the study of channel estimation algorithms of ofdm system in fast―moving conditions

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1、TheStudyofChannelEstimationAlgorithmsofOFDMSysteminFast―movingConditions　　【摘要】Inthispaper，WeproposeanimprovingalgorithmoftheEMabouttheOFDMsystemundertheconditionoffast-movingforchannelestimationimprovementalgorithm.Thisalgorithmisgreatlyreducedcomputationalcomplexit

2、ycomparedwiththeoriginalalgorithmandmakestheSNRperformanceclosethanwithoutjamming.Onthedevelopmentofmobilecommunicationshasagoodtheoreticalsignificance.　　【关键词】High-speedmobileconditionImprovingtheEMalgorithm　　【中图分类号】G642【文献标识码】A【文章编号】2095-3089（2016）11-0245-03　　Intro

3、duction：　　OFDMtechnologywasconcernedofeveryonewhoresearchingthehigh-speedmobilebecauseitcanbeimprovingthetransmittedeffectivelyspeedatthesametime，avoidingkindsofinterferenceandhasgoodnoiseimmunity，anti-multipathinterferenceandhighspectrumefficiency.However，inpractic

4、e，especiallywhenatthetimeundertheconditionoffast-moving，becausethechannel9spectrumcoverage，theorthogonalityofchannelwillbedestroyed，Channelsignalinterference（ICI）ordistortion，theotherwirelesschannelunderhighspeedconditionswillproducealargeDopplerfrequencyshift，which

5、willcauseatime-varyingcarrierfrequencyoffsetandcauseinterferencebetweenthecarriers，inturn，dramaticallyreducingcommunicationsperformance.Thirdly，duetorapidlychangingchannelunderhighspeedconditions，producingtimeselectivefadingwhichslowthesystemperformance.　　Fortheabov

6、e-mentionedreasons，weneedtosolvesomequestions：Firstly，wewillneedtoestimate，trackandcalibratetime-varyingcarriersfrequencyoffsetcausedbyDopplerfrequencyshift.Secondly，weneedtoestimatepreciselyaboutrapidlytime-varyingchannel.Thirdly，wemusteliminatemutualinterferencebe

7、tweencarrierproblem.Finally，weneedtoovercometheproblemofchannelchangecausedbytimeselectivefading.　　Inconclusion，wepresentanimprovedEMalgorithmbasedonchannelestimation，whichsolvedtheproblemfromtraditionalalgorithmfacetocomplexityandlowsignaltonoiseratio（SNR）undertheh

8、igh-speedmobilecondition.　　I.BasicprincipleofOFDMsystem　　1.1Thebasicidea9　　Channelscanbedividedintoseveralorthogonalchannels，high-speeddat