Abstract: Theperformanceoflowdensityparitycheckcode（LDPC）basedonprotopraphexpansiongreatlydependsontheexpansionmethod.AnewQC-LDPCconstructionmethodwasproposed.Twomainstepsintheparitycheckmatrixconstructionincludethemulti-edgeseliminationofprotographandquasi-cycleexpansion.Thefirststepmakelocalgirthmaximumundertheconstraintofedgepermutation.Inthesecondstep,optimumshiftvaluesofthepermutationmatriceswereobtainedbysearchingtheclosedloopswithinthespecifiedlengthandcomparingthelengthandapproximatecycleextrinsicmessagedegree(ACE)ofcycles,aimingatreducingsmallcycleswithlowconnectivitywhichwasharmfultothecodeperformance.Forprotographwithoutmulti-edges,theonlystepwasthequasicycleexpansion.Asprovedbysimulation,theconstructedQC-LDPChasexcellentperformanceinbothdecodingthresholdanderrorflooraspects.

Key words: Quasi-cyclic low-density parity-check code, Protograph, Progressive edge-growth, Approximate cycle extrinsic message degree, Satellite communication