A Max-log-MPA algorithm based on serial and threshold in SCMA system

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Sparse code multiple access (SCMA) is a nonorthogonal multiplexing technology based on multidimensional codebook in 5G mobile communication system, which has good flexibility and adaptability. In the SCMA system, although the original Message Passing Algorithm (MPA) has good bit error ratio (BER) performance and complexity, the algorithm complexity is very high because of the exponential algorithm. The Maximum Logarithm Message Passing Algorithm (Max-log-MPA) uses approximate and maximum calculation, which results in some information loss and poor system BER performance. The Threshold-based Message Passing Algorithm adopts the hard decision mechanism, which reduces the complexity of the algorithm, but has the problem of high BER performance with low threshold. The Serial Message Passing Algorithm (S-MPA) uses the user node information update fusion in the resource node information update, which effectively reduces the algorithm complexity, but the user information BER performance is poor. On the basis of the previous algorithm, this paper proposes a Maximum Logarithm Message Passing Algorithm based on Serial and Threshold (S-T-Max-log-MPA), In this algorithm, the threshold is used to determine the necessary conditions of the stability of the user node, and then the user node information update is integrated into the resource node information update, so that the system can maintain good BER performance, especially when the threshold is low, the BER performance of the system is better. The simulation results show that the BER performance of this algorithm is better than that of Max-log-MPA algorithm with the decrease of threshold.