Joint Beamforming, RIS Configuration, and Antenna Positioning for Active RIS-Assisted ISAC With Movable-Antenna Arrays

We propose a novel integrated sensing and communication (ISAC) framework that combines active reconfigurable intelligent surfaces (RIS) with a movable antenna (MA) array at the base station to jointly enhance the communication throughput and the radar sensing resolution. Unlike conventional architectures that employ passive RIS or fixed antenna arrays, the proposed framework leverages dual-domain reconfigurability, electromagnetic and geometric, by jointly optimizing transmit beamforming, RIS reflection coefficients with amplification constraints, and the spatial positions of the mobile antennas. The system is modeled under a practical RIS noise amplification model and subject to the constraints of stringent signal-to-interference-plus-noise ratio (SINR), radar beampattern, and transmission power. A unified optimization problem is formulated and decomposed into tractable subproblems using an alternating optimization approach based on semidefinite relaxation (SDR), successive convex approximation (SCA), and convex programming. Numerical results confirm that the proposed design significantly outperforms conventional passive RIS and fixed array systems in terms of both radar and communication metrics, particularly under dynamic channel conditions and constrained power budgets.