阿尔卡特LTE频率规划方案.docx

阿尔卡特LTE频率规划方案.docx

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阿尔卡特LTE频率规划方案

3GPPTSGRANWG1#41R1-05-0407

Athens,Greece

9.–13.May2005

Title:

InterferenceCoordinationinnewOFDMDLairinterface

Source:

Alcatel

AgendaItem:

13.2,EvolvedUTRA,FurtherdiscussiononMultipleaccessschemes

Documentfor:

DiscussionandDecision

1.Introduction

Inthe3GPPstudyitemonLongTermEvolutionmultipleaccessschemeshavetobeevaluatedthatshallbeusedforuplinkanddownlink.ImportantcriteriafortheevaluationoftheschemeswerederivedontheLTEworkshopinToronto.AccordingtotheagreedTextproposalRP-050155theyshallnowbegatheredintheRequirementTR25.812.TheagreedtextproposalRP-050155liststherequirementsfromwhichwehighlightthenumber3andnumber1:

Theyare:

-Increase“celledgebitrate”whilstmaintainingsamesitelocationsasdeployedtoday.（No.3）

-Efficientsupportofthevarioustypesofservices,especiallyfromthePSdomain（e.g.VoiceoverIP,Presence）.（No.1,formerNo.15）

Inordertoreachspectralefficiencytargetsanewairinterfaceisassumedtoachieveafrequencyre-useof1likeWCDMAdoes.

Inthisdocumentweconcentrateonthedownlink.Inthelongtermallserviceswilldesirablybebasedonpackettransmission.ConsideringthisweconcludethatthecelledgebitrateandQualityofService（QoS）isanimportantcriterionwhichleadstotheproposalofOFDMwithinterferencecoordinationtechniquesespeciallyaddressingthisissue.Furtherweproposetoavoidasoft-handoverbutinsteadgoforsimplifiedRANarchitectureandprotocols.AfterthatwereviewthephysicalreasonsforthedifferencesbetweenOFDMandCDMAinthatcontext.FinallyweproposetouseOFDMwithinterferenceavoidancestrategies.Twoofthemaresummarizedandcomparedtoshowtheirbenefitsandextendibilitytoadaptivesubcarrierallocation.

2.PacketTransmissionatCellBorder

Consideringthetasksofthenewairinterfaceinthelongterm（evenincoexistencewithWCDMA）itisexpectedthatallservicesshouldbecarriedbypacketbearerse.g.VoIPandpacketwithQoS.

Foranewairinterfaceweassumethatafrequencyre-useof1shouldbeapproximated.ThecelledgetransmissionthensuffersfromaverylowSIR.Inthatcasethecelledgepackettransmissionbecomesaprobleminordertoguaranteethatsuchaconnectiondoesnotbreak.ThusthecelledgebitrateandtheQoSatthecelledgee.g.forguaranteeingahighnumberofseamlessserviceconnectionsbecomesdecisive.

InWCDMA（ande.g.voiceconnections）thereisasoft-handovertoaddressthisissue.IfasofthandoverisusedforpackettransmissionsthismeansthatpacketretransmissionshavetogoovertheRNCwhichmayhazardrealtimeservices.

NowthecelledgeproblemcanbeaddressedbyOFDMwithinterferencecoordinationtechniquessinceOFDMcancopewiththecellbordersituationandachievebetterthroughput.Theapproachisthereforetoavoidasoft-handoverandgoforasimplifiedRANarchitectureandprotocolsbyusingthispropertyofOFDM.

SoweproposethattechniquesofinterferencecoordinationbeforeseeninanOFDMairinterface（withorwithoutpowerplanning）toaddresstheproblemofcelledgebitrateandqualityofserviceatthecellborder.

Thiswillsimplifythearchitectureandinthelongtermisanimportantmethodtoallowforallservicestobecarriedonpacketbearers.

3.ProblemDescriptionofFrequencyRe-useof1Systems

Innetworkswithfrequencyre-useof1thethroughputatthecellborderisverymuchlimitedbytheinterference.SincetheneighborcelltransmitsonthesamebandareceptionwithanSIR=0dBhastoberealized.Sotheinterferencebytheneighborcelllimitsthethroughput.

NowOFDMallowsforinterferenceavoidanceincontrasttoCDMA.ThisistruesinceinOFDMthetransmittedsubcarriersaretheeigenfunctionsofthechannelincontrasttothecodesinWCDMA.SoafterchanneltransmissioninOFDMtheorthogonalityoftheindividualusersignals（subcarriers）ispreserved.Thisappliesalsototheinterferingsignals.

ThisoffersthepossibilityinOFDMtopredictandavoidinterferencetoimprovethesituationatthecellborder.Forthatitissensibletousefrequencypatternsthatareallocated（ornot）tousersintheborderregion.ThedecisionontheUEsituationistherebysupportedbypilotmeasurementsreportsfromtheUE.

ThusInterferenceCoordinationinanOFDMfrequencyre-use1systemcanbedonewithorwithoutadaptivepatterncoordinationbetweentheNodeBs.Aschemewithadaptivecoordinationismoreflexible（itinvolvesanegotiationinthecoordinationsimilartoCDMAsoft-handoverand,thus,morecontroleffort）,whileaschemewithoutadaptivecoordinationrequiressomeamountofnetworkplanning.

4.ProposalforOFDM–InterferenceCoordination

Toexemplifytheproposalstheyareexplainedforspecificapproaches.

4.1.Pilotpatterndistribution

Toallowchannelestimationinthecelloverlappingregionoftwocells,pilotsubcarriersmustnotbedisturbedbyneighborcell（dataorpilot）subcarriers.Soitisassumedthatpilotsubcarriershavehigherenergythandatasubcarriersandthatpilotpatternsindifferentcellsaredifferent.Thisalsoallowstheidentificationofthecells.

4.2.Usertrafficpatterns

InasynchronousneighborNode-Bstimeisnotadimensionwithwhichinterferencecanbeavoided.ButinOFDMthefrequencydimensionremainsasresourceforinterferenceavoidance.

SincesynchronizedNode-BscannotbeassumedintheUTRANweproposefrequencypatternsfortheusertrafficmultiplexing.Sothetime-frequencyplaneisdividedinto（regular）frequencypatterns.Thesefrequencypatternscanbeconstructedtobecompatiblewiththepilots.WiththesepatternsinterferenceavoidancecannowbedonewhilesynchronizationfortheNode-Bsisnotrequired.ThesepatternsareschematicallydepictedinFigure1.

Figure1:

ProposedfrequencypatternforasynchronousNode-Bs

EachsuchpatterncorrespondstooneOFDMunitof480QAMsymbols.WefurtherdetailitfortheSet2ofphysicalparametersfromthepreviousstudyitem[1].Itconsistsof11times4=44subcarrierswherethespreadingover11blockstakescarethatthefrequencydiversityissufficientlyexploited,furtheritalsocontainsplaceholderstoputpilotcarriersin.Thisallows16ofthesefrequencypatterninanOFDMsymbolforSet2since16x44=704subcarriers.

Thesefrequencypatterns（FP）arenowmanagedbytheRadioResourceManagement（RRM）.SotheFPsareassignedtotheUEsbytheNodeBscheduler.

Twopracticalstrategieshowinterferencecanbeavoidedarenowillustrated.

4.3.Interferencecoordinationstrategy1（Networkpowerplanning）

Forthatineachcellsomefrequencypatternscanonlybeusedwithreducedpower.Sothenumberoffrequencypatternsispartitionedin

subsets

andthenalwaysadifferentsubset

hasreducedpowerineachcellaccordingtoanetworkplanning.Soincell

thepowerofthesubset

correspondingtothecellnumberislimited.Forexample,thenumberofsubsetscanbe

or

.Thesubset

isnowusedbyterminalsinneighborcellsapproaching

fromtheoutside.InFigure2forsimplifieddenotationthecell

isjustmarked

.SoforexampleinFigure2ifaterminalapproachestheborderregiontoanothercellsay

itgetsallocatedfrequencypatternsfromsubset

wherethisothercellcannotdisturbmuchduetoitspowerlimitationin

.Forexampleifterminal

approachescell

asdepictedbythegreenarrowitgetsallocatedfrequencypatternsfromsubset

.

Figure2:

SectorizedcellpatternandsubsetFnallocationtoterminalsinborderregion.Forsimplicitythecell

isdenotedjust

Soallterminalsapproachingcell

fromtheoutsidegetallocatedfrequencyblock

bytheirrespectiveservingbasestationaslongastheyareintheborderregionandbeforeahandoverhastotakeplace（thisismarkedbyrednumbers1intheFigure）.

Aspartofthetechniquethisflexibleallocationisrealizedbyterminalsthatreportbacktotheirservingbasestationwhichotherbasestationsarestronglyreceivedandwhichisthestrongest.Thisisknownfromclassicalhandoveralgorithmsanddoesnotrequireadditionalsignallingtobeintroduced.Itisjustnecessarythatthebasestationnumberidentifiestheinhibitedfrequencysubset.Theterminalisthenscheduledontheinhibitedsubsetofthatstrongestinterferingbasestation.

AscanbeseenfromFigure2ifonemarksthestripsatcellborderstotheothercellsalsowiththeallocatedfrequencyblocknumberintheborderregioninsidecell

sixsubsets（2to7）areused.Soasaresultherein6/9ofthespectrumtheinterferenceisreducedsothattheSIRisstronglyimproved.ThisyieldshigherthroughputandimprovedQoS.ItallowsservingoftheUEevenifitentersfurtherintheneighborcellorifitexperiencesfurtherworsenedradioconditions.

4.4.Interferencecoordinationstrategy2（Ondemandbasis）

Anotherstrategyisexplainedandproposedthatdoesnotneedanetworkplanningtodealwithterminalsapproachingthecellboundary.

Iftheterminal

asdepictedinFigure3approachesthecellboundarybetween

and

（asindicatedbythegreenarrow）andsensestheinterferencefrom

itreportsthisbacktoitsservingNode-B

.Basedonthisinformation（andmaybeothercriterionssuchasload）bycooperationandcoordinationbetweentheinvolvedNode-Bsasetoffrequencypatterns（resource）getsapowerrestrictioninbasestation

’scellandisgrantedtobasestation

.SotheblackarrowinFigure3meansthataresourcefrom

istakenandassignedto

.

Figure3:

TerminalT1servedbybasestationB1andapproachingbasestationB2.AresourcefromB2isassignedtoB1