Movable Antenna Enabled RIS-Aided ISAC Systems With Self-Interference Suppression

Abstract

In this paper, a movable antenna enabled reconfigurable intelligent surface (RIS)-aided ISAC system is investigated, where the monostatic BS attempts to detect a single target while providing communication services for multiple users by utilizing a RIS. To characterize the inherent performance trade-off between sensing and communication, an optimization problem of maximizing the weighted sum of mutual information of sensing target and achievable rate of all users is formulated. Suffering from the self-interference from transmit to receive antennas of BS, it requires a joint design of transceiver beamforming, RIS phase shift and transceiver antenna positions. To address this highly non-convex problem with multiple coupled variables, an effective fractional programming-alternating optimization (FP-AO) framework is proposed, where FP is adopted to transform the original problem into several subproblems, and then an AO-based algorithm is proposed to iteratively solve them. Specifically, closed-form solutions of transceiver beamforming are derived through utilizing the Karush–Kuhn–Tucker conditions, and the transceiver antenna positions are optimized by the proposed two-stage method integrating coarse-grained search and projected gradient ascent. At 40 dBm BS transmit power, the proposed FP-AO framework outperforms the random phase shifts, direct gradient ascent, and fixed-position antenna by 4.2%, 7.4%, and 11.3% in ISAC performance, respectively.