Sparse or Dense: A Comparative Study of Code-Domain NOMA Systems

This paper is focused on code-domain non-orthogonal multiple access (CD-NOMA), which an emerging paradigm to support massive connectivity for future machine-type wireless networks. We take a comparative approach study two types of overloaded CD-NOMA, i.e., sparse code (SCMA) and dense (DCMA), are distinctive from each other in terms their codebooks having sparsity or not. By analysing individual diversity orders (DO) Rayleigh fading channels, it found that DCMA can be designed with the aid generalized sphere decoder (i.e., nonlinear multiuser detector) enjoy full DO equal maximum number resource nodes system. contrast SCMA whose error rate suffers limited codebook effective occupied by user). conduct theoretical analysis design criteria propose use detection. numerically evaluate schemes under “ 4×6” six users communicate over four subcarriers) 5×10” NOMA settings reveal gives rise significantly improved performance whilst decoding complexity comparable SCMA.