Beampattern Design for RIS-Assisted Secure Dual-Function Radar-Communication Systems

In this paper, we investigate a beampattern design for reconfigurable intelligent surfaces (RIS)-assisted secure dual-function radar-communication (DFRC) systems. To minimize the difference between the obtain and the desired beampattern gain, we jointly optimize the transmit beamforming of base station (BS) and phase shift of RIS while satisfying the secrecy rate required by legitimate users, the transmit power budget of the BS, as well as the unit-modulus constraint at RIS. To solve this non-convex problem, we decompose it into two sub-problems. To solve them, the Riemannian trust-region (RTR) algorithm based on alternating optimization (AO) scheme and successive convex approximation method are proposed. Simulation show that the proposed scheme can reduce the mean square error of radar detection performance compared with the existing scheme, and achieve better convergence performance. Moreover, the secrecy rate can be significantly improved by deploying RIS in the DFRC system, compare to the scenario without RIS.