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1、2106IEEETRANSACTIONSONCOMMUNICATIONS,VOL.52,NO.12,DECEMBER2004AMoreAccurateOne-DimensionalAnalysisandDesignofIrregularLDPCCodesMasoudArdakani,StudentMember,IEEE,andFrankR.Kschischang,SeniorMember,IEEEAbstract—Weintroduceanewone-dimensional(1-D)analysisofperformver
2、yclosetotheShannonlimitusingdensityevolutionlow-densityparity-check(LDPC)codesonadditivewhiteGaussianasaprobe[5],[12],i.e.,findingtheconvergencethresholdofnoisechannelswhichissignificantlymoreaccuratethansimilardifferentirregularcodesbydensityevolutionandchoosingthe
3、1-Dmethods.OurmethodassumesaGaussiandistributioninmes-bestone.sage-passingdecodingonlyformessagesfromvariablenodestochecknodes.Comparedtoexistingwork,whichmakesaGaussianDensityevolutionmaybeunattractiveforafewreasons.assumptionbothformessagesfromchecknodesandfromv
4、ariableFindingagooddegreesequenceusingdensityevolutionre-nodes,ourmethodoffersasignificantlymoreaccurateestimatequiresintensivecomputationsand/oralongsearch,sincetheofconvergencebehaviorandthresholdofconvergence.Similartooptimizationproblemisnotconvex[5];furthermor
5、e,itdoesnotpreviouswork,theproblemofdesigningirregularLDPCcodesre-provideanyinsightinthedesignprocess,anditisintractableducestoalinearprogrammingproblem.However,ourmethodal-lowsirregularcodedesigninawiderrangeofrateswithoutanyforsomeofthecodesdefinedongraphs.limito
6、nthemaximumvariable-nodedegree.WeuseourmethodAnotherapproachforfindingconvergencebehaviorofiter-todesignirregularLDPCcodeswithratesgreaterthan14thatativedecodersistouseextrinsicinformationtransfer(EXIT)performwithinafewhundredthsofadecibelfromtheShannoncharts,e.g.,
7、[7],[8],[15],and[16].Althoughthismethodislimit.Thedesignedcodesperformalmostaswellascodesdesignednotasaccurateasdensityevolution,itslowercomputationalbydensityevolution.complexityanditsreasonablygoodaccuracymakeitattractive.IndexTerms—Degreedistribution,densityevo
8、lution,extrinsicEXITchartsprovideaone-dimensional(1-D)analysis,whichinformationtransfer(EXIT)charts,Gaussianassumption,irreg-allowsonetovisualizetheconv
