A Fast Convergence Multiuser Detection Scheme for Uplink SCMA Systems

Sparse code multiple access (SCMA) is a competitive non-orthogonal multiple access technique for fifth generation wireless communication networks which can accommodate massive connectivity. Among the existing multiuser detection schemes for uplink (UP) SCMA systems, the asynchronous message passing algorithm (ASYN-MPA) scheme, where messages are updated sequentially, generally converges faster than the synchronous variant, where all messages are updated in parallel manner. Nevertheless, the specific pre-defined order of the ASYN-MPA scheme is not always the best option. In this letter, we tackle the problem of how to schedule message for the ASYN-MPA scheme that results in the best convergence rate. Specifically, a novel residual-aided message propagation approach for scheduling messages in the ASYN-MPA scheme, termed residual-aided MPA, is proposed for UP SCMA systems, which exploits the dynamic selection of the message which has the largest residual. Simulations show that the proposed scheme with two iterations provides very similar bit error rate performance to the existing multiuser detection schemes with six iterations (only less than 0.05 dB degradation), whose complexity is reduced substantially.