Low Complexity Iterative Receiver Design for Sparse Code Multiple Access

• Published in: IEEE transactions on communications Vol. 65; no. 2; pp. 621 - 634
• Main Authors: Wei, Fan, Chen, Wen
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.02.2017; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Binary system; Codes; Complexity; Complexity theory; Computer simulation; Decoding; Iterative decoding; Lattices; list sphere decoding; Maximum likelihood decoding; Message passing; message passing algorithm; node pruning; NOMA; Non-orthogonal multiple access; Nonorthogonal multiple access; Redundancy; SCMA; Search algorithms
• ISSN: 0090-6778; 1558-0857
• DOI: 10.1109/TCOMM.2016.2631468

Sparse code multiple access (SCMA) is one of the most promising methods among all the non-orthogonal multiple access techniques in the future 5G communication. Compared with some other non-orthogonal multiple access techniques, such as low density signature, SCMA can achieve better performance due to the shaping gain of the SCMA code words. However, despite the sparsity of the code words, the decoding complexity of the current message passing algorithm utilized by SCMA is still prohibitively high. In this paper, by exploring the lattice structure of SCMA code words, we propose a low-complexity decoding algorithm based on list sphere decoding (LSD). The LSD avoids the exhaustive search for all possible hypotheses and only considers signal within a hypersphere. As LSD can be viewed a depth-first tree search algorithm, we further propose several methods to prune the redundancy-visited nodes in order to reduce the size of the search tree. Simulation results show that the proposed algorithm can reduce the decoding complexity substantially while the performance loss compared with the existing algorithm is negligible.