Design Of Spatial Coupled LDPC Codes Based On Protographs

With the rapid development of digital communication,the requirement of reliability in data transmission is increasing day by day in communication process,and error correction coding technology is becoming more and more important.In the field of error correction encoding,LDPC codes have attracted wide attention for their excellent performance.Moreover,the SC-LDPC codes based on the protographs is an important branch of the LDPC codes for better iterative decoding thresholds and asymptotic minimum distance characteristics.In order to achieve the effectiveness and reliability of the communication system,the design of SC-LDPC codes based on the protographs is studied in this paper.The main research contents of this paper are as follows:First,an improved edge expansion algorithm is proposed in the construction of the SC-LDPC codes based on protographs.Due to the special structural features of the SC-LDPC codes,the circle structure that has been formed may be broken when the base matrix is split in the process of the construction,decoding performance can be improved as well.From this,this paper proposes an improved edge-expanding algorithm based on the PEG algorithm,which can reduce the number of short circles in the construction of the SC-LDPC code by adding parameter constraints.The simulation analysis of the pipeline iterative decoding algorithm concluded that the SNR of the SC-LDPC code constructed by the improved edge-expanding algorithm has0.2dBgains when BER equals10^-6,which represents favorable error correction performance,as well as achieving local girth with higher probability.Second,this paper introduces a design scheme of rate compatible SC-LDPC code family.It has been shown that SC-LDPC codes are characteristic of threshold saturation,and the rate compatibility enables coding system to easily adapt to changing channel conditions.However,the current design scheme for rate-compatible SC-LDPC code family is complicate.In order to reduce the complexity,this paper designs a rate compatible SC-LDPC code family based on the present design scheme,adopting the random expansion scheme to construct the code family whose rate is lower than the mother codes and applying the random punctured scheme to construct the code family whose rate is higher than the mother codes.The advantages of presented scheme in this paper are as follows:on the one hand,it can be achieved easily by three parameters in calculating target rate,including the repetition times,the selecting proportion and the punctured proportion,with no need to design the complex scheme of expansion and puncture for each rate.On the other hand,the results of thresholds analysis show that the threshold of the designed bit-rate compatible SC-LDPC code family is very close to Shannon limit over the BEC channel.Especially in the case of low rate,it is obviously superior to the rate compatible SC-LDPC code family constructed by the existing schemes.