Weighted message passing algorithm for SCMA

Sparse code multiple access (SCMA) is a new frequency domain non-orthogonal multiple-access technique which can make full use of limited spectrum resources in wireless communication system. In SCMA, multiple users share the same time-frequency resources of orthogonal frequency division multiple access (OFDMA). However, message passing algorithm (MPA) is used in the process of SCMA decoding. And when the iteration number of MPA is large, the decoding complexity of SCMA is very high. In this paper, we propose an algorithm to decrease the decoding complexity of SCMA by introducing weight factors to replace MPA algorithm iterative process. We give each codeword in the codebook an original probability value which is related to the distance between received signal and the codeword. We set a corresponding weight factor for each probability value to change the original probability distribution of each codeword in the codebook. Simulation shows that this algorithm can greatly decrease the decoding complexity of SCMA while suffering only a bit of performance loss.