A Novel DCMA Codebook Design Scheme Over Downlink Rayleigh Fading Channels

Dense Code Multiple Access (DCMA) is a variant of sparse code multiple access (SCMA) that replaces sparse codewords with dense ones, enhancing diversity gain. In this letter, we propose a novel approach to DCMA codebook design for downlink Rayleigh fading channels. First, SCMA codebook with a separable structure is designed to ensure uncorrelated signals across different resource elements (REs). Next, the codebook is extended using a corresponding linear constellation precoding (LCP) matrix to produce the final DCMA codebook. By ensuring uncorrelated signals across REs, the diversity gain enhancement from LCP is maximized. Simulation results demonstrate that the proposed codebook outperforms existing DCMA codebooks.