多用户OFDM系统子载波分配算法研究-豆柴文库

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多用户OFDM系统子载波分配算法研究
Introduction
Withtheadvancementofwirelesscommunicationtechnology,multi-userOFDMsystemshavebecomeincreasinglypopular.Oneofthekeychallengesinsuchsystemsisefficientsubcarrierallocationfromasharedpoolofsubcarrierstodifferentusers.Inthispaper,wewillinvestigatevarioussubcarrierallocationalgorithmsformulti-userOFDMsystems.
OverviewandAdvantagesofOFDM
Orthogonalfrequency-divisionmultiplexing(OFDM)isapopularmodulationtechniquethatdividesadatastreamintoseveralparalleldatastreamsandtransmitsthemsimultaneouslyovermultiplesubcarriers.Thedataratecanbeincreasedbyshiftingthesubcarriersclosertogetherandincreasingthenumberofsubcarriersinuse.OFDMhasseveraladvantagesovertraditionalmodulationschemessuchasimprovedspectralefficiency,robustnessagainstmulti-pathfading,andincreasedresistancetointerference.
SubcarrierAllocationMethods
Thereareseveralapproachestoallocatingsubcarriersinmulti-userOFDMsystems,whichcanbebroadlyclassifiedintotwocategories:fixedanddynamicallocation.
FixedAllocation
Thefixedallocationmethodassignsafixedsetofsubcarrierstoeachuser.Thismeansthatthesubcarrierallocationispredeterminedanddoesnotchangeovertime.Thisapproachhastheadvantageofbeingsimpleandeasytoimplement.However,itmayleadtosuboptimalperformanceasthesubcarrierdistributionisnotoptimizedbasedonthechangingchannelconditions.
DynamicAllocation
Thedynamicallocationmethodassignssubcarriersbasedonthechangingchannelconditionsandthequalityofservice(QoS)requirementsofeachuser.Thisapproachmakesuseofchannelestimationandfeedbackmechanismstoallocatesubcarriers.Adynamicallocationalgorithmoffersbetterperformancecomparedtothefixedallocationmethodasthesystemadaptstothechangingconditions.However,dynamicallocationrequiresmoresystemresources,whichmaybeadrawbackinsomecases.
SubcarrierAllocationStrategies
Severalsubcarrierallocationstrategieshavebeenproposedformulti-userOFDMsystems.Inthissection,wewilldiscusssomeofthemostcommonapproaches.
1.ProportionalFair(PF)Allocation
TheProportionalFair(PF)allocationalgorithmaim