A Lattice-Based SCMA Codebook Design for IoMT Communications

Sparse code multiple access (SCMA) is a competitive non-orthogonal multiple access (NOMA) technique for the internet of medical things (IoMT). The essential problem of SCMA is to design the large scale codebooks with high coding gain. In this article, a new lattice-based codebook design method is proposed to generate the multi-dimensional constellation. Firstly, an optimization problem about multi-dimensional constellations is constructed to quest the real constellation with maximum coding gain. Secondly, by combining the dimensions of the real constellations, we construct the basic complex mother constellation. The mother constellation can increase the power diversity and ensure the constant Euclidean distance between constellation points. Finally, we generate the mother codebooks with designed mapping matrix by constellation rotation. Simulation results demonstrate that the designed codebook has higher coding gain with large codebook size, especially under the high signal to noise ratio (SNR) condition.