Structure Design And Optimization Of Spatially Coupled LDPC Codes

Low-density parity-check(LDPC)codes have attracted much attention with the development of 5th generation(5G)digital communications.And LDPC codes have become an enhanced mobile broadband(e MBB)scenario data channel coding scheme due to excellent error correction characteristics.Spatially coupled LDPC(SC-LDPC)codes are obtained by coupling multiple identical LDPC codes,and the belief propagation(BP)threshold of the SC-LDPC codes is close to the maximum a posteriori(MAP)threshold of the underlying LDPC codes,which is called "threshold saturation" properties.Therefore,the structural design and performance optimization of SC-LDPC codes have become the focus of researchers.Because of the irregularity of the boundary,the rate of SC-LDPC codes is lower than that of their construction unit,LDPC code.In order to improve the rate loss of SC-LDPC codes,a series of structural design schemes were proposed.In this paper,the structures of SC-LDPC codes are designed with improving the rate as the starting point.The main research as follows:(1)A new structure of SC-LDPC codes which can improve the rate is proposed by improving the edge spreading rules of the conventional SC-LDPC codes.Compared with the conventional structure,except the first position,the variable nodes in other positions are connected to the check nodes where the position indexes all move one to the left correspondingly.,and a new spatial coupling structure is constructed.The base matrix,code rate,decoding complexity and threshold are analyzed.And the results show that,compared with the conventional SC-LDPC code,the rate of the new structure is improved and decoding complexity is slightly increased when the chain length is the same;the new structure also has the "threshold saturation" effect and the threshold is better than the conventional structure.Finally,the superiority of the proposed spatial coupling new structure decoding performance isverified by BP decoding.(2)The edge spreading rules are further improved.According to the coupling width,the edges of the variable nodes at the beginning and end of several positions are symmetrically distributed,and the variable nodes of the intermediate position connected to the position index of the check nodes are correspondingly reduced.Therefore,a kind of rate-loss-free SC-LDPC codes are obtained.The threshold analysis and performance simulation of the variant structure over the additive white gaussian noise(AWGN)channel are implemented by extrinsic information transfer(EXIT)functions and BP decoding respectively.The results show that compared with the conventional structure of SC-LDPC codes,the variant structure of SC-LDPC codes proposed in this paper can avoid the rate loss,and have better threshold and performance when the chain length is shorter.