Fully Connected Reconfigurable Intelligent Surface Aided Rate-Splitting Multiple Access for Multi-User Multi-Antenna Transmission

Abstract: Rate-splitting multiple access (RSMA) has been recognized as a promising and powerful multiple access (MA) scheme, non-orthogonal transmission framework and interference management strategy for 6G. Inspired by the appealing spectral efficiency gain achieved by RSMA over conventional MA schemes in multi-user multi-antenna transmission, in this paper we introduce RSMA to reconfigurable intelligent surface (RIS)-aided multiple-input single-out (MISO) broadcast channel (BC). To further enhance the spectral efficiency, a more generalized RIS architecture called fully connected RIS is considered. By jointly optimizing the scattering matrix of the fully connected RIS and the transmit beamformers to maximize the sum-rate, we show that the proposed fully connected RIS aided RSMA transmission scheme significantly improves the spectral efficiency compared with the conventional single connected RIS schemes and the schemes without RIS. It acts as a new benchmark for linearly precoded multi-user multi-antenna networks.