The Max-Re-LOGMPA for SCMA Demodulation

Abstract

Sparse code multiple access (SCMA) is one of the algorithms in non-orthogonality multiple access. The algorithm utilizes advanced multi-dimensional codebook to acquire high shaping gain, meanwhile, SCMA takes advantage of message passing algorithm (MPA) to obtain low computation complexity in demodulation. The traditional MPA still has inherent computation complexity, so that it’s extremely difficult to be implemented on hardware platform. Therefore, log-domain message passing algorithm (LOG-MPA) and max log-domain message passing algorithm (MAX-LOG-MPA) were proposed to dispose the problem. But LOG-MPA has problem in numerical stability, more concretely, zero will emerge at denominator at some middle steps in high signal noise ratio (SNR), which will bring numerical instability. In this paper, we propose a novel algorithm named max reference point LOGMPA (Max-Re-LOGMPA) to improve numerical stability and bit error ratio (BER) performance in high SNR. Final numerical analysis shows that, the Max-Re-LOGMPA’s numerical stability and the robustness are higher than LOG-MPA, the BER is lower than that in MAX-LOG-MPA as well.