阿尔卡特LTE频率规划方案Word格式.docx
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阿尔卡特LTE频率规划方案Word格式.docx
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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
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