Multicast Secrecy Rate Maximization for Reconfigurable Intelligent Surface Backscatter Communication

This letter innovatively studies a reconfigurable intelligent surface (RIS) backscatter multicast secrecy communication system. In this system, a RIS acts as a transmitter to multicast confidential information for multiple single-antenna legitimate users by the backscatter of the radio frequency signal from a power beacon (PB), while multiple passive multi-antenna eavesdroppers lurking nearby attempt to intercept and recognize the confidential information with linear decoders. To maximize the multicast secrecy rate, we develop an alternative algorithm to optimize the reflection matrix at the RIS and the beamforming vector at the PB under the constraints of total transmit power and unit modulus. Simulation results verify the feasibility of the considered system and show the achievable secrecy performance of the proposed optimization scheme.