RIS-Aided Covert Communications with Statistical CSI: A Multiport Network Theory Approach

A novel framework for covert communications aided by Reconfigurable Intelligent Surfaces (RIS) is proposed. In this general framework, the use of multiport network theory for modelling the RIS consider various aspects that traditional RIS models in communication theory often overlook, including mutual coupling between elements and the impact of structural scattering. Moreover, considering a two-timescale RIS optimization approach, RIS optimization operates on a long timescale by leveraging statistical knowledge about the intended receiver, namely Bob. The proposed approach is validated through numerical results, demonstrating that communication with the legitimate user is successfully achieved while satisfying the covertness constraint. Moreover, while in classical communication scenarios the RIS offers little to no benefit when the direct link between transmitter and receiver is sufficiently strong, in covert communications the RIS can still provide significant advantages, even in the presence of strong direct paths.