Synergizing Beyond Diagonal Reconfigurable Intelligent Surface and Rate-Splitting Multiple Access

This work focuses on the synergy of rate-splitting multiple access (RSMA) andbeyond diagonal reconfigurable intelligent surface (BD-RIS) to enlarge thecoverage, improve the performance, and save on antennas. Specifically, weemploy a multi-sector BD-RIS modeled as a prism, which can achieve highlydirectional full-space coverage, in a multiuser multiple input single outputcommunication system. With the multi-sector BD-RIS aided RSMA model, we jointlydesign the transmit precoder and BD-RIS matrix under the imperfect channelstate information (CSI) conditions. The robust design is performed by solving astochastic average sum-rate maximization problem. With sample averageapproximation and weighted minimum mean square error-rate relationship, thestochastic problem is transformed into a deterministic one with multipleblocks, each of which is iteratively designed. Simulation results show thatmulti-sector BD-RIS aided RSMA outperforms space division multiple accessschemes. More importantly, synergizing multi-sector BD-RIS with RSMA is anefficient strategy to reduce the number of active antennas at the transmitterand the number of passive antennas in BD-RIS.