On the Complexity Reduction of Uplink Sparse Code Multiple Access for Spatial Modulation

TL;DR

This paper introduces three low-complexity algorithms for uplink SM-SCMA detection, significantly reducing computational complexity while maintaining near-optimal BER performance, enabling practical high-spectral-efficiency systems.

Contribution

It proposes the first successively detected, modified, and sphere decoder algorithms for uplink SM-SCMA, enhancing detection efficiency and performance.

Findings

FCSD achieves near-optimal BER with reduced complexity.

MSUD offers a good trade-off between complexity and BER.

Algorithms support parallel hardware implementation.

Abstract

Multi-user spatial modulation (SM) assisted by sparse code multiple access (SCMA) has been recently proposed to provide uplink high spectral efficiency transmission. The message passing algorithm (MPA) is employed to detect the transmitted signals, which suffers from high complexity. This paper proposes three low-complexity algorithms for the first time to the SM-SCMA. The first algorithm is referred to as successive user detection (SUD), while the second algorithm is the modified version of SUD, namely modified SUD (MSUD). Then, for the first time, the tree-search of the SM-SCMA is constructed. Based on that tree-search, another variant of the sphere decoder (SD) is proposed for the SM-SCMA, referred to as fixed-complexity SD (FCSD). SUD provides a benchmark for decoding complexity at the expense of bit-error-rate (BER) performance. Further, MSUD slightly increases the complexity of SUD with a significant improvement in BER performance. Finally, FCSD provides a near-optimum BER with a considerable reduction of the complexity compared to the MPA decoder and also supports parallel hardware implementation. The proposed algorithms provide flexible design choices for practical implementation based on system design demands. The complexity analysis and Monte-Carlo simulations of the BER are provided for the proposed algorithms.