A Method for Analysing and Improving the Multi-user Detection Algorithm of SCMA

Sparse code multiple access (SCMA) is a novel kind of non-orthogonal multiple access technology which combines the ideas of CDMA and OFDMA. The modulation scheme based on the mapping of the codebook can be regarded as a kind of spread spectrum coding technology and the encoding gain helps to improve spectrum utilization, system capacity and transfer rate. At the receiver, the message passing algorithm (MPA) whick is employed to detect multi-user signals can reduce the computational complexity because of the sparse structure. In this paper, we use the extrinsic information transfer chart (EXIT chart) to analyze MPA detection performance under different SNR conditions and propose serial MPA algorithm based on fairness which can improve the convergence performance of the algorithm and reduce the computational complexity. The theoretical derivation and simulation results demonstrate that serial MPA can improve the algorithm convergence performance and MPA detection are not apply to low SNR scenario.