RIS-Assisted Non-orthogonal Multiple Access System Based on SSK

A novel reconfigurable intelligent surface (RIS)-assisted non-orthogonal multiple access (NOMA) system is presented in this paper. The system’s multi-user (MU) capability is based on coded NOMA (cNOMA). The proposed downlink transmission system uses space shift keying (SSK), allowing a simple but effective optimization of the phases at the RIS. The proposed system is evaluated considering a channel with spatial correlation and channel state information (CSI) errors. Theoretical and simulation results show that the proposed RIS-NOMA-SSK system achieves more than 25 dB gain in BER performance compared with a similar system that does not use RIS. Compared with the conventional RIS-assisted MU orthogonal multiple access (OMA) system, the proposed system outperforms the reference schemes by 10–20 dB under similar conditions and parameters. Mainly, the proposed system relaxes the overhead caused by CSI dissemination in conventional RIS-assisted OMA systems.