SCMA Codebook Based on Optimization of Mutual Information and Shaping Gain

Sparse code multiple access (SCMA) is a promising non-orthogonal multiple access (NOMA) technique for the fifth generation (5G) and beyond wireless networks. The performance of the SCMA-based NOMA system is sensitive to the codebook design. Since there is no optimum method of codebook design, these are designed, in general, using sub-optimal methods. The high values of the mutual information and the shaping gain of the multidimensional constellation points improve the SCMA codebook's performance. Hence, in this paper, we design an SCMA codebook by optimizing the mutual information and the shaping gain of constellation points with the constraints of fixed minimum Euclidean distance and average power. Simulation results show that the SCMA system with the proposed codebook outperforms those with the existing codebooks. Further, it is observed that the message passing algorithm converges faster to successful detection with the proposed codebook.