Low Complexity Iterative Receiver Design for Sparse Code Multiple Access

TL;DR

This paper introduces a low complexity decoding algorithm for SCMA that leverages lattice structure and list sphere decoding, significantly reducing complexity with minimal performance loss.

Contribution

It proposes a novel LSD-based decoding method for SCMA that prunes redundant nodes, lowering complexity compared to traditional message passing algorithms.

Findings

Decoding complexity is substantially reduced.

Performance loss compared to existing algorithms is negligible.

The method effectively exploits the lattice structure of SCMA codewords.

Abstract

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 (LDS), SCMA can achieve better performance due to the shaping gain of the SCMA codewords. However, despite of the sparsity of the codewords, the decoding complexity of the current message passing algorithm (MPA) utilized by SCMA is still prohibitively high. In this paper, by exploring the lattice structure of SCMA codewords, 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.