ROBUST SECURE TRANSMISSION AND TARGET DETECTION IN ISAC NETWORKS VIA UAV-MOUNTED ACTIVE RIS UNDER EAVESDROPPER UNCERTAINTY

Abstract

Integrated Sensing and Communication (ISAC) has emerged as a key enabler for next-generation wireless systems, requiring simultaneous execution of secure information transmission and high-precision target detection. This paper proposes a novel ISAC framework using a UAV-mounted active Reconfigurable Intelligent Surface (RIS) to enhance both secrecy performance and radar sensing reliability in dynamic environments characterized by eavesdropper location uncertainty. The UAV acts as a mobile 3D reconfigurable platform that adaptively positions the active RIS to strengthen the legitimate communication link while shaping the sensing beams toward radar targets. We develop a unified optimization model that jointly designs the UAV trajectory, active RIS amplitude-phase coefficients, and ISAC transmit beamforming to maximize the secrecy rate and radar detection probability simultaneously. The secrecy metric includes the worst-case uncertainty in eavesdropper positions while the sensing metric captures the received echo power of the reflected LFM radar waveform. Then, the non-convex optimization problem is transformed into a solvable form by using successive convex approximation (SCA) and chance-constrained robust optimization that allows iterative refinement of both communication and sensing parameters. Simulation results illustrate that the UAV-mounted active RIS yields significant gains regarding secrecy rate, sensing SNR, and detection probability compared to passive RIS and static deployment baselines. Therefore, these results confirm the efficacy of active RIS-enhanced UAV platforms as a robust solution to the secure operation of ISAC under uncertain and adversarial environments.