LTE MIMO 模式的學(xué)習(xí)理解1

/MIMO學(xué)習(xí)心得EllenwangLTE的7個傳輸模式中6個分別應(yīng)用了四種MIMO技術(shù)方案：傳輸分集（TD），波束賦型（Beamforming），空間復(fù)用（SM），多用戶MIMO（MU-MIMO）：為普通單天線傳輸模式。TransmitDiversity模式：分2發(fā)送天線的SFBC，和4發(fā)送天線的SFBC+FSTD兩種方案。

2發(fā)送天線的SFBC:SFBC是由STBC（SpaceTimeBlockCode）演變而來，由于OFDM一個slot的符號數(shù)為奇數(shù)，因此不適于使用STBC，但頻域資源是以RB=12個子載波來分配的，因此可以用連續(xù)兩個子載波來代替連續(xù)兩個時域符號，從而組成SFBC。而當(dāng)使用4發(fā)送天線時，SFBC+FSTD（FrequencySwitchedTransmitDiversity）被采用。SM-openloop，UE僅僅反饋信道的RI（RankIndicator）。此時基站會使用CDD（CycleDelayDiversity）技術(shù)。SM-closeloop，UE根據(jù)信道估計(jì)的結(jié)果反饋合適的PMI（PrecodingMatrixIndicator）。(如利用系統(tǒng)容量最大計(jì)算合適的PMI)MU-MIMO，該方案將相同的時頻資源通過空分，分配給不同的用戶。closelooprank1——SMorBF，UE反饋信道信息使得基站選擇合適的Precoding。UESpecialRS——BF，和BeamForming的前一種方式不同，這種方式無需UE反饋信道信息，而是基站通過上行信號進(jìn)行方向估計(jì)，并在下行信號中插入U(xiǎn)ESpecialRS?；究梢宰孶E匯報(bào)UESpecialRS估計(jì)出的CQI?？臻g復(fù)用是為了提高傳輸數(shù)據(jù)數(shù)量，基于多碼字的同時傳輸，即多個相互獨(dú)立的數(shù)據(jù)流通過映射到不同的層，再由不同的天線發(fā)送出去。碼字?jǐn)?shù)量與天線數(shù)量未必一致。（當(dāng)然天線數(shù)量>＝碼字?jǐn)?shù)量）。傳輸分集主要用于提高信號傳輸?shù)目煽啃裕绮捎每諘r編碼（STC）、循環(huán)延時分集（CDD)與天線切換分集等，LTE中用的比較多的是SFBC編碼。傳輸分集（TM2）用來提高信號傳輸?shù)目煽啃?，主要是針對小區(qū)邊緣用戶，TM3，TM4主要是針對小區(qū)中央的用戶，提高峰值速率。MU-MIMO是為了提高吞吐量，用于小區(qū)中的業(yè)務(wù)密集區(qū)。TM6，TM7是用于增強(qiáng)小區(qū)覆蓋，也是用于邊緣用戶。不過6是針對FDD，7是針對TDD而已。 在學(xué)習(xí)理解MIMO之前，需要理解幾個基本概念：codeword:相當(dāng)于TranportBlock,即物理層需要傳輸?shù)脑紨?shù)據(jù)塊.LTE可支持在同一塊資源同時傳輸2個相對獨(dú)立的codeword，這是通過空間復(fù)用（SM）技術(shù)實(shí)現(xiàn)的。layer：數(shù)據(jù)被分為不同layer進(jìn)行傳輸，layer總數(shù)<=天線個數(shù)。和信道矩陣的rank是對應(yīng)的。相當(dāng)于空分的維度。rank：相當(dāng)于總的layer數(shù)。atennaport：其實(shí)并不等同于天線個數(shù)，而是相當(dāng)于不同的信道估計(jì)參考信號pattern。對端口0~3，確實(shí)對應(yīng)多天線時，RS的發(fā)送pattern；對于端口4，對應(yīng)于PMCH，MBSFN情況的RS；對于端口5，對應(yīng)于UESpecialRS。TDD-LTE中支持的傳輸模式使用的DCIformat。在每一種模式中都可以通過改變DCIformat切換到發(fā)射分集模式（TM2），并且TM3、TM4模式下，也支持在不改變DCIformat的情況下從空分復(fù)用切換到發(fā)射分集模式（TM2），這時需要通過在DCIformat中的precodinginformationfield來指示所使用的precodingmatrixvector。From36.213Table7.1-5Table7.1-5:PDCCHandPDSCHconfiguredbyC-RNTIMode2DCIformat1ACommonandUEspecificbyC-RNTITransmitdiversity(seesubclause7.1.2)DCIformat1UEspecificbyC-RNTITransmitdiversity(seesubclause7.1.2)Mode3DCIformat1ACommonandUEspecificbyC-RNTITransmitdiversity(seesubclause7.1.2)DCIformat2AUEspecificbyC-RNTILargedelayCDD(seesubclause7.1.3)orTransmitdiversity(seesubclause7.1.2)Mode4DCIformat1ACommonandUEspecificbyC-RNTITransmitdiversity(seesubclause7.1.2)DCIformat2UEspecificbyC-RNTIClosed-loopspatialmultiplexing(seesubclause7.1.4)orTransmitdiversity(seesubclause7.1.2)Mode7DCIformat1ACommonandUEspecificbyC-RNTIIfthenumberofPBCHantennaportsisone,Single-antennaport,port0isused(seesubclause7.1.1),otherwiseTransmitdiversity(seesubclause7.1.2)DCIformat1UEspecificbyC-RNTISingle-antennaport;port5(seesubclause7.1.1)PDSCHprocessflow:LayermappingNowcodeword-to-layermappingsupport3types:Layermappingfortransmissiononasingleantennaport1codeword-to-1layerLayermappingforspatialmultiplexing2antennaports:1codeword-to-1layer2codewords-to-2layers4antennaports:1codeword-to-1layer1codeword-to-2layers2codewords-to-2layers2codewords-to-3layers2codewords-to-4layersTable6.3.3.2-1:Codeword-to-layermappingforspatialmultiplexing.NumberoflayersNumberofcodewordsCodeword-to-layermapping1122213242Layermappingfortransmitdiversity1codeword-to-2layers(2antennaports)1codeword-to-4layers(4antennaports)Table6.3.3.3-1:Codeword-to-layermappingfortransmitdiversity.NumberoflayersNumberofcodewordsCodeword-to-layermapping2141IftwonullsymbolsshallbeappendedtoPrecondingNowprecodingsupport3types:PrecodingfortransmissiononasingleantennaportPrecodingfortransmitdiversityPrecodingwithoutCDDClosed-loopspatialmultiplexingscheme(TM4)PrecodingforlargedelayCDDLargedelayCDDscheme(TM3)andcangetfrombelowtableaccordingtodifferentlayerTable6.3.4.2.2-1:Large-delaycyclicdelaydiversity.Numberoflayers234Forcanselectedfromcodebookdefinedin36.211Table6.3.4.2.3-1.Table6.3.4.2.3-1:Codebookfortransmissiononantennaports.CodebookindexNumberoflayers120123-PMIUEwillreportthesuggestedcodebookindexbyPMIandeNBwillsendthecodebookinfowhicheNBwilluseforPDSCHbyDCI.Fordifferenttransmissionmode,thePMIwillusedifferentnumberofbits.Table7.2-1b:Numberofbitsincodebooksubsetrestrictionbitmapforapplicabletransmissionmodes.Numberofbits2antennaports4antennaportsTransmissionmode324Transmissionmode4664Transmissionmode5416Transmissionmode6416Transmissionmode8632Transmissionmode3: PMIwilluse2bitsFor2antennaports:means2layerscodebookindex0means1layercodebookindex0meanstransmitdiversityTransmissionmode4:PMIwilluse6bitsFor2antennaports,definedin36.211Table7.2-1c:means1layercodebookindex0means1layercodebookindex1means1layercodebookindex2means1layercodebookindex3means2layerscodebookindex1means2layerscodebookindex2Table7.2-1c:AssociationofbitsincodebookSubSetRestrictionbitmaptoprecodersinthe2antennaportcodebookofTable6.3.4.2.3-1in[3].CodebookindexNumberoflayers120a0-1a1a42a2a53a3-PrecodinginfoinDCIeNBwillsendtheprecodinginfoinDCIformat2/2A.Transmissionmode3:DCIformat2A:Precodinginformation–numberofbitsasspecifiedinTable5.3.3.1.5A-1Forantennaports2,theprecodinginformationfieldisnotpresent.Table5.3.3.1.5A-1:Numberofbitsforprecodinginformation.NumberofantennaportsateNodeBNumberofbitsforprecodinginformation2042Thenumberoftransmissionlayersisequalto2ifbothcodewordsareenabled;transmitdiversityisusedifcodeword0isenabledwhilecodeword1isdisabled.ButthePDCCHformatwilluseDCIformat2Anomatterspatialmultiplexingortransmitdiversity.Transmissionmode4:DCIformat2:Precodinginformation–numberofbitsasspecifiedinTable5.3.3.1.5-3(36.212)Table5.3.3.1.5-3:Numberofbitsforprecodinginformation.NumberofantennaportsateNodeBNumberofbitsforprecodinginformation2346 Forantennaports2,thereare3bitsforprecodinginformation,detailinfoseebelowtable: Precodinginfobitfieldmappedtoindex: For2layers:Precodinginfocodebookindex 00means2layers–precodingmatrix 11means2layers–precodingmatrix 2Xmeans2layers–precodingmatrixusedthelatestPMIreportonPUSCH,usingtheprecoder(s)indicatedbythereportedPMI(s) For1layer:Precodinginfocodebookindex 00means2layers:Transmitdiversity 11means1layer–precodingmatrix 22means1layer–precodingmatrix 33means1layer–precodingmatrix 44means1layer–precodingmatrix 5Xmeans1layer–precodingmatrixwillusethelatestPMIreportonPUSCH,usingtheprecoder(s)indicatedbythereportedPMI(s),ifRI=2wasreported,using1stcolumnmultipliedbyofallprecodersimpliedbythereportedPMI(s) 6Xmeans1layer–precodingmatrixwillusethelatestPMIreportonPUSCH,usingtheprecoder(s)indicatedbythereportedPMI(s),ifRI=2wasreported,using2ndcolumnmultipliedbyofallprecodersimpliedbythereportedPMI(s)36.212Table5.3.3.1.5-4:Contentofprecodinginformationfieldfor2antennaports.Onecodeword:Codeword0enabled,Codeword1disabledTwocodewords:Codeword0enabled,Codeword1enabledBitfieldmappedtoindexMessageBitfieldmappedtoindexMessage02layers:Transmitdiversity02layers:Precodingcorrespondingtoprecodermatrix11layer:Precodingcorrespondingtoprecodingvector12layers:Precodingcorrespondingtoprecodermatrix21layer:Precodingcorrespondingtoprecodervector22layers:PrecodingaccordingtothelatestPMIreportonPUSCH,usingtheprecoder(s)indicatedbythereportedPMI(s)31layer:Precodingcorrespondingtoprecodervector3reserved41layer:Precodingcorrespondingtoprecodervector4reserved51layer:PrecodingaccordingtothelatestPMIreportonPUSCH,usingtheprecoder(s)indicatedbythereportedPMI(s),ifRI=2wasreported,using1stcolumnmultipliedbyofallprecodersimpliedbythereportedPMI(s)5reservedTM7mode:Fortransmissionmode7,cansupportoneportandtwoports.NumAntennaPort=1tansmissionMode=TM7DCI1-port5beamformingCell-RSport0D-RSport5/////////////////////////////////////////////////////////////////////////////////////////////////////////NumAntennaPort=2tansmissionMode=TM7DCI1-port5BeamformingCell-RSport0,port1D-RSport5/////////////////////////////////////////////////////////////////////////////////////////////////////////Forbeamforming,thePDSCHwilluseport5,andnomaterRRUhas2or4or8physicalantenna,Basebandwillsendthesamesignalinallthesephysicalantennas,justeveryantenna