A New Code-Block Index-Modulation-Aided DCSK System Based on Sparse Code Multiple Access

A new code-block index-modulation-aided differential chaotic shift keying system based on sparse code multiple access, referred to as CBI-SCMA-DCSK, is proposed in this paper. With the aim to improve the spectral efficiency, we construct a code-block index structure for SCMA, which is employed in multi-carrier DCSK (MC-DCSK) system. Therefore, the information bits of each user can be conveyed not only by their own codebook, but also by the indices of the code blocks. Additionally, the SCMA mapping codewords are modulated by a chaotic reference signal, enhancing signal transmission reliability over multipath fading channels. At the receiver, we design a log-domain message passing algorithm for the de-indexing detection (DID-Log-MPA) for the CBI-SCMA-DCSK system to recover the information bits of each user. Simulation results conclusively demonstrate that the proposed CBI-SCMA-DCSK system outperforms existing SCMA-DCSK and MC-DCSK systems in terms of bit-error-rate (BER) performance.