毕业设计OFDM信号峰值窗函数限幅法模拟研究译文

西安邮电大学毕业设计（译文）论文题目：OFDM信号峰值窗函数限幅法模拟研究院（系）：通信与信息工程学院专业：电子信息科学与技术班级：电科0901学生姓名：郭常号导师姓名：邵朝职称：教授1ANewPAPRReductionTechniqueforOFDMSystemsUsingAdvancedPeakWindowingMethodSungkeunCha,MyongheePark,Member,IEEE,SungeunLee,StudentMember,IEEE,Keuk-joonBang,andDaesikHong,SeniorMember,IEEEI.INTRODUCTIONOrthogonalfrequencydivisionmultiplexing(OFDM)isapromisingtechniqueforhighdataratetransmissioninmobilefadingchannels.However,onemajordrawbackisitshighpeak-to-averagepowerratio(PAPR)resultinginnonlineardistortionanddegradationofbiterrorrate(BER)attheoutputofhighpoweramplifier.Themoststraightforwardwayofmitigatingthisproblemistointroduceanamplifierback-off,whichprovidessufficienthead-roomforthehighmodulatedsignalpeakstobeamplifiedinthelinearregion.Ofcourse,largeamountofback-offresultsinasignificantpenaltyintermsofthepowerefficiency.Therefore,anattractivesolutionforacosteffectivesystemistoreducePAPRofOFDMsignals.Numerousliteratureshavebeenpublishedinrecentyears,whichhavethepotentialforprovidingdiversesolutionsformitigatingthePAPRproblem.AmongthesediversePAPRreductiontechniques,peakwindowingfounditswayintopracticalimplementationwithoutsideinformationwhilemaintainingagoodspectralcharacteristiccomparedwiththeclippingmethod.Inarealsystem,however,whensuccessivepeaksemergelessthanahalfofthewindowsize,windowswillunfortunatelyoverlap.Asaresult,thesignalpeaksaresuppressedmuchmorethantherequiredthresholdanddegradetheBERperformance.Inthispaper,weproposeanadvancedpeakwindowingmethod.TheproposedmethodovercomesthedrawbackoftheconventionalonewhilemaintainingalmostthesamespectralmaskandprovidingmoreefficientBERperformance.Throughanumericalanalysisandcomputersimulation,weshowthattheproposedschemecanbeimplementedbyusingamatrixformandexceedstheconventionalwindowingmethod.Therestofthispaperisorganizedasfollows:SectionIIpresentsthesystemmodel.SectionIIIfirstprovidestheconventionalpeakwindowingmethod,andthenproposesouradvancedmethod,whichincludesthetechniquetogeneratethenewweightingcoefficients.InSectionIV,theadvantageoftheproposedmethodisverifiedbycomputersimulations.Finally,SectionVpresentsourconclusions.2II.PEAK-TO-AVERAGEPOWERRATIOINOFDMSYSTEMSA.SystemModelFig.1showsanOFDMblockdiagramunderconsideration.Thebinaryinformationbitsaremappedtocomplex-valuedM-QAMsymbolsina2-dimensionalsignalconstellation.Theoutputofthemapperisserial-to-parallelconvertedandprocessedusinganN-pointcomplexinversefastFouriertransform(IFFT).TheNcomplex-valuedtimedomainsignalsarethenfollowedbyaguardinterval(GI),whichcontainsthenumberoflastL−1samples(NL).TheGIconsistsofapartialrepetitionofanOFDMsymbolsoitdoesnotaffectthePAPR.Therefore,wedonottaketheGIintoconsiderationhere.PassingthroughaPAPRreductionblocksuchaspeakwindowing,thesignalsundergoesadigital-to-analogconversionandaretransmittedafterhighpoweramplifier.Atthereceiver,thereceivedsignalscanbedemodulatedbythereverseprocessofthetransmitter.Ifweassumetheinputcomplex-valueddatasymbolofNsubcarriersaskXfork=0,...,L,N−1,theoutputsignaloftheIFFTblockisgivenbyNTteXtxNktfjkk0,)(102(1)wherekfisthefrequencyofthek-thsubcarrierdefinedasfkfk,NTf/1andTisthesampleinterval.B.PeakPoweranditsEffectsWhiletherearealotofadvantages,somedrawbacksbecomeapparentwhenusingOFDMintransmissionsystems.AmajorshortcomingisthatthemultiplexedsignalaftertheIFFTexhibitsaveryhighPAPR.Therefore,ifnotproperlyamplified,nonlinearitiesmayoccurwithhighsignalpeaks,causingadistortionbetweensubcarriersand,morecritically,undesiredout-of-bandradiation.Ifpoweramplifiersareoperatedwithoutenoughpowerback-offs,itisimpossibletokeeptheout-of-bandpowerbelowaspecifiedlimit.3ThisleadstoveryinefficientamplificationandexpensivetransmitterssothatitishighlydesirabletoreducethePAPR.Inthispaper,weapproximatethepeakleveloftheOFDMsignalx(t)bytheoversampledsignal)/()(PnTxnx,wherePistheoversamplingfactor.Asshownin,wechooseP=4forthegoodapproximationonthePAPRpropertiesofx(t).Thereforethepeaklevelcanbedefinedas20)(max)(nxnxNPnp(2)Theaveragepowershouldcorrespondtotheaveragevaluetakenoveralltimes.ThisleadstothePAPR,oftendefinedas2)()(nxnxPAPRp(3)4III.PAPRREDUCTIONTECHNIQUEUSINGADVANCEDPEAKWINDOWINGMETHODInthissection,weoutlinetheconventionalpeakwindowingmethodandproposeanewPAPRreductiontechnique.Theproposedmethodovercomesthedrawbackoftheconventionalmethodwhensuccessivepeaksemergewithinahalfofthewindowsize.ConventionalPeakWindowingMethodanditsDrawbacks.TheclippingmethodisthesimplestwaytoreducePAPR.However,itdistortssignalsnonlinearlyandsignificantlyincreasestheout-of-bandradiation.Adifferentapproachistomultiplylargesignalpeakswithacertainwindowfunction.Inordertomaintaintheout-of-bandradiationwithinacertainlevel,itisbenefittoincreasethewindowlength.Ontheotherhand,thewindowshouldnotbetoolong,becausealongwidowlengthimpliesthatmanysignalsamplesareaffected,whichdegradestheBERperformance.ExamplesofsuitablewindowfunctionsaretheCosine,Kaiser,Hamming,andHanningwindow.Ingeneral,Kaiserwindowisusedbecauseitiseasytoshapespectrumbychangingwindowlengthandshapeparameter.TheKaiserwindowfunct