Joint Power Control and Passive Beamforming Design for RIS-Assisted Secure Communication Systems

In this letter, considering the problem of signal blockage in the scenario of dense buildings, we study joint transmit power and phase shift design for the reconfigurable intelligent surface (RIS) assisted secure uplink communication systems. In particular, a friendly user with better channel state information than other users is selected as a jammer to interfere the eavesdropper. We aim to maximize the secrecy rate under the constant-modulus constraint for RIS phase shift. To handle the non-convex problem, we propose an alternating optimization based algorithm, where the successive convex approximation technique and manifold optimization are utilized for the optimization of transmission power and RIS phase shift, respectively. By introduce RIS into this system, the problem of signal blockage is solved. Moreover, simulation results show that the proposed scheme improves the system secrecy rate compared with the other benchmark schemes.