Secure Wireless Communication in Active RIS-Assisted MISO DFRC System

This paper considers a dual-functional radar and communication (DFRC) system with an active reconfigurable intelligent surface (RIS) and a potential eavesdropper. Our purpose is to maximize the secrecy rate (SR) by jointly designing the beamforming matrix at the DFRC base station (BS) and the reflecting coefficients at the active RIS, subject to the signal-to-interference-plus-noise-ratio (SINR) constraint of the radar echo and the power consumption constraints. An SDR-MM-based alternating optimization (AO) algorithm is applied to solve the problem. Specifically, we first apply the semidefinite relaxation (SDR) and successive convex approximation (SCA) methods to transform the two subproblems into more tractable forms. Then, the majorization-minimization (MM) method is applied to derive a concave surrogate function and iteratively solve the subproblems. Finally, simulation results indicate that the active RIS can better confront the impact of "multiplicative fading" effect and outperform traditional passive RIS in terms of both secure communication and radar sensing functions.