This work focuses on the synergy of rate-splitting multiple access (RSMA) and beyond diagonal reconfigurable intelligent surface (BD-RIS) to enlarge the coverage, improve the performance, and save on antennas. Specifically, we employ a multi-sector BD-RIS modeled as a prism, which can achieve highly directional full-space coverage, in a multiuser multiple input single output communication system. With the multi-sector BD-RIS aided RSMA model, we jointly design the transmit precoder and BD-RIS matrix under the imperfect channel state information (CSI) conditions. The robust design is performed by solving a stochastic average sum-rate maximization problem. With sample average approximation and weighted minimum mean square error-rate relationship, the stochastic problem is transformed into a deterministic one with multiple blocks, each of which is iteratively designed. Simulation results show that multi-sector BD-RIS aided RSMA outperforms space division multiple access schemes. More importantly, synergizing multi-sector BD-RIS with RSMA is an efficient strategy to reduce the number of active antennas at the transmitter and the number of passive antennas in BD-RIS.

翻译：本工作聚焦于速率分割多址接入（RSMA）与超越对角可重构智能表面（BD-RIS）的协同作用，旨在扩大覆盖范围、提升性能并节省天线资源。具体而言，我们在多用户多输入单输出通信系统中，采用以棱柱为模型的多扇区BD-RIS，其能够实现高度定向的全空间覆盖。基于多扇区BD-RIS辅助的RSMA模型，我们联合设计了非完美信道状态信息（CSI）条件下的发射预编码器与BD-RIS矩阵。该鲁棒设计通过求解随机平均和速率最大化问题实现。利用样本平均近似与加权最小均方误差-速率关系，该随机问题被转化为含多个块结构的确定性优化问题，各模块通过迭代方式设计。仿真结果表明，多扇区BD-RIS辅助的RSMA优于空分多址方案。更重要的是，多扇区BD-RIS与RSMA的协同是减少发射端有源天线数量及BD-RIS无源天线数量的有效策略。