无线OFDM系统中的同步和信道估计算法研究

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1、北京交通大学硕士学位论文无线OFDM系统中的同步和信道估计算法研究姓名：刘桓申请学位级别：硕士专业：通信与信息系统指导教师：谈振辉20080601ABSTRACTABSTRACTABSTRACT：Orthogonalfrequencydivisionmultiplexing(OFDM)techniquehasbeenwidelyusedinvariouswirelesscommunicationsfields，withtheincreasingneedsforbroadband，mobileandpersonalcommunications．OFDMsystemsare

2、extremelysensitivetosynchronizationerrors，whichwillleadtoseriousInter-channelInterference(ICI)andInter-symbolInterference(ISI)，anddegradesystemsperformancesgreatly．Channelestimationtechniqueisusedtoresistthefadingthroughoffsettingtheimpactofsub—channelsfading，accordingtothechannelestimat

3、ionresults．Sothedemodulationinformationcallbereceivedaccuratelyinthereceiver．Therefore，synchronizationandchannelestimationaretwoimportantissuesunderthewirelessfadingchannelinbroadbandwirelesscommunications．BasedonthesimulationoftheOFDMphysicallayersystems，thisthesistakesthesynchronizatio

4、nandchannelestimationalgorithmsofOFDMsystemsasresearchsubjects．Analyzedtheinfluencesofthesymbolsynchronization，frequencysynchronizationandsamplingsynchronizationerrorsontheOFDMsystems，thisthesisresearchesondifferentkindsofsynchronizationalgorithms，includingMaximumLikelihoodEstimationofti

5、meandfrequencyoffsetandSchmidl&Coxalgorithm．Forthepurposeofaccuracy,thisthesisproposestwomethodstoimprovethetimingoffsetestimationperformanceofSchmidl&Coxalgorithm．Oneistomodifytheslidingwindowoftrainingsequencetomakecorrelationoperation；theotheristomodifythestructureoftrainingsymb01．Sim

6、ulationresultsshowthatbothoftheproposedmethodsimprovetheperformancesofthesymbolsynchronization，whichareclosetotheidealityondifferentSNR．Meanwhile,thisthesisalsogivessometypicalchannelestimationalgorithmsinOFDMsystems，andcomparesLeastSquare(LS)，LinearMinimumLinearMinimumMean-Square—Error(

7、LMMSE)andLowOrderLMMSEmethodsthroughsimulationaswell．Therearesomeintimaterelationshipsamongtimingsynchronization，frequencysynchronizationandchannelestimationinOFDMsystems．Thetimingandfrequencyoffsetwillaffecttheaccuracyofchannelestimation．Theerrorsamongthemwillinterferemu