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1、ZHOULAYOUT2/21/081:33PMPage38TOPICSINRADIOCOMMUNICATIONSOFCDM:APromisingBroadbandWirelessAccessTechniqueYiqingZhouandTung-SangNg,UniversityofHongKongJiangzhouWang,UniversityofKentKenichiHiguchiandMamoruSawahashi,NTTDoCoMoABSTRACTFuturemobilecommunicationsystemsaimtoprovideextremelyhig
2、h-speeddatatransmission,especiallyinthedownlink.Thebroadbandorthogonalfrequency-andcode-divisionmulti-plexingsystemwithtwo-dimensionalspreading(timeandfrequencydomainspreading)is)'0.0282Tc0.0217Tw(becomingaverypromisingtechniqueforhigh-)'0.0067Tc0.0433Tw(speedwirelesscommunicationsdue
3、toitsadvan)'20.870310TD0Tc(-tagesoverOFDM.ThisarticlepresentsthebasicstructureandmainfunctionsoftheOFCDMsystem.Anonsequentialcodeassignmentschemeisintroduced.ThenoveldetectionmethodfortheOFCDM,calledhybridmulti-codeinterferencecancellationandminimummeansquareerrordetection,isdescribed
4、.TheapplicationofadvancedtechniquestotheOFCDM,suchasturbocodingandMIMO,isalsodiscussed.ItisshowninthisarticlethatOFCDMissuperiortoOFDM.INTRODUCTIONTheeraofhigh-speeddatatransmissioninmobilecommunicationsisapproachingrapidly.Widebandcode-divisionmultipleaccess(WCDMA),oneofthethird-gene
5、ration(3G))'0.0466Tc0.0033Tw(wirelessnetworks,waslaunchedfirstbyNTT)'0.0034Tc0.0466Tw(DoCoMo,Japan,in2001.Withabandwidthof5)'T*0.024Tc0.026Tw(MHz,aWCDMAsystemcanprovidemultime-diaserviceswithdataratesupto2Mb/s.Inaddition,high-speeddownlinkpacketaccess(HSDPA)hasbeenintroducedintheWCDMA
6、)'0.0454Tc0.0045Tw(systembyusingadvancedtechniques,suchas)'0.0688Tc-0.0187Tw(adaptivemodulationandcodingandhybrid)'0.0284Tc0.0215Tw(automaticrepeatrequest(ARQ),andthedata)'0.0038Tc0.0462Tw(ratecanbeincreasedto14Mb/s.Withhighdata)'0.0254Tc0.0245Tw(rates,subscribersoftheWCDMAnetworkcan)
7、'0.0518Tc-0.0018Tw(getrichermultimediaservices.However,the)'0.0024Tc0.0475Tw(dataraterequirementincreasesdramaticallydue)'0.0269Tc0.023Tw(todemandforhigh-speedmultimediaservices.)'0.057Tc-0.007Tw(Inthe2010s,theexpectedwirelessdatarate)'0.0029Tc0.0471Tw(couldbeuptoseveralgigabitspersec
8、ond,w
