Uplink Spatial Modulation SCMA System

Multiple-input multiple-output (MIMO) and sparse code multiple access (SCMA) are two effective techniques supporting high spectral efficiency and massive connectivity, respectively. Although the combination of these two techniques, namely MIMO-SCMA, can further improve the spectral efficiency, it deteriorates the error performance and greatly increases the computational costs. In this letter, in order to enhance the error performance and reduce the receiver complexity of the uplink MIMO-SCMA system, we propose a new scheme named spatial modulation sparse code multiple access (SM-SCMA). At the receiver, a low complexity joint message passing algorithm based on the principle of the maximum a posterior probability and the simplified factor graph is proposed. Simulation results show that the SM-SCMA can achieve a better bit-error-rate performance while significantly reducing the receiver complexity compared with the conventional MIMO-SCMA.