Research On Spatially Coupled LDPC Codes In High-order Modulation FTN System

With the proliferation of wireless mobile communication services,limited bandwidth resources have become very valuable.The emergence of the Faster-Than-Nyquist sampling(FTN)technology has brought relief to tight spectrum resources.It can effectively improve the system’s spectrum utilization by increasing the transmission rate of symbols,so it has attracted widespread attention.In terms of channel coding,the spatially coupled low-density parity-check code(SC-LDPC code)has both the memory characteristics of a convolutional code and the structure of a sparse check matrix.With the "threshold saturation" effect,it can approach the Shannon capacity limit.This paper combines these two technologies to study SC-LDPC codewords in high-order modulation FTN systems and proposes corresponding optimization methods.This article introduces the basic principles of FTN technology and the corresponding system model,and proposes optimization schemes for SC-LDPC codes from the three aspects of codeword construction,termination structure,and degree distribution for high-order modulation FTN systems.Specifically,in terms of codeword construction,a single-diagonal structure of split variable node construction optimization and progressive joint matrix construction optimization are proposed,so that the constructed SC-LDPC codeword can be directly systematically encoded,and has good cycle、girth characteristic,in the 4/5 code rate Nyquist system,compared with QC-LDPC code,it can obtain Eb/NO gain of 0.2 dB～0.23 dB(BER=1E-6).In terms of termination structure,through the additional coding at the end and the structural improvement of the check matrix,the optimized SC-LDPC codeword can be integrated into the Turbo iteration of the high-order modulation FTN system,and compared with the QC-LDPC code in this system,the Eb/NO gain of almost 0.2 dB@BER=lE-06 is still obtained.In terms of degree distribution,a degree distribution search algorithm based on Simulated Annealing Particle Swarm Optimization(SA-PSO)is proposed to find the degree distribution that best matches a particular high-order modulation FTN system and construct the corresponding irregular SC-LDPC codeword.In the high-order modulation FTN system with 3/4,4/5 code rates,the Eb/NO gain of this codeword compared with QC-LDPC codes can be expanded to 0.3 dB～0.4 dB@BER=1E-06.