RIS-Empowered Passive Radar for Covert UAV Detection

In urban areas, the detection of unmanned aerial vehicles (UAVs) in no-fly zones is crucial for privacy protection and security. The low radar cross section (RCS) of UAVs requires the use of high-power active radars for precise positioning. Unfortunately, deploying active radars in cities may lead to interference with radio communications and their detectability prompts UAVs to employ evasive maneuvers. This paper introduces a reconfigurable intelligent surfaces (RIS)-assisted passive radar positioning scheme to tackle these challenges. We propose a minor modification to the existing transmission protocol, specifically for RIS assistance, enabling the utilization of existing base station (BS) signals for positioning. The scheme utilizes the information from direct signals, UAV-reflected signals, and additional signals provided by the RIS link to estimate the spatial features of the UAV. This collaborative approach significantly decreases the miss detection rate (MDR) of the UAV detection, as well as enhances accuracy in UAV positioning. Numerical simulations verify the feasibility of our proposed scheme, demonstrating its superior performance in terms of UAV positioning accuracy.