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1、[DavidGesbert,MariosKountouris,RobertW.HeathJr.,Chan-ByoungChae,andThomasSälzer]©DIGITALVISIONShiftingtheMIMOParadigmhelasttenyearshavewitnessedthetransitionofmultiple-inputmulti-ple-output(MIMO)communicationfromatheoreticalconcepttoapracticaltechniqueforenhancingperformanceofwireless
2、networks[1].Point-to-point(single-user)MIMOcommunicationpromiseslargeTgainsforbothchannelcapacityandreliability,essentiallyviatheuseofspace-timecodes(diversitygainoriented)combinedwithstreammultiplexedtransmission(ratemaximizationoriented).Insuchatraditionalsingle-userviewofMIMOsystem
3、s,theextraspatialdegreesoffreedom(DoF)broughtbytheuseof[multipleantennasareexploitedtoexpandthedimensionsavailableforsignalpro-Fromsingle-usercessinganddetection,thusactingmainlyasaphysical(PHY)layerperformancebooster.Inthisapproach,thelinklayerprotocolsformultipleaccess(uplinkandtomu
4、ltiuserdownlink)indirectlyreaptheperformancebenefitsofMIMOantennasintheformofgreaterper-userratesormorereliablechannelqualitydespitenotrequiringfullcommunications]awarenessoftheMIMOcapability.ThesituationwithmultiuserMIMO(MU-MIMO)techniquesisradicallydiffer-entasthesetechniquesimplyth
5、euseofspatialsharingofthechannelbytheusers,thusdeeplyaffectingthedesignofthemultipleaccessprotocol.Inspatialmultipleaccess,theresultingmultiuserinterferenceishandledbythemultipleantennas,which,inadditiontoprovidingper-linkdiversity,alsogivetheDoFnec-essaryforspatialseparationoftheuser
6、s(seee.g.[1]PartIV).Inpractice,MU-MIMOschemeswithgoodcomplexity/performancetradeoffscanbeimplementedtorealizetheseideas.Ontheuplinkormultipleaccesschannel(MAC),thedevel-opmentofMU-MIMOtechniquesappearsasageneralizationofknownsingle-userDigitalObjectIdentifier10.1109/MSP.2007.904815IEE
7、ESIGNALPROCESSINGMAGAZINE[36]SEPTEMBER20071053-5888/07/$25.00©2007IEEEMIMO(SU-MIMO)conceptstothemultiusercase.Asusualinlinearapproaches.Examplesofthelatterarevectorperturba-informationtheory,thedownlinkorbroadcastchannel(BC)tion,DPCtechniques,andTomlinson-Harashimaprecodingcaseisbyfar
8、themo