Joint Active and Passive Beamforming Design for RIS-Aided D2D Communication in Downlink Underlay Cellular Communication

This paper proposes a joint optimization framework for active and passive beamforming in reconfigurable intelligent surface (RIS)-aided downlink device-to-device (D2D) communication systems underlaying cellular networks. The proposed framework aims to enhance the weighted sum rate of the system by optimizing active beamforming at the base station (BS) and passive beamforming via the RIS. The optimization problem, formulated as a multivariate and non-convex task, is addressed using advanced techniques, including closed-form approaches such as the Lagrangian dual transform and quadratic fractional programming. This study highlights the potential of RIS technology to reshape propagation environments and improve communication reliability, providing a foundation for efficient and adaptive designs in dense wireless networks. Simulation results demonstrate the effectiveness of the proposed method when compared with benchmark schemes.