An Enhanced Multi-User SCMA Codebook Design Over an AWGN Channel

Sparse code multiple access (SCMA) technology has become a research hotspot over the past decade, particularly the SCMA codebook design. The minimum Euclidean distance between superimposed codewords (MEDs) is a key performance indicator to measure the performance of the SCMA communication system over an AWGN channel. This letter presents a design of the heavily-overloaded SCMA codebooks with large MEDs. Different from most of the existing codebooks, the separable codebook structure is used as the structure of our proposed codebook. Moreover, we formulate a non-convex problem and solve it by the convex-concave procedure (CCP). With this approach, we can obtain the SCMA codebooks for up to
$\boldsymbol {300\%}$
overloading factor. Compared with the existing advanced codebooks, our proposed codebooks improve the MEDs at high overloading factors, and have great BER performance by using a group transmission strategy over the downlink Rayleigh fading channel.