cellular network planning and optimization part6

8/8/2019 Cellular Network Planning and Optimization Part6

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Cellular NetworkPlanning andOptimization

Part VI:WCDMABasicsJyriHmlinen,

Communications andNetworking Department,TKK,24.1.2008


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Networkelements


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Networkelements

Networkelementsina3GWCDMAbasedPLMN

Ourmainfocusarea


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Networkelements

TypicallyPLMNisoperatedbyasingleoperator

ConnectedtootherPLMNs andnetworkslikeInternet

UserEquipment(UE)contains

Mobileequipment(ME):RadiocommunicationoverUuinterface

UMTSSubscriberIdentityModule(USIM):Subscriberidentityinformation,authenticationalgorithms,encryptionkeysetc


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Networkelements

UMTSTerrestrialRadioAccessNetwork(UTRAN)

NodeB(BaseStation):Handles/managesthetrafficbetweenUu andIub interfaces.Basictaskslikecoding,interleaving,rateadaptation,modulation,spreadingetc.

RadioNetworkController(RNC):Controlradioresourcesinitsoperationarea.ProvideservicesforCoreNetwork(CN).Loadandcongestioncontrol,

admissionscontrol,codeallocation,radioresourcemanagementtasks.


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Networkelements

MobileServicesSwitchingCentre(MSC)/VisitorLocationCentre(VLR) HandlesswitchinginCircuitSwitched(CS)connectionsand

holdvisitingusersserviceprofiles. ServingGPRSSupportNode(SGSN)

SimilarfunctionalityasinMSC/VLRbutusedforPacketSwitched(PS)services

OtherCNelements GatewayMSC(GMSC):HandlesincomingandoutgoingCS

connections GatewayGPRSSupportNode(GGSN):LikeGMSCbutin

PSdomain HomeLocationRegister(HLR):Mastercopyofusers

serviceprofiles


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Physicallayer


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Uplinktransmissionpath

Spreadingcodesareusedtoseparatedataandcontrolofauser.

Scramblingcodesareusedtoseparatedifferentusers.

DualchannelQPSKmodulation(dataandcontrolintodifferentI/Qbranches)

Modulation Spreading


Data

ControlScrambling


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Downlinktransmissionpath

Userswithinacell(sector)areseparatedbyorthogonalspreadingcodes(sometimesalsocalledaschannelizationcodes)

Cells(sectors)areseparatedbyscramblingcodes QPSKmodulation



.

.

.

.

.

.

Stream1

StreamN

Scrambling


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Spreading

Spreadingisdoneusingorthogonalcodes

Codesremainorthogonalonlyifsynchronizationis

perfect Multi-pathfadingwillreducetheorthogonality

[1]

[1,-1]

[1,1]

[1,-1,1,-1]

[1,-1,-1,1]

[1,-1,-1,1,-1,1,1,-1]

[1,-1,-1,1,1,-1,-1,1]

[1,1,-1,-1]

[1,1,1,1]


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Spreading

Data

Spreadingcode

Signalafterspreading

frequency frequency

SpreadingFactor(SF)defineshowmanychipsareusedtorepresentonedatasymbol

Spreadingexpandsthesignaltowideband


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Spreading

Spreadingprovidesprocessinggain.Letusdenote

W=systemchiprate

R=userbitrateThenprocessinggainisdefinedby

Whileuserdatarateincreases,theprocessinggaindecreasesaswellasthespreadingfactor.Hence,itisharderforthereceivertodetectthesignalcorrectly.

Sometimeswealsousetermspreadinggain.Itreferstovalue

=

R

WPG 10log10

( )SF10log10gainSpreading =


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Spreading

SomemeasuresthatareusedinWCDMAreceiverinvestigations

CINR=Carriertointerferenceandnoiseratio,alsoSINRisused

CIR=Carriertointerferenceratio,alsoSIRisused

SNR=Signaltonoiseratio E=Energyperuserbitdividedbythenoisespectral

density=processinggain*powerthatisneededto

overcometheinterferencefromotherusers.

NotationiscommonlyusedforE0/NEb


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Spreading

InWCDMAchiprateis3.84Mcps. Temporaldurationofthechipis1/3.84*10^6=

260.4ns. Signaltravels78.125metersduringthechipduration

Thisdistancedefinesthemaximumaccuracybywhichreceivercanresolvedifferentsignalpaths.

Signalamplitude

delaytime

longechos,usuallyonlyinHillyterrainenvironment

directpath

nearbyscatterers

RAKEoperations

Chipduration


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RAKE

AbasicreceiverthatisusedinWCDMAiscalledasRAKE Themultipathchannelthroughwhicharadiowavepropagates

canbeviewedasasumofmanydelayedcopiesoftheoriginaltransmittedwave,eachwithadifferentmagnitudeandtime-of-arrivalatthereceiver.Eachmultipathcomponentcontainstheoriginalinformation=>ifthemagnitudeandtime-of-arrivalofeachmultipathcomponentisknown(throughchannelestimation),thenallthemultipathcomponentscanbeaddedcoherently

RAKEisdesignedtocountertheeffectsofmultipathfading.Itdoesthisbyusingseveralfingers,eachdelayed(byorderofsomechips)inordertocatchtheindividualmultipathcomponents.

Componentsignalsfromfingersarecombinedcoherentlyforthesumsignalthatisusedindecoding.


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Scrambling

+1

-1

+1

-1

+1

-1

Signalafterspreading

Scramblingcode

Signalafterscrambling


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Scrambling

Scramblingcodesareusedtoseparateusersinuplinkandcellsindownlink

Scramblingisusedontopofspreading

Scramblingisnotchangingthesignalbandwidth

Indownlinkscramblingcodesareallocatedtothecells(sectors)innetworkplanningphase

Numberofscramblingcodesishigh=>codeplanningisatrivialtaskandcanbeautomated


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Spreadingandscramblingsummary

Noimpacttotransmissionbandwidth

IncreasestransmissionbandwidthBandwidth

UL:38400chips=10ms=framelength

DL:38400chips=10ms=framelength

UL:4-256chipsDL:4-512chips

Codelengthdefinessymbolrate

Length

UL:Separationofusers

DL:Separationofcells

UL:Separationofcontrolanddatafromthesameuser

DL:Separationofconnectionswithinacell

Usage

ScramblingcodesSpreadingcodes


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Importantchannels/uplink

Uplinkdedicatedchannel

PhysicallayercontrolinformationinDedicatedPhysical

ControlChannel(DPCCH),spreadingfactor=256 DataiscarriedinDedicatedPhysicalDataChannels

(DPDCH).Variablespreadingfactor

TherecanbemultipleDPDCHs butonlyoneDPCCH.

Note:Thereis

usuallyapowershiftbetweendataandcontrol

channels


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ControlinformationinDPCCH

Pilotbitsforchannelestimation Alwayspresent

TransmitPowerControl(TPC)bitsfordownlinkpowercontrol Alwayspresent

TransportFormatCombinationIndicator(TFCI) Informreceiveraboutactivetransportchannels

FeedbackBitInformation(FBI)

Presentonlywhendownlinktwo-antennaclosedlooptransmitdiversityisapplied


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UplinkDPDCHdatarates

Dataratesinthetableachievedwith rate

coding Parallelcodesnotused

inpracticeduetoreducedpoweramplifier

efficiency

Maximumratebelow500kbps.

Note:Inuplinkeachuserhaveallspreadingcodesinitsuse

2.8Mbps4,6parallelcodes

480kbps4

240kbps8

120kbps16

60kbps32

30kbps64

15kbps128

7.5kbps256

UserdatarateSpreadingfactor


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Importantchannels/downlink

Downlinkdedicatedchannel

DownlinkcontrolinformationiscarriedinDedicated

PhysicalControlChannel(DPCCH) DownlinkdataiscarriedinDedicatedPhysicalData

Channel(DPDCH)

Spreadingfactordependsontheservice


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CommonPilotChannel(CPICH)

CPICHaidchannelestimationattheterminal

Spreadingfactor=256 Terminalmakeshandoverandcellselectionmeasurements

fromCPICH=>CPICH shouldbeheardeverywhereinthecell

CellcoverageandloadcanbeadjustedthroughCPICH IfCPICHpowerisreducedpartoftheterminalswillhand

overtoadjacentcells

Synchronizationchannel(SCH)

Synchronizationchannelisneededforcellsearch

Spreadingfactor=256

(*)Importantpropertyfromnetworkplanningperspective

(*)

(*)

(*)


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PrimaryCommonControlPhysicalChannel(PrimaryCCPCH)

Carrybroadcastchannelandallterminalsinthesystemshouldbeabletoreceiveit.

IfCCPCHdecodingfailsthenterminalcannotaccesstothesystem=>CCPCHtransmissionpowerhigh.

Nopilotbits,channelestimationdonefromCPICH

whichistransmittedwithsameantennaradiationpattern

Spreadingfactor=256, ratecoding

(*)Importantpropertyfromnetworkplanningperspective

(*)


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DownlinkDPDCHdatarates

Dataratesinthetableachievedwith rate

coding Indownlinkallusers

sharethespreadingcodes=>numberof

orthogonalcodesdefinesahardlimitforcellcapacity

Partofthespreadingcodesarereservedforcontrolchannels

1-3kbps512

2.8Mbps4,3parallelcodes

936kbps4

456kbps8

215kbps16

105kbps32

45kbps64

20-24kbps128

6-12kbps256

UserdatarateSpreadingfactor


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Downlinkcontrol

Fromnetworkplanningperspectiveitisimportanttokeepinmindthatcontrolchannels

takepartoftheDLpower


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Radioresourcemanagement


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General

RadioResourceManagement(RRM)iselementarypartofWCDMA.

RRMisresponsibleforefficientutilizationoftheairinterfaceresourcesitisneededto

GuaranteeQualityofService(QoS)

Maintaintheplannedcoveragearea Optimizethecellcapacity

TheimportanceofRRMismostlyduetothe

featuresoftheUMTSsystem;interferencelimitednatureandadaptiveservices


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RRMalgorithms

FamilyofRRMalgorithms:

Powercontrol

Fastpowercontrol(NodeB,UE) Outerlooppowercontrol(RNC)

Handovercontrol(RNC)

Admissioncontrol(RNC) Loadcontrol(RNC)

Fastloadcontrol(NodeB)

Packetscheduling(RNC)


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Powercontrol

Objectives Maintainthelinkqualityinuplinkandindownlinkbycontrolling

thetransmissionpowers

Preventsnear-fareffect Minimiseeffectsoffastandslowfading Minimisesinterferenceinnetwork

Accuracyofthepowercontrolisimportant Notime-frequencyseparationofusers,allusethesame

bandwidth Inaccuracyinpowercontrolimmediatelyliftsthenetworks

interferencelevel,whichcorrespondinglylowersthecapacity Duetousersmobilitythespeedofpowercontrolisalsoa

criticalissue


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Near-farprobleminuplink

TherecanlargepathlossdifferencebetweenUE1(cell

centre)andUE2(celledge)

IfbothUEsaretransmittingwiththesamepowerthenUE1willblockUE2(andothercelledgeuserstoo)

PowercontrolwilldrivetransmissionpowersofUE1andUE2totheminimumlevelthatisrequiredtomeetQoS

InNodeBreceivedpowersfromUE1andUE2willbethesameforsameservices

UE1

UE2


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Powercontrol

PowerControlonthecommonchannels ensuresthattheircoverageissufficient bothtosetupUE-originatingandUE-terminatingcalls.

PowerControlonthededicatedchannels ensuresanagreedqualityof connectionintermsofBlockErrorRate(BLER),whileminimizingtheimpact onotherUEs.

UplinkPowerControl increasesthemaximumnumberofconnectionsthatcan beservedwiththerequiredQualityofService

(QoS),whilereducingboththe interferenceandthetotalamountofradiatedpowerinthenetwork.

DownlinkPowerControl minimizesthetransmissionpoweroftheNodeB and compensatesforchannelfading.Minimizingtransmittedpowermaximizesthedownlinkcapacity.


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Powercontrol

Mainpowercontrolapproaches

Fastpowercontrol:

Aimistocompensatetheeffectoffastfading Gainfromfastpowercontrolislargestforslowly

movingUEs andwhenfadingisflat,i.e.thereismulti-pathdiversity

Fastpowercontroldrivesthereceivedpowertoa

targetSIR.Thisvalueisdiscussedmorecloselyinconnectionwithdimensioning.

Outerlooppowercontrol AdjustthetargetSIRaccordingtoserviceQoS.


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PCmechanism

OuterloopPC:RNCadjustthetargetSIRinorder

tomeettargetBLER

FastPC:NodeBcommandterminaltochangetransmitpowerinordertomeettargetSIR ReceivedSIR

Outerlooppowercontrol

Fastpowercontrol


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UplinkouterloopPC

ThegoalistocontrolthetargetSIR inordertoremainthewantedQoS withminimumtransmitpower

ThetargetBLERisdefinedwiththeadmissioncontrolalgorithm

TheuplinkalgorithmiscontrolledinRNCanddownlinkalgorithminUE

Updatefrequencyfrom10Hzupto100Hz Outerlooppowercontrolwillraiseorlowerthetarget

SIRaccordingtostepsize,whichisdefinedbyradionetworkplanning.

Theequipments performancedefinestheminimumvaluefortargetSIR


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Fastpowercontrol

Idealfastpowercontrolinvertthechannel

Inpracticepowercontrolaccuracyisreducedby

feedbackerrors, Betterfigure,PCheadroometc

Fastfadingchannel

Transmittedpower


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UplinkfastPC

Update rate 1.5kHz=>fastenough totrack andcompensate fastfading up toxkm/hmobilespeed

If receivedSIR>targetSIRinNodeB=>UEiscommanded todecrease its transmitpower.Similarly UEiscommanded toincrease its transmissionpowerifreceivedSIR


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DownlinkfastPC

Similar asDLfastPC:

UEmeasures SIRonDLDPCCHduring thepilot

period UEmaintainstheQoS bysendingfastpowercontrol

commands(TPCbits)requestingpower adjustment

Poweroffsets can be used inDLinordertoimprovecontrolreliability.Offsets are network parameters thatcan be setinplanning phase

cellular network planning and optimization part6

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