A Low-Complexity Codebook Design for Large-Scale SCMA

Sparse-code multiple-access (SCMA) is an effective non-orthogonal multiple-access (NOMA) technique, which ranks one of the most promising candidates for future wireless. However, most of the existing work prefer a low-connectivity SCMA system because of the difficulties in designing proper codebook, which limits its priorities for massive connection. In this paper, we propose a systematic, low-complexity codebook design for large-scale SCMA. Stage-based generation with quadrature amplitude modulation (QAM) is adopted in the codebook design for SCMA system with arbitrary parameters, where the layer operator of each user is fixed as constellation rotation for simplification. Extension from known codebook is another proposed design manner, which allocates the known codeword repetitively based on specific allocation order. With a effectiveness metric, numerical results reveal advantages of our work. Hardware architecture of the detector is also proposed in this paper.