EVM与误码率分析

AnalyticalEVM,BER,andTDperformancesoftheOFDMsystemsinthepresenceofjointlynonlineardistortionandIQimbalanceHassanZareian&VahidTabatabaVakiliReceived:14September2008/Accepted:5May2009/Publishedonline:27May2009#InstitutTELECOMandSpringer-VerlagFrance2009AbstractTheorthogonalfrequency-divisionmultiplexing(OFDM)systemsarehighlysensitivetothenonlineardistortionsintroducedbythehigh-poweramplifieratthetransmitterandtothein-phaseandquadrature(IQ)imbalanceofthedownconverteratthereceiver.Inthispaper,thejointeffectsoftheseimpairmentsontheperformanceoftheOFDMsystemswithMsignalpointsquadratureamplitudemodulation(M-QAM)areinvestigated.Moreover,theanalyticalformulationsfortheerrorvectormagnitude,thebiterrorrate,andthetotaldegradationperformancesoftheM-QAM-OFDMsystemsinadditivewhiteGaussiannoisechannelsasafunctionoftheoutputbackoffandIQimbalanceparametersarederived.Thecomputersimulationresultsconfirmtheaccuracyandvalidityofourproposedanalyticalapproach.KeywordsOFDM.Nonlineardistortion.IQimbalance.Theoreticalanalysis1IntroductionTheorthogonalfrequency-divisionmultiplexing(OFDM)modulationformatcanprovidehighbitratesduetoitsrobustperformanceinwirelesschannelswithconsider-abledispersionandhasbeenproposedasthestandardforavarietyofdigitalcommunicationapplications,suchasdigitalvideobroadcasting-terrestrial(DVB-T),digitalaudiobroadcasting,andwide-bandwirelesscommunica-tionsystems[1].However,duetoagreatlyvariableenvelopeorhighpeak-to-averagepowerratio,amajorimpairmentfortheOFDMsystems,especiallyinbroad-castingapplications,isthepresenceofanonlinearhigh-poweramplifier(HPA)atthetransmitter,whichintroducesnonlineardistortion[2].Thehighsensitivitytoin-phaseandquadrature(IQ)imbalanceisalsoanotherserioussourceofimpairment[3].TheaimofthispaperistoanalyticallystudytheperformanceofOFDMsystemsbyjointlytakingintoaccounttheIQimbalanceandnonlineardistortioninadditivewhiteGaussiannoise(AWGN)channels.Theperformancefiguresconsideredhereinincludetheerrorvectormagnitude(EVM),biterrorrate(BER)andtotaldegradation(TD),asafunctionoftheoutputbackoff(OBO)valuesandIQimbalanceparameters.Uptonow,intheliterature,theeffectsofthenonlineardistortionintroducedbyHPAandtheIQimbalanceofdownconverterontheperformanceoftheOFDMsystemhavebeeninvestigatedseparatelyinmanypapers[4–14].TheeffectsofIQimbalancesontheOFDMsystemperformancehavebeendiscussedin[4–8].In[4,5],theIQimbalanceeffectsinOFDMtransmissionhavebeeninvestigatedbyusingsimulation.TheimpactsoftheIQimbalanceofthequadraturedownconverterontheperformanceofaQuadraturePhaseShiftKeyingOFDMsystemareanalyticallystudiedin[6].Also,ananalyticalmodelofIQimbalanceinmulticarrier-basedcommunica-tionsystemsispresentedin[7].However,ananalyticalexpressionfortheBERisnotderivedfortheOFDMsystems.In[8],ananalyticalclosedformfortheBERperformanceofOFDMsystemsinthepresenceofIQimbalanceasfunctionsofthegainandphaseimbalanceisprovidedthatcanbeusedtostudythejointeffectsoftheIQAnn.Telecommun.(2009)64:753–762DOI10.1007/s12243-009-0116-zH.Zareian(*):V.T.VakiliIranUniversityofScienceandTechnology(IUST),Tehran,Irane-mail:[e-mail]-mail:[e-mail]eriousimpairmentssuchasnonlineardistortionintroducedbyHPAontheOFDMsystemperformance.MostofthepaperswhichinvestigatedthenonlineardistortioneffectsinOFDMtransmission[9–17]treatthenonlineardistortionnoiseasanadditiveGaussianprocessandapplyvarioussimulationandanalyticalapproachestoderivethevarianceofsuchaGaussiannoise.In[9],thepowerofthenonlinearnoiseisobtainedbysimulation,whilein[10–13]ananalyticalexpressionisderivedforthevarianceorautocorrelationfunctionandhencethepowerspectraldensity(PSD)ofthenonlinearnoise.In[12,13],ananalyticalexpressionfortheoutputautocorrelationfunctionbasedonHPAmodelingwithBesselseriesexpansionisderived.ByusingFouriertransform,theoutputautocorrelationfunctioncanprovideinformationonthePSDattheHPAoutput,and,atthesametime,itallowstheanalyticalcalculationofthepowerofthenonlineardistortionnoise.Moreover,anewanalyticalapproachforthedescriptionoftheeffectsofnonlineardistortionusebymodelingthenonlineardistortionfunctionofHPAbyorthogonalpolynomialsisdevelopedin[14].In[15],thejointeffectsinducedontheOFDMsignalbytheamplifiernonlinearityandbythephasenoisearestudied.ThecombinedeffectsofnonlineardistortionandimperfectparametersestimationontheperformanceoftheOFDM-basedsystemsareinvestigatedin[16,17].However,accordingtotheauthors’knowledge,thereisnopaperdealingwiththejointeffectsofnonlineardistortionandtheIQimbalanceontheOFDMsystemperformanceandnoclosedformsfortheEVMandBERperformanceshavebeenpublishedintheliterature.Inthispaper,wedevelopaneasytheoreticalanalysisandderivetheexactEVM,BER,andTDperformancesofMsignalpointsquadratureamplitudemodulation(M-QAM)-OFDMoverAWGNchannelsinthepresenceofjointlynonlineardistortionandIQimbalance.Therestofthispaperisorganizedasfollows.“Section2”describesthesystemmodel.ThenonlineardistortionofHPAandtheIQimbalanceofthedownconverterarealsointroduced.In“Section3,”thejointeffectsofthenonlineardistortionandtheIQimbalanceontheE