Active RIS Aided Integrated Sensing and Communication Systems

This paper considers an active reconfigurable intelligent surface (RIS)-aided integrated sensing and communication (ISAC) system. We aim to maximize Radar signal-to-interference-plus-noise-ratio (SINR) by jointly optimizing the beamforming matrix at the dual-function Radar-communication (DFRC) base station (BS) and the reflecting coefficient at the active RIS subject to the quality of service (QoS) constraints of communication users (UE) and the transmit power constraints of active RIS and DFRC BS. Due to the coupling of the optimization variables, we use the alternating optimization (AO) method to solve the problem. Given reflecting coefficients, we apply majorization-minimization (MM) and semidefinite programming (SDP) to deal with the nonconvex QoS constraints and Radar SINR. An initialization method is proposed to obtain a high-quality converged solution, and a sufficient condition of the feasibility of the original problem is provided. After applying the MM algorithm, the Radar SINR and the transmit power of the active RIS can be expressed as quartic functions of RIS coefficients, which is solved by a semidefinite relaxation (SDR)-based algorithm. Finally, simulation results validate the potential of active RIS in ISAC system compared to the passive RIS, and indicate that the transmit power and physical location of the active RIS should be carefully chosen.