UAV-Mounted RIS Enabled Maritime Secure Sensing With Joint Beamforming and Trajectory Design

This paper considers a challenging maritime secure sensing system, in which, a legitimate shipborne radar L needs to detect in real-time the state of a collaborative unmanned aerial vehicle (UAV) in the presence of an illegitimate or unauthorized shipborne radar U. To address this challenge, we propose a novel UAV-mounted reconfigurable intelligent surface (RIS) assisted approach, where the RIS is mounted on the UAV for enhancing/suppressing its reflected signal towards the L/U to facilitate/prevent its detection of the UAV. Furthermore, the UAV target can also adjust its flight route to move closer to/away from the L/U to improve/decrease the sensing performance. Due to the mobility of both the shipborne radars and UAVs, the Doppler shift effects of the RIS-ship channel need to be considered. In such a setup, the maximization of the received power at the L is formulated into an optimization problem while suppressing the received power at the U below a certain threshold by jointly designing the reflecting phase shifts of RIS and the 3D flight trajectory of UAV. The non-convex optimization problem is decomposed into two subproblems and solved via an iterative algorithm. Simulation results are presented to corroborate the effectiveness and tremendous potential of UAV-mounted RISs in the maritime secure sensing.