Improved Serial Scheduling-Based Detection for Sparse Code Multiple Access Systems

Abstract

Sparse code multiple access (SCMA), which is a novel non-orthogonal multiple access, has been proposed to address the challenges of massive connectivity and higher spectral efficiency for fifth generation mobile network. Among the existing message passing algorithm (MPA)-based multiuser detection schemes for SCMA systems, the serial scheduling strategy, where messages are updated sequentially, generally converges faster than the parallel variant, where all messages are updated in parallel manner. Nevertheless, the ascending order of the serial scheduling strategy is not always the best option. In this letter, to further accelerate the convergence rate of the serial scheduling strategy, an improved serial scheduling-based MPA (ISS-MPA) detection scheme is proposed, where the user node scheduling order is first selected based on the maximum number of newly available message updates in the corresponding factor graph. Accordingly, the proposed ISS-MPA scheme can take full advantage of most reliable message updates in a timely manner, which leads to a faster convergence rate. Simulations demonstrate that the proposed ISS-MPA scheme with 2 iterations provides very similar bit error rate performance to the existing multiuser detection schemes with 6 iterations (only less than 0.3 dB degradation), whose complexity is reduced substantially.