Passive Covert Communications Based on Reconfigurable Intelligent Surface

In this letter, a reconfigurable intelligent surface (RIS)-based passive covert communication scheme is proposed, where source node Alice covertly transmits information to receiver Bob by using a RIS and reflecting the incident signals from an ambient radio frequency source. The key idea is to adjust the phase shifts of the RIS to align the phases of the received reflected signals at Bob and meanwhile to adjust the reflection amplitude to satisfy the covert constraint. The detection error probability at warden Willie and the decoding error probability at Bob in Rayleigh fading channels are derived analytically. It is shown that the proposed scheme can enhance transmission reliability while satisfying the covert constraint by increasing RIS’s elements.