Sum-Rate Maximization for RIS-Aided In-Band Full-Duplex Multi-User Systems

In-band full-duplex (IBFD) technology has become a potential key technology for sixth-generation (6G) wireless communications due to its capability to double spectral efficiency (SE). However, the strong self-interference (SI) of the IBFD system hampers its practical application. Fortunately, using reconfigurable intelligent surface (RIS) in the IBFD system helps mitigate SI while simultaneously enhancing useful signals, thereby improving system's uplink-downlink (UL-DL) sum-rate performance. This paper considers a RIS-aided IBFD multi-user system and proposes a novel algorithm for the UL-DL sum-rate maximization based on iterative minimization of weighted mean-square error (MSE). The proposed algorithm leverages block coordinate descent (BCD) and gradient descent with momentum (GDM) techniques to jointly optimize the RIS phases and the precoding matrix. Simulation results demonstrate that our BCD-GDM algorithm significantly outperforms conventional SI cancellation methods, showcasing marked improvements in UL-DL sum-rate performance.