Low Complexity Decoding Method for SCMA in Uplink Random Access

Sparse code multiple access (SCMA) has been presented as a promising solution for uplink transmission since it enables random access so that the pre-establishment of link can be omitted. However, this randomness could cause codebook collision when different users pick the same codebook. Though the message passing algorithm (MPA) is employed to decode nonorthogonal codewords to lower the complexity, it needs an unacceptably high amount of calculation when serious collision happens, which also drastically increases the worst case latency (WCL) of access. In this paper, we propose a new decoding method dedicated to solve the high-complexity problem through simplifying the decoding factor graph. Simulation results demonstrate near optimal performance with greatly reduced complexity concerning two specific schemes of the proposed method.