RIS Optimization for Covert Communications by Using Multiport Network Theory

A novel optimization approach for Reconfigurable Intelligent Surfaces (RIS) in a covert communications scenario is proposed. Specifically, the RIS is modeled using multiport network theory, which incorporates several aspects overlooked by traditional RIS models used in communication theory, such as mutual coupling among scattering elements and the presence of structural scattering that results in a strong specular component of the arriving signal on the RIS. Furthermore, we make the reasonable assumption that only limited knowledge about the channel and/or the position of the warden is available at the transmitter. Numerical results demonstrate the effectiveness of the proposed approach, enabling communication with the legitimate user while ensuring compliance with the covertness constraint.