(PPT)Open-Source-Implementation-of-a-Digital-Radio

Open-SourceImplementationofaDigitalRadioMondiale(DRM)ReceiverDipl.-Ing.AlexanderKurpiersDipl.-Ing.VolkerFischerDarmstadtUniversityofTechnologyInstituteofCommunicationTechnologyDream09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver2Survey•Introduction&Motivation•ChannelEstimation–2DInterpolation–1DWienerInterpolationinTime-andFrequencyDirection•Synchronization–Acquisition•Frequency:FFT-basedAlgorithm•TimeandRobustnessModeDetection:Guard-IntervalCorrelation•DRMFrameSynchronization–Tracking•FrequencyandSampleRate:UsingPhaseIncrementofPilots•Time:UsingChannelEstimation•PerformanceSimulation•ConclusionandOutlook09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver3Motivation•DRMhasasmallbandwidthoflessthan20kHz-easytohandlewithcurrentPCsoundcards•Real-timesoftwareimplementationpossible•Nopubliclyavailableopen-sourceDRMreceiverWelookedforatestbedforOFDMalgorithmdevelopment(channelestimation,ICIcompensation,synchronisation)Aim:completeDRMReceiverunderGPLProjectstartedinsummer2001DigitalRadioMondiale(DRM)isanewOFDM-baseddigitalradiostandardforthelong-,medium-andshort-waveranges09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver4IntroductionOFDM•Vulnerabletofrequencyoffsets(causesICI)•Timingcriticalifdelayspreadisintherangeoftheguard-interval•Onlyonecoefficientpercarrierandsymbolhastobeestimatedforequalisation09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver5SoftwareOverviewsoundcardinterfacefrequencyacquisitionsampleratecorrectionrob.modedetectiontimingacquisitionusefulpartextractionfrequencycorrectionOFDMdemodulationresample,freq.offsettrackingframesync.channelestimationtimingtrackingsourcedecoders,channeldecoders,OFDMdemux09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver6ChannelEstimationTimeOFDMCarrierIndexOneveryOFDMcarrierthechanneltransferfunctionhastobeestimatedlkH,09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver7ChannelEstimationTimeOFDMCarrierIndexScatteredpilotsallowforeasychannelestimation09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver8ChannelEstimationTimeOFDMCarrierIndextwodimensionalWienerInterpolatorisoptimalbuttoocomplex09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver9ChannelEstimationTimeOFDMCarrierIndexWienerInterpolatorcanbeseparatedintotwo1Dfilters09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver10ChannelEstimation:WienerInterpolation•MMSEsolution:pRRhˆˆ1ˆˆˆ-=ppphphˆR:Cross-covariancematrixbetweenandthenoisypilotestimateshpˆppˆˆR:Auto-covariancematrixofthepilotestimatesIRRSNR1ˆˆ+=pppp•Dopplerprofileofatypicalshortwavechannel:Resultingcorrelationfunction:2d222d21)(σπσfefH-=()()2d2kNTfekrdΔ-=Δπσ•Assuminguniformdelaypowerspectrumwiththelengthoftheguard-interval:()
Δ=ΔNNllrGsincτ:Lengthofguard-intervalGNN:Lengthofusefulpart09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver11ChannelEstimationinFrequencyDirectionThefollowingparameterswereusedinthissimulation:RobustnessmodeB,10kHzbandwidth,20dBSNR,channelNo.3(USConsortium)Themeansquarederror(MSE)betweentheestimatedchannelandanidealchannelestimationisplotted.•Blueline:Linearinterpolation•Greenline:WindowedDFTalgorithm•Redline:Wienerinterpolation(usingallpilotcarriersforeachinterpolatedcell010203040-26-24-22-20-18-16-14-12CarrierIndexMSE[dB]09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver12FrequencyAcquisition(I)•Exploitingthepowerdifferenceofthethreefrequencypilotcellsanddatacells–Pilotcells:boosted,continuoustones–Datacells:powerspreadduetomodulation•FFT-basedalgorithm–SquarednormofFFTcalculatedovermorethanonesymbol(EstimationofPSD)–Correlationwithknownfrequencypilotpositions•EffectsofalargeFFTwindow:–Statisticalpropertiesofdatacellsmoredistinct,peakdetectionimproved–BUTfadingchanneleffectsreduceperformance3000Hz2250Hz750Hzkl09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver13FrequencyAcquisition(II)•PlacementofFFTwindowarbitraryNopriortiminginformationneeded•Averageerrorrate10%forallchannelsandrobustnessmodes•EstimationofPSD ==+20),(acsacqacmaxˆilipmmfRNff2102,acac-=-+=NnnmNjlnlmerRπ•Correlationwithpilotpositions09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver14TimeAcquisition(I)•Guard-intervalcorrelation•Usingenergyinguard-interval-Formultipathfadingchannel()-+ΘΘ==Θ1G)(GNmmeλExample(idealised):TNG0tChannel•istheresultingestimatedtimingposition{})(maxargGΘeNGNGuard-intervalUsefulparttGN0i()iλ0Θ)(GΘeGN()()[]-+=+++-=122*GNiinNnnNnnrrrriλ09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver15TimeAcquisition(II)InfluenceofGuardEnergyConsiderationonatwopathfadingchannel:OnlycorrelationCorrelationwithguardenergyconsiderationRobustnessmodescanbedetectedbyusingtimedifferencebetweenpeaks(periodequalsusefulpartduration)NT09/07/2003OpenSourceImplementationofaDigitalRadioMondiale(DRM)Receiver16FrameSynchronization-=+-+-=1021)(,22)(,1)(,)(,)(TtGtttLiipkNNjipkipkipkzecczkπ