DS-CDMA中基于MMSE相关器的RAKE接收机-豆柴文库

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DS-CDMA中基于MMSE相关器的RAKE接收机
Introduction
DirectSequenceCodeDivisionMultipleAccess(DS-CDMA)isawidelyusedmultipleaccesstechniqueinmodernwirelesscommunicationsduetoitsabilitytosupportmultipleusersonthesamechannelwithoutinterference.DS-CDMArequiresthereceivertoperformmultipletaskssuchasdetectionofthedesiredsignal,interferencereduction,andchannelestimation.
TheRAKEreceiverisapopularreceiverstructureusedinDS-CDMAsystems.Itusesmultipleantennastocombinethereceivedsignalandreducestheeffectsofmultipathfading.TheRAKEreceiverisbasedonmaximalratiocombining(MRC)andcombinessignalsfrommultiplepathstoincreasethesignal-to-noiseratio(SNR)ofthereceivedsignal.However,interferencefromotheruserscansignificantlyaffecttheperformanceoftheRAKEreceiver.Tomitigatethisinterference,amulti-userreceiverbasedontheminimummeansquareerror(MMSE)criterioncanbeemployed.
Inthispaper,wewilldiscusstheMMSE-basedRAKEreceiverinDS-CDMAsystems.Thestructureofthereceiver,itsworkingmechanism,andthebenefitsofusinganMMSE-basedRAKEreceiverwillbehighlighted.
RAKEReceiverStructure
TheRAKEreceiverstructureinaDS-CDMAsystemconsistsofmultipleantennas,eachofwhichreceivesacopyofthetransmittedsignal.ThesesignalsarethencombinedusingMRCtoimprovetheSNRofthereceivedsignal.MRCisatypeofbeamformingthatmaximizesthepowerofthedesiredsignalwhileattenuatingthenoiseandinterferencefromotherusers.
TheRAKEreceiverseparatesthecombinedsignalintoseparatepathsbasedonthetimedelaysofthereceivedsignal.Eachpathcorrespondstoadifferentsignalcomponentthathasundergoneadifferentpathandattenuation.Thesepathsarethenmultipliedbytheirrespectivedelayprofilestoalignthesignalsintime.Finally,thesignalsarecombinedusinganaddertoformtheoutputsignal.
AlthoughtheRAKEreceivercanmitigatemultipathfading,itisstillsusceptibletointerferencefromotherusers.Theseuserstransmittheirsignalsatthesamefrequencyandtimeslotsasthedesireduser,causinginterference.Toaddressthisissue,anMMSE-basedRAKEreceivercanbeemployed.
MMSE-BasedRAKEReceiver
TheMMSE-basedRAKEreceiverusestheMMSEcriteriontoi