Robust and secure communications using dynamic rotations reconfigurable intelligent surface

This paper investigates the secure transmission problem using a dynamically reconfigurable intelligent surface (RIS). Considering an eavesdropping scenario where a multi-antenna eavesdropper has inadequate channel state information, a resilient beamforming strategy is proposed to simultaneously optimize the active beamforming at the base station and rotational angles of the RIS in order to improve the system's secrecy rate. A continuous-time propagation model is used to explain the dynamically rotating RIS to maximize the cascaded channel gain. Simulation findings validate the security benefits of the resilient beamforming approach, and the dynamic rotation technique increases the secrecy rate while reducing delay spread.