A Dimension Distance-Based SCMA Codebook Design

For sparse code multiple access (SCMA) with traditional codebooks, the initial information of message passing algorithm (MPA) receiver is easily susceptible to noise and multipath fading, and the convergence reliability of the first detected user in each decision process is unsatisfactory. Driven by these problems, an optimized codebook design for SCMA is presented in this paper. In the proposed SCMA codebook design, we first use turbo trellis coded modulation technology to design a basic complex multi-dimension constellation, which can increase the minimum Euclidean distance. Then, phase rotation and coordinate interleaving are added on the constellation to increase diversity and coordinate product distance between any constellation points. Based on these, we propose a novel criterion to select the most appropriate permutation set, which can capture as large as the sum of distance between dimensions of interfering codewords multiplexed on each resource node and maximize the diversity over the set of the sums of distance between dimensions of interfering codewords multiplexed on all resource nodes. Benefiting from the proposed codebook design, the quality of initial information of MPA receiver on each resource node and the convergence reliability of the first detected user in each decision process will be improved. Simulation results show that the bit error rate performance of SCMA with the proposed codebooks outperforms SCMA with traditional codebooks, low-density signature, and orthogonal frequency division multiple access under the same load.