performance comparison of dsp and vhdl implementation of trellis coded demodulation

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1、PerformanceComparisonofDSPandVHDLimplementationofTrellisCodedDemodulationAMITS.AWATI,HRISHIKESHR.KANITKAR,MAHIMANANDA,NIKHILG.LADDHA,SAVITAG.KULKARNI,ANURADHAC.PHADKEandALWIND.ANUSEElectronicsandTelecommunicationDepartmentPuneUniversityMaharashtraInstituteofTechnologyPaudRoad

2、,KothrudPune–411038.IndiaAbstract:Inmostwirelesscommunicationsystems,convolutionalcodingisthepreferredmethodoferrorcorrectioncodingtoovercometransmissiondistortions.Inthispaperwehavecomparedtheperformanceoftrelliscodeddemodulator(viterbidecoder)implementedonTMS320C54XXDSPchip

3、andFPGASpartanIIXC2s50PQ208kit.Inthispaperwealsopresentamodifiedviterbialgorithminwhichwehavecompletelyeliminatedregisterexchangeandtracebackapproachi.e.noretracingofthesurvivorpathisrequiredwhichtherebyreducesmemoryrequirement,powerconsumptionandreducesthetimerequiredforgett

4、ingthedecodedoutput.Introduction:Viterbidecodersareusedtodecodeconvolutionalcodingwhichhasbeenusedindeepcommunicationaswellaswirelesscommunications.AwirelesscellularstandardforCDMA(codedivisionmultipleaccess),IS-95employsconvolutionalcoding.Athirdgenerationwirelessstandardado

5、ptsturbocoding.TheViterbialgorithmistofindamaximum-likelihoodsequenceofstatetransitions,equivalentlyapath,inatrellisbyassigningatransitionmetrictopossiblestatetransitions.Atransitionmetriciscalledbranchmetric,andthecumulativebranchmetricsalongthepathfromtheinitialstatetoagive

6、nstateiscalledthepathmetricofthestate.Whentwoormorepathsendatthesamestate,thepathwiththesmallestpathmetricisselectedasthemostlikelypath.Thesurvivorpathobtainedbybacktrackingintimecorrespondstothedecodedoutput.Thedesignofhighperformanceviterbidecodershasbeeninvestigatedintensi

7、velyinthepastthreedecades.Apreviouslyimplementedalgorithmusingtracebackmethodusesthecumulativeapproachforrecordingthesurvivorpathwhereasinouralgorithmwehavecompletelyeliminatedregisterexchangeandtracebackapproachi.e.noretracingofthesurvivorpathisrequiredwhichtherebyreducesmem

8、oryrequirement,powerconsumptionandreducesthetimerequiredforgettingth