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1、IEEEJOURNALONSELECTEDAREASINCOMMUNICATIONS,VOL.SAC-5,NO.5,JUNE1987879TheEffectsofTimeDelaySpreadonPortableRadioCommunicationsChannelswithDigitalModulationJUSTINC-ICHUANGAbstract-Frequency-selectivefadingcausedbymultipatbtimede-11.MODELlayspreaddegradesdigitalcommunicationchannelsbyca
2、usinginter-symbolinterference,thusresultinginanirreducibleBERandimpos-Amultipathradiopropagationchannelcanbedescribedingaupperlimitonthedatasymbolrate.Inthispaper,afrequency-mathematicallybyitsimpulseresponseh(t).Abasebandselective,slowlyfadingchannelisstudiedbycomputersimulation.The
3、modelofamultipathradiochannelisshowninFig.1.AunfilteredBPSK,QPSK,OQPSK,andMSKmodulationsareconsid-quasi-staticchannelisconsideredinthisstudy,thatis,eredfirsttoillustratethephysicalinsightsandtheerrormechanisms.thechannelisassumedtobetime-invariantovermanyTwoclassesofmodulationwithspe
4、ctral-shapingfilteringarestudiednexttoassessthetradeoffbetweenspectraloccupancyandtheperfor-symbolperiods.Thisisareasonableassumptionforamanceundertheinfluenceoftimedelayspread.Thesimulationisveryportablecommunicationssystemwitharound1GHzcar-flexiblesothatdifferentchannelparametersca
5、nbestudiedandopti-rierfrequencyandseveralhundredkbits/ssignalingrate,mizedeitherindividuallyorcollectively.TheirreducibleBERaver-sincethemaximumDopplerfrequencyisonlyontheor-agedoverfadingsampleswithagivendelayprofileisusedtocomparederoflop5timesthebitrate.differentmodulation/detecti
6、onmethods,whilethecumulativedistri-butionofshort-termBERisemployedtoshowallowabledatasymbolLetu(t)bethebasebandrepresentationofthemodu-ratesforgivenvaluesofdelayspread.ItisfoundthatbothGMSKandlatedwaveform.ThetotalreceivedwaveformisthenQPSKwitharaised-cosineNyquistpulsearesuitablefor
7、aTDM/TDMAdigitalportablecommunicationschannel.z(t)=r(t)+n(t)(1)wheren(t)istheadditiveGaussiannoiseandI.INTRODUCTIONr(’t)=u(t)*h(t).(2)THEemergenceofademandforpersonalportablecommunications,alongwithaneedforintegratedIntersymbolinterference(ISI)causedbythedelayspreadvoiceanddatainourm
8、obilesociety
