Low Complexity Message Passing Algorithm for SCMA System

Sparse code multiple access (SCMA) is a novel non-orthogonal air-interface technology in which several users share a same frequency resource simultaneously. The SCMA decoder is based on a message passing algorithm (MPA) for the sparsity of codeword. In the original MPA, all the users update a message until the maximum number of iterations is reached, resulting in high computational complexity. This letter puts forward a threshold-based MPA, where a belief threshold is applied to control the algorithm process. Simulation results show that the proposed scheme obtains a low computational complexity with only a slight performance degradation when the threshold is set appropriately.