Fundamentals_Wireless_Communication_chapter8

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1、CHAPTER8MIMOII:capacityandmultiplexingarchitecturesInthischapter,wewilllookatthecapacityofMIMOfadingchannelsanddiscusstransceiverarchitecturesthatextractthepromisedmultiplexinggainsfromthechannel.Weparticularlyfocusonthescenariowhenthetransmitterdoesnotknowthechannelrealiza

2、tion.InthefastfadingMIMOchannel,weshowthefollowing:•AthighSNR,thecapacityofthei.i.d.RayleighfastfadingchannelscaleslikenminlogSNRbits/s/Hz,wherenministheminimumofthenumberoftransmitantennasntandthenumberofreceiveantennasnr.Thisisadegree-of-freedomgain.•AtlowSNR,thecapacityi

3、sapproximatelynrSNRlog2ebits/s/Hz.Thisisareceivebeamformingpowergain.•AtallSNR,thecapacityscaleslinearlywithn.Thisisduetoacombi-minnationofapowergainandadegree-of-freedomgain.Furthermore,thereisatransmitbeamforminggaintogetherwithanoppor-tunisticcommunicationgainifthetransm

4、ittercantrackthechannelaswell.Overadeterministictime-invariantMIMOchannel,thecapacity-achievingtransceiverarchitectureissimple(cf.Section7.1.1):independentdatastreamsaremultiplexedinanappropriatecoordinatesystem(cf.Figure7.2).Thereceivertransformsthereceivedvectorintoanothe

5、rappropriatecoordinatesystemtoseparatelydecodethedifferentdatastreams.Withoutknowledgeofthechannelatthetransmitterthechoiceofthecoordinatesysteminwhichtheindependentdatastreamsaremultiplexedhastobefixedapriori.Inconjunctionwithjointdecoding,wewillseethatthistransmitterarchi

6、tectureachievesthecapacityofthefastfadingchannel.ThisarchitectureisalsocalledV-BLAST1intheliterature.1VerticalBellLabsSpace-TimeArchitecture.ThereareseveralversionsofV-BLASTwithdifferentreceiverstructuresbuttheyallsharethesametransmittingarchitectureofmultiplexingindependen

7、tstreams,andwetakethisasitsdefiningfeature.3323338.1TheV-BLASTarchitectureInSection8.3,wediscussreceiverarchitecturesthataresimplerthanjointMLdecodingoftheindependentstreams.Whilethereareseveralreceiverarchitecturesthatcansupportthefulldegreesoffreedomofthechannel,apar-ticu

8、lararchitecture,theMMSE-SIC,whichusesacombinationofminimummeansquareestimation(MMS