Inner coverage areas for higher supplemental channeldata rates

Forward link Analysis of the forward link is best conducted by numerical simulation;however, the computational load associated with such calculationsdrives the need for simpler planning tools. In the following, we brieflyconsider several alternatives for simplified forward link analysis. Therelative merits of each are discussed.

All techniques can be employed in two basic planning configurations.The first or embedded configuration is determined by a single data rate,e.g., 76.8 kbps. This data rate corresponds to the physical edge of thecell and thus determines the physical cell footprint. The second orconcentric configuration is determined by two data rates, e.g., 76.8kbps and 9.6 kbps. The lower data rate determines the physical edge ofthe cell, i.e., the outer boundary. The higher data rate corresponds to theboundary of an inner footprint within the cell where the higher data ratecan be supported. The inner footprint is thus a subset of the overall cellcoverage.

This concept is illustrated in Figure 3-5. The concentric configurationis more common, since upgrades to 3G-1X frequently involve overlayon existing networks where the outer physical boundary is determinedby the IS-95 voice data rate.

- 9.6 kbps Fundamental Voice or Data Coverage- 19.2 kbps Supplemental Coverage

- 153.6 kbps Supplemental Coverage

- 38.4 kbps Supplemental Coverage- 76.8 kbps Supplemental Coverage

Cell Citegamma

alphabeta


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401-614-040Issue 2, February 2003

Figure 3-5 Concentric configuration: inner and outer boundariesdictated by two data rates

In the following, we consider the application of symmetric link budgetanalysis and Monte Carlo link analysis to the forward link. Note thatthe former is essentially identical in form to a spreadsheet analysis inwhich all terms (including symmetric terms common to each link) areemployed; however, the discussion below focuses on the symmetricapproach in order to more compactly indicate the concepts involved. Ineach case, application to embedded and concentric configuration isdiscussed.

Symmetric forward data link analysis

The purpose of symmetric forward link analysis is to establish the pathloss within which a given data rate can be supported. This analysismight be done to assess whether a footprint established by reverse linkcan be supported, or to establish limits on path loss imposed by forwardlink considerations alone. The latter is useful in situations where, bydesign, the forward link is expected to carry higher data-rate trafficthan the reverse link. In this case, support of the footprint establishedby the lower-rate reverse link would not be relevant; rather, the designfootprint would be established solely by forward link limitations.

The data rate to be supported at the cell edge is chosen. This rate is therate desired for the supplemental channel. A path loss to the cellboundary is computed (e.g., from reverse link considerations), orsimply presumed as a starting point for analysis. All forward links arepresumed to burst at this data rate, and the mobile receivers aresymmetrically arranged in a worst-case situation at the cell edge. Theanalysis then determines whether the available forward link power is

Outer boundary; e.g., 9.6 kbps

Inner boundary; e.g., 76.8 kbps

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401-614-040Issue 2, February 2003

sufficient to achieve the required forward link Eb/Nt at the mobilereceiver in light of fading phenomena across the links. The symmetricarrangement of the mobiles ensures that the Eb/Nt requirement for eachlink is identical, and renders the problem soluble without extensivenumerical computation.

Although the approach is conceptually similar to voice analysis,important differences exist. Unlike voice, the rates of all links are notidentical. The analysis must consider mobiles employing both the low-rate fundamental and the high-rate supplemental channels. The formerare mobiles transmitting at low levels while waiting to burst, i.e.,waiting for a supplemental channel. The latter are mobiles bursting,i.e., transmitting on a supplemental channel. In addition, soft handoff isonly available for the fundamental channel. No soft handoff exists onthe forward link supplemental channel.

Furthermore, the definition of “cell edge” in this analysis depends uponthe configuration employed. In the embedded configuration, there is noambiguity: the cell edge corresponds to the physical outer perimeter ofthe cell. In the concentric configuration, the cell edge in analysiscorresponds to the physical edge of an inner coverage circle where thedata rate of interest can be supported. The outer coverage boundary ofthe cell is dictated by a lower data rate and corresponds to the physicaledge of the actual cell footprint (see Figure 3-5). To avoid confusion,we will refer to the edge corresponding to the high data rate of interestas the data cell edge. The data cell edge is the boundary of cellfootprint in an embedded configuration, but is the edge of the innerboundary in the concentric configuration.

With these definitions, we proceed as follows for both configurations.

We first establish the path loss corresponding to the data cell edge bynoting the sensitivity required for the uplink at the data rate of interest(e.g., 76.8 kbps):

Equation 3-3

{ }

−+−==

αηβ )1)(1(max

min

Nd

gWFN

SES t

)(max

min

fadegw

Sa

net

=


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401-614-040Issue 2, February 2003

The above expression essentially corresponds to reverse link analysisfor the supplemental channel data rate of interest (see "Reverse link"section on Page 3-19). Note that the processing gain g must equal theratio of bandwidth to data rate, R, as in voice. However, the processinggain may well be modest (in comparison to voice) since thesupplemental channel data rate can be as high as 153.6 kbps. Thereceiver sensitivity is used to solve for the attenuation (path loss) a,which will serve as a starting point for forward link analysis.

Alternatively, a value of a could be assumed. We compute the value inthis way for this example under the presumption that it is desired thatboth links achieve the same supplemental channel data rate at the datacell edge, regardless of whether concentric or embedded configurationsare employed.

We now proceed by placing all mobiles at the data cell edge. Mobilereceiver Eb/Nt requirements and total forward power constraints arethen used to produce the governing relationship that must be satisfiedwith high probability.

Equation 3-4

This form of Equation 3-4 is essentially identical to that employed forvoice. In spite of this similarity, the value and meaning of many of theunderlying parameters are different. The summation is over bothsupplemental and fundamental links. Accordingly, the values ofchannel activity α, forward link Eb/Nt requirement d, interference ratioβ, and processing gain g extend across both supplemental andfundamental channels. This extension is the reason behind the subscripti on the processing gain. Unlike voice, this value is not constant perlink, but varies in accordance with whether the link is fundamental orsupplemental.

Accordingly, we alter the form as follows:

[ ]total

iii

N

i i

iii

Q

Qgd

g

dlinksmax

1

)1()//1(1

γβηβα −≤−+∑

=

[ ] ( ) [ ] )1()//1(1)//1(111

γηηηβξβαηηηβξβεε

αη −≤−+=−+

∑∑

==ggdii

N

i

newidgdii

N

i gi

d

id

linkslinksi

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401-614-040Issue 2, February 2003

where:

and

Equation 3-5

Presuming that the total number of links Nlinks is composed of Nsuppl andNfund links, the means of d and g are readily computed by using constantvalues of d and g for supplemental links and constant values of d and gfor fundamental links:

Equation 3-6 Composite means over fundamental andsupplemental channels for processing gain and required Eb/Nt

The newly defined channel activity has statistics defined by thefundamental and supplemental channel activities, weighted by thedeviations of Eb/Nt, d, and processing gain g from their means. Thisrandom variable is independent of others in the sum. The solution forsatisfying this relation with high probability, provided that it isunderstood that the channel activity variable in this solution is thenewly defined channel activity above is:

Equation 3-7 Forward link budget statement

Satisfaction of this inequality indicates that the supplemental andfundamental channels can indeed be supported at the data cell edge.The forward link budget essentially evaluates the left-hand side

gggi

dddi

ii

ii

gEg

dEd

ηεε

ηεε

==

==

( )

=

gi

di

newi

i

εε

αα

plfundtotal

fundtotal

fundpl

total

plg

fundtotal

fundpl

total

pld

NNN

where

gN

Ng

N

N

dN

Nd

N

N

sup

supsup

supsup

+=

+=

+=

η

η

[ ]dgd

linkslinksg N

k

Nηηηηξ

ησ

ησ

ηησσ

ηηγη β

α

α

β

β

βα

βα

βα

≥−+

+++− −

−

1

)1(

2

2

2

2

22

22

)//1(11)1(


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401-614-040Issue 2, February 2003

expression, and ensures that it is greater than or equal to the right handside. This analysis, encapsulated in the spreadsheet, can be used tosolve for alternate values, given others.

For example, the current format uses an assumed path loss and total J4power to assess the Eb/Nt that can be achieved with high probability inorder to compare this value to the right hand side requirement inEquation 3-7. Alternatively, the required Eb/Nt and J4 power can beused as inputs to solve for the path loss that can be tolerated while stillsatisfying Equation 3-7 with high probability.

Equation 3-7 can also be evaluated using a more detailed calculationthat simply includes symmetric terms like antenna gain. As expected,the results are identical since the precise value of the symmetric termshas no effect in establishing forward link viability. Nevertheless, themore detailed spreadsheet (see Table 3-4) is sometimes preferred sinceit lists such terms explicitly.

With the exception of terms related to the interference ratio β andnewly defined channel activity α, all other factors required to evaluateEquation 3-7 can be found in Equation 3-6. We now consider theevaluation of these channel activity and interference ratio terms.

The computation of the mean and variance of the newly definedchannel activity can be done in a conventional way provided that thestatistics of this random variable are known. These are readilydeveloped as follows. We presume that the shared supplementalchannel(s) are continuously employed; accordingly, their activity is 1.In contrast, the fundamental channels operate at 1/8 of the fundamentalchannel rate of 9.6 kbps, i.e., a low rate sufficient to maintain the callbetween bursts. Considering the definition in Equation 3-5, thestatistics underlying the newly defined channel activity are:

Equation 3-8 Voice activity for data link budget

With probability Nsuppl/Ntotal:

gpl

dplnew

g

d

ηη

α/

/)1(

sup

sup=

With probability Nfund/Ntotal:

gfund

dfundnew

g

d

ηη

α/

/)8/1(=

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401-614-040Issue 2, February 2003

Note that the former is simply the value of new channel activity for asupplemental channel. The latter is the value of new channel activityfor a fundamental channel. The Equation 3-8 completely characterizesthe statistics of the newly defined channel activity; accordingly, meanand variance can be computed in the standard fashion.

We assume that the values and statistics of interference ratio areidentical for both fundamental and supplemental channels. Thisassumption generally follows from the symmetric placement of allmobiles at data cell edge, and is either accurate or simply conservativedepending upon the configuration employed (see below).

In the embedded configuration, the value of Pother/Phost for thesupplemental channel is larger than in voice applications, since theforward link supplemental channel does not enter into soft handoff atthe data cell edge. Accordingly, the value of Pother is raised since thebroadcasts from the neighbor cell(s) can no longer be treated as asource of signal rather than of interference. (In voice, the power fromneighbor cell[s] does not contribute to Pother since these cells contributea soft handoff link). The value for supplemental channel thus increasesfrom –4 dB (voice) to nearly +2 dB. The latter value can also be used asa very conservative estimate for the fundamental channels, which doenter into soft handoff in a manner similar to a voice channel.

In the concentric configuration, the value of Pother/Phost for bothfundamental and supplemental channels varies depending upon thedata rates that establish the inner boundary (data cell edge) and outerboundary (physical perimeter) of the cell. Generally, the outerboundary is well removed from the inner; accordingly, neitherfundamental nor supplemental channels are in soft handoff and theproperties of Pother/Phost are identical for both. In the forward linkbudget, the constant value of Pother/Phost is determined in an offlinefashion by simply computing the sum of received interference fromneighbor cells. The relevant path loss in this computation is not the lossfrom neighbor cell to host cell boundary, but the path loss fromneighbor cell to the data cell edge (i.e., inner boundary). This value isdetermined by presuming a simple path loss law; e.g., 38 dB/decade.The distance between inner boundary (data cell edge) and outerboundary (physical perimeter) is essentially determined by examiningdifference in high and low data rates (e.g., 76.8 kbps, 9.6 kbps)characterizing the two.

These considerations are illustrated in Figure 3-6 and Figure 3-7 below.


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401-614-040Issue 2, February 2003

Figure 3-6 Embedded configuration cell boundaries

In an embedded configuration, the physical boundary of the cellcorresponds to the data cell edge. A mobile at cell edge receives powerfrom its host and power (interference) from other surrounding cells.The interference from all surrounding cells must be considered, as theforward link supplemental channel is not in soft handoff with any cell.In contrast, for a voice channel, surrounding cells supporting themobile in soft handoff would be sources of signal, and not contributeinterference. The value of beta for the supplemental channel istherefore greater than the values employed for voice.

mob

X

XX

Host

Other Cell

Other

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401-614-040Issue 2, February 2003

Figure 3-7 Concentric configuration cell boundaries

In a concentric configuration, the data cell edge corresponds to an innerboundary where the higher data rate is available. The outer (physical)boundary of the cell corresponds to a lower data rate. Thisconfiguration is common for upgrades/overlays of 3G-1X data on a2G-voice footprint, since the 2G voice data dictates the outer (physical)boundary of the cell. A mobile at the data cell edge receives powerfrom its host and power from surrounding cells; however, theinterference from surrounding cells is proportionately less than the hostpower since the mobile is no longer equidistant to all cell sites. Thevalue of beta for the supplemental channel varies according to the innerand outer data rates.

The computation of Pother/Phost for the embedded configuration ignoresthe effect of supplemental channel anchor transfer. This transfer isessentially a very fast hard handoff in which the forward data link isdynamically switched to the best serving cell. This switching isfacilitated by information provided by the mobile’s forward linkfundamental channel, which can enter soft handoff with surroundingcells as appropriate. The presence of anchor transfer should reduce theeffects of other cell interference by ensuring that the strongest cell is

mobile

Host Cell

Other Cell

Other Cell


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401-614-040Issue 2, February 2003

always a source of signal rather than of interference; nevertheless, inlink budget analysis, we make the conservative assumption of ignoringany anchor transfer gain.

An example forward link spreadsheet for the 3G-1X fixed 153.6 kbpsdata application is shown below. The spreadsheet uses the approachesdescribed above, but with symmetric terms (e.g., antenna gain) addedfor example completeness. The example is conservative in that:

• The embedded configuration is employed. As described above,the embedded configuration establishes the data cell edge as thephysical cell boundary. The symmetric arrangement of mobiles atthis cell edge maximizes the interference from surrounding cellswhile minimizing host signal power.

• The chosen rate of 153.6 kbps minimizes the spread spectrumchannel processing gain (W/R). The ability of the supplementalchannel to reject interference from surrounding cells is thereforereduced.

• No gains are allowed for anchor transfer.

In spite of these restrictions, the spreadsheet indicates 11 fundamentalchannels (i.e., 11 mobiles) can be supported at data cell edge. Inaddition, a single supplemental channel can be simultaneouslysupported. This channel essentially operates at a channel activity of 1,downloading high-speed (153.6 kbps) bursts of data to each mobile inturn. Note that the specific mobile served by the supplemental channelat any time is not relevant to the link budget calculation due to thesymmetric arrangement of the mobiles.

Example forward link budget

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401-614-040Issue 2, February 2003

Table 3-4 Example forward link budget for PCS 3G-1X 3-sector Melodizes with fixed 153.6 kbpspacket data application

Line # Description Power W Power CommentsTransmit Power calculations

5 Nominal available power at J4 point 16 W 42.0 dBm Maximum power available6 Pilot Channel Power 2.4 W 33.8 dBm Set at 15% of max. power7 Sync Channel Power 0.2 W 23.8 dBm Set at 10% of pilot power8 Paging Channel Power 0.8 W 29.3 dBm Set at 35.1% of pilot power9 Power available for the traffic Channel 12.5 W 41.0 dBm 78.2% of total power

10 Total Overhead 21.8 % C10 = 100*(1 - (c9/c5))11 SCH rate 153.6 kbps 51.9 dB12 FCH rate 9.6 kbps 39.8 dB13 Required SCH Eb/Nt 1.8 2.5 dB No SHO on SCH14 Required FCH Eb/Nt 2.5 4.0 dB15 Number of FCHs per sector 11 Total number of simulta-

neously active data users16 Number of SCHs per sector 1 Total number of simulta-

neously active supplementalchannels users

17 Overhead factor for FCH 1.75 2.4 dB Due to users being in 2 wayand 3 way hand-off; from IS-95B new handoff algorithm

18 Total number of active FCH power channels 19.3 # of Fundamental channelssupported by the transmitter

19 Overhead factor for SCH 120 Total number of active SCH power channels 1.0 0.0 dB # of Supplemental channels

supported by the transmitter21 Mean Voice Activity Factor (VAF) for Fundamental

Channel0.125

22 Mean Voice Activity Factor (VAF) for SupplementalChannel

1

23 Average Traffic Channel Power for Fundamental Chan-nel

0.14 W 21.4 dBm

24 Average Traffic Channel Power for SupplementalChannel

9.9 W 39.9 dBm

25 Peak Traffic Channel Power per Fundamental Channel 1.1 W 30.4 dBm26 Peak Traffic Channel Power per Supplemental Channel 9.9 W 39.9 dBm27 Cell site Cable Loss 2.0 3.0 dB28 Cell site Transmit Antenna Gain 44.7 16.5 dBi29 Fundamental Traffic Channel EIRP per user at full rate 24.6 W 43.9 dBm30 Supplemental Traffic Channel EIRP per user at full rate 221.1 W 53.4 dBm31 Total EIRP 358.2 W 55.5 dBm32 Propagation loss33 Maximum Path Loss 6.46E+12 128.1 dB34 Lognormal Fade Standard Deviation 6.3 8.0 dB 90% edge coverage;

Assume no SHO for SCH35 Multiplier for fading standard deviation (e.g., 1.3 for

90th percentile)1.3

36 Mobile RX Signal power Calculations37 Mobile Receive Antenna Gain 1.6 2.0 dBi38 Mobile Body Loss & Building Penetration Loss and

Cable Loss31.6 15.0 dB


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401-614-040Issue 2, February 2003

39 Mobile Rx Fundamental Channel Signal power at fullrate

1.91E-13 W -97.2 dBm

40 Mobile Rx Supplemental Channel Signal power at fullrate

1.72E-12 W -87.7 dBm

41 Mobile Rx Total pwr from the Serving cell 2.78E-12 W -85.6 dBm42 Interference Power Calculations43 Orthogonality Factor for Other users in Serving Cell 0.16 -8.0 dB From same sector's other

Walsh channels44 Standard Deviation of SCH Activity Factor 0.045 Standard Deviation of FCH Activity Factor 0.2046 Ratio of mean other sector interference to same sector

power at cell edge1.8 2.6 dB for SCH

47 Other Cells Interference Power 5.06E-12 W -83.0 dBm48 Thermal Noise Calculations49 Mobile Noise Figure (F) 8 9 dB50 Thermal Noise Density (No = KT) 3.98E-21 -174.0 dBm/Hz51 Total thermal Noise power per Hz (NoF) 4.07E-20 -163.9 dBm/Hz52 Spreading bandwidth (W) 1.23E+06 Hz 60.9 dB53 Total thermal noise power (NoWF) 5.01E-14 W -103.0 dBm54 External (intermod/spectrum clearance) interfer-

ence1.58E-15 W -118.0 dBm

55 Noise Floor and Other Cell Interference to theFundamental traffic channel

5.33E-12 W -82.7 dBm

56 Noise Floor and Other Cell Interference to the Funda-mental traffic channel per Hz

4.34E-18 W/HZ -143.6 dBm/Hz

57 Noise Floor and Other Cell Interference to the Supple-mental traffic channel

5.33E-12 W -82.7 dBm

58 Noise Floor and Other Cell Interference to the Supple-mental traffic channel per Hz

4.34E-18 W/Hz -143.6 dBm/Hz

59 Mean of Other Cell to Serving Cell Interference Ratiofor SCH

1.92 2.8 dB

60 Mean of Other Cell to Serving Cell Interference Ratiofor FCH

0.49 -3.1 dB

61 Standard Deviation of Other Cell to Serving Cell Inter-ference Ratio for SCH

0.53 -2.8 dB

62 Standard Deviation of Other Cell to Serving Cell Inter-ference Ratio for FCH

0.53 -2.8 dB

63 Aggregate Margin for SCH Interference Ratio andActivity Factor

1.32 1.2 dB

64 Aggregate Margin for FCH Interference Ratio andActivity Factor

1.32 1.2 dB

65 Adjustment for SCH due to Serving Cell Interferenceand Orthogonality Factor

1.05 0.2 dB

66 Adjustment for FCH due to Serving Cell Interferenceand Orthogonality Factor

1.32 1.2 dB

67 Bit Energy to Interference calculations68 Fundamental Traffic Channel Bit Rate 9600 bps 39.8 dB69 Fundamental Channel Energy per bit at full rate 1.99E-17 W/Hz -137.0 dBm/Hz70 Fundamental Traffic Channel Eb/(No+Io) 2.6 4.19 dB71 Supplemental Traffic Channel Bit Rate 153600.0 bps 51.972 Supplemental Channel Energy per bit at full rate 1.12E-17 W/Hz -139.5 dBm/Hz73 Supplemental Traffic Channel Eb/(No+Io) 1.859258 2.69 dB

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401-614-040Issue 2, February 2003

In this example, a 128 dB path loss (line 33) has been analyzed. Thispath loss corresponds to the reverse link budget for a 153.6 kbpsreverse supplemental link under the conditions of:

• 0 dB head loss

• 16.5 dBi antenna gain

• 3.0 dB cable loss

• 4.0 dB noise figure

• 0.8 dB Eb/Nt requirement

• 10.3 dB fade margin

• 15 dB building penetration margin

• 5.5 dB interference margin.

Accordingly, the spreadsheet indicates that the fundamental andsupplemental channel numbers listed above can be supported withinthis footprint since the average forward link Eb/Nt requirement is met.(This requirement is the right-hand side of the condition Equation 3-7).Since the analysis employs very conservative assumptions (see above),the actual number could be larger.

The average forward link Eb/Nt requirements for all data rates aretabulated below for reference. These values can be used in symmetricforward link analysis (embedded or concentric) for any rate chosen.Note that the values employed can be used for mobile or fixedapplications; in the latter case; improvements in power control relativeto 3G suggest that any Eb/Nt advantage for a fixed user may benegligible.

Table 3-5 Average Eb/Nt requirements for forward link budget datachannel analysis (8 kbps RC3)

The symmetric link budget analysis has the advantages ofcomputational simplicity; however, the approach may be overlyconservative. This conservatism is especially evident in the embeddedconfiguration, since all high-rate supplemental channels must besupported at the physical cell boundary without allowance for anchortransfer gain. In contrast, the Monte Carlo analysis allows for randomdistribution of the data subscribers but adds complexity to the planninganalysis. This approach is further discussed, below.

Channel Data Rate (kbps)

Average Eb/Nt Require-ment (dB)

TBD TBD TBD TBD TBD


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Monte carlo forward link analysis

This work is in progress.

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

RF engineering for dataResource management: RF scheduling


401-614-040Issue 2, February 2003

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

Resource management: RF scheduling

Introduction In the above sections, the essential strategy of the network in managingRF resources has been used in order to assess performance. Suchstrategies include the sharing of high-rate supplemental channels andthe exploitation of “bursty” subscriber behavior (e.g., idle think timebetween web page downloads) to maximize the number of datasessions served. In the followings, we consider the aspects of resourcemanagement in greater detail.

Efficient radio resource management is critical for the success of 3Gwireless data in the multi-user environment. The CDMA2000-1Xstandard defines physical channels with transmission rates of up to153.6 kbps, more than a 10-fold increase compared with IS-95A.However, the ultimate end-user data experience depends to a largedegree not only on data rate capability, but also on transmission latency,resource availability, and service coverage. Complex interactions areexpected within the radio resource management function due tocompetition between multiple user demands and due to the self-regulating delay-sensitive nature of upper layer data protocols such asTCP. Additionally, resource management has to support both voice anddata services on the same frequency carrier without compromisingvoice quality achieved in 2G systems.

Scheduling algorithm Fundamental Channel (FCH) assignment and release

A fundamental channel (FCH) is mandatory for the data call and isneeded for carrying signaling and control information. This channelmust be established for each user before a high-rate connection canstart. The FCH is set up in both directions, forward and reverse, and ituses the same modulation and coding for data and voice. Lucent 3G-1Ximplementation supports data FCH using Radio Configurations 3 and 4(RC3 and RC4) on the Forward link and RC3 on the Reverse link. Asfor voice service, the data FCH reduces its rate according to the datasource activity in order to reduce co-channel interference to other users.In other words, the FCH reverts to the 1/8 rate when there is no data orsignaling to transmit. Figure 3-8 (reproduced here for convenience)depicts an example of how data (e.g., web pages) can be transmittedover the 1X air interface in the Lucent implementation. In the followingsections, the details of channel management are discussed in greaterdetail.


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


401-614-040Issue 2, February 2003

Figure 3-8 Data traffic model for web browsing application with 3G-1X packet data

FCH assignment

The Fundamental channel is set up every time a data call enters anActive state. This occurs in the beginning of the call, or when the userreturns from a Dormant state. The Dormant-to-Active transition mayhappen due to both mobile origination and termination. The data FCHis established in the same way as the voice traffic channel afterexchanging signaling messages on Paging and Access channels.

FCHs are assigned to users on a first come, first served basis. Useradmission algorithms are designed to maximize the number ofsimultaneous active users while protecting the system from overload.To achieve this goal, the system continuously monitors performanceand resource availability and takes appropriate corrective measureswhen resource utilization becomes sub-optimal. A set of admissionthresholds is designed to provide acceptable level of service to allexisting and incoming users. A decision whether to establish the FCHis based, among other things, on current power (forward) andinterference (reverse) loading, frame error rate performance,

38.4

153.6SCH

SupplementalChannelBursts

AccessTime

76.8SCH

9.6 kbps FCH

76.8SCH

153.6SCH

9.6 FCH

Web Browsing Session

Active Dormant Active

MouseClick

MouseClick

NetworkDelay Queuing Delay

( incl. SCH Setup Delay)

FirstData

Arrivedat IWF

"Think" Time

Dormancy TimerDuration

DownloadTime

FundamentalChannels

Dormant

StartReading

Web Page

76.8SCH

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401-614-040Issue 2, February 2003

availability of base-station and back-haul hardware resources, etc. Inthe first implementation of Lucent 3G-1X, the system treats FCHassignment for voice and data calls in the same way.

FCH assignment and resource allocation for both voice and data callstakes precedence over the Supplemental Channel allocation to ensurecoverage for signaling and minimum rate data traffic over the same cellarea as voice. If resources needed for setting up an FCH are unavailabledue to their utilization by an existing SCH, the system releases the SCHto make room for the incoming FCH (early SCH release is discussed in"Early F-SCH termination" section on Page 3-40). The probability ofthis scenario can be made low by providing sufficient margins whenallocating SCH resources such that in the majority of cases, there areenough resources to admit a new FCH during SCH operation withouttriggering the early SCH termination.

The FCH is used for transmitting signaling information and may alsobe used for transmitting data traffic. For example, if the Supplementalchannel is not active, the data traffic is transmitted on the Fundamentalchannel. On the forward link, the system prefers transmission of newtraffic data on the high-rate Supplemental channel. However, theretransmit data may be sent over the Fundamental channel even if theSupplemental channel is active. On the reverse link, it is left up to themobile station to decide whether to send data over FCH and SCHsimultaneously.

Active-to-dormant transition and FCH release

Data users go into a Dormant state after a period of inactivity. WhenActive-to-Dormant transition occurs, the user loses any air-interfaceconnection with the base station. However, the PPP connection ismaintained throughout the transition. The transition is triggered by theexpiration of the Dormancy timer. The value of the timer setting is thesame for all users and can be adjusted by the operator via translation.

Forward link supplemental channel (F-SCH) assignment andrelease

Forward link SCH (F-SCH) can be established using the followingphysical transmission rates: 19.2 kbps, 38.4 kbps, 76.8 kbps, and 153.6kbps of Radio Configurations 3 and 4. The duration of F-SCHallocation can span multiple 20-ms frames, depending on the amount ofthe data buffered for transmission. F-SCH transmission may becontinued beyond this initial duration if more data is buffered, and ifresource availability conditions permit.


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401-614-040Issue 2, February 2003

F-SCH rate and duration allocation

There are a number of factors used by the scheduling algorithm whenchoosing transmission rate and duration of the F-SCH assignment.Some of the most important factors considered by the algorithm arelisted below:

• Fraction of amplifier power required by the supplemental channel.This metric is determined as a result of RF measurements, servicenegotiations and translation settings in the following areas:

• Mobile RF environment including fast and shadow fadingeffects

• Propagation path loss between the mobile and the basestation

• Interference level experienced by the mobile

• Radio Configuration used for the supplemental channel

• Turbo coding support

• Target Frame Error Rate for each data rate

• Fraction of amplifier power consumed by other voice and datausers and a corresponding power fraction available forestablishing the supplemental channel (power computationprovides sufficient margins for ensuring a low probability ofoverload during SCH operation and therefore a low probability ofearly SCH termination)

• Channel element, back-haul, Walsh function and other hardwareand system resource availability at the serving base station thatcan be assigned to the supplemental channel

• Amount of data buffered for transmission to the mobile

• Scheduling policy that prevents monopolizing system resourcesby one or a small group of users for an extended period of time.

The system makes the best effort to satisfy above constraints/requirements when assigning a forward SCH rate. The duration of SCHassignment is determined by the amount of data in the transmit buffer,the handoff state of the user, and the transmission rate resulting fromthe algorithm described above.

F-SCH continuation

If, at the end of current F-SCH transmission, the user still has data inthe transmit buffer, the F-SCH burst may be continued using the samerate. This happens only if the system determines that the available

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401-614-040Issue 2, February 2003

resources are sufficient to proceed with such continuation. The durationof continuation burst is determined using the same calculation as forinitial burst transmission.

The number of consecutive continuations is limited to prevent one, or asmall number of users, from monopolizing system resources for a longperiod of time. The number of allowed continuations is a translationparameter. This limit takes effect if there is a contention for SCHresources from other users. Otherwise, continuation beyond the limit isallowed.

Transmission rate of the supplemental channel may be increased if,after certain number of continuations, the system determines that asignificantly larger amount of resources have become available for thedata user.

Normal F-SCH termination

The Supplemental channel is terminated normally if transmission onthis channel spans exactly the duration assigned to the mobile in theExtended Supplemental Channel Assignment Message (E-SCAM)before the start of the F-SCH burst.

Early F-SCH termination

F-SCH may be terminated earlier than specified in the E-SCAM. Earlytermination may be caused by power overload reached during F-SCHoperation due to power control operation or due to the increasedloading and/or interference. Early termination may also occur due to aneed to free up base station resources to admit new of handoff F-FCHchannel (data and voice). SCH resource management providessufficient margins to make the probability of early termination low. Inthe event that early termination does occur, the user may be assigned anew SCH at a lower rate based on the re-evaluation of resourcesavailable at the time of termination.

Note that F-SCH operation will not be terminated early if soft handoffadds or soft handoff drops occur, or some combination of them. This isbecause the F-SCH resides on only one leg and is not effected bychanges in the mobile’s active set unless the serving cell itself drops.


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401-614-040Issue 2, February 2003

Reverse link supplemental channel (R-SCH) assignment andrelease

Reverse link SCH (R-SCH) may be established using the followingphysical transmission rates: 19.2 kbps, 38.4 kbps, 76.8 kbps, and 153.6kbps of Radio Configurations 3. The duration of R-SCH allocation canspan one or more 20-ms frames, depending on the amount of data in themobile’s transmit buffer.

R-SCH rate Allocation

Unlike the single-leg F-SCH operation, the operation of the R-SCHwill be on all legs of the call. Therefore, the rate of the burst isdetermined by the minimum rate that can be supported among all legs.Some of the most important factors considered by the reversesupplemental channel rate allocation algorithm are listed below:

• Maximum mobile transmit power available for R-SCH

• Additional loading that would be produced by the supplementalchannel after it is assigned. This projected loading increase isdetermined as a result of RF measurements, service negotiationsand translation settings in the following areas:

– Mobile RF environment including fast and shadow fadingeffects

– Propagation path loss between the mobile and all sectors inthe Active set

– Target Frame Error Rate for each data rate

– Turbo coding support

• Current loading and interference levels on all handoff sectors(Active set) of the call and corresponding loading and interferencebudgets available to support a new SCH (interference budgetcomputation provides sufficient margins for ensuring a lowprobability of overload during SCH operation and therefore a lowprobability of early SCH termination)

• Channel element and back-haul availability at all handoff sectorsof the call

• Amount of data buffered for transmission by the mobile.

System makes the best effort to satisfy the aboveconstraints/requirements when assigning a Reverse SCH rate.

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401-614-040Issue 2, February 2003

R-SCH normal termination

Normal termination is triggered when the mobile station completestransmission of data in its buffer. Mobile station requests the R-SCHrelease by sending a Supplemental Channel Request Message (SCRM),specifying that zero amount of data needs to be transmitted.

R-SCH early termination

R-SCH could be terminated by the system prior to mobile requestingsuch termination. This early termination may be caused by reverse linkinterference overload reached during R-SCH operation due to powercontrol operation or due to the increased loading. Early terminationmay also occur due to a need also to free up base station resources toadmit new or handoff R-FCH channels (data and voice). SCH resourcemanagement provides sufficient margins to make the probability ofearly termination low. In the event when the early termination doesoccur, the user may be assigned a new SCH at a lower rate based on there-evaluation of resources available at the time of termination.

Unlike in the single-leg only F-SCH case, early R-SCH terminationmay also happen as a result of handoff activity, e.g., adding newhandoff legs.

Load Balancing

Overview

System supports carrier load balancing on origination. With thisalgorithm, the system directs originating users to a different carrier ifthe load of initial carrier is larger than the load of that new carrier bymore than a translation-defined delta load. Handoff calls are admittedon the carrier independently of carrier load.

Dual 3G/2G deployments

There is also a mechanism providing load balancing in dual 3G/2Gdeployments. Specifically, the system may be configured with thetranslation to give preference to 3G carriers for originating 3G mobiles,and to 2G carriers for originating 2G mobiles. A degree of allowed loadimbalance between 2G and 3G carriers resulting from this approach islimited through the translation parameter that can be adjusted bysystem operator. This parameter specifies the maximum load imbalancebetween carriers beyond which 2G mobiles are directed to a 3G carrier,or 3G mobiles capable of 2G are directed to a 2G carrier, to mitigate theimbalance.


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401-614-040Issue 2, February 2003

Additional load delta parameter is provided for handling load balancingfor data calls. This translation parameter specifies the additional loadimbalance between carriers beyond which 3G data mobiles are directedto a 2G carrier.

Conclusions RF resource scheduling is an essential part of the LucentCDMA2000-1X data system. It consists of a set of call admission, loadbalancing, channel and rate assignment algorithms designed tooptimize resource utilization, system capacity and performance. Futureenhancements will provide even greater flexibility in carrierscheduling, non-assured QoS support, and throughput optimization.

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401-614-040Issue 2, February 2003

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4 System deployment

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Overview

Purpose This chapter describes the deployment issues, with focus on transitionfrom 2G to 3G-1X.


Spectrum use: Carrier assignments and guard band 4-4

Cellular band 4-4General considerations 4-4Frequency planning for systems with 3G-1X and AMPS 4-7

PCS 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

Estimating capacity: Mix of 3G-1X voice and 2G voice 4-13Planning: Mixed vs. dedicated carriers for 3G-1X 4-15

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

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System deploymentIntroduction


401-614-040Issue 2, February 2003

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Introduction

Implementation of 3G-1X is straightforward. The key points includethe following:

• Most existing Lucent 2G systems may be upgraded to 3G viaaddition of the 3G channel card and the appropriate softwarerelease

• The 3G-1X channel card (CCU-32) is dual-mode, supporting both3G-1X and 2G calls. The card automatically makes this decision,depending upon the nature of the mobile trying to originate a call.

• Since the 3G-1X and 2G voice footprints are comparable, a 1:1upgrade provides 3G-1X coverage that is better than or equal tothat of 2G voice coverage

• 3G-1X may be implemented in spectrum cleared for this purpose(dedicated 3G carrier), or within spectrum already serving 2Gsubscribers (shared 2G/3G carrier). In the latter case, the net voiceErlang capacity is intermediate between that of a 3G-only carrierand a 2G-only carrier.

• Mobile standards specify that the 3G-1X mobile be dual-mode,supporting both 2G and 3G-1X calls

• 3G-1X need not be deployed ubiquitously. The 3G-1Xinfrastructure supports 3G to 2G handoffs for mobiles exiting a2G/3G area into a 2G-only area.

Given the above, an existing 2G system can be gradually upgraded to3G-1X simply by implementing the appropriate software release,seeding the subscriber population with 3G-1X mobiles, and deployingthe appropriate channel cards. The last may be done selectively (limited3G/2G area) or ubiquitously (3G throughout). The 3G-1X mobiles mayoperate in the same spectrum as an existing 2G carrier. Since bothmobiles and cards are dual-mode, exact knowledge of the proportion of3G-1X voice users is not required in order to properly provision the cellsite. Alternatively, the 3G-1X mobiles could be deployed within acarrier dedicated to that purpose.

3G-1X can also be implemented as a greenfield design, i.e., within anarea that does not already possess 2G service. In this case, theprocesses of spectrum clearance, system design, and cell provisioningare analogous to that of 2G. Furthermore, if designed for full 3G voicecapacity and ubiquitous 3G voice (as opposed to high-speed data)

System deploymentIntroduction

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401-614-040Issue 2, February 2003

coverage, the cell count should be virtually identical to that of a 2Gdesign. This comparison is useful for service providers that desire tospecify the coverage design prior to deciding whether to initiallyimplement 2G or 3G service.

In the following sections, we provide further detail on deploymentissues, such as carrier assignments, underlay/overlay considerations,and the mix of 2G and 3G within available radio spectrum. The mix of3G voice and data is also considered.

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System deploymentSpectrum use: Carrier assignments and guardband


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Spectrum use: Carrier assignments and guard band

Carrier assignments and guard band remain the same as in 2G. Therecommendations for carrier assignments are provided for two bandclasses: Band Class 0 (i.e., the cellular band) and Band Class 1 (i.e., thePCS band) defined by the IS-2000. For detailed information, pleaserefer to Lucent documents 401-614-012, AUTOPLEX® Cellular CDMARF Engineering Guidelines, and 401-703-201, PCS CDMA RFEngineering Guidelines.

Cellular band This section will address frequency planning considerations in dualmode systems, which support AMPS and IS-95 standards as well as3G-1X. This section assumes that the reader is familiar with thefrequency planning considerations and techniques used in AMPS, andis not intended to be a tutorial in basic frequency planning. It willaddress only those frequency-planning issues that are the result of dualmode system operations.

General considerations

Table 4-1 lists the five bands of 832 channels available to the A- and B-Band service providers. Valid channels for 3G-1X assignments aredesignated by “CDMA” in the “Valid CDMA Frequency Assignments”column, and invalid assignments by “//////////”. This information istaken from the IS-2000 and provided here for convenience. Note thatBand Class 0 is also referred to as the cellular band in North America.


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Table 4-1 AMPS and 3G-1X channel numbers and correspondingfrequencies for Band Class 0

System Band Valid CDMAFrequency

Assignments

Number of AnalogChannels

AMPS/CDMAChannelNumber

TransmitterFrequency

Assignment (MHz)

Mobile Base

A''(1 MHz)

///////////////// 22 991

1012

824.040 869.040

824.670 869.670

A''(1 MHz)

CDMA 11 1013

1023

824.700 869.700

825.000 870.000

A(10 MHz)

CDMA 311 1

311

825.030 870.030

834.330 879.330

A(10 MHz)

///////////// 22 312

333

834.360 879.360

834.990 879.990

B(10 MHz)

////////////// 22 334

355

835.020 880.020

835.650 880.650

B(10 MHz)

CDMA 289 356

644

835.680 880.680

844.320 889.320

B(10 MHz)

////////////// 22 645

666

844.350 889.350

844.980 889.980

A'(1.5 MHz)

///////////// 22 667

688

845.010 890.010

845.640 890.640

A'(1.5 MHz)

CDMA 6 689

694

845.670 890.670

845.820 890.820

A'(1.5 MHz)

///////////// 22 695

716

845.850 890.850

846.480 891.480

B'(2.5 MHz)

///////////// 22 717

738

846.510 891.510

847.140 892.140

B'(2.5 MHz)

CDMA 39 739

777

847.170 892.170

848.310 893.310

B'(2.5 MHz)

///////////// 22 778

799

848.340 893.340

848.970 893.970

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401-614-040Issue 2, February 2003

The non-allowed bands of channels are 22 AMPS channels in widthand are dictated primarily by the 1.23 MHz bandwidth (41 AMPSchannels) of the 3G-1X channel. These valid 3G-1X assignments donot take into account practical considerations such as guard-band needsand/or the channel needs for AMPS in dual mode systems. Thesubsections below discuss the channel needs for AMPS and 3G-1X thatshould also be considered when allocating the spectrum in dual modesystems.

Because of the need for guard bands and/or channels in dual modesystems, it should be understood that allocations of spectrum channelsto a specific standard should be done as much as possible in terms ofcontiguous channels/bands for each (AMPS/3G-1X) technology. Byusing contiguous channels/bands for one standard, there is only a singleguard band penalty for the overall spectrum allocation given to thestandard in question. For example, if an A-Band, dual mode, 3G-1Xapplication required two 3G-1X channels, a good first 3G-1X channelselection would be channel 283. In the case of a dual mode (AMPS/3G-1X) system, this is the highest available channel in the 10 MHzA-Band that could be selected without concern for interference in theA-Band setup channels (313-333). This channel selection alreadyprovides a 0.27 MHz guard band of channels between the nominal 1.23MHz 3G-1X channel band and the AMPS setup channels (313-333)required for the A-Band service provider.

The logical choice for the second 3G-1X channel would be channel242, which that is 41 channels away from 283 for a carrier frequencyseparation of 1.23 MHz. Any selection resulting in a carrier frequencyseparation of less than 41 channels would result in the two 3G-1Xcarriers being separated by less than the nominal 1.23 MHz 3G-1Xchannel bandwidth and would cause excessive interference between thetwo carrier bands. Using a separation of greater than 41 channelsresults in inefficient use of the spectrum.

Two preferred channel assignments specified in the IS-2000 are:

• Primary Setup Channel - Channels 283 and 384 for A- andB-Band, respectively

• Secondary Setup Channel - Channels 691 and 777 for A- andB-Band, respectively.

If the 3G-1X mobile supports the preferred roaming list feature definedby the IS-683, then any valid channel assignment can be used by themobile station for initial acquisition. Otherwise, an operational CDMAsystem must use at least one of the two channels, primary and/or


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401-614-040Issue 2, February 2003

secondary in every CDMA cell, and therefore, the selection for CDMAfrequencies in any start up system requiring only one CDMA channelper cell is quickly narrowed to one of these two preferred channels.

Frequency planning for systems with 3G-1X and AMPS

It is recommended that for the 3G-1X and AMPS operating in the samecellular band (A Band or B Band), the guard band of 270 kHz beimplemented on both sides of the consecutive 3G-1X carriers and noguard band between the 3G-1X carriers be required. For the derivationof the 270 kHz guard band, please refer to Lucent document 401-614-012, AUTOPLEX® Cellular CDMA RF Engineering Guidelines.Table 4-2 and Table 4-3 below show frequency assignments for dualmode AMPS and 3G-1X operations in the A- and B-Band spectrums.These assignments are given for various numbers of 1.23 MHzbandwidth 3G-1X channels. As highlighted by the asterisks (*) in theAMPS columns, the frequency assignments and number of availablechannels includes the 21 setup channels.

Table 4-2 Recommended A-Band 3G-1X center frequencyassignments for Band Class 0

Number ofCDMA Channels

CDMACenter Frequency

Assignments

Number of AMPSChannels*

AMPS ChannelAssignments*

1 283 356 1-252, 313-333,667-716, 991-1023

2 242, 283 315 1-211, 313-333,667-716, 991-1023

3 201, 242, 283 274 1-170, 313-333,667-716, 991-1023

4 160, 201, 242, 283 233 1-129, 313-333,667-716, 991-1023

5 119, 160, 210, 242, 283 192 1-88, 313-333,667-716, 991-1023

6 78, 119, 160, 201, 242,283

151 1-47, 313-333,667-716, 991-1023

7 37, 78, 119, 160, 201,242, 283

110 1-6, 313-333,667-716, 991-1023

8 691, 37, 78, 119, 160,201, 242, 283

60 1-6, 313-333,991-1023

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401-614-040Issue 2, February 2003

Table 4-3 Recommended B-Band 3G-1X center frequencyassignments for Band Class 0

In both the A- and B-Band cases, the Secondary Setup Channel was thelast 3G-1X channel added. The reason for this is that this channelincurs the greatest AMPS channel loss because it requires its ownguard band penalty in addition to the 0.54 MHz guard band penalty forthe other 7 CDMA channels. If added setup channel capacity is needed,this channel may have to be implemented sooner than assumed here.

PCS band Although the 3G-1X channel numbering algorithm with 50 KHzchannel spacing implies the availability of 1200 of 50 kHz for 3G-1Xcarriers, not all 1200 are actually usable. Table 4-4 indicates theavailability of the channels by classifying them as valid (usable)channels, conditionally valid, or not valid.

The designation of channels 0-24 and 1176-1199 as being not valideliminates the possibility of interference between PCS systems and theservices allocated to the spectrum above, below, and between the two60 MHz spectrum allocations comprising the PCS spectrum.

The channels specified as conditionally valid are the 25 lowest (exceptfor Block A) and the 25 highest (except for Block C) channels in eachblock. These channels are valid only under the condition that theservice provider also owns the adjacent block of spectrum.

Looking at it another way, all channels are valid for use as 3G-1Xcarriers except for the 25 lowest channels and the 25 highest channelsin each block. Thus, there are 251 channels unconditionally available

Number ofCDMA

Channels

CDMACenter Frequency Assignments

Number ofAMPS

Channels*

AMPS Channel Assign-ments*

1 384 356 334-354, 415-666, 717-799

2 384, 425 315 334-354, 456-666, 717-799

3 384, 425, 466 274 334-354, 497-666, 717-999

4 384, 425, 466, 507 233 334-354, 538-666, 717-999

5 384, 425, 466, 507, 548 192 334-354, 579-666, 717-799

6 384, 425, 466, 507, 548, 589 151 334-354, 620-666, 717-799

7 384, 425, 466, 507, 548, 589, 630 110 334-354, 661-666, 717-799

8 384, 425, 466, 507, 548, 589,630, 777

57 334-354, 661-666, 717-746


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401-614-040Issue 2, February 2003

(i.e., “Valid”) for designation as carrier frequencies in each ofFrequency Blocks A, B, and C, and there are 51 unconditionallyavailable channels for each of Blocks D, E, and F. If a service providerwere to obtain licenses in two adjacent blocks, then an additional 50channels would become available from the conditionally availablechannels. Note that Band Class 1 is also referred to as the PCS band inNorth America.

Table 4-4 3G-1X channel allocation availability for Band Class 1

Not all of the valid and conditionally valid channels can be usedsimultaneously as carriers in a given system. Once a channel numberhas been specified for use as the first carrier in a system, there areminimum spacing rules for carriers in use, which limit how close thenew carrier can be above or below the previously existing carrier(s).While the classification of channels as valid and conditionally valid is

Frequency CDMA Frequency CDMA Transmit Frequency (MHz)

Block Assignment Validity Channel Number Personal Station Base station

A Not Valid 0-24 1850.000-1851.200 1930.000-1931.200

(15 MHz) Valid 25-275 1851.250-1863.750 1931.250-1943.750

Conditionally Valid 276-299 1863.800-1864.950 1943.800-1944.950

D Conditionally Valid 300-324 1865.000-1866.200 1945.000-1946.200

(5 MHz) Valid 325-375 1866.250-1868.750 1945.600-1948.750


B Conditionally Valid 400-424 1870.000-1871.200 1950.000-1951.200

(15 MHz) Valid 425-675 1871.250-1883.750 1951.250-1963.750


E Conditionally Valid 700-724 1885.000-1886.200 1965.000-1966.200

(5 MHz) Valid 725-775 1886.250-1888.750 1966.250-1968.750


F Conditionally Valid 800-824 1890.000-1891.200 1970.000-1971.200

(5 MHz) Valid 825-875 1891.250-1893.750 1971.250-1973.750


C Conditionally Valid 900-924 1895.000-1896.200 1975.000-1976.200

(15 MHz) Valid 925-1175 1896.250-1908.750 1976.250-1988.750

Not Valid 1176-1199 1908.800-1909.950 1988.800-1989.950

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401-614-040Issue 2, February 2003

by FCC decree, the minimum spacing between active carriers isdetermined by 3G-1X technology considerations. Generally, thechannels are specified as dictated by the minimum carrier spacing of 253G-1X channels, which is consistent with the nominal 1.25 MHzbandwidth for 3G-1X.

Preferred channels The preceding subsection specified the channels which are valid, or atleast conditionally valid, carrier frequencies that the service providercan specify for use in the system's frequency plan. The selection ofthese frequencies might be dictated by issues dealing with inter-systemor intra-system interference. If these issues are not significant factors inthe system performance, the number of channels that the serviceprovider might consider for carrier frequencies can be reducedsignificantly to the list of “preferred channels” in the table below.These are the channel numbers that a personal station will “scan” whenlooking for service. Thus a system must use at least one (or more) ofthese carriers at each site in the system if the sites are to be capable orproviding (CDMA) access to the system.

Table 4-5 Preferred CDMA channels for Band Class 1

Conditionally valid channels 300, 400, 700, 800, and 900 are excludedfrom the above list because they can only be used if the serviceprovider has licenses for both the frequency block containing thechannel and the immediately adjacent frequency block, e.g., Channel300 is a likely carrier channel if the service provider has licenses forboth Blocks A and D. If conditionally valid channels are used, theyshould be used for traffic only and not access.

For details about intra-system and inter-system frequency planning,please refer to Lucent document 401-703-201, PCS CDMA RFEngineering Guidelines.

Frequency Block Preferred Channel Numbers

A 25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275

D 325, 350, 375

B 425, 450, 475, 500, 525, 550, 575, 600, 625, 650, 675

E 725, 750, 775

F 825, 850, 875

C 925, 950, 975, 1000, 1025, 1050, 1075, 1100, 1125, 1150, 1175

System deployment2G/3G-1X spatial and frequency design

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

Coverage (spatial) design:overlay and greenfield

A PCS Modcell reverse link budget example for 3G-1X 9.6 kbps voiceapplication was presented in Chapter 2, "Link budget" section on Page2-14. This example indicates a fundamental governing principle indeployment planning for 3G-1X, that the 3G-1X voice coverage(footprint) is (slightly) better than or equal to the 2G footprint.Accordingly, a new or “greenfield” 3G deployment will haveessentially the same cell count as a greenfield 2G deployment. Inaddition, upgrade or migration of a 2G network to a 3G network can beaccomplished through a 1:1 overlay of 3G on 2G, i.e., 3G voicecoverage is obtained by upgrading each 2G cell to 3G functionality.The resulting 3G coverage will match or slightly better that of theunderlying 2G network.

This comparison applies to the situation where 3G-1X and 2G are eachfully loaded. A lighter design loading on 3G-1X will expand the voicecoverage at the expense of cell capacity. This design trade-off isidentical to the coverage-capacity trade-off that exists in 2G systems.Since full 3G-1X loading is required to reach the full 3G-1X voicecapacity (see Table 2-1, "Air interface capacity" on Page 2-9), wepresume a fully loaded system in the following discussions.

Link budgets for the 19.2 kbps - 153.6 kbps packet data applicationshave also been presented in Chapter 3, "Data link budgets" section onPage 3-19. These examples show that the radio coverage (footprint) for3G high-rate packet data can be considerably less than that of (2G or3G) voice. This difference is fundamental, and a straightforwardconsequence of the higher rates at which the supplemental channelmust operate.

The coverage difference between data and voice is a key issue indesign. We consider two scenarios, overlay and greenfield deployment,below.

Consider a 2G system upgraded to (overlaid by) 3G-1X. The physicalouter perimeter of the cell is determined by the existing 2G design. The3G-1X voice coverage extends to this perimeter. Since the link budgetcomparison indicates that the voice system supports a greatermaximum path loss than the 3G-1X high-rate packet data, the high-ratedata service will be available only within an inner circle of cellcoverage. In this case, the supportable packet data rate for a calloriginated within the inner circle will dynamically reduce when the

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401-614-040Issue 2, February 2003

mobile moves closer to the cell edge. This reduction will be controlledby the radio resource management algorithms (see Chapter 3,"Resource management: RF scheduling" section on Page 3-36), whichassign data rates based on reported RF conditions as well as otherfactors, e.g., mobile history. Similarly, the data rate will dynamicallyincrease as the mobile moves closer to the cell center.

Now consider the scenario where the overlaid 3G-1X system mustprovide an ubiquitous coverage for the high-rate 3G-1X data. In thiscase, the link budget based on the high-rate supplemental channel isused for 3G cell layout since the design coverage of the high-rate datachannel must extend out to the 3G cell edge. The footprint of these cellsis modest compared to a voice footprint. A 1:1 overlay would not befeasible since the high data rate could not be supported at all locationsbetween the cells. Additional 3G cells must be added to obtainubiquitous high-rate data coverage. The overlay would increase from1:1 to N:1 (i.e., N 3G cells required for each 2G cell). The N:1restriction could be relaxed under several conditions. These includescenarios where:

• High-rate data subscribers possess an additional advantage, suchas a directional antenna, to compensate for the lack of coverage.This advantage must be symmetric, i.e., applicable to both linkdirections; for example, the provision of higher mobile transmitpower to the high-rate subscribers would not be effective sincethis change would not provide a forward link benefit as well.

• The underlying 2G system is not coverage but capacity-driven. Inurban or dense urban areas where the cell count is driven by thecapacity, the actual path loss between a 2G mobile and the servingbase station in the existing 2G network could be less than themaximum allowable value dictated by the 3G link budget. Undersuch a circumstance, the 1-to-1 overlay of CDMA2000 on the IS-95 may still be a feasible migration.

• The design restriction of extending high-rate data coverage to the3G cell edge is removed. If voice rate coverage to the 3G cell edgeis acceptable, then a 1:1 overlay becomes feasible (see above). Inthis case, mobile data rates would be dynamically adjusted,depending upon their location within the coverage area.

Further means for extending data coverage relative to voice arediscussed in “Mixed 3G-1X voice/data capacity and coverage” sectionbelow.


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401-614-040Issue 2, February 2003

The issue of achieving comparable coverage at high data rates isobviated in greenfield deployments, since there is no underlyingnetwork for comparison. In these scenarios, the cell design is driven byselecting the data rate required out to the cell edge and then using theappropriate link budget in design. Selection of a very high data ratedecreases the cell footprint and increases the design cell countconsiderably. Design alternatives employing a more modest data rate atcell edge may be more cost-effective, especially if the coverage ofanticipated high-rate users is enhanced by the use of subscriberdirectional antennas.

Frequency design The implementation of 3G-1X within available radio spectrum offers arich array of possibilities. 3G-1X can be deployed as 1.23 MHzwideband carriers within spectrum cleared for this purpose.Alternatively, 3G-1X can be deployed within an existing 2G carrier,yielding a net per-carrier capacity that lies between that achieved by3G-1X alone and that achieved by 2G alone.

Decisions regarding specific implementation paths depend uponseveral factors, including the availability of radio spectrum, theprediction (and accuracy) of voice and data demands, and the priorityplaced upon obtaining maximum air interface capacities and maximumchannel element efficiency. Some insight into these factors is suppliedin the discussions below.

Estimating capacity: Mix of 3G-1X voice and 2G voice

We consider a scenario where the anticipated demand is a known mixof 3G-1X traffic and 2G traffic. For simplicity, we examine the casewhere all 3G-1X traffic is voice only; the extension of concepts toinclude data traffic as well is straightforward, although computationallymore difficult.

In scenarios where 2G and 3G are implemented as distinct carriers, thetotal Erlang capacity per sector is readily computed as an appropriatelyweighted sum of the two. For example, let:

E3G = Total voice Erlangs per carrier per sector for 3G-1XE2G = Total voice Erlangs per carrier per sector for 2GN2G = Total number of 2G carriers per sectorN3G = Total number of 3G carriers per sector.

Then, the total Erlangs per sector is readily computed as:

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401-614-040Issue 2, February 2003

Equation 4-1: Total Erlang calculation for 2G-3G mix

Equation 4-1 can be used in planning situations where the demand of3G and 2G traffic is known. In these situations, the best fit of theinteger numbers N2G and N3G are obtained to ensure that the demand ismet.

In scenarios where 2G and 3G are mixed within each carrier, the totalErlangs are best determined by simulation but can be approximated inthe following manner. The total number of 2G voice Erlangs is anupper bound that cannot be exceeded when the subscriber populationconsists of 2G users alone. Trivially:

Equation 4-2

Let fraction x of the total Erlangs be 2G, and fraction (1-x) of the totalErlangs be 3G. Assume that the Erlang values E2G and E3G that can beachieved by each population alone are proportional to the totalinterference that can be tolerated. The equivalent 2G Erlangs generatedby each 3G user is therefore the 3G Erlangs scaled by the ratio E2G/E3G.For example, a 3G user generates about half the interference as a 2Guser; accordingly, the 3G usage must be scaled by a factor of ½ intotaling equivalent 2G usage. The total 2G Erlangs can therefore becomputed and limited by the upper bound E2G:

Equation 4-3

In Equation 4-3, the first term on the left hand side is the number of 2GErlangs, which is a fraction x of the total. The second term is thenumber of 3G Erlangs (a fraction 1-x of the total) scaled to anequivalent number of 2G Erlangs. The sum of (equivalent) 2G Erlangsis then limited to the same upper bound as a population consistingentirely of 2G users. Equation 4-3 can be solved for Etotal:

GGGGtotalENENE

3322+=

GtotalEE

2≤

GG

Gtotaltotal

EE

EExxE

23

2 )()1( ≤−+


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Equation 4-4: Total Erlang capacity based on 2G & 3G capacities

The result Equation 4-4 is a planning approximation, and requires amodification in the interpretation of E3G and E2G in order to beemployed. Specifically, in order to convert Erlangs from onepopulation into equivalent Erlangs of another, the values of E3G and E2G

employed must each correspond to the same interference margin, i.e.,the same loading with respect to pole. This requirement ensures thateach population see the same interference rise under full load. Since the2G population tolerates a lower (~55%) loading than the 3G population(~72%), the 2G loading must be used. Use of a higher loading could betolerated by the 3G population, but would require the 2G population tooperate within a background interference that is too high, therebycompromising 2G performance.

The E3G employed within the above calculation therefore must be the3G Erlangs that can be achieved when a 3G carrier is loaded to thelower (55%) point, rather than its maximum of 72%. The restriction of3G to a lower loading in a mixed carrier scenario influences thedecision of deploying 3G in a mixed or dedicated mode, as describedbelow.

Planning: Mixed vs. dedicated carriers for 3G-1X

The decision regarding deployment via mixed or dedicated carriers isdriven by several factors. The relative importance of each of thesefactors ultimately drives the decision. These factors are discussedbelow.

Accurate mixing proportions

Employment of dedicated carriers naturally restricts the possible mixesof subscribers. For instance, if only two carriers are available for twopopulations, the only possible mix is to dedicate one carrier to the firstpopulation and the other carrier to the second population. Thiscombination cannot reflect all possible target mixes of the twopopulation. In contrast, mixing populations within the same carrierallows tailoring to a much larger set of possibilities.

GGtotal ExEx

E32

/)1(/1

−+=

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For example, suppose that only two carriers are available and theprinciple of dedicated carriers is employed. Further suppose that theanticipated subscriber Erlangs are 2/3 3G voice and 1/3 2G voice. Thismixture of total Erlangs is readily addressed by devoting one carrier to2G voice and one carrier to 3G voice, since the 3G voice carrierhandles twice as many Erlangs as the 2G voice carrier. However, thissolution would not be adequate if the anticipated mix was 60% 2Gvoice and 40% 3G voice. Within the two-carrier limit, there is nocombination using dedicated carriers that would support theseproportions when both carriers were fully loaded.

In contrast, this mix could be achieved within each of the two carriersindividually if non-dedicated carriers are allowed (see Equation 4-4).The sum across the two carriers would then match the design 60/40target.

Accordingly, the decision of dedicated vs. mixed carriers can beinfluenced by the desire to accurately achieve a design or target mix ofsubscribers. Mixing carriers allows more degrees of freedom inachieving specific values. If only approximate values relative to atarget need be achieved, this distinction becomes less important.Further, if many carriers rather than few are available, the ability toachieve a specific mixture improves since more design degrees offreedom are available.

Maximum total capacity

The computation of capacity for any combination of dedicated carriersis straightforward (See “Estimating capacity: Mix of 3G-1X voice and2G voice” section). The total capacity achieved is simply the linearcombination of the capacities offered by each carrier.

The computation of total capacity for mixed carriers is more complex,since a truly accurate result for mixed subscribers within the carriermust account for nonlinearities. The impact of these nonlinearitiesdepends upon the differences between the subscriber populations; forexample, if two populations are distinguished solely by a smalldifference in Eb/Nt requirement, the impact of nonlinearities becomesnegligible. In contrast, these effects can become important for large Eb/Nt differences.

Presuming that the achievement of an exact mix of subscribers (seeabove) is unimportant, the presence of nonlinear effects means that thetotal Erlang capacity in a mixed subscriber situation is always lessthan or equal to the total Erlang capacity that can be achieved with


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dedicated carriers. The latter is actually an upper bound on theformer, and often used as a reasonable approximation in planningscenarios. The validity of this approximation decreases as thedifferences between the populations become more distinct.

These concepts were outlined in “Estimating capacity: Mix of 3G-1Xvoice and 2G voice” section and are expanded upon here. Consider thereverse link. A 13 kbps 2G population can tolerate about 3 dBinterference rise over the noise floor. An 8 kbps 3G-1X population cantolerate about 5 dB interference over the noise floor. In a dedicatedcarrier scenario with all carriers full, each population experiences andtolerates its maximum rise. In contrast, in a mixed carrier scenario, the3G population must be limited to (roughly) a 3 dB interference rise,since a larger value would result in a background interference thatcompromises the ability of the accompanying 2G population to reachthe cell site. More 3G users could be added without loss of 3Gperformance since each 3G user can tolerate a higher interference level,but this higher level would degrade the performance of the 2Gpopulation. Since the 3G population is constrained by the presence ofthe 2G users, the total capacity (2G plus 3G) must be less than whatcould be achieved by dedicating carriers to each group. For 55%loading (the typical 2G value) the 3G capacity is reduced from 26.4Erlangs (see Table 2-1, "Air interface capacity" on Page 2-9) to 18.4Erlangs.

The effects described above are mitigated somewhat by other factors(e.g., the 2G population benefits somewhat by the statistical benefits ofmore total users within a single carrier), but in all cases the dedicatedcarrier scenario remains an upper bound on achievable capacity. Sincethese effects depend upon the extent and nature of the differences inproperties between the populations mixed, they are best assessed on acase-by-case basis. In the situation of small differences, the mixedcarrier scenario may indeed approach the upper bound of performance.

Efficient use of channel elements

A 2G channel element can accommodate only 2G calls. In contrast, a3G channel element is dual-mode, accommodating both 2G and 3Gcalls. In addition, the 3G channel elements are offered in packs withhigher density than 2G elements, e.g., 32 per pack vs. 20 per pack.

From a provisioning point of view, the choice of mixed or dedicatedcarriers has little impact for fully loaded carriers. In the dedicated case,a requisite number is employed per carrier. In a mixed case, the totalnumber required can be calculated from the anticipated subscriber

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mixture. The calculation need not be that accurate, since 3G CE willsupport both 2G and 3G calls. A conservative estimate of 3Grequirements, i.e., overprovision rather than underprovision, minimizesthe impact of any inaccuracy. Extra 2G cards in this process can beremoved, thereby using all elements to best advantage.

In contrast, the mixed/dedicated choice becomes important in a growthscenario where the 3G population is slowly becoming a sizablepercentage of the total traffic. In the dedicated case, this small 3Gpopulation is placed on a dedicated carrier, requiring 3G channelelements. Since the density of each 3G pack is large, a sizable fractionof the CE present may be idle, particularly when the nascent 3G trafficis low. In contrast, CE are used to better efficiency if the emerging 3Gtraffic is mixed into a 2G carrier. Within this scenario, a 3G pack isadded to accommodate the 3G traffic. The existence of any extra idleCE can be balanced by removing the corresponding number of 2G CE,since the 3G CEs are dual-mode. The use of mixed carriers thereforeuses hardware resources more efficiently in the traffic growth stages.This distinction may not be important if growth on a dedicated 3Gcarrier is expected to be rapid.

Conclusions

The decision regarding dedicated vs. mixed carriers is therefore drivenby several factors. These must be weighted in overall importance sinceall do not indicate the same decision. As an example, a possibledeployment scenario could entail mixing 3G users into 2G carriers inthe early stages of 3G growth. As 3G traffic becomes significant, 3Gusers could be migrated to a dedicated carrier(s). This scenario couldapply in a situation where there is need to accurately meet in earlygrowth a forecasted target demand (target mixture of total capacity)within the constraint of available spectrum, and to use CE as efficientlyas possible. This scenario also provides for the maximum possiblecapacity in later phases of growth, as dedicated carriers are thenemployed. These advantages must be weighed against thedisadvantages of not providing the maximum possible capacity in earlyphases, and against the difficulty of migrating 3G users to a separatecarrier later on.

System deploymentMixed 3G-1X voice/data capacity and coverage

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

In the following discussion, we presume that 3G-1X is deployed withina dedicated carrier, and consider the impact of mixing voice and datawithin the carrier. We further assume that the 3G-1X is an upgrade (1:1overlay) of an existing 2G network, where the cell spacing is dictatedby the 2G voice footprint. This scenario is of particular interest sincemany service providers desire to upgrade their current 2G networks to3G.

When the 3G-1X packet data service is introduced into the voicenetwork, the high speed data will have an impact on the voice capacityand coverage. Analysis of the 3G technology indicates that therequirement of ubiquitous high rate packet data coverage is generallymore stringent than that of voice coverage for comparable assumptionson RF parameters. This difference mainly comes from the decrease inprocessing gain. As mentioned in Chapter 3, “Data link budgets” and“Coverage (spatial) design: overlay and greenfield” sections of thischapter, if the design goal of a 3G-1X system is to provide anubiquitous coverage for a high-rate data service, then the link budgetbased on the supplemental channel rate should be used for cell layout.If the voice link budget is used, then the high-rate data service will beavailable in an inner circle of the cell coverage. In this case, thesupportable data rate will reduce when the mobile moves close to thecell edge.

In order to extend the data coverage, the following methods may beemployed:

• Relaxing the target FER for the data application without causingsignificant TCP/IP throughput degradation

• Considering less body loss when using a data terminal

• Using higher gain antenna at the data terminal

• Increasing the base station transmit power and data terminaltransmit power

• Implementing a scheduling policy to provide fair access to datausers on the cell edge

• Increasing the number of cell site to provide additional coverage.This could also require re-design of the network and re-location ofsome of the existing sites and addition of new cell sites.

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The total capacity for the mixed voice and data system is expressed astwo numbers, the data throughput capacity and voice Erlang capacity.The higher data subscriber percentage, the more data throughput andthe fewer voice erlangs. Data throughput and voice Erlang capacity willclearly vary depending upon the mix of voice and data users. Based onthe voice and data traffic projection for a service area, a serviceprovider can calculate the percentages of voice Erlang and datasessions, and then determine the trade-off between voice capacity anddata throughput.

Calculating the capacity values for the mixed voice and data capacity isa somewhat involved process. In both cases, capacities are calculatedfrom maximum number of channels from the traffic (Erlang) model.The general model is described in Chapter 3, “General Erlang model”section, and is characterized by random arrivals at a system with finitequeues and fixed number of channels (servers).

For voice, the Erlang B (a.k.a, blocked calls cleared) version of thetraffic model is typically used. The Erlang B version is the GeneralErlang model with no (zero length) queue. No queue implies nowaiting. When a call arrives it is either served or turned away(blocked). The carried load on N channels is measured in Erlangs(average active channels). The associated performance is measured byprobability of blocking, i.e., all channels busy.

For data, the Erlang C (a.k.a., blocked calls delayed) version of thetraffic model is typically used. The Erlang C version is the GeneralErlang model with infinite length queue. An infinite length queueimplies that all arrivals are (eventually) served: hence, there is noblocking in the Erlang C model. The carried load on N channels (N datapipes) is measured by throughput (kbits/sec). The associatedperformance is measured by average wait in queue.

The specification of throughput and Erlangs for a particular mixtherefore depends upon the performance requirements (blockingpercentage for voice, average delay for data) imposed on eachpopulation within the mix.


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The methodology used to estimate the capacity for mixed voice-datanetworks uses the following steps:

• Select mix (e.g., 70% voice, 30% data)

• Treat mix as forward power constraints, i.e., 70% is used for voiceand 30% is used for data

• For data portion:

• For each assigned channel rate:

• Obtain probability distribution of number of supplementalchannels over the coverage area from system level simulation

• For each possibility, compute throughput under average waittime constraint using Erlang C

• Obtain throughput via weighted sum

• Then obtain overall average throughput by using probabilityof seeing each rate.

• For voice portion:

• Determine the number of RF channels the forward linkpower can support

• Compute carried Erlangs at required probability of block forthe number of RF channels.

• Repeat for different mixes.

Following this methodology yields a collection of (Erlang, throughput)points for the range of mixes. A different curve can be generated byvarying the performance specifications, either wait time constraint fordata or blocking for voice. Typically, voice blocking is held constantacross all curves and average data delay time is varied to produce afamily of curves. However, there is no inherent reason that theperformance specifications must be the same across the family ofcurves. Varying the performance specifications will change the shapeof the curve. Figure 4-1 shows two curves. The straight line is obtainedby varying the wait time specification for the data services for thedifferent mix ratios, i.e., longer wait times for lower percentage of dataversus voice. The straight line is an approximate upper bound and isrecommended for provisioning purposes (i.e., packet pipe and CEs).The lower curve represents a constant wait time specification (5seconds) and is recommended for capacity planning purposes.

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Figure 4-1 Voice capacity versus packet data throughput in a mixedcarrier

For example, if the demand for a typical sector was expected to be 18voice Erlangs and 70 kilobits, the RF engineer would start by plottingthis point on the figure above. Clearly, the point lies above the capacitycurve and cannot be supported by a single carrier. The RF engineerwould then divide both demand numbers by N until he got a point thatfell below the curve. N is then the number of carriers required tosupport the capacity demand. In this N=2 gives 9 voice erlangs and 35kilobits per carrier, which falls below the capacity curve, and hence,can expect to be supported.


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5 Handoff

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

Overview

Purpose This chapter discusses the soft handoff procedures, algorithms,coverage, cost and benefits for the CDMA 3G-1X voice and packetdata calls.


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

Forward link 5-8Reverse link 5-8

Coverage contour 5-8Discussion 5-12

Soft handoff costs on channel elements and packet pipe 5-12Soft handoff cost on forward link 5-12Soft handoff advantages 5-13

Qualitative description of reverse linksoft handoff gain 5-14Quantitative description of reverse linksoft handoff gain 5-19

Qualitative description of forward linksoft handoff benefit 5-21

Quantitative description of forward linksoft handoff benefit 5-24

IS-95B parameters 5-24

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401-614-040Issue 2, February 2003

T_ADD, T_DROP 5-26T_TDROP 5-28T_COMP 5-29

SOFT_SLOPE, DROP_INTERCEPT, ADD_INTERCEPT 5-29SCH anchor transfer vs. SHO 5-30

Fundamental Channel (FCH) – voice and data 5-30Data Supplemental Channel (SCH) 5-31

Hard handoffs 5-35

References 5-36

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Introduction

Soft handoff definition In soft handoff, multiple cells simultaneously support the mobile's call.In softer handoff, the mobile's call is simultaneously supported bymultiple sectors of the same cell. The mobile continuously scans for thepilot signals transmitted by each cell/sector (site), and establishescommunication with any site/sector (up to 6 6) whose pilot powerexceeds a given threshold. Communication with the site/sector isterminated when the pilot power drops below a threshold for a timeperiod.

These types of handoff do not require an interruption of thecommunication link as a new link (“leg”) is added before an old leg isdropped. In contrast, a hard handoff (e.g., AMPS) requires a briefinterruption of the link as the single supporting link is switched fromone cell to another. Hard handoffs can also occur in CDMA when themobile executes a handoff between carriers.

Procedure The soft and softer handoff procedures dictate the way in which a call ismaintained as a mobile crosses boundaries between CDMA cells. Insoft handoff, multiple cells simultaneously support the mobile's call; insofter handoff, multiple sectors of the same cell simultaneously supportthe mobile's call. The distinction between soft and softer handoff isimportant since the same Channel Element (CE) is shared to supportthe handoff legs in the softer handoff case, but a separate CE is requiredto support each handoff leg in the soft handoff case. Each sectortransmits a pilot signal of sufficient power to be detected by mobileswithin its vicinity. The mobile continuously scans for pilots, andestablishes communication with any sector (up to six) whose pilotexceeds a given threshold. Similarly, communication with sectorswhose pilot drops below a threshold is terminated. The identification ofdistinct pilot signals by the mobile relies on the fact that each pilotexhibits a different time offset within the same PN code.

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

6 Typically, mobiles only have three “fingers” that demodulate three differentsignals (soft handoff legs or multipaths of a single leg). In six-way soft handoff,signals are transmitted from six different sectors. The mobile chooses the bestthree to demodulate, so not all signals are used by the mobile. Previously, onlythree-way soft handoff hand been supported. Even in three way soft handoff themobile’s three fingers might demodulate different multipaths of the same trans-mission and not use a signal from one of the transmitting sectors. The six-wayhandoff feature is useful in pilot pollution areas. The feature needs to be carefullyoptimized so as to not compromise system capacity - see CDMA Translation Application

Note #4: Handoff.

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The mobile's search for pilots is facilitated by the fact that these offsetsare in integer multiples of a known time delay. The pilots identified bythe mobile, as well as other pilots specified by the serving sector(s), arecategorized by the mobile as follows:

• The Active Set consists of those pilots whose sites are currentlysupporting the mobile's call

• The Candidate Set consists of those pilots whose sites, based onthe received strength of their pilots, could also support themobile's call

• The Neighbor Set consists of those pilots whose sites are not in theactive set or the candidate set, but are nevertheless likelycandidates for soft handoff; for example, these sites may be inknown geographic proximity. Each sector in the network has anassociated “neighbor list” provisioned. As sectors are added to theactive set the network sends a Neighbor List Update message withthe “best” 20 neighbors from the combined neighbor lists of allactive set participants. The mobile uses the information from thenetwork, as well as the normal movement of pilots (i.e., pilots inthe candidate for longer than T_TDROP seconds), to populate theneighbor set.

• The Remaining Set consists of those pilots within the CDMAsystem but not within the other three sets. The mobile may movepilots from the remaining set to the candidate set. However, themobile typically uses more resources on the neighbor set than theremaining set; hence, it is less likely for pilots in the remaining setto move into the candidate set, than it is for the pilots in theneighbor set. Furthermore, because of the possible confusionabout the unique identification of a sector by PN offset, thenetwork does not add pilots from the remaining set to the activeset that do not appear on the neighbor list. The undeclaredneighbor list feature can be used to track these occurrences so thatneighbor lists can be optimized. Note that provisioning ofneighbor lists is one of the most important optimization activitiesto assure system performance.

Movement of pilots among the sets is determined by the mobile'sassessment of pilot signal strength and a set of (adjustable) thresholds.This movement is coordinated with the serving sector. The mobileassesses pilots by comparing pilot strengths to one another, and bycomparing each pilot's power to the total received forward link power.The latter comparison (normalized pilot strength) is the ratio of the

HandoffIntroduction

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pilot energy in a time chip to the spectral density of total receivedforward link power. This ratio is called pilot channel Ec/Io and isdefined as:

Equation 5-1: Pilot channel Ec/Io definition

where:

µ = Fraction of sector power allocated to the pilot channelPi = The power received from the ith sectorF = Mobile receiver noise figureNo = Thermal noise densityW = The carrier bandwidth.

Pilots in the neighbor and/or remaining set whose Ec/Io exceeds athreshold are associated with sites that can support the call;accordingly, these pilots are moved to the active or candidate set. Thethreshold is a fixed number (T_ADD) in IS-95A and a dynamic numberin IS-95B that depends on the quality of the pilots in the active set.Similarly, pilots in the active and/or candidate set whose Ec/Io dropsbelow a threshold (T_DROP for IS-95A and dynamic for IS-95B) for aperiod of time exceeding the parameter T_T_DROP are moved to theneighbor or remaining set. Finally, a candidate set pilot whose strengthexceeds an active set pilot by at least T_COMP (and an additionaldynamic criteria for IS-95B) will be moved to the active set, possiblydisplacing that pilot, as shown in Figure 5-1.

∑+⋅=

jalljo

i

io

c

PWFN

P

I

E

_

µ

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

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Figure 5-1 Simplified Pilot Set transactions (diagram does not showall possible transitions)

Figure 5-1 is a simplified diagram showing the movement of pilotsbetween sets. Rather than attempting to show every possible event, wefocus the diagram on those events most influenced by the translatablehandoff parameters.

IS-95B soft handoffalgorithm

The field data shows that under some conditions there may be moresoft handoffs occurring than are necessary when using the current IS-95A handoff algorithm. Such handoff overheads may also overusesystem resources, thereby degrading total system capacity. Animproved soft handoff algorithm was defined in IS-95B and will beused for 3G-1X. The new soft handoff algorithm is intended to improvethese situations by introducing the dynamic handoff thresholddetermined by combining the pilot strengths from all pilots in the activeset. IS-95B added the following three new parameters to the softhandoff algorithm:

• SOFT_SLOPE

• ADD_INTERCEPT

• DROP_INTERCEPT.

Active

Candidate

Neighbor

Remaining

Pilot replacedby Candidatepilot

Pilot is below T_DROP forT_TDROP seconds

T_TDROPexpires

Pilot exceedsT_ADD

Active set not full andPilot exceeds T_ADD

OrActive set full but swap

criteria met (see text)

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These parameters lead to a variable threshold for adding and droppingpilots as opposed to the fixed threshold in IS-95A (i.e., T_ADD andT_DROP). The threshold is a function of the mobile's measure of thestrength of the pilot's in the active set. The stronger the sum of thepilots strength the less likely a mobile is to add a pilot to the active setand more likely the mobile is to drop a pilot from the active set.

The equations for the thresholds are:

where PSi is the mobile's measure of pilot Ec/Io and the sum isperformed over all pilots in the active set. The threshold is plotted asfunction of combined active set pilot strength below.

Figure 5-2 IS-95B dynamic add/drop thresholds

Under this algorithm, the mobile will send out a PSMM message torequest the base station to add a pilot into the active set only when thepilot is worthy of being added. This benefit can be seen in the figure asthe gray area of pilot strengths that are not added in IS-95B that wouldhave been added to the active set in IS-95A. The better the pilots themobile is currently using (further to the right on combined active setpilot strength axis), the less likely is that a pilot will be added to the

+××= ∑

∈ Aii

ADDTINTADDPSSLOPESOFTTHRESHADD _,_log10_max_

+××= ∑

∈ Aii

DROPTINTDROPPSSLOPESOFTTHRESHDROP _,_log10_max_

IS-95AT_ADD

AddThreshold

IS-95B

Combined Active Set Pilot Strength

Pilots not addedin IS-95B thatwould have beenadded in IS-95A

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active set (higher add threshold). A similar figure can be drawn for thedrop threshold. The mobile will request the base station to drop a pilotfrom the active set if the pilot contributes little. These improvementswill reduce the time a call is in soft handoff and also filter outunnecessary handoffs from each call; therefore, the average number oflegs for each call is reduced and the forward link capacity is increased.Intuitively this makes sense since additional base station power shouldnot be spent on a mobile that is receiving strong signals elsewhere.Improving forward link power utilization efficiency will lead toincreased system capacity. Simulations have shown a range ofimprovements for the soft handoff power overhead factor used inforward link budgets. For forward link budget planning purposes, areduction from the typical value of 1.85 for IS-95A to 1.75 for IS-95Bis recommended.

Signal combining Forward link

On the forward link, all of the signals from the sectors in soft and softerhandoff are combined in the mobile in a Maximum Ratio Combining(MRC) technique (see CMDA Systems Engineering Handbook, JhongSam Lee & Leonard E. Miller). In MRC, each of the soft handoff legs,in addition to any discernible multipaths, are added together with aweighting for the channel quality, which for IS-95 based systems is thepilot channel Ec/Io.

Reverse link

For sectors involved in softer handoff the signals from the mobile arecombined in the Channel Element in a MRC fashion as described forthe forward link.

For cells involved in soft handoff, the signals from the mobile are notactually combined, but a “frame selector” at the MSC chooses the“best” signal. The CRCs for the physical layer frames are examined,and the frame without an error is chosen as the best. If neither packethas an error, the decision is made randomly.

Coverage contour Mobiles evaluate base stations' suitability for providing a servingtraffic channel by measuring the base stations' pilot signal strengthsrelative to total forward link power, or Ec/Io, as described above.

One criteria for determining a coverage contour is that the mobile haveat least one pilot with Ec/Io that is equal to the value of T_ADD: Valuesof Ec/Io within the contour will be greater than T_ADD; values outsidethe contour will be less. Accordingly, a mobile crossing the boundary

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into the cell will add that cell's pilot to its active set. (A mobile crossingthe boundary out of the cell will not necessarily drop the pilot, as thisfunction depends on the values of T_DROP and T_T_DROP.)Coverage areas also change with varying T_ADD.

Figure 5-3 T_ADD coverage contour

Consider the sequence shown in Figure 5-3 (note the figure is drawn sothat the T_ADD boundary for both cells exactly coincides. In practicethe boundaries overlap given the geometry of the cell layout). As amobile moves from Cell 1 to Cell 2, it will go through the followingsequence:

1. As the mobile moves past the T_DROP boundary for Cell 2,nothing happens

2. When the mobile reaches the T_ADD boundary, it will add Cell 2to its active set and will be in soft handoff with Cell 1 and Cell 2

3. When the mobile moves past the T_DROP boundary for Cell 1, itwill drop Cell 1 from its active set and leave the soft handoff state.

A mobile moving in the opposite direction, from Cell 2 to Cell 1, goesthrough the following sequence, as shown in Figure 5-4.

Figure 5-4 T_ADD contour mobile moves opposite direction

1. As the mobile moves past the T_DROP boundary for Cell 1,nothing happens

2. When the mobile reaches the T_ADD boundary, it will add Cell 1to its active set and will be in soft handoff with Cell 1 and Cell 2

3. When the mobile moves past the T_DROP boundary for Cell 2, itwill drop Cell 1 from its active set and leave the soft handoff state.

XCell 1

XCell 2

T_DROP - Cell 2 T_DROP - Cell 1T_ADD - Both

Mobile insoft

XCell 1

XCell 2

T_DROP - Cell 2 T_DROP - Cell 1T_ADD - Both

Mobile insoft handoff

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Note that designing coverage contours for pilot channel Ec/Io values ofT_DROP will lead to coverage holes. Consider the followingFigure 5-5:

Figure 5-5 T_DROP coverage contour leads to coverage holes

As a mobile moves from Cell 1 to Cell 2, it will go through thefollowing sequence:

1. As the mobile moves past the T_ADD boundary for Cell 1,nothing happens

2. When the mobile reaches the T_DROP boundary, it will drop Cell1 from its active set. The pilot signal from Cell 2 will still bebelow T_ADD, and hence, should not be in the active set. Themobile will not drop the pilot since it is its only active pilot, butbecause the pilot is weak, the mobiles performance (FER) willdegrade and the call may drop.

Of course given the geometry of cell site coverage, it is impossible tohave T_ADD contours matching exactly between cells. Therefore, it isimportant that in designing a network that all areas receive at least onepilot that is above T_ADD. This design approach will lead to mostareas having overlapping pilots above T_ADD. In these overlappingareas, the mobile will be expected to be in soft handoff. The mobile willalso be expected to be in soft handoff outside these overlappingT_ADD contours, but the specifics of the soft handoff locations dependon the mobile direction of travel.

For networks with fixed subscribers, the soft handoff areas will besolely the areas of overlapping pilot strength above T_ADD. The areasof soft handoff in a mobile with one pilot below T_ADD (but aboveT_DROP) and another above T_ADD will not be soft handoff areas ina fixed network.

Note that this discussion uses IS-95A terminology (i.e., T_ADD andT_DROP) but is applicable to IS-95B as well. As discussed earlier(“IS-95B soft handoff algorithm” section), the add and drop thresholdsin IS-95B are a function of aggregate pilot Ec/Io. However, the IS-95B

XCell 1

XCell 2

T_ADD - Cell 1 T_ADD - Cell 2T_DROP - Both

No pilot!!!

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thresholds will equal the IS-95A fixed thresholds for areas withoutstrong pilot coverage, i.e., low aggregate pilot Ec/Io. The cell edge isexpected to fall into this category of low aggregate pilot Ec/Io, andhence, the thresholds for an IS-95B network at the cell edge areexpected to be T_ADD and T_DROP.

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Discussion

Soft handoff costs onchannel elements and

packet pipe

The cost of soft-handoff is two-fold:

1. Increased number of channel elements (CE). A CE is required atevery cell that supports a soft handoff leg. In the case of softerhandoff

2. Increase in backhaul network capacity required. Since multiplecells support the call and the frame selector that chooses the bestsoft handoff leg resides at the MSC, backhaul capacity will berequired from all cells supporting soft handoff legs.

However, the benefit of soft handoff is increased coverage. Therefore,fewer base stations are required to cover the same area. The reductionin base station count outweighs the increase in CE and backhaul facilitycount. For example, for 95% probability of area coverage, the reverselink soft handoff gain is 4.0 dB. For a typical path loss slope of38.5 dB/decade, the increase in cell radius is 27%, which equates to anincrease of 61% in cell area. The same area can be covered with 38%fewer cells. This reduction in cell count typically outweighs the costassociated with the extra CEs and backhaul facilities for those cells.

Softer handoffs require fewer resources than soft handoff in terms ofchannel elements and packet pipe bandwidth, since the signals arecombined in a single channel element. The differentiation is importantfor provisioning required channel element and packet pipe resources.

Soft handoff cost onforward link

The cost of soft handoff is forward link capacity in that the soft handofflegs on the forward link require power that cannot be used to supportother users. This cost is captured in the forward link budget with theline item “Overhead factor to convert from mobiles to the number ofactive power channels”, commonly referred to as the “power overheadfactor”. The value used is a function of soft handoff algorithm (IS-95Avs. IS-95B), terminal mobility, and cell site antenna configuration. Thefollowing table captures values typically used for planning purposes,which are rounded to nearest 5/100ths.

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Table 5-1 Soft handoff overhead factors for voice link budgets

The soft handoff legs also consume Walsh codes. The power overheadfactor is slightly different than the overhead for Walsh codes. However,the Walsh code overhead is only an issue when there are insufficientWalsh codes. Typically, Walsh codes are not a limiting factor. Networkswith fixed subscribers that have high capacities are cases where theWalsh codes may be limiting.

Note also that the power overhead factor is not the same as the ChannelElement (CE) overhead factor. Since softer handoff does not requireextra CEs, the CE overhead factor is less than the power overheadfactor.

Soft handoff advantages Further insight into soft handoff operation can be gained by contrastingthis process with the hard handoff process used in an analog system. Inan analog system, each cell is assigned a set of narrowband channelsfor use in communication links. Co-channel interference is controlledby not reusing the same channels in adjacent cells. A mobileproceeding out of one cell into another must switch to an availablechannel in the new cell. This switch requires a brief interruption of thecommunication link. In a CDMA system, the same wideband channelis reused in every cell. Co-channel interference is accepted butcontrolled so as to achieve greater capacity. Accordingly, soft/softerhandoff does not require channel switching and its associated linkinterruption.

Moreover, with proper threshold settings, the acquisition of new sites isaccomplished before the old (serving) sites are too far away to beuseful. The soft handoff procedure is more robust because theconnection with the new host(s) is made before the connection with theold is broken. This process is often referred to as a make-before-breakconnection, as opposed to the analog break-before-make. The make-before-break handoff is more robust and leads to fewer dropped calls athandoff boundaries.

Cell Antenna Terminal Mobility

Mobile Indoor Fixed Outdoor Fixed

IS-95A Omni 1.50 1.35 1.0

3-sector 1.85 1.60 1.25

IS-95B Omni 1.45 1.30 1.0

3-sector 1.75 1.55 1.25

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Soft handoff also provides for advantages in terms of coverage andcapacity. These advantages appear on both the forward and reverselinks.

Soft handoff provides a diversity gain without which some areas at thecell boundary (the locations furthest from base stations) would beregions of poor link quality because of shadow fading. The mobiles inthese fringe areas would also be more susceptible to base stationinterference (see Chapter 2). Furthermore, the soft handoff state assuresthat the mobile is in a two-path channel. Two-path channels generallyhave lower Eb/Nt requirements relative to own-path channels.

These effects increase the probability that a call will be dropped, sincea hard handoff procedure would typically not be initiated until a mobilereached this area; that is, until the mobile noted a drop in signalstrength from its host cell. In addition, the use of power control withoutsoft handoff could create a situation where a mobile generatesconsiderable amounts of interference to neighbor cells. Suchinterference would reduce capacity.

The last situation arises because the mobile would detect a drop inreceived signal strength before it requested a handoff. Since cellboundaries overlap, this reporting point could be well into the boundaryof the neighbor cell. Within this area, power control would boost themobile's transmit signal strength in an attempt to maintain the link withthe (distant) serving cell. This call-dragging phenomenon reduces thecapacity of the neighbor cell because the mobile 's transmissionsincrease the level of interference at the neighbor cell. In contrast, if themobile were in soft handoff, power control commands from both cellswould ensure that the mobile did not produce undue interference; infact, the reverse link could be maintained at a lower level of mobiletransmit power due to the gain involved in combining the signalsreceived at the two base stations.

Qualitative description of reverse link soft handoff gain

The effect of soft handoff gain can be understood by considering asimple case of a mobile driving from one base station to another basestation, as shown in the following figure.

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Figure 5-6 Mobile traveling between two base stations

The mobile must generate enough signal (Smob) to overcome the pathloss (Lp) and provide the required signal (Sreq which accounts forinterference from other users) at the base station. This can be expressedmathematically as:

Smob = Sreq + Lp

Clearly, as the path loss increases, the required power from the mobilewill increase. In an ideal case, the path loss profiles would looksomething like the following.

Figure 5-7 Mobile required power with and without soft handoff

The following are shown in the above figure:

• The dashed line shows the path loss to base station A

• The solid line shows the path loss to base station B

• The heavy dashed line shows the required mobile power for asystem without soft handoff

Base Station A Base Station B

Pathloss to Base Station B Pathloss to Base Station A


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• The heavy solid line shows the required mobile power for asystem with soft handoff.

The system with soft handoff decides frame by frame which path is thebetter one, allowing the switch from base station A to base station B tohappen immediately. The switch can be immediate since both basestations, A and B, are receiving and processing the signal from themobile and the MSC is deciding which signal is best - hence the “soft”part of the handoff. In a system without soft handoff, the switch will bemade later since it needs to have some hysteresis and has delayassociated with signaling, etc. The difference in power during the delayin switching is not the gain claimed for soft handoff, but demonstratesthe critical factor of a soft handoff: the fact that the decision of the bestpath is done frame by frame allowing the best path to always be chosen.

The specific gain for soft handoff is shown in the following examplethat shows the effect of a fade.

Figure 5-8 Mobile required power during fade with soft handoff

The following are shown in the above figure:

• The dashed line shows the path loss to base station A

• The solid line shows the path loss to base station B

• The heavy solid line shows the required mobile power for asystem with soft handoff.

The figure demonstrates the benefit of soft handoff. As the mobile goesinto a fade to base station A, it does not have to increase its power tothe level of the fade, even for a short period. The mobile only has toincrease its power to the level to reach base station B, which is unlikelyto be also faded with respect to the mobile. The difference between

Pathlossto BaseStation B

Pathlossto BaseStation A


Fade to BaseStation A

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these two levels is what leads to “soft handoff gain”, which is afunction of the extent of dissimilarity (decorrelation) between thefading processes with respect to A and B.

It is difficult to definitively measure soft handoff gain in the same waythat other link budget parameters such as antenna gain can bemeasured. This difficulty arises from the fact that the specific gain isvariable. The gain depends upon the decorrelation of the fadingprocesses, which can vary by market/morphology, and even by driveroutes within a market.

However, for planning purposes, a gain based upon a conservativedecorrelation can be used in link budget analysis (see "Link budget"section on Page 2-14). Furthermore, this gain can be shown to mapdirectly into reduction in mobile transmit strength, thus enhancingcoverage as the link budget dictates. This demonstration is discussedfurther below.

Lucent’s lab environment allows us to set up a specific path loss for amobile. Utilizing this capability, the following path loss profile wascreated.

Figure 5-9 Path loss profile

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The mobile was then put through this simulated path loss environmentand the mobile transmit power was measured. The following figurefocuses in on the area called “Jump #6” in Figure 5-9 (note that thetime scales are different).

Figure 5-10 Observed mobile power without soft handoff

As one would expect, the mobile power increases by 12 dB, the samemagnitude as the fade (increase in path loss).

A second path loss profile for a different sector was also created asshown in the following figure.

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Figure 5-11 Additional path loss profile for second soft handoff leg

The test was rerun with the mobile receiving from and transmitting tothe two separate base stations through the two path loss profiles shownabove. The mobile power transmit power was measured and is plottedin the figure below.

Figure 5-12 Measured mobile power with soft handoff

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In this case with soft handoff, the mobile power only increases by 6 dB.As can be seen from the two plots, the soft handoff case reduces themobile power by the difference between the fade magnitude and thedifference in path loss to the two base stations.

Quantitative description of reverse link soft handoff gain

In a CDMA system, there is an advantage due to soft hand-off gain thatresults in effectively lowering the fade margin required to obtain aspecific probability of edge coverage, as compared to othertechnologies. The soft handoff gain calculation methodology sketchedout below follows the development in Reference [1] of this chapter. Fora CDMA system that admits soft handoff, for any given frame, thebetter, or alternatively, stronger of two or more base stations’ receptionwill be utilized at the switching center. For simplicity, consider that thedecision will depend only on the attenuation, and that the base stationwith lesser of the two or more attenuations will control the AT. Theattenuation of an AT to base station i is given by

Equation 5-2

Where:

α(di,ζi) represents a function of d and ζdi is the distance to the ith base stationζ is the corresponding lognormal shadowingµ is the path loss exponent.

One problem is that the random component of the attenuation to thedifferent base stations [the various ζs (i=0,1,2,...)] could be correlatedwith one another. To get around that problem, theζs are alternatelyexpressed in terms of two independent random variables. Followingalong the same lines as the development in Reference [2] of thischapter, we define ζi = aΣ+ bΣi , where, a2+b2 = 1. The idea here is thatby using different values for a and b, we can vary the correlationbetween the ζ’s. a = 1, b = 0 is the completely correlated case, while a =0, b = 1 represents the completely uncorrelated case. For numericalcalculations, values of a =b=1/√2, a partially (50%) correlated case, willbe considered. Next, we evaluate the excess link margin required in this

iiiidd ζγζα += )log(10),(log(10

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case. Consider the scenario when a AT is in two way soft handoff. Linkoutage will occur in this case only if attenuation to both soft handoffsectors is greater than the margin γ. Hence,

Equation 5-3

Even before we evaluate the above expression, a review of the equationgives us an idea of why we have gain due to soft handoff. Instead of asingle random variable, ξ, being greater than a fixed value resulting inan outage, we now need two partially independent random variables,each of which has to be greater than the fixed value to have an outage.The probability of the later event occurring is certainly less than theformer, or alternatively, for the same outage probability, we need lessmargin in the later case. This is the advantage of the soft handoffcapability in reducing the margin required, which effectively translatesinto soft handoff gain.

We do not go into the details of evaluating Equation 5-3. The interestedreader is referred to Reference [2] of this chapter. For a = b = 1/√2, pathloss exponent of 4, and fading standard deviation of 8 dB, andprobability of edge coverage the soft handoff gain numerically worksout to 4 dB. For probability of edge coverage of 75%, the handoff gainis less and a value of 3 dB is used in the link budget.

Due to the soft handoff feature, excess link margin requirement hasdropped by 4 dB, from 10.3 dB to 6.3 dB. The soft handoff gain for thecase of fading standard deviation equal to 8 dB, but probability of edgecoverage of 75% (probability of area coverage of 90%) works out toapproximately 3 dB. Due to the soft handoff feature, the excess linkmargin requirement has dropped by 3 dB from 5.4 dB to 2.4 dB. Thisreduction in link margin is the advantage due to soft handoff that resultsin increased coverage. Reverse link budgets typically contain the fademargin entered for the no-soft handoff case. Then, a separate line calledsoft handoff gain is included to capture the effect of soft handoff. Thevalues typically used in the reverse link budget are conservativelyrounded down from the values calculated by the methodology above,since the precise correlation is not known. The values used in thereverse link budget for fading standard deviation of 8 dB are shown inthe following table.

}]log10,log10[Pr{1100

γζµζµ >++= ddMinPout

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Table 5-2 Reverse link soft handoff gain

For standard deviations other than 8 dB, the required margin to achievea specified outage (probability of edge coverage) criteria can benumerically determined using the methodology outlined in Reference[1] of this chapter. The soft handoff gain to be entered in the linkbudget is just the difference between the computed required margin andfade margin.

Qualitative description offorward link soft handoff

benefit

The co-channel nature of CDMA makes soft handoff critical for theforward link. A mobile at the cell edge will see equal strength signalsfrom at least two base stations. In a non-CDMA system, the adjacentbase station would not be using the same frequency channel. In CDMAthe adjacent will be using the same frequency channel. Soft handoffallows for these co-channel signals that would be interferers tocontribute to supporting the call. Consider this simplified case of amobile receiving equal signals from two different base stations, nothermal noise and perfect orthogonality.

Figure 5-13 Mobile in soft handoff

Probability ofEdge Coverage

Reverse LinkFade Margin

Reverse Link SoftHandoff Gain

75 5.4 3.0

80 6.7 3.3

85 8.3 3.5

90 10.3 4.0

Base Station 1 Base Station 2

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In the no-soft handoff case, the Eb/No at the mobile is:

where g is the processing gain and µ is the fraction of power from basestation 1 required to support the traffic channel for the mobile. If weassume that the signals from the two base stations of are equal strength,we can solve for µ as follows:

In the soft handoff case, we know from the theory of maximum ratiocombining that the achieved Eb/No is the sum of the Eb/No's (linear)from the different soft handoff legs. Therefore, the combined Eb/No atthe mobile is:

If we assume that the total power (Si) from each base station is the sameand the power fraction for the two base stations are equal, i.e., µ1 equalsµ2, µ can be solved as:

Therefore, the power required from each base station in the softhandoff case is half of what would have been required without softhandoff. Of course, Base Station 2 is now transmitting power (utilizingits forward link capacity) to support the call, which it was not doing inthe no soft handoff case; however, the net power received by othermobiles in the vicinity is unchanged since each base station istransmitting half of the original power.

The benefit of soft handoff on the forward link comes from the fact thatthe mobile receives signals from different base stations that provide adiversity gain against fading. When a mobile enters a fade with respectto one base station, it is unlikely that it will be also be in the same fadewith respect to the other base stations in its active set. Hence, the base

2

1

S

Sg

N

E

o

b ⋅⋅= µ

o

bshono N

E

g

1_

=µ

( )21

222

211

1

22

2

11

SS

gSS

S

Sg

S

Sg

N

E

o

b

⋅⋅⋅+⋅=⋅⋅+⋅⋅= µµµµ

o

bsho N

E

g⋅=

2

1µ

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station will not require power to overcome the deepest fade a mobile atthe edge may enter, since during that fading period the mobile can relyon signals from other base stations in its active set.

We can consider the same example with the mobile entering a fade (F)to Base Station 1, the benefit of soft handoff becomes very clear.

The combined Eb/No is then:

If we assume equal power from both base stations, the equationsimplifies to:

If we assume that F is large, the µ1 term can be expected to be muchless than the µ2 term. If then compare to the previous (non-faded case)Eb/No and require that the Eb/No be maintained at the same level:

we see that the traffic fraction must be:

The traffic fraction will not increase if the fade is greater than 2 (3 dB)and actually decreases for deeper fades. This analysis makes it appearthat fading is beneficial, due to the assumptions of perfectorthogonality and no thermal noise leading to the single cell being theonly interference term for the given leg. Hence, the deeper the fade theinterferer is in, the better. If that perfect orthogonality assumption isremoved, the self-interference (from the same cell) will become thepredominant interference term for the non-faded leg during a fade to

2

11

1S

FSg

N

E

o

b⋅⋅

=µ

FS

Sg

N

E

o

b

1

22

2

⋅⋅= µand

21

2222

21

1

SFS

SF

S

N

E

o

b

⋅

⋅+⋅

=⋅µµ

⋅+=

⋅

+

=⋅

21

221

1µµµµ

FF

g

F

gF

N

E

o

b

nofadeSHOggF −⋅⋅=⋅⋅ µµ 2

2

FnofadeSHO−⋅

=µ

µ2

2

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other soft handoff legs. Of course, the faded leg will benefit fromhaving the self-interference reduced by the same fade amount as thetraffic signal.

Quantitative description of forward link soft handoff benefit

The impact of soft handoff is captured in the Monte Carlo simulationsused to derive parameter values for the forward link budget. Thesesimulations capture the benefit of lower power per handoff leg due bothto the diversity gain against fading and maximum ratio combining atthe mobile.

The forward link budget contains a term for the soft handoff poweroverhead factor. This term increases the number of traffic channels theforward link is supporting. For IS-95A, empirical data shows that avalue of 1.85 to be a good estimate. No empirical data exists for IS-95B. However, simulations suggest a reduction in this value to 1.75 asa good estimate for planning purposes.

IS-95B parameters IS-95B added the following three new parameters to the soft handoffalgorithm. Lucent's 3G-1X system supports the IS-95B handoffalgorithm and hence has these parameters.

• SOFT_SLOPE

• ADD_INTERCEPT

• DROP_INTERCEPT.

These parameters lead to a variable threshold for adding and droppingpilots as opposed to the fixed threshold in IS-95A, i.e., T_ADD andT_DROP. The threshold is a function of the mobile's measure of thestrength of the pilot's in the active set. The stronger the sum of thepilots strength, the less likely a mobile is to add a pilot to the active setand more likely the mobile is to drop a pilot from the active set.Intuitively this makes sense since additional base station power shouldnot be spent on a mobile that is receiving strong signals elsewhere.Improving forward link power utilization efficiency will lead toincreased system capacity.

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The equations for the thresholds are as follows:

where PSi is the mobile's measure of pilot Ec/Io , and the sum isperformed over all pilots in the active set.

Figure 5-14 IS-95B dynamic threshold

These thresholds are also applied when applying the T_COMP (see"Procedure" section on Page 5-3) criteria.

T_ADD, T_DROP

Lower T_ADD and T_DROP thresholds lead to the mobile havingmore pilots in its active set. More pilots mean that mobile will havemore forward link legs to support it. More forward links can help amobile in disadvantageous RF conditions. However, this must betraded off against the cost of supporting those forward links. The powerrequired to support those soft handoff legs will not be available tosupport other calls, thereby possibly lowering capacity. There are twofactors that mitigate those costs.

+××= ∑

∈ Aii

ADDTINTADDPSSLOPESOFTTHRESHADD _,_log10_max_

+××= ∑

∈ Aii

DROPTINTDROPPSSLOPESOFTTHRESHDROP _,_log10_max_

IS-95AT_ADD

AddThreshold

IS-95B

Combined Active Set Pilot Strength

Pilots not added inIS-95B that wouldhave been addedin IS-95A

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First, the IS-95B dynamic thresholds, as described above, reduce thenumber of soft handoff legs by not assigning legs to mobiles that havehigh good pilots already. The quality of the pilots the mobile is seeingis determined by the aggregate Ec/Io term.

Second, the faster forward link power control in 3G-1X allows thesectors involved in soft handoff to realize a greater gain from softhandoff. When a soft handoff leg is added in 3G, the mobile will see animmediate improvement in Eb/No and ask for less power from all basestations involved in the handoff. The base stations can quickly reducethe power for those links. In IS-95, the impact of adding a soft handoffleg was realized much more slowly as the power control is EIB based.The power is reduced slowly while no errors are reported from themobile.

The impact of faster power control is illustrated in the followingsimulations. Figure 5-15 and Figure 5-16 show time series plots of the2G EIB based power control and the 3G-1X Eb/Nt (800 Hz) basedpower control. The top sub-plot of each figure shows mobile receivedEc/Io from various pilots. Bolded lines indicate the pilots in the activeset. As shown in the figures, the mobile gets into 3-way hand-offaround the 82nd second. Hence, the geometry increases dramaticallyfrom simplex to 3-way handoff. However, the EIB based power controlmethod cannot track the geometry changing very efficiently. Thisresults in transmitting excessive power. On the other hand, the 3G Eb/Nt (800 Hz) based power control can fully take advantage of trackingcapability and results in saving transmit power.

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Figure 5-15 2G EIB based power control

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Figure 5-16 3G-1X Eb/Nt based power control

T_TDROP

A timer is started when the strength Ec/Io of an active or candidate setpilot falls below T_DROP (or dynamic threshold for IS-95B). Anactive set pilot that falls below T_DROP for a period exceedingT_TDROP is moved to either the candidate or neighbor set (thedecision is based on the serving site direction). A candidate set pilotthat falls below T_DROP for a period exceeding T_TDROP is movedto the neighbor set. It is expected that the settings for T_TDROP forboth the IS-95B and IS-95A implementations will be similar.

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T_COMP

The parameter T_COMP controls movement of pilots from thecandidate set to the active set. A candidate set pilot with strength Ec/Ioexceeding that of an active set pilot by T_COMPx0.5dB is moved tothe active set, replacing that pilot. T_COMP is measured in units of0.5 dB.

SOFT_SLOPE,DROP_INTERCEPT,

ADD_INTERCEPT

The SOFT_SLOPE, DROP_INTERCEPT, and ADD_INTERCEPTterms determine the dynamic portion of the add/drop threshold. Highervalues will lead to fewer pilots in the active set, while lower values willlead to more pilots in the active set. More SHO legs can benefit a calland lead to fewer dropped calls and possibly lower error rates.However, more SHO legs will reduce base station capacity as moreforward link power is used for SHO legs. These parameters need to beoptimized to find the correct trade-off. Such optimization can be done,for example, in pre-commercial drive test.

Insight into the initial settings for the new IS-95B parameters can begained by plotting the improvement in aggregate pilot channel Ec/Io(i.e., the linear sum of Ec/Io's of pilots in the active set) for a giveninitial aggregate pilot channel Ec/Io and additional leg Ec/Io.

Figure 5-17 Improvement in aggregate pilot strength

0.0

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401-614-040Issue 2, February 2003

Following any one specific line representing an additional pilot at afixed Ec/Io, the plot shows the benefit of adding that pilot decreases asthe aggregate Ec/Io increases. The knee of the curve defines a logicalpoint for deciding whether to add that pilot or not. The knee is notprecisely defined, but an approximate inflection point can bedetermined where the benefit of adding the additional pilot diminishes.

SCH anchor transfer vs.SHO

While soft handoff is clearly beneficial for voice communications, thecost benefit trade-off is not as clear for bursty data transmissions on theSCH (see Chapter 3, "RF engineering for data"). For this reason,Lucent has chosen not to implement soft handoff for the SCH forwardlink. Lucent instead has implemented an optimized fast switchingalgorithm (i.e., anchor transfer) that provides similar performance tosoft handoff without the drawbacks. In contrast, soft handoff isprovided for the fundamental channel that serves voice and provides acontinuous support link for the supplemental channel bursts. Moredetail is provided below.

Fundamental Channel (FCH) – Voice and data

A fundamental channel is defined as a circuit-switched 9.6 kbpschannel, supporting either voice or data.

An FCH for voice is required to maintain a target Quality of Service(QoS) in terms of FER over the duration of a call. Call holding timescan be several seconds to tens of minutes. During the call, the user mostlikely moves through a variety of RF conditions, crosses multiple cellboundaries, changes speed, etc. Soft handoff is designed to reliablymaintain the call without speech quality degradation during any part ofthe call through these changing conditions.

An FCH for data provides underlying support for data bursts on thesupplemental channel (SCH), as well as to transmit low speed data.Similarly to voice calls, the FCH for data may stay active for durationsof several seconds to durations of hundreds of minutes. The FCH isused to reliably deliver signaling and to guarantee minimum rate dataservices throughout the coverage area. Therefore, Lucent hasimplemented soft handoff for the FCH for both voice and data.

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Data Supplemental Channel (SCH)

Data service requirements

High rate packet data transmissions are bursty in nature. SCHs are setup for durations expected to be much shorter than the typical voice call,in the range from hundreds of milliseconds to a few seconds.Additional reliability for SCH is provided by the RLP protocol thatautomatically retransmits physical layer frames in error. Therefore, theSCH does not have the same requirement for a continuous, low error-rate channel.

Soft handoff cost

Soft handoff has a built-in cost in terms of both backhaul facilitiesbetween the base station and the Internet infrastructure and channelelements. Facilities, which are one of the highest operating expensesfor network providers, would be required between every cell in the softhandoff and the MSC. This cost of facilities and channel elements isworthwhile for voice that requires a continuous, low latency channel.

Qualitative performance impact of soft handoff

Supporting forward link soft handoff would increase the setup time forthe channel, and hence the latency any given transmission would see.TCP flow control is very sensitive to round trip delay. At high datarates, even if the pipe is large (i.e., high bandwidth channel), it will notbe fully utilized unless the end-to-end latency is minimized. Providinghigher rate channels provides no advantage unless latency is controlled.

But setting up a data burst in soft handoff would necessarily take longerand introduce more delay. Soft handoff requires coordination amongthe different base stations for the following:

• Channel element availability

• Backhaul facility availability

• RF resource availability

• Time synchronization of the transmission of the burst.

Furthermore, to support soft handoff requires that all base stationsproviding a forward link as a soft handoff leg have sufficient power.Data channels are expected to require, on average, more power thanvoice channels. Therefore, it is more likely in data, as opposed to voice,that sufficient power will not be available to support the desiredforward link rate. The channel rate would have to be reduced to supportthe weakest leg with the least available power.

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Lucent anchor transfer solution

Lucent has implemented an anchor monitoring and transferringsolution for the forward link SCH. “Anchor” means the sector that isdetermined to provide the best server for a given mobile. The mobilemonitors the pilot Ec/Ios of the nearby base stations, and reports thesemeasurements to the network on the reverse link. The network can thendetermine which base station will provide the best forward linkperformance. In this manner, most of the diversity advantage of softhandoff is maintained. Currently, the mobile reports its measurementsup to every 2 seconds. Enhancements to the standard provide formobile reporting when significant changes in pilot strengths areobserved.

Quantitative comparison of capacity and coverage impact of anchortransfer

Lucent has performed performance simulations to study theperformance of ideal anchor transfer compared to soft handoff. Thesimulation had the following assumptions:

• Cell layout is based on 3G-1X voice link budget

• Lognormal shadow fading with standard deviation of 8dB and50% site-to-site correlation

• Maximum supplemental channel transmission power fraction is-3dB with respect to full power.

• Due to load variation (voice and/or data), half of the time themaximum Supplemental channel transmission power fraction forcalls in handoff is restricted to -6 dB in at least one of the legs. Therest of the time, all handoff legs have up to -3dB available. Thisassumption is the most critical for the performance comparison.Different distributions for available power among the proposedhandoff legs will yield different results.

• No transmission diversity

• Turbo codes for SCH

• Mobile environments: AWGN, 3kmph one-path Rician (K=2,K=5)

• IS-95B handoff algorithm.

The first plot shows the average SCH power, relative to total power, asa function of RF environment and SCH channel rate. Lower values areclearly better, as less power per user means that more users can be

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supported. From the plot, it is clear that handoff does not provide acapacity advantage, and in many cases, provides a capacitydisadvantage.

The second plot shows the SCH coverage area, relative to FCHcoverage, as a function of RF environment and SCH channel rate. In allcases, the no handoff case provides equal or better coverage comparedto the handoff case.

Figure 5-18 Simulation results 1 - soft handoff impact on dataperformance

Figure 5-19 Simulation results 2 - soft handoff impact on dataperformance

Average SCH Power as a Function of RF Environment and Rate

-12

.2

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AWGN19.2

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K=576.8

AWGN76.8

K=2153.6

K=5153.6

AWGN153.6

Ave

rag

eS

upp

lem

enta

lC

han

ne

lEc/

Ior(

dB

HandoffNo Handoff

SCH Area Coverage as a Function of RF Environmentd R t

100%

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%

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153.6

SC

HC

ove

rag

e(%

of

FC

HC

ove

rag

e)

Handof

No

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K=2 AWGN AWGNK=5 K=5

38.4 38.4 76.8 153.6 153.6

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R-SCH

Lucent’s equipment does support soft handoff on the reverse SCH.Reverse link soft handoff has no cost from an air capacity point ofview, and does provide benefit in reducing the mobile required power.The mobile is only broadcasting a single channel that is received bymultiple base station receivers. Compare this to the forward link wherethe different base stations in soft handoff are transmitting separatesignals, consuming part of their power and hence capacity. Supportingreverse link soft handoff does require extra channel elements andbackhaul facilities, but given the expected asymmetrical nature of data,the cost is expected significantly less than if forward link soft handoffwere supported.

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Hard handoffs

Although the focus of this chapter is on soft handoff, it should be notedthat, hard handoffs also occur in a 3G network. Briefly, hard handoffswould occur in the following cases:

• From 3G-1X to 3G-1X on a different carrier

• From 3G-1X to 2G on the same carrier

• From 3G-1X to 2G on a different carrier

• From 3G-1X to AMPS on a different carrier.

Note that hard handoffs from 2G to 3G and AMPS to 3G are notcurrently supported.

Of course, hard handoffs from 3G-1X to either 2G or AMPS require themobile to support the other technology being handed to (i.e., dual modemobile).

The reliability of hard handoffs is enhanced by carrying forward all ofthe improvements in hard handoff that Lucent has made for 2G IS-95.These improvements include:

• CDMA Inter-frequency Handoff Trigger Improvement (IFHOTI)

• Pilot-Only Carriers

• CDMA Multiple Pilots Interfrequency Handoff (CMPIFHO).

The combination of these features has led to extremely robust inter-frequency handoff performance. Further information can be found inthe Reference [2] of this chapter.

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References

[1]. “Soft Handoff Extends CDMA Cell Coverage and IncreasesReverse Link Capacity,” Andrew Viterbi, Audrey Viterbi, KleinGilhousen, Ephraim Zehavi, IEEE Journal On Selected Areas inCommunications, Vol. 12, No. 8, October 1994.

[2]. “CDMA Multi-Carrier Performance Enhancements,” NeilBerstein, October 1998.

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6 Power control

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

Overview

Purpose This chapter describes the power control functions for both the forwardlink and the reverse link for the CDMA 3G-1X voice and packet datacalls.


Reverse power control 6-4

Reverse power control for voice traffic 6-5RPC open loop for voice traffic 6-6RPC closed loop for voice traffic 6-6

RPC 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 6-12FPC inner loop for voice 6-13FPC Outer Loop for Voice 6-14

Forward power control for packet data traffic 6-15F-FCH power control for packet data 6-16Forward SARA for 3G-1X packet data calls 6-18

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401-614-040Issue 2, February 2003

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

Introduction

This chapter describes the power control functions for both the forwardlink (base station transmitting signal to mobile) and the reverse link(mobile to base station) for the CDMA 3G-1X voice and packet datacalls.

The primary objective of power control mechanism is to maintainsatisfactory traffic channel quality and reliability with minimal requiredpower while maximizing system capacity within the design coveragearea. The quality of each channel depends strongly on the ratio ofsignal power to the interference power, or Eb/Nt, Eb being the energyper signal bit and Nt the spectral density of the interference and noise.The required Eb/Nt is a function of vehicle speed and channelconditions. In addition, the forward link Eb/Nt requirement can also beaffected by the mobile location with respect to the serving cell andother mobiles. This varying signal-to-noise ratio influences the frameerror rate (FER) and the measured FER values can best characterize thevoice quality for the CDMA system providing voice services. Thepower control algorithm is formulated based on tracking the measuredFER values and comparison against the FER design target.

The reverse power control (RPC) is more complex than that of theforward link. The RPC consists of an open loop and a closed loop. Thelatter consists of an inner loop and an outer loop. The open loop powercontrol algorithm primarily resides in the mobile. This serves to adjustthe mobile transmit power level to compensate for larger scaled, slowvarying effects such as propagation loss and shadow fading. The closedloop algorithm involves both the base station and the mobile, andmainly serves to compensate for fast power fluctuation such asRayleigh fading. The outer loop algorithm continuously updates theappropriate target Eb/Nt value required to maintain a desired averagereverse FER for signals received at the serving cell. The inner loop thencompares the measured Eb/Nt value with the target value. As the basestation examines each reverse traffic frame reported by the mobile viathe inner loop with each frame subdivided into 16 power control groups(PCG) having 1.25 msec time duration. The reported FER value is usedas a reference in the outer loop to determine a new Eb/Nt target value.

Both 2G and 3G RPC algorithms support the same basic open andclosed loop functions, although the 3G algorithm offers significantenhancement over the 2G. The 2G average reverse link output power

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for sub-rate frames (non-voice frames) is reduced by gating off PCG’sin the reverse traffic channel while maintaining the same power levelper PCG. This reduces the reverse link power control speed forsub-rate frames. For instance, for 1/8-rate frames, the power controlspeed is reduced from 800 Hz (for full–rate frames) down to 100 Hz.The 3G reverse power control allows for continuous transmissionrather than the gated transmission for the sub-rate frames, thusmaintaining the 800 Hz power control speed regardless of the framerate.

In addition, the 3G fundamental and supplemental channels areadjusted using a simple integrated scheme, established by introducingthe reverse link pilot channel (R-PICH), which serves as a reference inthe inner closed loop for measuring the mobile Ec /Io level and forscaling.

The forward link power control (FPC) algorithm is less complex thanthat of the reverse link. The mobile measures the FER statistics over atime frame and reports that to the base station. The measured FER isthen compared with the FER target value. Upon comparison, the basestation increases the forward link output power level if the measuredFER is higher than the target, and vice versa.

Unlike the 2G FPC, which was not designed to effectively mitigatefading, the 3G-1X FPC algorithm adopts a faster FPC schemeoperating at a higher rate up to 800 Hz. The 3G power controlmechanism facilitates a faster tracking of RF fades and provides atighter gain adjustment to satisfy the minimum required Eb/Nt per call,thereby enhancing forward link capacity. The 3G FPC algorithm forvoice calls operates at 800 Hz. For packet data service, the forwardfundamental channel (F-FCH) power control operates at 800 Hz whenthe power control function for forward supplemental channel (F-SCH)is off. The F-FCH power control rate reduces to 400 Hz during theF-SCH bursts while F-SCH power control is on, also at a rate of400 Hz.

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Reverse power control

The primary objective of reverse link power control is to resolve thenear-far issue, where a mobile that is near the serving cell yields abetter signal path than a mobile that is far away from the cell. Thus themobiles near the cell may possibly raise too much RF interference toallow for the mobiles far away to reach the serving cell with sufficientsignal-to-noise ratio. This issue can be resolved by dynamicallycontrolling the mobile transmit power such that the serving cellobserves the same signal-to-noise ratio from each mobile.

The 3G-1X reverse power control (RPC) algorithm consists of an openloop as well as a nested closed loop. The RPC supports the integratedfundamental and supplemental channel power control algorithms byintroducing the R-PICH. The R-PICH provides a phase reference to thebase station on a per-PCG basis for coherent detection of the reversefundamental channel (R-FCH). The power allocated to the R-PICH isrelated to the R-FCH power by a translation value. The R-PICH Ec/Iois also closely correlated with the transmission of the estimated R-FCHEb/Nt value and other power control commands from the base stationto the mobile.

In the 3G reverse open loop, the mobile estimates the requiredtransmitted power of the reverse link channels based on the measuredaggregate received power. Similar to the 2G RPC algorithm, the 3GRPC open loop function is performed in the mobile, using necessaryoperating parameters supplied by the base station via signalingmessages in the overhead channels and the forward traffic channel. The3G system applies several new open loop parameters, which were notincluded in the 2G RPC algorithm before. These include, for example,the mobile determined R-PICH mean output power (as a function of theaccess channel power) and a gain-adjusting cell translation parameter,RLGAIN_ADJ. This parameter is set by the base station and sent to themobile via the Extended Channel Assigned Message (ECAM). Theseallow for the mobile to compute the R-FCH mean output power to betransmitted based on the R-PICH mean output power.

Both the 2G and 3G reverse closed loop power control algorithmsconsist of nested inner and outer loops, although there is a majordifference between the 2G closed loop function and the 3G. In the 2Ginner loop algorithm, the mobile reduces the average power for sub-rateframes by gating off certain PCGs, thus reducing the output power


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level per frame. For example, for half-rate frames, eight PCGs aregated off. For ¼-rate frames, twelve PCGs are gated off. As the 2Gmobile outputs the same power level for each non-gated PCG, the basestation only measures the traffic channel Eb/Nt for the non-gated PCGs.Although the average reverse link power is regulated as required, suchgating reduces the closed loop operating speed. In lieu of such PCGgating, the baseline 3G RPC algorithm applies a continuoustransmission scheme by reducing power level per PCG, and avoidsreducing the power control speed during sub-rate frame transmission.

It should be noted that the IS-2000 protocol allows for a reverseeighth-rate gating feature, also known as R-FCH gating. Whentransmitting the R-FCH at 1/8 rate, in order to reduce the mobile powerconsumption and conserve the battery, the mobile may request for suchR-FCH gating via the page response message or the originationmessage. The base station shall then address its response to such arequest via the signaling messages.

If the R-FCH gating is enabled for the 1/8-rate frame transmission, theFPC inner loop at the base station only receives half the PCGs in thereverse PC sub-channel. For the gated PCGs, the base station receives anoisy signal without any knowledge of the frame rate and gatingsituation. This prevents the CMS-5000 ASIC from locking the fingerenergy for those gated PCGs, but rather maintaining the previousF-FCH gain and thus preventing the FPC inner loop function frombeing impaired. In this case, the effective FPC inner loop speed for the1/8-rate frame R-FCH is reduced by half.

In the RPC inner loop, up power control commands will be sent to themobile as the base station measures noisy finger energy for the gatedPCGs. The frame rate information being available, the mobile willexecute only the PC commands associated with non-gated PCGs andignore those gated while the gated PC commands are discarded. This isbased on information concerning the relative delay between theR-PICH PCG number and the F-FCH PCG carrying the PC commandsassociated with the R-PICH measurement, as per the IS-2000 standard.

Reverse power control forvoice traffic

For 3G-1X voice service, the RPC algorithm consists of an open loop,and nested inner and outer closed loops. The details for the open loopand the closed loops are provided below.

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RPC open loop for voice traffic

The primary algorithm for the open loop resides in the mobile. Thisserves to adjust the mobile transmit power level to compensate forlarger scaled, slow varying effects such as propagation loss and shadowfading.

As per IS-2000.2, for voice calls, two equations are used for computingthe open loop mean R-PICH and R-FCH output power levels frommobile respectively.

First, the mean R-PICH power is computed via:

where RLGAIN_ADJ is a base station translation parameter for initialpower variation, sent to the mobile via ECAM signaling message.

The mean output power of the R-FCH can then be computed based onthe mean R-PICH power and other parameters as per the IS-2000standard. These parameters include the band class constant, channelpower adjustment parameters, and a parameter that is set by the basestation and a power offset parameter, RLGAIN_TRAFFIC_PILOT.

RLGAIN_TRAFFIC_PILOT is a translation parameter set at the basestation and transmitted to the mobile via signaling messages forupdating the relative power between R-PICH and R-FCH power. Thedetailed translation information is described in CDMA TranslationApplications Note #3V.

RPC closed loop for voice traffic

As stated in the “Introduction” section of this chapter, the 3G-1Xreverse power control closed loop consists of a nested inner /outer loop.The inner loop algorithm primarily determines and regulates theR-FCH output power level based on the detected R-PICH signalstrength and the outer loop adjusted full rate Eb/Nt set point value. Thisnew Eb/Nt set point value is determined in the outer loop based on themonitored reverse FER. The following is a functional block diagram ofthe RPC closed loop function for 3G-1X voice traffic.

ADJRLGAINdBmPdBdBmPCHACCESSPICHR

_)(5.8)( ++−= −−


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401-614-040Issue 2, February 2003

Figure 6-1 RPC closed loop for 3G-1X voice

As shown in the above diagram, the reverse outer loop computes a newR-FCH Eb/Nt set point iteratively based on the base station detectedreverse frame errors at full rate. The base station then converts thisEb/Nt set point value to a R-PICH signal-to-noise ratio (Ec/Io) set pointvalue. This updated R-PICH Ec/Io set point is mapped to an R-PICHenergy threshold provided in a lookup table in the ASIC. As anembedded ASIC function, the inner loop algorithm compares themeasured R-PICH pilot energy with the above threshold anddetermines the reverse power control bits to be sent to the mobile viathe forward power control sub-channel.

As a voice call is initially set up, the F-FCH is assigned prior to theR-PICH and R-FCH assignments and this F-FCH also carries theforward power control sub-channel. During this initial period, theforward power control sub-channel sent to the mobile from each legalternating up and down commands to maintain a zero net gain inmobile transmit power in the inner loop. If the call starts in multiplelegs, the first leg acquiring the R-PICH sends special preamble framesto the frame selector, which echoes the best frame to all active legs. Theouter loop is initialized upon the cell receiving the first R-FCH with agood frame, and meanwhile, the inner loop stops sending thealternating PC commands to the mobile. Consequently, upon

ForwardPower ControlSub-Channel

in F-FCH

REVERSE LINK POWER CONTROL CLOSED LOOP FOR 3G1X R-FCH

ATTRIBUTE_ADJUSTMENT_GAINRLGAIN_TRAFFIC_PILOT

FROM BASE STATION

NOMINAL_ATTRIBUTE_GAIN

FROM MOBILE STATION

MEASURERECEIVED S/N OFREVERSE PILOT

CHANNELOUTERLOOP

CONVERTR-FCH Eb/Nt

SETPOINTTO

REVERSEPILOT ENERGY

THRESHOLD

BASE STATION MOBILE STATION

REVERSEPILOT

MOBILE STATIONREVERSE

POW ER CONTROL

R-FCH

INNER LOOP OUTER LOOP

REVERSE PILOTAND R-FCHCHANNEL

TRANSMITTERR-FCH FERESTIMATION

INNERLOOP

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receiving the R-PICH measurement, the inner loop begins its normalroutine. For Simplex calls, the inner loop starts as soon as the R-PICHis measured.

The R-PICH Ec/Io set point value used in the voice R-FCH inner loopis determined as follows:

where:

ξ is the R-FCH set point in dB, as R-FCH outer loop output,GF = 1228800/R-FCH (full information rate),

GF is the R-FCH processing Gain,

ηF is the R-FCH power to R-PICH power offset at the mobile.

F in the above equation denotes the R-FCH at full rate with the datarate equal to 9.6 kbps for RC3 and 14.4 kbps for RC4. The frames areeach 20 msec in length, with convolution coding.

RPC for packet data traffic The reverse power control algorithm for packet data traffic is capableof performing power control functions on the R-FCH and the R-SCHseparately. When the data session is an active mode, the base stationregulates the mobile output power levels for the R-FCH and R-SCHwhen assigned. During the dormancy periods, the RPC function isdisabled.

Similar to that for voice services, the RPC algorithm for packet dataservices consists of an open loop and a nested inner/outer closed loop.

The R-FCH power control open loop algorithm for packet data isanalogous to that for voice service. During the R-SCH bursts, the openloop algorithm determines and regulates the R-SCH output power.

The mean R-SCH transmit power is computed based on the meanR-FCH power, mean R-PICH power and parameters similar to those fordetermining R-FCH power. The data calls involve an offset translationparameter that defines different percentages for reverse pilot powerrequired for voice calls and for data to achieve the desired FER.

,)(log10)int(_10 FFoc

GdBsetpoIEPICHR ηξ −−=−

=

t

Fb

N

E10

log10ξ

=

PC

FC

F E

E10

log10η


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For 3G-1X packet data services, there is only one inner loop in thereverse power control algorithm. This inner loop is controlled by theR-FCH RPC outer loop. Similar to that for the R-FCH, an R-SCH outerloop is designed to meet the R-SCH target frame error rate. The R-SCHouter loop detects the R-SCH frame errors and generates an updated R-SCH Eb/Nt set point value according to the correlation between thetarget R-SCH FER set point and that measured. Although the outputfrom the R-SCH outer loop does not affect the reverse inner loop andthe R-FCH outer loop, the R-SCH outer loop function depends on theperformance of the inner loop and the R-FCH outer loop.

The detailed R-SCH outer loop algorithm is implemented via two steps.In the first step, if the based station is in soft or softer handoff, it detectsthe R-SCH frame quality and sends a quality indicator to the FCHframe selector in the switch via R-FCH. The frame selector determinesthe best R-SCH frame and sends back to the base station via F-FCH.Based on this frame quality, the R-SCH outer loop algorithmdetermines an updated R-SCH Eb/Nt set point value. If in simplexmode, the R-SCH outer loop directly uses the frame quality bit fordeducing a new Eb/Nt set point and bypasses the frame selectorprocess.

In the second step, the R-SCH Eb/Nt and R-FCH Eb/Nt set point valuesare compared in a frame-by-frame basis. If the difference for a framerelative to the difference for the previous frame is greater than an offsetthreshold, a signaling message will be sent to the mobile to adjust forthe R-SCH mean output power relative to the R-FCH mean outputpower.

Reverse SARA for 3G-1Xpacket data calls

The R-SCH bursts typically transmit much higher power than that ofthe low-rate R-FCH for voice or for low speed packet data traffic. Asthe base station receives much greater RF power from such SCH burststhan that from weaker mobiles, the reverse links for the latter maypossibly be impaired. The reverse supplemental air resource allocation(R- SARA) mechanism functions to assess the impact of admitting anew R-SCH burst on the current system performance and regulate anypossible new R-SCH assignments.

For each new R-SCH burst request, the call-processing algorithmidentifies the highest rate that may possibly be assigned based on thehardware and software resources available and other serviceconstraints. Each leg then independently executes the R-SARAalgorithm for this call, and determines the maximum R-SCH rate thatcan be supported based on the assessed RF performance while

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considering the impact of adding this new R-SCH. To assess the impactof adding a new R-SCH, the RF loading must be evaluated. Thecontribution to the loading from active R-SCH bursts can besignificant, and this is greatly dependent on how strongly it is receivedat the sector.

Contrary to using the assumed constant receive Eb/Nt for RC3 for theactive fundamental channel, an actual measurement of the receivedreverse link pilot signal strength is used to estimate the loadingcontribution from an active R-SCH burst at each of the active legs.Such estimate is based on the number of the current active Walsh codeson the sector under consideration. Also included are the reversefundamental active channels along with any R-SCH bursts.

If the difference between the strongest pilot Ec/Io among thenon-active set and that of the current strongest active set is greater thana threshold, the R-SCH request will be rejected.

Power controlForward power control

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401-614-040Issue 2, February 2003

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

Forward power control

As discussed above, in the 3G-1X forward link, each serving sectortransmitter must ensure that the required Eb / Nt is achieved at eachmobile within that sector.

The required Eb/Nt range is significantly influenced by mobile speedand multipath conditions due especially to the fact that the mobilereceiver does not employ antenna diversity.

The 3G-1X forward power control algorithm is designed to compensatefor the fast varying Eb/Nt and other cell interference via a fast trackingclosed loop in a sub-frame interval in place of the slower FER basedalgorithm used in the 2G FPC algorithm. Thus, tighter base stationtransmit gain adjustment can be achieved and this results in anincreased forward link capacity.

The 3G forward power control feature is highlighted below:

• Compatible with TR45 TIA/EIA/IS-2000 Standard

• Supports voice and low speed data (9.6 kbps and sub-rates) inF-FCH and high speed data (up to 153.6 kbps) in F-SCH

• Supports Convolution and Turbo coding for F-SCH data rates of19.2 kHz, 38.4 kHz, 76.8 kHz and 153.6 kHz. For Release 20 andhigher, 307.2 kbps will be supported as well.

• F-FCH can be in soft or softer handoff, while F-SCH is currentlydesigned for single leg (anchor leg) condition namely ReducedActive Set. Softer handoff for F-SCH will be available for futurerelease.

• Supported by first release of 3G-1X product for voice and datatraffic.

The forward closed loop power control algorithm consists of an outerloop and an inner loop and the algorithm is implemented effectively ata rate of up to 800 Hz.

As per IS-2000, the FPC algorithm for 3G-1X voice and packet datatraffic is designed for the mobile station to support up to two innerloops. One is the “primary inner loop” that controls operation of theF-FCH for voice and the low speed packet data (at 9.6 kbps data rate);the other is the “secondary inner loop” that controls the F-SCH packetdata traffic with data rates of 19.2 kbps, 38.4 kbps, 76.8 kbps and 153.6kbps. Additionally, if a forward link dedicated control channel

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401-614-040Issue 2, February 2003

(F-DCCH) is assigned, its output power is also controlled by the sameinner loop algorithm. Any other F-SCH assigned will also be controlledby the secondary inner loop. Though the closed loop algorithm in themobiles has not been standardized, the most common procedure for theprimary inner loop is based on the power control bits (PCB), which iscorresponding to the signal-to-noise ratio (S/N) measured at themobile. The secondary inner loop function is based on the mobilemeasured F-SCH traffic S/N.

In the forward link, the base station configures the mobile and passesthe following information to the traffic channel:

• Forward Target FER values for the F-FCH and the F-SCH

• Initial, minimum and maximum Eb / Nt set point values

• Ratio of PCB power in primary channel over primary channeltraffic power at full rate (denoted as FPC_SUBCHAN_GAIN)

• Primary channel (F-FCH or F-DCCH) and secondary channel (F-SCH) with possible inner loop rates at (800,0), (400, 400) Hz or(200, 600) Hz.

Forward power control forvoice traffic

The FPC functional diagram for voice service is illustrated inFigure 6-1. As shown in this diagram, the main functionality of bothinner and outer loops resides in the mobile. The key functional blocksinclude the following:

• The F-FCH Eb/Nt detector

• The primary inner loop block that generates the PC commandssent to the base station

• The F-FER detector

• The main outer loop block, which adjusts the Eb/Nt target value atthe mobile.

More detailed description for the voice FPC inner and outer loops areprovided below.


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401-614-040Issue 2, February 2003

Figure 6-2 Forward power control function for voice service

FPC inner loop for voice

The voice FPC inner loop algorithm is an iterative procedure. As theF-FCH traffic channel power is being transmitted from the base stationto the mobile, the mobile monitors the F-FCH received PCB andestimates the Eb/Nt for the full-rate traffic bit based on the value of thebase station provided FPC sub-channel gain (denoted asFPC_SUBCHAN_GAIN). When compared with the current Eb/Nt targetvalue, if the performance degrades, the inner loop commands the basestation (via the RPC sub-channel) to increase the traffic channeltransmit power gain. On the contrary, if the forward link qualityexceeds the updated Eb/Nt target value, then it commands the basedstation to reduce the transmitting power. The base station ASIC detectsthe forward link power control commands in the reverse power controlsub-channel via R-PICH at a rate of 16 per 20 msec frame, or 1.25msec, which amounts to 800 Hz. This 1.25 msec is the time interval ofeach power control group (PCG).

The following initial parameters are required for executing the voiceFPC inner loop algorithm:

• Forward power control initial gain, FPC_INI_GAIN

BASE STATION

MEASURERECEIVED Eb/Nt OF

FUNDAMENTALCHANNEL

F-FCH FERESTIMATION

F-FCHOUTERLOOP

MOBILE STATION

FORWARD LINK POWER CONTROL CLOSED LOOP FOR 3G1X F-FCH

INNER LOOP OUTERLOOP

FORWARDFUNDAMENTAL

CHANNELTRANSMITTER

Reverse PowerControl Sub-Channel in

Reverse PilotChannel

BASE STATIONFORWARD

POWERCONTROL

FPC_MODEFPC_PRI_CHANFPC_FCH_FERFPC_MIN_SETPTFPC_MAX_SETPT

FROM BASE STATION

FPC_FCH_INIT_SETPTFPC_SUBCHAN_GAIN

FROM BASE STATION

Forward PowerControl Sub-

Channelin F-FCH

PRIMARYINNER LOOP

F-FCH Eb/Nt SETPOINT

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401-614-040Issue 2, February 2003

• Forward minimum gain

• Forward maximum gain

• Gain adjustment step size (up step size and down step bias).

The units of the initial, minimum, and maximum gain values are in dB,relative to the forward pilot power. The initial gain setting is not ascritical because the inner loop operates at a speed of 800 Hz which issufficient for adjusting the forward gain to meet the updated Eb/Nt setpoint without much delay. However, the values for the minimum andmaximum gains are critical. The values required for achieving optimalcapacity are dependent on the radio configuration and the number ofsoft handoff legs of the call. In soft handoff, the primary leg passes theabove four parameters to each active leg thus allowing for differentgain constrains and power control steps for different calls in the samecell/sector.

For troubleshooting and/or RF optimization, one may disable the F-FCH inner loop by setting the inner loop power control step sizes (bothup step and down step bias) to 0 dB via translation parameter settings.With such settings, the power control commands received andprocessed by the cell allows the F-FCH forward gain to remainconstant via the cell ASIC. By disabling the inner loop, the forwardpower control is effectively turned off, regardless of the on/off status ofthe outer loop.

FPC Outer Loop for Voice

Because the primary objective for the FPC for voice traffic is tomaintain an acceptable voice quality while maximizing the systemcapacity, and FER is a performance measure that well characterizes thevoice quality, maintaining an acceptable FER is an important part of theFPC. However, given that there is no direct close mapping betweenFER and the measured Eb/Nt, some adjustment in the inner loop isrequired in order to maintain an acceptable averaged forward link FER.Specifically, the F-FCH Eb/Nt target value used in the inner loopfunction must be continuously adjusted based on the detected FERvalue. This FER detection is performed in the outer loop. In addition,the outer loop algorithm also includes estimating FER and dynamicallydetermining the appropriate Eb/Nt target value. These outer loopfunctions are implemented in the mobile on a per-frame basis at a rateof 50 Hz.


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401-614-040Issue 2, February 2003

At the time a call is just being set up, the outer loop is configured by thecell via layer 3 signaling via the paging channel and continuouslyupdated via the F-FCH. The following are the required parameters forconfiguring the outer loop:

• Forward target FER

• Initial Eb/Nt target value

• Minimum Eb/Nt target

• Maximum Eb/Nt target.

These parameters are passed to the mobile during call setup via theECAM signaling messages, the service connect messages, and theforward power control message when the mobile is assigned an F-FCH.In handoff, the outer loop parameters are updated to reflect the newnumber of soft and softer handoff legs that affects the minimum andmaximum Eb/Nt target values.

For troubleshooting and/or RF optimization, one may disable the outerloop regardless of the inner loop status. This is achieved by “freezing”the output Eb/Nt set point value, either to the current target value or aspecific base station determined value that is passed to the mobile viathe power control message. The outer loop function will be resumed asthe cell sends to the mobile a new power control message with updatedminimum and maximum Eb/Nt set point values.

Forward power control forpacket data traffic

In 3G-1X packet data mode, the forward traffic data is transmitted viathe F-FCH and F-SCH channels, where the F-FCH transmits signalingand low rate data (at 9.6 kbps) and F-SCH transmits packet data athigher rates as discussed above. A data session consists of one or moreactive periods where data is transmitted over the air interface. Theseactive periods are separated by periods of inactive mode, or dormantmode. In dormant mode, neither the F-FCH nor the F-SCH is assignedand thus any information stored in the base station associated with theprevious data call is erased. When in active mode, the F-FCH is on atall times, while F-SCH may be on or off, depending on the availabilityof the air interface resources and the amount of data in the bufferawaiting to be sent. For trouble shooting and/or optimization, the 3G-1X F-FCH and F-SCH FPC functions can be disabled separately bysetting the inner loop power control step sizes to 0 dB.

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401-614-040Issue 2, February 2003

F-FCH power control for packet data

When the 3G-1X packet data calls are in active mode, the F-FCHpower control algorithm follows the same closed loop process, whichconsists of nested inner and outer loops as that for the 3G-1X voicecalls. However, some of the required translation parameter values mustbe set differently because of the following reasons:

• The FER target for a voice call is dictated by the voice qualityrequirement, while the FER target for a packet data call isestablished by signaling traffic requirements (delay and reliability)as well as the radio link protocol (RLP) performance.

• The minimum and maximum gain values are dependent on therate at which the power control operates. The F-FCH forwardpower control (FPC) for voice calls operates at 800 Hz, while forpacket data calls only operates at 800 Hz when the F-SCH is off.The F-FCH FPC rate reduces to 400 Hz during an F-SCH burst.

As per IS-2000, the closed loop may operate in several modes. Thebase station selects the mode and configures the mobile via the layer 3messages at the instance when the F-FCH is first assigned. It alsoupdates the mobile configuration via an in-band signaling during theF-FCH operation. The packet data FPC algorithm is designed such thatthe base station may configure up to two reverse power controlsub-channels via the R-PICH and this closes up to two independentinner loops. When there is no F-SCH assigned, mobile is configured tosupport only one reverse power control sub-channel, operating at 800Hz. During an F-SCH burst, two reverse power control sub-channelsare configured in a time-multiplexed fashion via the single R-PICH,such that the combined speed of these two inner loops becomes 800 Hz.

Two traffic channels, defined as primary and secondary traffic channels(as per IS-2000), are mapped to the above two inner loops. The primarychannel refers to the forward traffic channel that carries the FPCsub-channel used by the primary FPC inner loop. The secondary trafficchannel is only meaningful when there are two co-existing inner loops.When the secondary FPC inner loop is active, the mobile performs theEb/Nt measurements via the secondary traffic channel.

At a data rate of 9.6 kbps, the packet data FPC algorithm is basicallyoperating with F-FCH inner/outer nested power control loops, similarto that for the voice FPC. The packet data also F-FCH supports softhandoff. As an F-SCH is assigned (with a data rate higher than 9.6kbps), for Release 20 and below, it only operates in a simplex mode so


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401-614-040Issue 2, February 2003

as to optimize the burst setup time. The packet data FPC algorithmconsists of two inner loops and two outer loops, whether the F-FCH isin the simplex mode or in handoff.

The Primary and Secondary power control loops are shown inFigure 6-3 and Figure 6-4 respectively.

Figure 6-3 Forward packet data primary closed loop for FCH FPC

BASE STATION

MEASURERECEIVED Eb/Nt OF

FUNDAMENTALCHANNEL

F-FCH FERESTIMATION

F-FCHOUTERLOOP

MOBILE STATION

INNER LOOP OUTERLOOP

FORW ARDFUNDAMENTAL

CHANNELTRANSMITTER

Reverse PowerControl Sub-Channel in

Reverse PilotChannel

BASE STATIONFORW ARD

POW ERCONTROL

FPC_MODEFPC_PRI_CHANFPC_FCH_FERFPC_MIN_SETPTFPC_MAX_SETPT

FROM BASE STATION

FPC_FCH_INIT_SETPTFPC_SUBCHAN_GAIN

FROM BASE STATION

Forward PowerControl Sub-

Channelin F-FCH

PRIMARYINNER LOOP

F-FCH Eb/Nt SETPOINT

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401-614-040Issue 2, February 2003

Figure 6-4 Forward packet data secondary closed loop for SCH FPC

Forward SARA for 3G-1X packet data calls

The forward supplemental air resources allocation (F-SARA) is amechanism residing at the base station and it determines whether theair interface resources are sufficient to be appropriately assigned to anF-SCH when the anchor cell receives a request for F-SCH assignment.

Prior to invoking the F-SARA, the call-processing algorithm estimatesa maximum F-SCH data rate based on CE availability, Walsh code,packet data, and other required hardware and software resourceswithout accounting for the RF air interface resources. This maximumF-SCH data rate serves as initial input to the F-SARA algorithm fordetermining a more accurate F-SCH maximum data rate that can besupported by the current RF conditions in the anchor sector/carrier.This new output data rate may be less than or equal to the earlier inputdata rate. Also predicted by F-SARA are the initial, the minimum, andthe maximum transmitted F-SCH power, and the initial, the minimum,and the maximum F-SCH Eb/Nt set point values corresponding to theoutput F-SCH data rate.

BASE STATION

MEASURE RECEIVEDEb/Nt OF

SUPPLEMENTALCHANNEL

F-SCH FERESTIMATION

F-SCHOUTERLOOP

MOBILE STATION

INNER LOOP OUTER LOOP

FORWARDSUPPLEMENTAL

CHANNELTRANSMITTER

Reverse PowerControl Sub-Channel

in Reverse PilotChannel

BASE STATIONFORWARD POWER

CONTROL

FPC_MODEFPC_FSCH_FERFPC_FSCH_MIN_SETPTFPC_FSCH_MAX_SETPT

FROM BASE STATION

FPC_FSCH_INIT_SETPT

FROM BASE STATION

Forward PowerControl Sub-Channel

in F-FCH

SECONDARYINNER LOOP

F-SCH Eb/Nt SETPOINT


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401-614-040Issue 2, February 2003

Under certain conditions, the call-processing algorithm may update thedata rate to a rate lower than that previously determined via the F-SARA algorithm. The F-SARA reassesses the power commitment as itdetermines an updated, maximum-allowable data rate iteratively.

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401-614-040Issue 2, February 2003


401-614-040Issue 2, February 2003

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

7 Extended carrier

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

Overview

Purpose This chapter provides guidelines for RF planning for “extended” carrierdeployment.


Single extended carrier 7-6


Forward link pilot channel 7-9Forward link traffic channel 7-10

Forward Data Capacity 7-14Growth strategies 7-15

Multiple extended carriers with traffic growth 7-15Additional cell sites with traffic growth 7-15

Applications 7-18Low traffic areas 7-18Building penetration 7-18

Concentric carriers 7-19

Core 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

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Extended carrier


401-614-040Issue 2, February 2003

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

Growth strategies 7-32

Summary 7-33

Extended carrierIntroduction

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401-614-040Issue 2, February 2003

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

Introduction

This chapter provides guidelines for RF planning for “extended” carrierdeployment.

An extended carrier, as used here, is a CDMA carrier that isintentionally designed to carry a limited amount of traffic in order toincrease the coverage area, or reap other benefits such as enhancingbuilding penetration or better matching the offered traffic density tosubscriber demands.

The concept of reducing design capacity in order to achieve extendedcoverage is not new; indeed, this fundamental trade-off exists in 2GCDMA and has occasionally been exploited to advantage (e.g., amodest number of large, lightly loaded cells covering a low-traffic ruralarea). These 2G trade-offs have been naturally limited by the lowreverse link interference margins7 (about 3 to 4 dB) used in 2G designs.For example, an interference margin of 3.5 dB (55% loading withrespect to pole) means that at most the cell can be expanded 3 dBrelative to this footprint, with associated reduction of the interferencemargin to 0.5 dB (10% loading with respect to pole). Further expansionof the footprint by sacrificing capacity is not possible, since the cellcapacity would be driven to zero.

The use of higher (i.e., typically 5.5 dB) nominal interference marginsin 3G-1X opens several new possibilities for design. These include:

• Single extended carrier. This concept embodies the standarddesign trade-off of capacity for coverage. This trade-off can bemore extensive, since there is more dB of interference margin(loading) to trade for coverage.

• Concentric extended. This configuration uses a modest number oflarge, lightly loaded single carrier cells for initial deployment. Theexpanded footprint of the cells is achieved by trading off capacity(interference margin) for coverage. Traffic growth isaccommodated by adding fully loaded carriers (of smallerfootprint) to each cell as needed. The first (extended) carrierprovides ubiquitous coverage, whereas the additional (smallerfootprint) carriers provide localized capacity relief.

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

7 Note that reverse link will be left off the name of the interference marginthroughout the rest of this chapter. The interference margin referenced here is al-ways a reverse link term.

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401-614-040Issue 2, February 2003

• Quasi-omni. This strategy services a 3-sectored configuration witha single (as opposed to three) transmitter/receiver. The coveragepenalties inherent in sharing the single transceiver via a splitterand combiner are offset by reducing the loading (the interferencemargin). This lightly loaded configuration can later be upgraded tofull capacity at the same footprint by adding two transceivers (theadditional equipment offsets the coverage penalties introduced bythe additional loading).

• Asymmetric cell (“split sector”). This strategy is similar to theprevious one but services a 3-sectored configuration with twotransmitters/receivers instead on just one. The first (dedicated)transceiver services the cell busy sector, which offers full capacity.The second transceiver services the remaining two sectors. Thecoverage of these two sectors is identical to that of the busy sector,since the penalties inherent in sharing (splitting) the transceiverare offset by reducing the sector loading. This configurationprovides full (nominal) coverage for cells with asymmetric trafficdistributions, at reduced cost.

In the following sections, we consider each of these methods in turn. Inthe "Single extended carrier" section on Page 7-6, the mechanics ofbasic capacity-coverage trade-offs are reviewed, with particularattention paid to required forward link adjustments in an expanded cell.The concentric configuration is discussed in "Concentric carriers"section on Page 7-19. The quasi-omni and asymmetric cellconfigurations are discussed in "Amplifier sharing - Quasi omni"section on Page 7-28 and "Amplifier sharing - Asymmetric cell"section on Page 7-31.

Note that all strategies discussed provide a potential means forreducing the cost of initial deployment either through reducing cell orequipment (transceiver) count. The optimal strategy for a givendeployment depends largely upon traffic needs and projected trafficgrowth. For example, a single extended carrier may not be feasible foran area with aggressive traffic growth, since the small design capacityper (large) cell would necessitate rapid addition of carriers. In such anarea, a configuration that begins with quasi-omni and is later upgradedto normal (3 transceiver) configuration may be a more suitable way tocontain initial deployment costs and smoothly migrate as needed tohigher capacity cells. Alternatively, if the projected traffic within thearea is likely to be asymmetric (one busy sector), then the best solution


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401-614-040Issue 2, February 2003

may be deployment of the split-sector configuration. Finally, if thetraffic growth is likely to be highly localized close to the cells, thenconcentric carrier may offer the best answer.

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

Extended carrierSingle extended carrier


401-614-040Issue 2, February 2003

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

Single extended carrier

This section describes the deployment of a carrier with extendedcoverage. If capacity demands exceed the capacity of the extendedcarrier, then either more extended carriers or more cells are required.

Reverse link The design trade-off for capacity and coverage in the reverse link isembedded in the interference margin term. The interference margin isdefined as:

(see Lucent document 401-703-201, PCS CDMA RF EngineeringGuidelines, equation 7.6)

where:µ is the ratio of the planned number of RF channels to the “pole

capacity”.

The reduced interference margin directly translates to an increasedmaximum allowable path loss. The cell radius is proportional to themaximum allowable path loss raised to the path loss slope. Therefore,changes in maximum allowable path loss can be translated to changesin cell radius as follows:

where the Rs are the respective cell radii, Ps are the respectivemaximum allowable path losses (in dBs), and S is the path loss slope(in dB/decade).

For a typical 3G-1X system with 3-sector cells and RadioConfiguration 3 (RC3), the pole capacity is 48.5 channels. Thefollowing table summarizes the capacity coverage trade-off.

µ−=

1

1im

R

−

= S

PP

R

R 21

102

1


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401-614-040Issue 2, February 2003

Table 7-1 Capacity versus coverage

Channels % load rela-tive to pole

Erlangs InterferenceMargin (dB)

Area rel to72% loading

1 2% 0.02 0.1 191%

2 4% 0.223 0.2 189%

3 6% 0.602 0.3 187%

4 8% 1.09 0.4 185%

5 10% 1.66 0.5 183%

6 12% 2.28 0.6 181%

7 14% 2.94 0.7 179%

8 16% 3.63 0.8 176%

9 19% 4.34 0.9 173%

10 21% 5.08 1.0 171%

11 23% 5.84 1.1 169%

12 25% 6.61 1.2 166%

13 27% 7.4 1.4 164%

14 29% 8.2 1.5 162%

15 31% 9.01 1.6 159%

16 33% 9.83 1.7 157%

17 35% 10.7 1.9 154%

18 37% 11.5 2.0 152%

19 39% 12.3 2.1 149%

20 41% 13.2 2.3 147%

21 43% 14 2.4 144%

22 45% 14.9 2.6 142%

23 47% 15.8 2.8 139%

24 49% 16.6 2.9 136%

25 52% 17.5 3.2 132%

26 54% 18.4 3.4 129%

27 56% 19.3 3.6 126%

28 58% 20.2 3.8 123%

29 60% 21 4.0 120%

30 62% 21.9 4.2 117%

31 64% 22.8 4.4 114%

32 66% 23.7 4.7 110%

33 68% 24.6 4.9 107%

34 70% 25.5 5.2 103%

35 72% 26.4 5.5 100%

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401-614-040Issue 2, February 2003

The following figure shows the trade-off of capacity versus covergraphically where the coverage is expressed as a percentage of thenominal case (72% reverse link pole loading):

Figure 7-1 Capacity vs. coverage

Of course it is important to remember that supportable Erlang density(traffic Erlangs divided by area) falls faster than the plot above (Erlangcapacity), since as the cell footprint grows the capacity decreases.Thus, the density (ratio of capacity to area) is negatively impactedtwice. The following plot illustrates supportable density relative tonominal case of 72% loading, versus area gain:

Figure 7-2 Traffic density versus coverage

Forward link It is necessary to verify that the forward link will support the extendedcoverage area by examining the impact on the forward link pilot andtraffic channels.

0

5

10

15

20

25

30

100% 120% 140% 160% 180% 200%

Area Relative to Nominal Case

Erl

ang

Cap

city

0%

20%

40%

60%

80%

100%

100% 120% 140% 160% 180% 200%

Area Relative to Nominal CaseTra

ffic

Den

sity

Rel

toN

om

inal


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401-614-040Issue 2, February 2003

Forward link pilot channel

As the maximum allowable path loss increases, pilot power must alsobe increased to maintain a constant pilot channel Ec/Io at the cell edge.Pilot Ec/Io is defined as follows:

where:Ec = The time chip energy received at the mobileIo = The total noise and interference from all sectorsδ = The fraction of sector power allocated to the pilot channelPj = The power received from the jth sectori = Index of serving sectorF = Mobile receiver noise figureNo = Thermal noise densityW = The carrier bandwidth.

For insight, we can consider two simple cases analytically: Thecompletely interference-limited case, and the completely noise-limitedcase.

In the interference-limited case, we assume the thermal noise power tobe small compared to the interference power (i.e., FNoW << ΣPj). Inthis case, as the maximum allowable path loss is increased, both thepilot signal and the interference are reduced by the same amount.Hence, in the interference-limited case, no increase in pilot power isrequired, as the cell area is increased by decreasing the loading.

In the noise-limited case, we assume that the interference power issmall compared to the thermal noise power (i.e., ΣPj << FNoW). In thiscase, the pilot power will need to be increased by the same amount asthe increase in path loss to maintain the same pilot Ec/Io at the celledge.

Intermediate cases (the most likely scenario) require the pilot channelpower to be increased somewhere between zero and the increase inmaximum allowable path loss.

The actual pilot power required, as a percentage of total amplifierpower, to maintain a given Ec/Io at the cell edge, was computed (viaspreadsheet) for the typical 3G-1X case for various values ofinterference margin (resulting in various cell footprint sizes), with thefollowing results:

∑+⋅

=

jalljo

i

io

c

PWFN

P

I

E

_

δ

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



401-614-040Issue 2, February 2003

Figure 7-3 Required pilot percentage of total power versus capacity

As can be seen from the graph, the pilot percentage only increases fromthe standard value of 15 percent at full loading of 26.4 Erlangs (72% ofpole capacity) to a little less than 18 percent at no loading. Theadditional amount of power required for the pilot channel can becalculated on a case-by-base basis and will reduce the power availablefor the traffic channels. The impact on capacity is examined in the nextsection.

Forward link traffic channel

The traffic channel is more complicated than the pilot channel sincetwo effects of lighter loading must be accounted for: The increase inpath loss, and the decreased number of users. In our analysis, weassume that all mobiles have an equal share of total base station power,which can be interpreted as all mobiles are located at the cell edge.

Where:

i is the index of the serving sectorP' is the transmitted power for all traffic channelsLp is the maximum allowable path lossn is the number of mobilesPi = The power received from the ith sectorγ is the orthogonality factor

15.0%

15.5%

16.0%

16.5%

17.0%

17.5%

18.0%

100% 120% 140% 160% 180% 200%


Pilo

t%

of

To

talP

ow

er

∑≠

⋅++⋅

′

=

ijijo

p

i

o

b

PPWFN

Ln

P

N

E

γ


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


401-614-040Issue 2, February 2003

F = Mobile receiver noise figureNo = Thermal noise densityW = The carrier bandwidth.

Again, for insight, we can consider two simple cases analytically: Thecompletely interference-limited case, and the completely noise-limitedcase.

In the interference-limited case, as the maximum allowable path loss isincreased, the P' terms stays the same since the pilot channel does notrequire any extra power, as discussed above. The increase in path lossreduces both the serving signal and the interfering signals equally. Thenumber of users (n) decreases to provide the reduced loading thatallows for the increase in maximum allowable path loss. Therefore, theEb/No for this case will necessarily increase. Alternatively, the totalpower required to maintain a given Eb/No will decrease. Accordingly,less power is required to support fewer users, even though the footprintis enlarged.

In the noise-limited case, the P' term will be decreased by amountequivalent to the increase in pilot power, which, from above, wouldequal the increase in path loss. If we assume that the Eb/Nt achieved forthe nominal case is acceptable, we can compare the achievable Eb/Ntfor the expanded carrier case. Here, the achieved Eb/Nt is the Eb/Ntthat is calculated for a mobile at the edge of a sector’s coverage area ifthat mobile receives 1/n of the available traffic power, where n is thenumber of channels supported by the sector. If the ratio of the extendedcarrier achievable Eb/Nt to the nominal achievable Eb/Nt is greaterthan one, we can assume that the extended carrier case has sufficientpower to close the forward link.

Let case 1 be the “nominal carrier case”, supporting n1 RF channels andcase 2 be the “extended carrier case”, supporting n2 RF channels.

If the overhead fraction is δ, then power available for all the trafficchannels is:

⋅

⋅

′′

=

⋅′⋅′

=

2

1

2

1

1

2

11

1

22

2

1

2

n

n

L

L

P

P

nL

P

nL

P

NE

NE

p

p

p

p

o

b

o

b

( )tot

PP ⋅−=′11

1 δ and ( )tot

PP ⋅−=′22

1 δ

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401-614-040Issue 2, February 2003

As stated above, the overhead fraction for this noise limited caseincreases by an amount equal to the increase in path loss:

Therefore, the ratio of total traffic powers can be expressed as:

Substituting back into the Eb/No ratio and simplifying gives:

The ratio of path losses can be related to the number of channels asfollows:

Substituting into the Eb/No ratio equation gives:

For 3G-1X, the loading for the nominal case is 72%, or µ is 0.72. Also,the pilot fraction for the nominal case (δ) is equal to 15%, or 0.15.

11

22

δδ ⋅=p

p

L

L

( )( )

1

11

2

1

2

1

2

1

1

1

1

δ

δ

δδ

−

⋅−=

⋅−⋅−=

′′ p

p

tot

totL

L

P

P

P

P

⋅

−

−=

⋅

⋅

−

⋅−=

⋅

⋅

′′

=

2

1

1

12

1

2

1

2

1

1

11

2

2

1

2

1

1

2

1

2

11

1

n

nL

L

n

n

L

LL

L

n

n

L

L

P

P

NE

NE

p

p

p

pp

p

p

p

o

b

o

b

δ

δ

δ

δ

2

1

1

2

1

2

2

1

1

1

1

11

1

µµ

µ

µ−−=

−

−==im

im

p

p

R

R

L

L

⋅

−

−−−

=

2

1

1

12

1

1

2

1

1

1

n

n

NE

NE

o

b

o

b

δ

δµµ


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


401-614-040Issue 2, February 2003

A plot of this function is shown in the figure below.

Figure 7-4 Eb/Nt versus loading

From the above figure it can be observed that the achieved Eb/No forthe extended carrier case will be less than for the nominal case forloadings between nominal (0.72) and about 0.16. Therefore no generalconclusion that the traffic channel will achieve the required Eb/Nt forthe noise limited case can be drawn. Therefore a full link budgetanalysis is required to examine real scenarios that fall between thenoise limited and interference limited cases.

The actual achieved forward link Eb/No at cell edge was computed (viaspreadsheet) for a typical case (i.e. not either extreme of interference ornoise limited) with the results shown in the following figure.

⋅

−

−=

⋅⋅

−

−−

−

=

222

max2

1

272.0

18.01

33.072.0

15.01

15.01

72.01

µµµ

n

n

NE

NE

o

b

o

b

222

2

2222

13.011.072.018.072.033.0

µµµ

µµµ −⋅+=⋅−

−⋅=

-2

-1

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8

Loading (mu)

Eb

/No

rela

tive

ton

om

inal

case

(dB

)

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



401-614-040Issue 2, February 2003

Figure 7-5 Achieved forward link Eb/Nt versus capacity

As can be seen from the above figure, the achieved Eb/Nt grows withthe decrease in Erlang capacity, which is to say that the required Eb/Ntis achieved, and the forward link should close.

Forward Data Capacity One would also expect that as the cell radius is increased, the datacapacity of the cell would decrease. There is no simple analyticalapproach to deriving a data capacity versus cell radius relation; hence,simulations were run to model the behavior. The simulations focusedon the impact to the forward link since data applications are expected tobe asymmetric and have much lower reverse link demands relative toforward link demands. The simulations assumed a typical link budget.The simulation was a set of single rate simulations, whose outputs (perrate throughputs) were combined with a standard rate distribution. Thesingle rate distribution was a typical forward link simulation where thenumber of users was increased until a certain probability of outage(defined as exceeding max amplifier power) was exceeded. The resultsof the simulation are shown in Figure 7-6.

0

5

10

15

20

25

100% 120% 140% 160% 180% 200%


Ach

ieve

dF

LE

b/N

o(d

B)


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


401-614-040Issue 2, February 2003

Figure 7-6 Forward link data capacity versus cell size

Growth strategies Multiple extended carriers with traffic growth

The simplest way to add capacity is to add carriers. Carrier additionsprovide a linear growth in capacity, i.e., two carriers doubles Erlangcapacity, and three carriers triples Erlang capacity, etc.8 However,adding cells has some advantage, as will be discussed next.

Additional cell sites with traffic growth

Adding cells enhances capacity in two ways:

1. The greater the number of cells, the less area per cell, and hence, ahigher interference margin can be tolerated.

2. The additional cell can carry additional capacity.

The network capacity is the product of the capacity per cell and thenumber of cells. Adding cells increases both of these terms, and hence,provides a double benefit to network capacity. For example, doublingnetwork capacity by adding carriers requires adding an additionalcarrier to all cells in the network. Doubling network capacity by addingcells does not require a doubling of cell count. For example, if thestarting point was cells designed for 1.5 times the nominal cell area byreducing the capacity to 12.3 Erlangs per sector, the network capacitycould be theoretically doubled by reducing cell area to 1.23 times

9092949698

100102104106108110112

100% 120% 140% 160% 180% 200%


Fo

rwar

dL

ink

Ag

gre

gat

eS

ecto

rT

hro

ug

hp

ut

(kb

ps)

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

8 The capacity growth versus number of carriers is slightly greater than strictlylinear due to trunking efficiency. The trunking efficiency is not the full value pre-dicted by Erlang B, but is greater than 0.

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



401-614-040Issue 2, February 2003

nominal with a capacity of 20.2 Erlangs per sector, since2*12.3/1.5=20.2/1.23. The increase in cell count would be 1.5 dividedby 1.23, or 22%. Whether this approach is more cost effective thansimply adding carriers depends on the relative costs of the hardware tosupport the additionally carriers versus the cost associated with the newcells (hardware, real estate, backhaul, etc.).

Although the above example demonstrates the nonlinear (more thanlinear) gain that can be achieved by cell addition, the result is at bestapproximate since it assumes that the cell count is simply the totalnetwork area divided by the area per cell. However, once a network isdeployed, it is unlikely that cells will be moved. So the actuallyincrease in number of cells would probably be higher than the 22%computed. Consider the following figure that shows the typicalhexagonal geometry for a 7-cell cluster. The cells are spaced at 1.5times the nominal cell spacing. The borders shown are the nominal cellsize borders.

Figure 7-7 Cell deployment at 1.5X typical cell radius

To fill the coverage holes would require on the order of 6 new cells, asshown in heavy red on the following figure.

-3 -2 -1 0 1 2 3

-3

-2

-1

0

1

2

3

Cell/Mobile Map

1 2

34

5

6 7


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


401-614-040Issue 2, February 2003

Figure 7-8 Cell deployment to fill holes at full capacity

This method of cell addition can clearly be inefficient in the sense thatcoverage overlay inevitably occurs; however, from a trafficperspective, this method of adding cells allows selective focus on areaswhere traffic demand is highest. Accordingly, the net cell count for acoverage-driven area with isolated hot traffic spots is likely to be lessthan the number required if an initial dense array of cells wereuniformly deployed.

Another issue associated with adding cells is that the network mayrequire reoptimization. However, the costs of reoptimization maybeminimized through the use of Lucent's Ocelot tool. Ocelot uses ageneral nonlinear optimization procedure to adjust certain parameters(e.g., antenna tilts, forward powers) of cellular networks in order tomaximize a particular “objective function”. The current objectivefunction is various combinations of coverage (the percentage of theserved area where a call can be made from) and capacity (how muchtraffic can be carried simultaneously). When Ocelot runs anoptimization, the user sees a Trade-off Curve window with differentcoverage/capacity points; clicking any point affords a detailedexamination of the proposed design in a graphical display of the marketarea. It is expected that the original design and optimization willprovide a baseline set of data that will allow Ocelot to generateaccurate predictions of the revised optimization settings appropriate foradditional cell sites.

-3 -2 -1 0 1 2 3

-3

-2

-1

0

1

2

3

Cell/Mobile Map

1 2

34

5

6 7

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



401-614-040Issue 2, February 2003

Applications Low traffic areas

The simplest application of extended carriers is to serve low trafficareas. Using larger cells will reduce cell count, reducing expensesassociated with each cell such as:

• Cell site hardware

• Real estate

• Backhaul facilities.

If traffic grows beyond the planned capacity coverage holes will occurunless steps (e.g., added cell count) are taken. Of course this statementis true regardless of whether the carrier is “extended” or not. However,the lower capacity of an extended carrier means that the plannedcapacity is lower than frequently employed, and hence, extra attentionmust be paid to traffic growth to ensure the extended carrier does notsuffer overload.

Building penetration

Another use for the extended carriers is to provide building penetrationmargin. The extra interference margin on the reverse link and extrapower on the forward link are used to provide building penetrationmargin rather than extended radius in this case. It would be expectedthat concentric carriers would be used, with the core carrier servingpedestrian traffic and vehicular traffic (and indoor traffic close to thecell site), while the extended carrier serving in-building traffic towardthe cell edge. Arguably, if buildings that are important are known, it isbetter to place cells near or in those buildings.

Extended carrierConcentric carriers

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401-614-040Issue 2, February 2003

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

Concentric carriers

Another application for extended carriers is a multi-carrier cell withcarrier-dependent coverage. In this scenario, an extended carrier isused to extend the coverage of the cell and a “core” carrier to providethe bulk of the capacity of the cell as shown in the following figure:

Figure 7-9 Core and extended carriers

In this scenario, the extended (first) carrier provides ubiquitouscoverage across the region of interest with a modest number of cellsites. Each extended carrier offers low capacity only, since its capacityhas been traded away for expanded coverage. As traffic increases,smaller full-capacity carriers are added as needed at selected cells. Thesmaller carriers address the additional capacity, which is presumed tobe locally concentrated around the cell sites. Handoffs between the coreand extended carriers allow mobiles to traverse between cells, whilerestricting the number of active mobiles on the extended carrier.

This configuration alters a number of RF engineering considerations,which typically apply to carriers of identical footprint. These arediscussed below, and include:

• Core carrier reverse link

• Core carrier forward link

• Core and extended carrier traffic densities.

Note that the RF engineering issues associated with the extendedcarrier reverse and forward link are identical to those in the "Singleextended carrier" section of this chapter and are not re-examined here.

Core Carrier

Extended Carrier

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401-614-040Issue 2, February 2003

Core carrier reverse link As explained in the Lucent documents 401-614-012, AUTOPLEX®

Cellular CDMA RF Engineering Guidelines and 401-703-201, PCSCDMA RF Engineering Guidelines, the pilot Ec/Io at the edge of a cellshould be equal to T_ADD9. The handoff zone is the area where onecell's pilot is above T_ADD and another cell’s pilot is above T_DROP.Therefore, it is expected that handoff zone is an area where the pilot Ec/Io changes by the difference between T_ADD and T_DROP, which istypically 2 dB. Changes in pilot Ec/Io are not precisely equal todifferences in path loss, but can be taken as an approximation. Thedifference between the core and extended carriers is expected to begreater than 2 dB. Therefore, little soft handoff is expected in the corecarrier coverage area. The impact of no soft handoff on the link budgetis to shrink the reverse link coverage by an amount equal to the softhandoff gain. The actual carrier coverages will look something like thefollowing figure, where:

• The extended carrier coverage is increased by reducing theinterference margin and maintaining full soft handoff gain

• The nominal carrier coverage is the coverage of a carrier withnominal interference margin (i.e., corresponding to 72% loading)and full soft handoff gain

• The core carrier coverage is the coverage of a carrier with nominalloading (i.e., corresponding to 72% loading) but with no softhandoff gain.

Figure 7-10 Core, nominal, and extended carriers

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

9 For simplification the IS-95A terms are used here, but the same discussion ap-plies to networks utilizing the IS-95B soft handoff algorithm.

Extended Carrier

Nominal Carrier

Core CarrierDifference inInterferenceMargin

Loss ofSoftHandoffGain


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


401-614-040Issue 2, February 2003

Since the coverage areas of the core carriers do not overlap or eventouch the expected interference ratio is less. The reduced interferenceratio will lead to an increase in reverse link capacity. This increase canbe advantageous since the core carrier by design services localizedareas of high traffic demand.

In the following we estimate the reverse link interference ratio in orderto compute the core carrier pole capacity. The loss of soft handoff gainwill cause the core carrier to be 4.3 dB less in maximum allowable pathloss than a nominal carrier. The difference between the nominal carriercoverage and the extended carrier coverage is the difference ininterference margin and is a design parameter. If we consider 3 dB to bea typical amount for the reduction in interference margin for theextended carrier, the total difference in path loss between the core andextended carrier is 7.3 dB.

Figure 7-11 Definition of different distances

Therefore the ratio of the radius of the extended carrier in terms of theradius of the core carrier is:

where Pec is the maximum allowable path loss for the extended carrier,Pcore is the maximum allowable path loss for the core carrier, and S isthe path loss slope. The difference between extended carrier and corecarrier maximum allowable path losses is 7.3 dB, as stated above.Therefore, the extended carrier radius is 1.55 times the radius of thecore carrier (assuming a path loss slope of 38.5 dB per decade). Thedistance between the centers of the cells, Rc-c, is 3.10 times the corecarrier (twice the radius of the extended carrier). Therefore, the pathloss from the center of one cell to the other cell in terms of the path lossto the edge of the core carrier is:

Rcore

Rext

Rc-c

S

PP

coreext

coreec

RR−

⋅= 10

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401-614-040Issue 2, February 2003

For the nominal case (72% loading), the center-to-center distance issimply twice the core carrier distance and hence the center-to-centerpath loss is:

Therefore, the extended carrier case has 7.3 dB more path loss betweena cell and its first tier interferers. The reverse link interference ratio, β,is defined as the ratio of the other cell to same cell interference. As afirst order approximation, we can treat the interference from other cellsas coming from a point at the center of the other cells. By increasing thepath loss by 7.3 dB to those other cells from the nominal case, theinterference from those other cells should be reduced by 7.3 dB. So theinterference ratio, β, should also be reduced by 7.3 dB. For the 3-sectorcase the interference ratio would then be reduced from 0.85 to 0.16.

The pole capacity for this reduced interference ratio is:

If the typical 3G-1X loading of 72% is assumed, the core carrier willsupport 55 RF channels. Since no soft handoff is expected on the corecarrier, this number of channels needs to be increased by only a factorto account for the softer handoff links, which is 1.3. Therefore, thenumber of channels is 72. This value exceeds the number of Walshcodes available, which is 59. Given the 1.3 factor for softer handofflinks, the Walsh code limit translates to a limit of 45 “primary” RFchannels per sector. The loading cannot simply be reduced to the valueassociated with this number of channels since as the loading, as apercentage of pole capacity is reduced, the interference margin isdecreased. However, this will change the coverage of the core carrier,and hence, our computed interference ratio. Therefore, the optimumsolution can only be found through an iterative trial and error process.A solution was found for the following conditions.

( ) 9.181.3log5.38log +=⋅+=

⋅+= −

− corecorecore

cccorecc

PPR

RSPP

( ) 6.112log5.38log +=⋅+=

⋅+=′ −

− corecorecore

cccorecc

PPR

RSPP

( ) ( )771

16.011058.0

1281

)1( 104max =+

+⋅⋅=+

+⋅⋅=

βα d

gn RF channels


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401-614-040Issue 2, February 2003

The process outlined above can be repeated for different values ofextended carrier interference margin reduction with the followingresults:

Core carrier forward link The core carrier forward link must be assessed on a case-by-base basisto ensure link balance. The issues affecting the ability of the forwardlink to support the reverse link are discussed below.

The forward link traffic channel coverage of the core carrier will alsosuffer due to the loss of soft handoff gain. Soft handoff gain is notexplicitly listed in the forward link Eb/Nt analysis, but instead is

Parameter Value

Interference Ratio 0.22

Pole capacity 73

Loading 61%

RF channel capacity 45

Erlang capacity 35.6

Interference Margin (dB) 4.1

Extended Car-rier

Core Carrier

InterferenceMargin Reduc-tion (dB)

Forward LinkInterferenceRatio (linear)

PoleCapacity

Loading(% of polepoint)

RF Chan-nelCapacity

ErlangCapacity

InterferenceMargin (dB)

0.5 0.329 67.06 67.1% 45 35.6 4.8

1 0.304 68.32 65.9% 45 35.6 4.7

1.5 0.281 69.64 64.6% 45 35.6 4.5

2.0 0.257 70.73 63.6% 45 35.6 4.4

2.5 0.237 72.14 62.4% 45 35.6 4.2

3.0 0.217 73.25 61.4% 45 35.6 4.1

3.5 0.197 74.22 60.6% 45 35.6 4.0

4.0 0.180 75.46 59.6% 45 35.6 3.9

4.5 0.164 76.54 58.8% 45 35.6 3.8

5.0 0.148 77.40 58.1% 45 35.6 3.8

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



401-614-040Issue 2, February 2003

embedded in a reduced fade margin for the forward link. The fademargin listed in the forward link is actually reduced fade margin. Thereduction is due to both soft handoff gain and other effects. Thereduction for 95% area coverage is 6.0 dB. While the Eb/Nt analysisdoes not state what proportion of this is due to soft handoff and what isdue to other effects (independence of fading within the cell, limiteddynamic range of forward link transmit power), it is expected that thesoft handoff gain would be no greater than the value for the reverse linksoft handoff gain, which is 4.0 dB.

However, the forward link benefits from the lack of soft handoff in thatno power must be allocated for the soft handoff legs. The impact of thelack of soft handoff is manifested in the forward link Eb/Nt analysis bysetting the soft handoff overhead factor to 1.3 (value for softer handoff)instead of 1.75 typically used for 3G-1X. This difference in softhandoff overhead factor leads to a corresponding increase in trafficchannel power of 1.3 dB. The net impact of no soft handoff on thereceived traffic channel signal in the Eb/Nt analysis is a loss of 2.7 dB(4.0 -1.3).

The forward link of the core carrier also benefits in terms of forwardlink interference ratio. The lack of soft handoff increases theinterference ratio since the power from all the sectors involved in thesoft handoff are excluded from the interference term. However, the factthat the border of the core carrier is within the cell border reduces theinterference ratio more than the lack of soft handoff increases it. Thereduction in interference ratio for the case considered here (no softhandoff on inner border and inner border 5 dB inside outer border) isbelieved to be up to 6 dB. The reduction in the interference ratioreduces the other cell interference term.

The overall effect on the core carrier forward link depends on to theratio of the other cell interference to the thermal noise. In anoise-limited system, the reduction in other cell interference willprovide little benefit and the forward link will fall short of power. In aninterference-limited system, the reduction in other cell interference willmore than make up for the reduced received traffic channel signal. Thetypical case considered here was analyzed, and the forward link didbalance.


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


401-614-040Issue 2, February 2003

The forward link pilot channel does not have a soft handoff gain. So theloss of soft handoff gain does not penalize the core carrier pilotcoverage. The reduced interference ratio will benefit the core carrierpilot channel, and hence the pilot channel coverage in the core carrierarea is not an issue.

Traffic density By design, the traffic density in the extended carrier coverage area mustbe less than the traffic density of the core carrier area. The differencedepends upon the extent to which the extended carrier capacity hasbeen lowered in design in order to expand coverage. The plot belowshows the design traffic density, relative to the design density in thecore carrier coverage area, versus the design area of the extendedcarrier relative to the nominal carrier design area. As coverage of theextended carrier grows, the traffic density between the core andextended carriers becomes more imbalanced.

Figure 7-12 Extended carrier traffic density versus coverage

Determining mobilelocation

To make the concentric carrier approach work, it is necessary to avoidviolating the design capacities of the core and extended carrier. To keepthe extended carrier lightly loaded, all mobiles in the coverage area ofthe core carrier need to be served by the core carrier. Also, mobilesoutside the core carrier coverage area need to be served by the extendedcarrier or they will suffer degradation (e.g., high FER, call drop, etc.).

Extended Carrier Erlang Density

0.00

0.20

0.40

0.60

0.80

1.00

1.00 1.20 1.40 1.60 1.80 2.00

Extended Carrier Area Relative to NominalCarrier

Ext

end

edC

arri

erE

rlan

gD

ensi

tyR

elat

ive

toC

ore

Car

rier

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



401-614-040Issue 2, February 2003

Through call processing, it is possible to have the mobile report(PPSMM message) pilot strength as measured in terms of Ec/Io andoverall interference in the band, Io. Multiplying these two termstogether will provide the mobile's received energy per pilot chip, Ec.The base station knows the transmitted energy per chip. The differencebetween transmitted and received energy per chip is the path loss. Thebase station can then use this path loss value to estimate whether themobile is in the core carrier's coverage area or the extended carrier'scoverage area10.

The same measurement of path loss would also be used for triggeringinter-frequency handoffs at the boundaries between the core andextended carriers.

Currently, the capability to make this estimate of path loss does notexist in the Lucent products. A new feature is required to support thiscapability.

The deployment of concentric carriers will cause an increase in inter-frequency hard handoff. While Lucent has implemented severalfeatures that increase the robustness of inter-frequency handoffs, inter-frequency handoffs are still hard handoffs are hence inherently lessreliable than soft handoffs. Therefore, it is possible that some increasein call drop rate could result from the deployment of concentriccarriers. This increase could be minimized by careful optimization,particularly in an area where the mobile locations are concentrated(e.g., along rural highways) and the locations of hard handoffs are wellknown.

Growth strategies As traffic demand grows in the core carrier region, clearly the growthpath is to add carriers. As traffic demand grows in the extended carrierregion the same alternatives (adding carriers or adding cells) and trade-offs apply as in the simple extended carrier case, as discussed in"Growth strategies" section on Page 7-15. Note that since the corecarriers are placed at traffic hot spots, the pattern of growth could welldictate that multiple additional core carriers are added well before asecond extended carrier is required.

Applications The concentric carrier approach makes sense for regions of low trafficdensity punctuated by localized hot spots, such as scattered small townsor villages surrounded by a rural area. The town would have to be smallenough to fit within the footprint of the core carrier. The traffic demand...........................................................................................................................

10 One caveat to this approach is that IS-98 does not specify how accu-rately the mobile must measure Io.


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401-614-040Issue 2, February 2003

from within the town would have to be small enough to be served bythe number of carriers available. The areas around the town areexpected to generate light traffic demand, and hence, be ideal for theextended carrier.

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

Extended carrierAmplifier sharing - Quasi omni


401-614-040Issue 2, February 2003

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

Amplifier sharing - Quasi omni

One novel application for extended carriers is amplifier sharing.Schematically, amplifier sharing can be illustrated by the followingfigure:.

Figure 7-13 Quasi-omni illustration

In this configuration, a single amplifier and single receiver service 3sectors (“quasi-omni”). The splitter splits the power from the linearamplifier three ways, reducing the power per antenna by1/3 or -4.8 dB.11 The combiner combines the signals from the threefaces (alpha, beta, and gamma), and hence, increases the reverse linknoise figure by a factor of 3 or 4.8 dB. The coverage advantage gainedby reducing capacity can be used to overcome the combiner and splitterdisadvantages instead of extending the cell radius. Each sector is lightlyloaded but the footprint of the cell remains the same as that of a fullyloaded, conventional 3-sector cell.

In the reverse link budget, the increased noise figure directly translatesto a decrease in maximum allowable path loss. In the forward link, asshown previously, the decrease in capacity will be sufficient to offsetthe loss in power (i.e., the link will balance), typically with somemargin.

Radio

LASp

litte

rC

ombi

ner

Tx Rx Rx Tx Rx Rx Tx Rx Rx

Alpha Beta Gamma

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

11 Note that no insertion loss is considered here since values of insertion lossmay vary widely. Once hardware is chosen and the insertion loss is known, itshould be considered as well.


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401-614-040Issue 2, February 2003

To fully overcome the combiner/splitter disadvantage of 4.8 dB wouldrequire reducing the capacity to 2.9 Erlangs per cell. As traffic demandincrease past this capacity, more radios and amplifiers are added andthe splitter/combiners removed. The penalty for the splitters andcombiners is removed from the link budget so there is no longer anyneed to reduce capacity. The cell can then run at full capacity of 26.4Erlangs per sector, or 79.2 Erlangs per cell, in the same footprint. Thisapproach has the advantage of lowering initial cost in a deployment(one as opposed to 3 transmitters/receivers per 3-sectored cell), andselectively paying over time as needed for the additional equipmentrequired to address traffic growth.

In the case analyzed here, the forward achieved Eb/No is 7.1 dB higherthan the nominal case (note that the pilot was increased to 16.8% oftotal power); clearly, the forward link has more than enough power.This asymmetry can be reduced by the use of Tower Top Low NoiseAmplifiers (TTLNA). As discussed in Chapter 8 of the PCS CDMA RFEngineering Guidelines, TTLNAs reduce the reverse link noise figure.The reduction depends on the value for cell site cable loss. Taking 2 dBas a typical value for cell site cable loss, the typical reduction in reverselink noise figure is 1.9 dB. Thus, the net increase between the signalcombiner and TTLNA is 2.9 dB (4.8 - 1.9). To achieve this reduction ininterference margin requires that the cell capacity be reduced to 14Erlangs per face, or 42 Erlangs per cell. The forward link shows thatthere is sufficient power to achieve the same pilot channel Ec/Io andtraffic channel Eb/No as the nominal case. Again, as traffic demandincreases past the capacity of the cell, the combiner/splitters can beremoved, as well as the TTLNA. The degree to which this approach isadvantageous depends on the relative cost of a single TTLNA versusthe cost of 2 amplifiers and radios.

Growth strategies The benefit of this approach is that it delays the cost of the second andthird amplifiers and radios until they are needed, while maintaining thesame cell footprint. Thus, a network provider can “pay as they grow”,by simply adding hardware to existing sites.

As traffic increases on the cell the network operator can either grow totwo amplifiers (see next section) if the traffic demand is asymmetricamong the three sectors or to three amplifiers if the traffic demand isroughly equal among the sectors. This decision requires someknowledge of the traffic distribution amongst the sectors. Since allthree sectors are served by the same radio, they have the same PN code,and hence, traditional service measurements will not capture per-sectortraffic information. However, a network operator can use the Lucent

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401-614-040Issue 2, February 2003

On-Demand PSMM Collection (ODPC) feature in conjunction withpost processing to determine traffic demand patterns. The ODPCfeature allows the network operator to collect periodic (period from 1to 10 minutes) pilot strength information from each mobile on several(up to 20) cells for a specified time period (up to 2 hours). The pilotstrength information is stored in a file at the OMP. Post-processing ofthe pilot strength measurement data, for example using the LucentEFLT (Enhanced Forward Link Triangulation) algorithm, candetermine the mobile location to accuracy sufficient to determine per-sector traffic demand.

Another issue associated with adding amplifiers is that the networkmay require reoptimization. This process could be required since theaddition of amplifiers will clearly impact the internal interferencedistribution throughout the network, thus necessitating changes in suchparameters as antenna downtilts, neighbor lists, and pilot power.However, the costs of reoptimization can be minimized through the useof Lucent's Ocelot tool. Ocelot uses a general nonlinear optimizationprocedure to adjust certain parameters of cellular networks in order tomaximize a particular “objective function”. The current objectivefunction is various combinations of coverage (the percentage of theserved area where a call can be made from) and capacity (how muchtraffic can be carried simultaneously). When Ocelot runs anoptimization, the user sees a Trade-off Curve window, with differentcoverage/capacity points; clicking any point affords a detailedexamination of the proposed design in a graphical display of the marketarea. It is expected that the original design and optimization willprovide a baseline set of data that will allow Ocelot to generateaccurate predictions of the parameter changes required when additionalequipment is added.

Extended carrierAmplifier sharing - Asymmetric cell

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Amplifier sharing - Asymmetric cell

An approach similar to the quasi-omni approach of the last section isthe asymmetric cell configuration. Instead of sharing a single amplifieramong all three sectors, two total amplifiers are employed. Oneamplifier is shared among two of the three of sectors, while theremaining amplifier is devoted to the third sector. This approach isappropriate for a cell that has high traffic demand on one sector, andlow traffic demand on the other two sectors. For a case of high demandon the alpha sector and low demand on beta and gamma sectors, thescheme would schematically look like the following figure.

Figure 7-14 Asymmetric cell illustration

The splitter splits the power from the linear amplifier two ways,reducing the power per antenna by 1/2 or -3.0 dB in the lightly loadedbeta and gamma sectors. The remaining amplifier services the fullyloaded alpha sector. The combiner combines the signals from the twolightly loaded faces (beta and gamma) and hence increases the reverselink noise figure by a factor of 2 or 3.0 dB. In this configuration, thecoverage footprint of all three sectors is the same. In beta and gamma,the coverage advantage gained by reducing capacity can be used toovercome the combiner and splitter disadvantages instead of extendingthe cell radius.

Radio

LA

Split

ter

Com

bine

rTx Rx Rx Tx Rx Rx Tx Rx Rx

LARadio

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Extended carrierAmplifier sharing - Asymmetric cell


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In the beta/gamma reverse link budget, the increased noise figuredirectly translates to a decrease in maximum allowable path loss. In theforward link, as was shown previously, the decrease in capacity helpsoffset the loss in power. The standard link budget cannot be used sincethe standard link budget uses an interference ratio that assumes that allsectors are at equal power. The problem is under study and we’re notcurrently prepared to deliver a split-sector budget, even though we’reintroducing the concept here.

To fully overcome the combiner/splitter disadvantage of 3.0 dB wouldrequire reducing the capacity to 14 Erlangs for the two lightly loadedsectors. The third sector that is equipped with its own amplifier wouldsupport the full capacity of 26.4 Erlangs. Thus, the cell's total capacityis 40.4 Erlangs.

Growth strategies If traffic demand grows in the same pattern, i.e., the busy sectorremains significantly higher loading than the other two sectors, then thelogical growth path is to add carriers in the same arrangement ofamplifier sharing. If traffic grows and the sectors are more uniformlyloaded, then a third amplifier should be deployed with each sectorbeing supported by its own amplifier. The penalty for the splitters andcombiners is removed from the link budget, so there is no longer anyneed to reduce capacity. The cell can then run at full capacity of 26.4Erlangs per sector, or 79.2 Erlangs per cell, in the same footprint.

If amplifiers are added, the network may require reoptimization.However, the costs of reoptimization can be minimized through the useof Lucent's Ocelot tool, as described before.

Extended carrierSummary

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Summary

In CDMA, cell design capacity can be lowered in order to expand cellcoverage. A carrier in which this design trade-off occurs is termed an“extended carrier”. Although this design trade-off exists in 2G systems,it is of greater interest in 3G systems since the allowed higher loadingof 3G yields more dynamic range in which to trade off capacity forcoverage.

The concept of extended carrier may be used in several ways, loweringdeployment costs by better tailoring the design to the specific needs ofthe network. These include:

Single extended carrier. This concept embodies the standard designconcept of lowering capacity to extend coverage. Such expanded, low-capacity cells may reduce deployment costs in lightly loaded (e.g., ruralareas) where traffic demand is slight. Additional extended carriers areadded when needed to address growth.

Concentric extended carrier. This concept uses a base-extended carrierto achieve ubiquitous, low capacity coverage over a large area. Trafficgrowth is addressed by adding reduced coverage, high capacity (core)carrier at the cell sites, which are centered in the traffic hot spots.Coverage is thus carrier-dependent. Mobiles crossing the boundarybetween core and extended carriers will hard handoff between the twocarriers. This configuration is useful for large low traffic areaspunctuated by traffic hot spots. To fully realize the benefits of thisconfiguration, feature development is required to determine mobilelocation to trigger handoffs between core and extended carriers.

Quasi-omni. This configuration services a 3-sector arrangement with asingle transmitter/receiver by lowering the design capacity and usingthe benefit to overcome splitter/combiner losses rather than expand thecoverage. The quasi-omni footprint is thus identical to that of astandard 3-sector serviced by 3 transmitters/receivers. Traffic growthcan be accommodated within the footprint by adding additionaltransmitters/receivers as needed, thus “paying as you grow”.

Asymmetric cell (split-sector). This configuration services a 3-sectorarrangement with two transmitters/receivers. One transmitter/receiverservices 2 sectors with low capacity, exploiting the benefit of lowertraffic to overcome splitter/combiner losses rather than expanding thefootprint. The split-sector footprint is thus identical to that of a standard

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Extended carrierSummary


401-614-040Issue 2, February 2003

3-sector serviced by 3 transmitters/receivers. This configurationminimizes deployment costs for cells where the traffic tends to beconcentrated on a single sector.

In each of the above scenarios, case-by-base analysis of the forwardlink is required in order to ensure link balance. Additionally, some ofthe growth scenarios may require re-optimization; however, use of theLucent’s Ocelot tool to specify recommended parameter settings canminimize any associated costs.


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8 Fixed wireless voice networks

Purpose This chapter provides detailed analysis of system performance of 2Gand 3G-1X CDMA fixed wireless voice networks.


Parameters for fixed wireless analysis 8-3

Reverse link interference ratio (βr) 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 8-9

System capacity calculation 8-10

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

Indoor 8-11Outdoor 8-14

Power requirements of forward link 8-17

3G-1X RC3 8-173G-1X RC4 8-213G-1X with SMV 8-21

Conclusions 8-23

References 8-24

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Fixed wireless voice networksIntroduction


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Introduction

This chapter provides detailed analysis of system performance of 2Gand 3G-1X CDMA fixed wireless voice networks.

The method of calculating voice Erlang capacity for 2G and 3G CDMAsystems (i.e., IS-95, and CDMA2000 or 3G-1X) is well understood andwell documented (see Lucent document 401-614-012, AUTOPLEX®

Cellular CDMA RF Engineering Guidelines, and 401-703-201, PCSCDMA RF Engineering Guidelines). The same methodology can beused to estimate the capacity of a CDMA system when the constraint isadded that the subscriber units are fixed. The capacity of a fixed systemis expected to be greater than for a full mobility system since the fixedcondition of the subscriber unit leads to a relaxed requirement for Eb/Nt (signal power to impairment power) of both the cell site andsubscriber receiver.

Fixed wireless networks are categorized into two types of applicationsbased on whether the subscriber unit is located within a building oroutside a building. For the indoor application, the subscriber unit withconventional omni-directional antenna is placed in fixed positionwithin a building. Here, the building penetration loss has to be takeninto account in network design due to signal attenuation through thewall of the building. For outdoor application, the subscriber unit withnarrow beam directional antenna is likely to be on mounted at aelevated location on a building wall or roof-top and connected totelephone terminal within the building through a wired connection. Thenarrow beam antenna at the subscriber unit reduces the interferencefrom a given subscriber to cells other than the serving cell. The narrowbeam antenna also reduces the average number of handoff legssubscribers will use, which will benefit forward link capacity. Theoutdoor application has coverage and capacity advantages over theindoor application due to both the directional antenna at the subscriberlocation and the lack of building penetration loss.

Fixed wireless voice networksParameters for fixed wireless analysis

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Parameters for fixed wireless analysis

Reverse link interferenceratio (βr)

For indoor applications, the interference ratio is the same as the mobilecase because omnidirectional antenna is used at the subscriber unit. It iswell known that the reverse link interference ratio of a mobile system is0.6, 0.85, and 1.2 for omni cell, 3-sector, and 6-sector, respectively.

Figure 8-1 Directional antenna points to desired base station

For outdoor application, as discussed earlier, the main effect of thedirectional antenna is to reduce interference to cells other than theserving cell. In order to determine how βr depends on the antennabeamwidth and cell site sectorization, simulations were done thatmodeled a network like that pictured in Figure 8-1with the followingassumptions:

• A total of 19 cell sites consisting of two tiers

• Subscriber units are randomly placed over the entire service area

• The subscriber unit antenna is correctly oriented toward theserving antenna

• Hata propagation mode is employed and the correlated log-normalshadowing effects is added in calculating path loss

• Perfect power control is assumed

• The horizontal and vertical antenna patterns as well as antennadowntilt in base station and uptilt in subscriber unit are included.

Figure 8-2 shows the simulated interference ratio as function ofantenna beamwidth from 300 to 600 and cell site sectorization. As wecan see, βr increases with increasing antenna beamwidth. At 600 ofantenna beamwidth, the interference ratio of omni cell (β=0.2) is lower

+

+

+

++

+

+

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401-614-040Issue 2, February 2003

than that of 3-sector (βr=0.3) and 6-sector (βr=0.27), at 450, βr of6-sector is the same as omni cell (βr=0.15) which is lower than that of3-sector (βr=0.22), and at 300, βr of 6-sector is slightly less than 0.1,which is interference ratio of omni cell. A explanation why 6-sectorconfiguration has low interference ratio is that for given antennabeamwidth of subscriber unit the 6-sector configuration can suppressthe interference from all other sectors due to using narrow beamantenna at base station. Compared to the indoor or mobile scenario, theinterference ratio of directional antenna is significant lower in the fixedwireless system. For estimation and comparison purposes, thecapacities in this paper for outdoor fixed wireless applications willassume a 500 beamwidth for the subscriber unit which leads to thefollowing values of reverse link interference ratio (omni-directional orindoor applications are included to make the table complete):

Table 8-1 Reverse link interference ratios

Figure 8-2 Interference ratio as function of antenna beamwidth ofsubscriber unit and cell site sectorization

Required reverse link Eb/Ntfor 3G

Reverse link required Eb/Nt is used both in capacity calculations (polecapacity equation) and in coverage calculations (link budgets).Required Eb/Nt is a function of channel condition. One of the main

Subscriber Antenna Cell Sectorization

Omni 2-sector (linear highway) 3 -Sector 6-Sector

Omni 0.6 0.3 0.85 1.2

Directional 0.15 0.09 0.25 0.2


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characteristics of the channel condition is subscriber speed. Subscribersat zero velocity are typically thought of being in an Additive WhiteGaussian Noise (AWGN) channel. However, field experience showsthat the AWGN value of required Eb/Nt may not properly reflect thesubscriber conditions due to the fact that the subscriber receiver seessome apparent motion due to movement of its surroundingenvironment. Therefore we derive a required Eb/Nt for the fixed casefrom an interpolation of the link level simulation results for the AWGNand slow speed channel models.

Link level simulation results for the 3G ASIC (CSM5000) at 1% FERshow that the worst-case total reverse link traffic Eb/Nt for 2 paths at9.6 kbps is 5.4 dB. This value corresponds to 5.4 –3 =2.4 dB trafficEb/Nt per diversity branch, and shall be used in further calculations forthe full mobility case. Note that the bit energy Eb in this valuecorresponds only to the traffic energy and does not include the energyembedded in the reverse link pilot signal.

The total per-branch Eb/Nt that must be applied in capacity or coverageapplications must include the pilot. The pilot is 3.75 dB below thetraffic channel, or 42% of the traffic channel. The total per-branchEb/Nt can be obtained from the traffic per-branch Eb/No by scaling thenumerator to contain both traffic and pilot energy:

We therefore take the full mobility total per-branch Eb/Nt as 4 dB.Similar calculations establish that the fixed Additive White GaussianNoise (AWGN) total per-branch Eb/Nt is 2.15, or approximately2.2 dB.

As stated previously, the AWGN value may not properly reflect thesubscriber conditions since the receiver sees some apparent motion dueto movement of its surrounding environment. For example, Qualcomm2G ASIC simulations indicated that the per-branch Eb/No for 0velocity AWGN was 3 dB. Later field measurements indicated that thevalue for fixed subscribers was higher: 4.6 dB. This difference suggeststhat the AWGN model underestimates the fixed receiver requirements.

This information can be used to estimate a reasonable 3G fixed Eb/Ntfrom available information. The 2G ASIC values for required Eb/Nt forthe cases of AWGN and full mobility are 3.0 dB and 7.0 dB,respectively. The observed fixed receiver Eb/Nt of 4.6 dB can be

( ) 393.01042.01 =+

=+

=

traffict

b

traffict

b

totalt

b

N

E

erTrafficPow

PilotPowererTrafficPow

N

E

N

E

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401-614-040Issue 2, February 2003

viewed as the Eb/Nt corresponding to a partial or limited mobility thatcorresponds to the situation of a fixed receiver within a surrounding,moving environment. Each of these values can be associated with arelative mobility index varying between 0 and 1, where AWGNcorresponds to index 0 and full mobility corresponds to index 1. Themobility index for a fixed receiver in a moving environment (i.e., themobility index corresponding to the observed Eb/Nt of 4.6 dB) can beestimated from a line fit to the AWGN and full mobility values.

Table 8-2 Eb/No values and mobility index for 2G/ASIC 1.0

The equation is a linear fit to the values in the table. The equation canbe solved for the value of mobility index, x (x=0.3) that corresponds tothe 4.6 dB associated with the fixed receiver in a moving environment.

A line can also be fit to the data from the CSM5000 in the samemanner, since the endpoints for 0 relative mobility (AWGN) and fullrelative mobility (1) are known. Since x=0.3 or 30% relative mobilityappears from the above to be the proper choice for a fixed receiver in amoving environment, the appropriate Eb/Nt requirement for 3G fixedwireless can be estimated by substituting x=0.3 into this equation.

Table 8-3 Eb/No values and mobility index for 3G ASIC

The substitution of x=0.3 into this equation yields Y=1.92, or anestimated per-branch Eb/Nt of 10*log(1.92)=2.8 dB. This value will beused to compute uplink fixed wireless capacity for 3G.

Walsh code overhead Each soft/softer handoff leg requires a Walsh code. Based on IS-95Ahandoff probabilities in Reference [1] of this chapter, we can calculatethe Walsh code overhead factors for 3-sector and omni configurations.

Condition Per-branch Eb/Nt (dB) Mobility IndexAWGN 3.0 0

Full 7.0 1

Fixed, moving environment 4.6 x?

( ) 3.03.07.046.0 10101010 +⋅−= x

Condition Per-branch Eb/Nt (dB) Mobility IndexAWGN 2.2 0

Full 4.0 1

Fixed, moving environment Y? 0.3 (from above)

22.022.04.0 103.0)1010( +⋅−=Y


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The maximum number of primary Walsh codes is the maximumnumber of Walsh codes available divided by this Walsh code overheadand then rounded down to the nearest integer. Note that the soft handoffWalsh code overhead differs from the forward link soft handoff poweroverhead (note that the latter term, power overhead, is the one thatappears in forward link budgets). This difference is due to the fact thatthe legs consume Walsh codes in the same manner regardless of the softhandoff state, but the amount of power consumed by a leg is a functionof its soft handoff state. For 3G-1X, IS-95B handoff algorithm is used.Due to the improvement in the IS-95B handoff algorithm, a 10%handoff reduction is applied to the IS-95A handoff probabilities. TheWalsh code limit for traffic channels in 2G and 3G-1X is 60 (fouroverhead channels: pilot, sync, paging and quick paging (althoughquick paging is not used in 2G, the Walsh Code is reserved to avoid anypossible conflicts with bordering 3G systems)). The addition of dualpaging channels (FID2064) will reduce the number by 1 to 59. Thecalculated Walsh code overhead and the number of primary trafficchannels supported with Walsh code limitation (61 for 2G and 60 for3G) are listed in Table 8-4 and Table 8-5 below.

Table 8-4 Walsh code overhead

Table 8-5 Walsh Code limitation to primary traffic channels for maxof 60 available

Subscriber Application 2G (IS-95 A) 3GOmni 3-sector Omni 3-sector

mobility (for comparison) 1.4 1.76 1.36 1.68

indoor fixed 1.29 1.54 1.26 1.49

outdoor fixed 1.00 1.25 1.00 1.25

Subscriber Application 2G (IS-95 A) 3G

Omni 3-sector Omni 3-sector

mobility (for comparison) 42 34 44 35

indoor fixed 46 38 47 40

outdoor fixed 60 48 60 48

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For the 3G-1X system, the Walsh code limit can be greatly increased(more than doubled) by using Radio Configuration 4 (RC4) on theforward link. Note that RC3 is still used for the reverse link, so anyreverse link air interface limit still exists. The cost of the extra Walshcodes for the forward link is an approximate 1 dB penalty in requiredEb/Nt. The impact of the increase in required Eb/Nt will be examinedlater in "Power requirements of forward link" section on Page 8-17. Asingle 3G-1X carrier can support both RC3 and RC4 on the forwardlink. Lucent has developed proprietary algorithms (FID 3747.2) thatmaximize forward link capacity optimizes the system capacity basedon the instant value of multiple parameters such as RF Power, RC3Walsh code usage, voice vs. data call, etc. The feature will make theRC3/RC4 assignment decision at call setup time.

Recommended loadingfactor

In a fixed wireless system, the recommended loading factors (relativeto pole capacity) are:

• 72% for 3G-1X systems (the standard 3G value)

• 65% for 2G systems with pole capacities greater than or equal to69 (the higher values of channels allows for higher loadingswithout risk of system instability since the larger number ofsubscribers tends to smooth potential instabilities)

• 55% loading otherwise (the standard 2G value).

Channel activity factor The channel activity factor for 2G voice systems is 0.40. The value for3G-1X must also account for the reverse link pilot and is 0.58. TheSelectable mode vocoders (SMV) will result in lower channel activityfactors. The following values are used by Lucent for estimatingcapacities of a SMV system:

Table 8-6 Reverse link channel activity factors for different SMVmodes

Mode Reverse Link VAF

Mode 0 0.58 (same as EVRC)

Mode 1 0.51

Mode 2 0.47

Fixed wireless voice networksReverse link coverage

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Reverse link coverage

Reverse link coverage for fixed wireless networks is estimated in thesame manner as for mobile networks (see "Link budget" section onPage 2-14). However, some of the parameters for fixed wirelessnetworks will be different, typically leading to larger predictedcoverage areas. The differences that expand coverage include:

• Lower Eb/Nt requirements

• Higher subscriber unit antenna gains for outdoor fixed wirelessnetworks

• Lower interference margins for cases when Walsh codes are thelimiting resource

• Lower building penetration margins for outdoor fixed wireless.

The differences that shrink coverage include:

• Higher interference margins for some 2G scenarios since thehigher values of channels allows for higher loadings without riskof system instability since the larger number of subscribers tendsto smooth potential instabilities (note that this item shrinkscoverage as opposed to the other items that expand coverage)

• Possibly higher building penetration margins or fade margins forindoor wireless case. Some customers may require higher buildingpenetration losses for indoor fixed systems since all subscribersare indoors. Other customers may require that the fade marginterm be increased to account for the variability of buildingpenetration values.

For a typical indoor fixed wireless system, the coverage advantage overa mobile network will be just the difference in Eb/Nts, which is 1.2 dBfor 3G-1X. For outdoor fixed wireless systems, the coverage advantagecan be quite large, since it includes both the gain of the directionalsubscriber antenna as well as the gain due to not having a buildingpenetration loss.

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Fixed wireless voice networksSystem capacity calculation


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System capacity calculation

Capacity calculationmethodology

The RF Engineering Guidelines (Lucent document 401-614-012,AUTOPLEX® Cellular CDMA RF Engineering Guidelines, and 401-703-201, PCS CDMA RF Engineering Guidelines) explain themethodology for computing system capacity, which is a five stepprocess as follows:

1. Compute the “pole capacity”:

where:g is the processing gain (bandwidth divided by channel rate)α is the channel activity factorβr is the reverse link interference ratiod is the required Eb/Nt expressed as a linear ratio (as opposedto dB)

2. Choose a loading factor, which is a relative amount of the polecapacity to determine maximum number of simultaneous RFchannels. This loading factor is directly related to the predictedcoverage through the interference margin term (sometimes callednoise rise). The higher the loading, the higher the interferencemargin and the smaller the coverage area.

3. This maximum number of channels must be checked against theforward link Walsh Code limit. If the Walsh Code limit is less thanthe computed value, the Walsh Code limit is the maximumnumber of channels.

4. Choose a grade of service and use that to translate maximumnumber of channels to voice capacity in terms of Erlangs. ErlangB tables are typically used for this mapping.

5. The forward link air interface capacity is then verified bychecking that the forward link has sufficient power to support thenumber of users.

For a fixed system, two parameters (reverse link interference ratio andrequired Eb/Nt) of the pole capacity equation are different than themobile case, as explained below.

1)1(

++⋅⋅

=r

pole d

gn

βα


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Reverse link basedcapacity calculations

The capacities considering just reverse link air interface limits andWalsh code limits (to Step 4 in the 5-step process described above) arepresented below.

Indoor

Table 8-7 2G ASIC 1.0 reverse link capacity of indoor fixed application

Table 8-8 2G ASIC 1.1 reverse link capacity of indoor fixed application

ASCI 1.0 Voice Indoor Fixed

Configuration 3-sector BS, omni terminal omni BS, omni terminal

Vocoder 8K 13K 8K 13K

Data rate 9600 14400 9600 14400

Eb/Nt in dB 4.6 4 4.6 4

d = Eb/Nt|rqd in ratio 2.9 2.5 2.9 2.5

g, processing gain 128 85.3 128 85.3

α, voice activity factor 0.4 0.4 0.4 0.4

reverse beta 0.85 0.85 0.6 0.6

Nmax = g/(alpha*d*(1+beta))+1 61.0 46.9 70.3 54.1

% of loading 55% 55% 65% 55%

N = Nmax*% of loading 33 25 45 29

Reverse Link Channel Capacity with Walsh code limitation 33 25 45 29

Reverse Link Erlang Capacity @ 1% blocking 22.9 16.1 33.4 19.5


ASCI 1.1 Voice Indoor Fixed



Data rate 9600 14400 9600 14400

Eb/Nt in dB 4 3.4 4 3.4




reverse beta 0.85 0.85 0.6 0.6


% of loading 65% 55% 65% 55%





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Table 8-9 RC3 reverse link capacity of indoor fixed application

Table 8-10 3G-1X RC4 Reverse Link capacity of indoor fixed application

3G-1X Voice RC3 Indoor Fixed



Data rate 9600 14400 9600 14400

Eb/Nt in dB 2.8 2.6 2.8 2.6




reverse beta 0.85 0.85 0.6 0.6


% of loading 72% 72% 72% 72%





3G-1X Voice RC4 Indoor Fixed


Vocoder 8K 8K

Data rate 9600 9600

Eb/Nt in dB 2.8 2.8

d = Eb/Nt|rqd in ratio 1.9 1.9

g, processing gain 128 128

α, voice activity factor 0.58 0.58

reverse beta 0.85 0.6

Nmax = g/(alpha*d*(1+beta))+1 63.6 73.4

% of loading 72% 72%

N = Nmax*% of loading 45 52

Reverse Link Channel Capacity with Walsh code limitation 45 52

Reverse Link Erlang Capacity @ 1% blocking 33.4 39.7



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Table 8-11 3G-1X RC4 with SMV Mode 1 reverse link capacity of indoor fixed application


3G-1X Voice RC4 & SMV Mode 1 Indoor Fixed


Vocoder 8K 8K

Data rate 9600 9600

Eb/Nt in dB 2.8 2.8













Vocoder 8K 8K

Data rate 9600 9600

Eb/Nt in dB 2.8 2.8











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Outdoor

The capacity improvement of a sector is an important benefit obtainedfrom the reduced in the outer sector interference when the directionalantenna is used.

Table 8-13 2G ASIC 1.0 reverse link capacity of outdoor fixed application

Table 8-14 2G ASIC 1.1 reverse link capacity of outdoor fixed application

ASCI 1.0 Voice Outdoor Fixed

Configuration 3-sector BS, directionalterminal

omni BS, directionalterminal


Data rate 9600 14400 9600 14400

Eb/Nt in dB 4.6 4 4.6 4d = Eb/Nt|rqd in ratio 2.9 2.5 2.9 2.5



reverse beta 0.25 0.25 0.15 0.15


% of loading 65% 65% 65% 65%





ASCI 1.1 Voice Outdoor Fixed




Data rate 9600 14400 9600 14400

Eb/Nt in dB 4 3.4 4 3.4




reverse beta 0.25 0.25 0.15 0.15


% of loading 65% 65% 65% 65%






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Table 8-15 3G-1X reverse link capacity of outdoor fixed application

Table 8-16 3G-1X reverse link capacity of outdoor fixed application

3G-1X Voice RC3/RC2 Outdoor Fixed




Data rate 9600 14400 9600 14400

Eb/Nt in dB 2.8 2.6 2.8 2.6




reverse beta 0.25 0.25 0.15 0.15


% of loading 72% 72% 72% 72%





3G-1X Voice RC4 (FL) Outdoor Fixed



Vocoder 8K 8K

Data rate 9600 9600

Eb/Nt in dB 2.8 2.8











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As we see, the capacity of outdoor is significant higher than that ofindoor with or without Walsh code limitation.


Configuration 3-sector BS,omni terminal

omni BS, omniterminal

Vocoder 8K 8K

Data rate 9600 9600

Eb/Nt in dB 2.8 2.8












Configuration 3-sector BS,omni terminal

omni BS, omniterminal

Vocoder 8K 8K

Data rate 9600 9600

Eb/Nt in dB 2.8 2.8











Fixed wireless voice networksPower requirements of forward link

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Power requirements of forward link

3G-1X RC3 To assess the forward link, we begin with the fundamental forward linkequation that conserves power at the J4 (antenna connector) port at thebase station (see "Forward link" section on Page 2-20):

where α and x are the forward link voice activity and forward linkpower allocation, respectively, for the jth link (user). The allocation isthe fraction of total transmit power allocated to the link, and isfrequently referenced as Ec/Ior. Qmax is the maximum power (e.g., 16watts for PCS Modcell) broadcast at the J4 port. The fraction µ is the(fixed) percentage of maximum power provided for overhead functions(e.g., pilot, page). At full power, the expression above reduces to:

The capacity is determined by the allowed number of links in the sum;i.e., for a given distribution of the random variables α and x, there is amaximum number N of links that can be supported in order to satisfythe equation above with a high degree of probability. We will use theequation above to estimate the difference between fixed and fullymobile capacity by projecting the allowed change in N when thedistribution of x’s is shifted from fully mobile to fixed only. Thisprocess requires estimation of the x values for both conditions.

To proceed further, we conservatively assume that all subscriber unitsare located at the edge of cell coverage, where “edge” in this contextdenotes a cell exit or entry point. This assumption can be exploited intwo ways:

• At the design edge, the ratio of received pilot strength to totalbackground interference (Ec/Io) must be optimized to be greaterthan the handoff add threshold T_ADD.(e.g., -12 dB). Thephysical boundary of the cell must correspond to this value (asopposed to T_DROP) in order to ensure that a subscriber enteringthe cell adds a new pilot before dropping the old one (the “makebefore break” rule of soft handoff).

• Given the subscriber placement, all subscribers are in a handoffstate, which (conservatively) establishes a minimum of two paths.

maxmaxmax QQQx jlinksall

j ≤+∑ µα

µα −≤∑ 1jlinksall

j x

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401-614-040Issue 2, February 2003

The value of x (Ec/Ior) for each subscriber can therefore be obtainedfrom curves of Ec/Ior vs. geometry for 2-path cases. These curves areavailable as a function of subscriber speed and for the AWGN cases.The curves are generated from link level simulations. In the reverselink analysis (see above), the AWGN values were scaled to obtainEb/Nt requirements for a fixed receiver in a moving environment. Thisscaling was done by comparing measurements of 2G fixed wirelessrequirements to AWGN values. Since there are less empirical results on2G forward link fixed wireless Eb/Nt requirements, the forward link3G AWGN values shall be used without adjustment as fixed wirelessrequirements.

The link level simulation curves12 plot Ec/Ior as a function of thegeometry. Geometry is defined as Ior/(FNoW+Ioc), where Ior = the sumof received power density from the cell(s) in the active set, FNoW is themobile noise floor, and Ioc = the received power density from allsurrounding cells not in the active set. The Ec/Ior value from the curvesapplies to the link from the host cell only. The Ioc term does not containthe receiver noise, as the underlying simulations were interference-limited. For the handoff case, this value becomes the ratio of the totalreceived power density from the two handoff cells (i.e.,Ior = Ior (1) + Ior (2)) to the total impairment density Ioc. The curveswere produced with 20% of the host power allocated to pilot.

To compute the appropriate value of Ec/Ior for the subscriber placementpresumed, the value of geometry for each subscriber must becomputed. The value of geometry can be computed by noting thefollowing:

• The pilot power is a constant fraction η of the total maximum cellpower (Ior1W)

• At the cell edge, each subscriber’s ratio of pilot power to totalbackground power is THRES

• At the cell edge, Ior1=Ior2 due to the placement of subscribers andthe assumption that all cells broadcast at full, equal power.

Accordingly:

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

12 These curves are found in the document “Simulation Study of the OTD Mode for theVoice Service Case in IS-2000”, by Qi Bi, Yung-Fang Chen, and Raafat Kamel; March2000.


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401-614-040Issue 2, February 2003

These three equations can be combined to yield:

Evaluation of this expression for THRES=-12 dB and a 20% ratio ofpilot to host power yields a geometry of 1.7, or 2.3 dB. Note that thisanalysis implies that the geometry is constant for all subscribers on theedge, regardless of effects such as lognormal fading. The constantvalue follows from the assumption that optimization for all possibleboundary (i.e., exit/entry) positions has established a value equal to theTHRES value in order to ensure handoff performance at the cell edge.

The value of Ec/Ior for AWGN and 3 velocities for a geometry of2.3 dB are tabulated below for 2 GHz. These values can therefore beused to analyze the relative increase between the 3G-1X full mobilityand 3G-1X fixed wireless capacities for the PCS case. These resultswill serve as a conservative estimate of the relative increase at lowerfrequencies (e.g., 450 MHz, 850 MHz) since at longer wavelengthstypical subscriber velocities will yield lower fast fading rates. Theserates will bias the spread of Ec/Ior for nonzero velocities towards theupper rows of the table,13 resulting in a slightly higher relative increasewhen the receiver is fixed.

WIWFN

WIWIGgeometry

WIWIWIWFN

pilot

WIpilot

oct

oror

THRES

ocorort

or

++

=

=+++

=

21

10/

21

1

10

η

12

10

1

10/ −

=− ηTHRES

G

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

13 For example, a speed of 100 km/hr. at 2 GHz is roughly equivalent to a speed of 400km/hr. at 450 MHz: each achieves the same fast fading rate, since the wavelength at 450MHz is approximately 4 times greater than that at 2 GHz. The value of -15.9 dB wouldtherefore be excluded from the 450 MHz case.

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401-614-040Issue 2, February 2003

Table 8-19 Ec/Ior for 2-path, d=0 (equal strength handoff legs),geometry is 2.3 dB, frequency=2GHz

For the full mobility case, presuming that each velocity is equallyprobable, the mean and standard deviation of the random variable x is0.028 and 0.0058, respectively. In contrast, for the fixed wireless casethe single constant value of x is 0.021 (equivalently, a mean of 0.021and a standard deviation of 0).

This information can now be used to evaluate the fundamental forwardlink equation for the fixed and fully mobile cases. The left hand side isa random variable that can be approximated as Gaussian since the sumis over a large number of independent variables (note that the voiceactivity and allocation x are independent). To satisfy the equation withhigh (e.g., 98%) probability, we require that the 98th percentile (thevalue corresponding to the mean plus two standard deviations) of theGaussian distribution be less than or equal to the right hand side. Insummary:

The last equation is quadratic in √N, and can be solved for N. Insolution, a value of µ=0.29 is employed since this is the fraction of totalpower consumed by a pilot at 20% total (the value employed in theEc/Ior simulations) and the additional overhead channels of page and

Velocity x = Ec/Ior

“0” km/hr. (AWGN) -16.7 dB (2.1%)

3 km/hr. -14.3 dB (3.7%)

30 km/hr. -15.3 dB (3.0%)

100 km/hr. -15.9 dB (2.6%)

[ ]

0)1(2

,

12

1

222222

222222

1

≤−−+++

++=

==

−≤+

−≤=∑=

µσησησσηη

σησησσσ

ηηη

µση

µα

αααα

ααα

α

xxxx

xxxy

xy

y

j

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jj

NN

yAccordingl

N

NyE

xy

y


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401-614-040Issue 2, February 2003

sync. Additionally, the mean and standard deviation of voice activityare estimated simply by presuming full rate (1) with a probability of 0.4and 1/8 rate with a probability of 0.6.

With these assignments, the quadratic equation in √N is evaluated for1) the N corresponding to full mobility; and 2) the N corresponding toAWGN. The ratio of the latter to the former is 1.4, or a 40% increase inchannels. Since the full-power (blocking) condition for full mobilityhas been estimated in simulations to be 35 channels (26.4 Erlangs), thecorresponding number of primary channels at the AWGN full-power(blocking) condition should be 35(1.4)=49. This corresponds to 37Erlangs at the 1% blocking condition and 39.3 Erlangs for the 2%blocking condition.

This estimate must be treated as an upper bound on the capacity for afixed receiver in a moving environment, since in arriving at this valueno adjustment was made to the Ec/Ior value obtained from the AWGNcondition. In contrast, the AWGN value in uplink analysis was scaledin order to account for motion in the surrounding environment.Nevertheless, the forward link result of 37 Erlangs is significant in thatit suggests that the forward link should be able to support the 34Erlangs estimated for the uplink. This conclusion is applicable tolower frequencies as well, since the relative increase between fixed andmobile capacity at PCS frequencies should be less than or equal to therelative increase at longer wavelengths (see above).

3G-1X RC4 In several cases, Walsh codes are the capacity limiting resource.Forward link RC4 allows for twice the number of Walsh codes relativeto RC3 (128 vs. 64). However, the cost of the extra Walsh codes ishigher, required power requirements to support RC4 subscriber units.The power fraction (Ec/Ior) versus Geometry curves show about 1 dBpower penalty for RC4. This 1 dB can be directly applied as an Erlangcapacity reduction. Thus, the 37 Erlangs for RC3 is reduced by 1 dB to29.4 Erlangs for 1% blocking and from 39.3 to 31.2 Erlangs for 2%blocking. In this case the limiting resource is forward link air interfacecapacity.

3G-1X with SMV The 1 dB Eb/Nt penalty from utilizing RC4 typically leads to theforward link air interface being the limiting resource. The SMV(Selectable Mode Vocoder) provides capacity gains for the forwardlink. The capacity gains for SMV in the forward link are expected to beas follows.

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401-614-040Issue 2, February 2003

Thus the increase in forward link capacity relative to the RC4 case forMode 1 is to 39.3 Erlangs for 1% blocking, or 41.8 Erlangs for 2%blocking. For Mode 2, the capacity increases to 48.2 Erlangs for 1%blocking, and 51.2 Erlangs for 2% blocking.

Mode Forward link gain

Mode 0 0%

Mode 1 34%

Mode 2 64%

Mode 3 80%

½ Max mode 1 70%

½ Mac mode 2 93%

Fixed wireless voice networksConclusions

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401-614-040Issue 2, February 2003

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Conclusions

The following table summarizes the capacities for variousconfigurations.

Where the highlighting indicates the limiting resource as follows:

• No highlighting indicates that the reverse link air interface is thelimiting resource

• Pink highlighting indicates that Walsh codes are the limitingresource

• Yellow highlighting indicates that the forward link air interface isthe limiting resource.

• Green highlighting indicates that further analysis is required toverify the forward link power requirements are satisfied.

Capacities for fixed wireless 3G-1X data networks are currently beingstudied.

Fixed Wireless Application Indoor (Omni SubscriberAntenna)

Outdoor (Directional SubscriberAntenna)

Base Station Antenna 3-sector omni 3-sector omni

Vocoder 8K 13K 8K 13K 8K 13K 8K 13K

1% blocking

ASCI 1.0 Voice 22.9 16.1 33.4 19.5 36.1 32.5 46.9 36.1

ASCI 1.1 Voice 27.3 19.5 34.3 23.8 36.1 36.1 46.9 42.4

3G-1X Voice RC3/RC2 (RL & FL) 29.0 24.6 35.2 29.9 36.1 36.1 46.9 44.2

3G-1X Voice RC4 (FL) 29.4 N/A TBD N/A TBD N/A TBD N/A

3G-1X Voice RC4 (FL) SMV Mode 1 39.3 TBD TBD TBD


2% blocking

ASCI 1.0 Voice 24.6 17.5 35.6 21.0 38.4 34.7 49.6 38.4

ASCI 1.1 Voice 29.2 21.0 36.5 25.5 38.4 38.4 49.6 44.9

3G-1X Voice RC3/RC2 (RL & FL) 31.0 26.4 37.5 31.9 38.4 38.4 49.6 46.8

3G-1X Voice RC4 (FL) 31.2 N/A TBD N/A TBD N/A TBD N/A



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Fixed wireless voice networksReferences


401-614-040Issue 2, February 2003

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References

[1]. “Range vs. number of subscribers for the forward and reverselinks,” Qualcomm, July 18, 1995.

3G RF Engineering Guidelines

Documents

Transcript of 3G RF Engineering Guidelines