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.

中文翻译：

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空间调制上行稀疏码多址复杂度降低研究


最近提出了稀疏码多址(SCMA)辅助的多用户空间调制(SM)来提供上行链路高频谱效率传输。采用消息传递算法（MPA）来检测传输的信号，其复杂度较高。本文首次针对SM-SCMA提出了三种低复杂度算法。第一种算法被称为连续用户检测(SUD)，而第二种算法是SUD的修改版本，即修改的SUD(MSUD)。然后，首次构建了SM-SCMA的树搜索。基于该树搜索，为 SM-SCMA 提出了球体解码器 (SD) 的另一种变体，称为固定复杂度 SD (FCSD)。 SUD 提供了解码复杂性的基准，但以误码率 (BER) 性能为代价。此外，MSUD 略微增加了 SUD 的复杂性，同时显着提高了 BER 性能。最后，FCSD 提供了近乎最佳的 BER，与 MPA 解码器相比，复杂性大大降低，并且还支持并行硬件实现。所提出的算法为基于系统设计需求的实际实现提供了灵活的设计选择。为所提出的算法提供了 BER 的复杂性分析和蒙特卡罗模拟。