Sum-Rate Maximization of Multi-RIS-Assisted RSMA Networks with In-Band Over-The-Air RIS Control and Feedback Links

In this paper, we propose a rate-splitting multiple access (RSMA) communication system assisted by multiple reconfigurable intelligent surface (RIS) devices, incorporating in-band over-the-air (OTA) control and feedback links for the RISs, and develop a corresponding radio resource allocation algorithm. To facilitate in-band OTA communication, each RIS is divided into two subsets: one dedicated to reflecting data signals from the base station (BS) toward users, and the other allocated for transmitting RIS feedback signals back to the BS. We present an alternating optimization approach that jointly optimizes the beamforming vectors at the BS and the reflection coefficients of the RISs. Specifically, our solution employs the weighted minimum mean square error (WMMSE) algorithm combined with a projection method to satisfy the RIS control rate constraints, while leveraging the Riemannian conjugate gradient algorithm for updating RIS reflection coefficients. Extensive simulation results demonstrate that the proposed scheme achieves robust and stable user sum-rate performance while effectively supporting the OTA control and feedback signaling. Additionally, the results provide insights into the impacts of RIS subset sizes, RIS control rate constraints, and BS transmit power on overall network performance.