blind channel estimation in mimoofdmsystems without guard intervaland virtual carriers

1、blind Channel Estimation in MIMO-OFDM Systems without Guard Interval and Virtual CarriersChineseJournalofElectronicsSemiblindChannelEstimationinMIMooFDMSystemswithoutandVirtualGuardIntervalCarriers术zuoZhidongandZHANGHailintTheNationalKeyLaboratoryonISN,XidianUniversity,Xian710071,ChinaAbstractfreque

2、ncydivisionmultiplexing(MIMOoFDM,systemsusemultipleantennasbothatthetransmitterandthere-videhighdatarate,butcoherentsignaldetectionrequiresreliableestimationofchannelimpulseresPonsesbetweenbasedonthenoisesubspacemethodforthechannelestigorithmisdifrerentwiththereportedsubspacemethods.istotakeadvantag

3、eofthesignalredundancyofreceiverdiversityandnoisespacecharacteristicsandmakeitpossibletoaccomplishtheestimationwithoutusingcyclicprefixtion.ForMIMo.oFDMsystemswithCyclicprefix(CP)orVirtualcarriers(VCs),theproposedmethodprovidesadditionalperformancegaintotheexistingblindchannelareprovidedtoillustrate

4、theefiectivenessoftheproposedmethod.KeywordsMultipleinputmultipleoutput,Orthog-onalfrequencydivisionmultiplexing,Channelestimation,Subspace,Cyclicprefix,Virtualcarriers.Multipleinputmultipleoutput?-orthogonalfrequencydivi-?sionmultiplexing(MIM00FDM)systemsusemultipleanten-nasbothatthetransmitterandt

5、hereceiver,whichhavere-centlybeenshowntoincreasethechannelcapacityandprovidehighdatarate,anddrawnmuchattentionforfuturewirelessnaldetectionrequiresreliableestimationofchannelimpulserecanbeestimatedbysendingatrainingsequence.However,estimatingMIMOchannelscanrequireasignificantamountoftrainingsequence

6、,andtrainingsequencesconsumeband-widthandthusincurspectralefficiencylossesespeciallyinrapidlyvaryingenvironments.Furthermore,trainingmethodschannelestimationforMIMOOFDMsystemshasbeenaveryposedanalgorithmforblindchannelestimationandequaliza-tionusingsecond-ordercyclostationarystatisticsinducedbyemplo

7、yingaperiodicnonconstantmodulusantennaprecoding.timationinMIM00FDMsystemsbyextendingthemethodproposedinandexploitingthecyclostationarityofMIM0.posedasubspacebasedblindchannelestimat,ionmethodusingposedasubspaceblindchannelestimatorforOFDMsystemstoOFDMsystemswithorwithoutCyclicprefixfCP).Thesubcarrie

8、rsthataresett0zerowithoutanyinformationarereferredtoasVirtualcarriersfVCs).CPorVCscanbeusedusefulresourceofthechannelutilization.0FDMchannelswithoutthepresenceofthevirtualcarriersandcyclicpre-channelestimationbyusingthereceiverdiversity,undertheconditionsthatsystemsareunderidealsynchronizationandtic

9、ular,theproposedmethodisdependentonthesubspacemethodtoMIMO一0FDMsystemsbutisdifferentwiththepliedforMIM0ingwhereblindestimationtechniquesbasedonCPcannotbeemployedandblindestimationtechniquesbasedonVCscan-notbeemployed,thereby,providesthesystemswiththep0-tentialtoachievereallyhigherchannelutilization.

10、ForMIM0.ridesadditionalperformancegaintotheexistingblindchannelestimationmethods.andVCs.InSectionIII,wedeveloptheblindchannelestima-IVcontainssimulationresultsdemonstratingtheperformanceoftheproposedalgorithm.Finally,conclusionisprovidedinSectionV.Inthissection,webrieflydescribeawirelesssystemconsid

11、eredinthispaper,wheretheMIMOOFDMtransceiver.ManuscriptReceivedNov.2005;AcceptedMar.2006.Semi-blindChannelEstimationinMIMO-OFDMSystemswithoutGuaxdIntervalandVirtualCarriers191AsthebasebandmodelforeachOFDMmodulatorwecon-siderthemodelthathasKsubcaxriersandusesthesub-carriersnumbered0toK一1fortheuserdata

12、.Thus,thereaxenoVirtualcarriersfVCs).Attransmissiontimen,thecomplexbasebanddatablockcanbewrittenasln,l,正h,叫:=0,一1&i=1,2,MT,whereMTmeansthenumberoftransmitantennas,K,andiarethenumberofsub-channelsoftheOFDMsystems,subchannel(ordefine:Tin,叫=(nn,叫,TM,叫),=0,一1Tn=(Tin,0】T,Tin,K一1】T)T,n=0,1,2,Assum

13、ingthelengthofcyclicprefixis0.andeach0FEMmodulatorhasnoVCsinsertedtothedatablock,itappliesaK.pointInversefastFouriertransformfIFFT)tothedatablock.anddoesn'tinsertCPinfrontoftheIFFToutputvec-tor.Then,MTtransmitaennassimultaneouslytransmittheseOFDMblockswithoutCP.b【nandVCs(Up/downconvertandntennas

14、etc.&ren'tshown)Toestimatethechannels,thereceiverscollectblocksofn,叫,whicharethereceivesignals.Letusdefine:Rn,叫=(R1n,叫,Rn】=(Rn,0】,RMRIn,叫)T,Rn,K一1】)T,=0,K一1n=0,1,2,WhenitissatisfiedforMR>MTandthechannelcoemcientsithasfullcolumnrankandhenceHisalsofullcolumnranksinceanymatrixpre-mul

15、tiplicationcanonlyreducetherank.W_eestablishasumcientconditionforchannelstobeidentifi.ableanddevelopanoisesubspacealgorithmforblindchannelestimationinMIMO.OFDMsystemswithreceiverdiversity.BasedontheMIMOOFDMsystemswhichareunderidealsynchronizationandreceivedatablocksareindependentwitheachother,letusd

16、enotethesourcedatabefore0FDMmod-ulationasTin】=(Tin,0】T,n,K一1T)TConsiderthefrequency-selectivechannelsbetweenMTtransmitantennasandMRreceiveantennasmodeledasMTMRindependentFIRfiltersandassumethatListheup-/thcOemcientmatrixofthechannelsash1】=(1)where,Jn,fdenotestheimpulseresponseofthechannelfromthei-th

17、transmitantennatotheJ-threceiveantenna.Thechannelimpulseresponsematrixisdefinedasrh(L)h(O)00Hn】:l?.o0I(2)】=1.1()I:'?''lL00h(L)h(O)JThematrixshouldbefuUcolumnrankforthechanneltobeRn】=Fhntion(Hn,Tin,n】)(3)whereTin,Nn】andRn】arethetransmitdatavectors,usdenote,RNb】=(冗】T(LMT:MRK),冗+1】T,?一,Rn+N

18、b1Tf1:MRKLMT)TTbn】=(IFFTTnT),IFFTTn+Nb一1T)4)ThereceiveddatablockscanbewrittenasRNbn】=HnTybn】+NNbn】=XNb+NNbn】(5)WheretheAdditivewhiteGaussiannoise(AWGN)vectorNbhasthecovaxiancematrix52IandNbisthenumberofdatablocks.WegettheSingularvaluedecomposition(SVD)ofRNbn】,R=?.VH=Us,Un?.v纠g+Us,Un?.纠Usisspannedbyt

19、hesignalsubspace,andUnisspannedbythenoisesubspace.When(MRMT)KMRMTL,Ufi】.U.=0(7)So,(厂Xm=0(8)Vfi】.Hn】=0(9)Then,Ufi】.Hn】=hn】.U,i=1,(MRMT)K(1o)Letusdefine=U.,i=1,(11)where=(MRMT)KSo司.日n=0_÷hn】.i:0=妻1.Il一,一+呈缈目奶192ChineseJournalofElectronics2007.HnJJ=.日fnJ.HHIn.:元n.i.元Hn矗nJargmin<盂竹】.元HfnJ:ar

20、gminh竹】.矗日竹】)vectorsofthechannelimpulseresponses,theutilizationof(12)chP.;stratethepotentialoftheproposedmethodwithregardto(13)b.thchannelestimati.nauccuraucyandchannelutilizati.n?Therefore,theestimatorshl'softhechannelresponsevectorsgiveninEq.(12)areassociatedwiththe竹】eigenvectorscorrespondingt

21、othesmallesteigenvaluesofthematrixNglgiveninEq.(11).nnJ:-】,hM.】?(14)whereQisa1constantambiguityvectorInthissection,wedemonstratetheperformanceoftheproposedalgorithmwithcomparisontoanotherchannelesti.mationmethodforMIMO.OFDMsystems.,VeconsidertheMIMO-0FDMsystemwith2transmitantennas(MT=2)and4receivean

22、tennasfMn4).ThenumberofsubcarriersKisofeachchannelhi,J(z)'sareindependentandrandomlygen-eratedfromcomplexckcularGaussiandistributionwithzeromean.Forthepurposeofevaluationoftheestimationerror,theambiguityvectorinthechannelestimateisresolvedbytheleastsquaressolutionundertheassumptionthatthetruecha

23、nnelresponsesareknown.up"2Training一,一I'':j:_l_一_:二:numberofdatablocksi0o10c,)乏10-一一_,2Cyclicprefix.;2l誊,functionofSNRTotesttheproposedchannelestimationalgorithmwere-algorithmandthetrainingbasedapproach(withonetrainingblockfromeachantenna1.,vecaninferfromthesesimula-trainingbasedapproach

24、inthissetupandisalsoabletotrackslowchannelvariations.dentchannelrealizations,anditshowstheestimatorNMSEasafunctionofSignalnoiseratio(SNR).Asexpected,theestimatorerrorofallmethodsdecreaseswithincreasingSNR.ForthemethodofnoVCs/CPandmethodofCyclicprefix(CP),aperformancegapexitsbetweenthenon-CPsystems.T

25、hisdemonstratesthatCPismoreadvantageousforthenoisedimensionofeacheigenvectorestimationspanningthenoisesubspace,therebyimposesmoreconstraintsontheestimationingreceiverdiversity,thenovelalgorithmisabletoimprovethechannelutilizationwithoutusingtheguardintervalandvirtualcarriers,undertheconditionsthatsystemsareunderidealsynchronizationand