A Low-Complexity Sparsity-Aware Detector for Downlink OTFS-SCMA Systems

Orthogonal time-frequency space (OTFS) modulation has emerged as a promising technique for high-mobility scenarios due to its robustness against channel dynamics. Meanwhile, sparse code multiple access (SCMA), a key non-orthogonal multiple access (NOMA) scheme, enables massive connectivity for future wireless networks. This letter investigates a downlink communication system that integrates OTFS with SCMA to address the challenges of high mobility and large-scale connectivity. To improve detection performance with reduced complexity, we propose a novel detector architecture that incorporates a sparsity-constrained generalized minimum residual (GMRES) algorithm within the MMSE-OSIC framework. By leveraging the inherent sparsity of SCMA codewords, the proposed scheme significantly lowers computational complexity while achieving notable gains in bit error rate (BER) and signal-to-noise ratio (SNR) performance compared to conventional approaches.