Intelligent Reflecting Surface Enabled Electromagnetic Stealth and Enhancement for Secure Sensing Without Explicit CSI

Conventional electromagnetic (EM) wave-absorbing materials can provide sensing security against the unauthorized radar station (URS). However, they also render targets invisible to the authorized radar station (ARS), thus posing a challenge in achieving both EM stealth for the URS and EM enhancement for the ARS simultaneously. To tackle this challenge, we propose an intelligent reflecting surface (IRS)- aided secure sensing system, where an IRS is mounted on a target to enhance/suppress the echo signal power towards the ARS/URS distributed in an authorized/unauthorized area. Unlike the existing works requiring perfect/exact channel state information, we investigate a more practical IRS passive beamforming design based on the coarse geographical information of the areas only, aiming to maximize the minimum reflection gain over the desired cascaded spatial frequency (CSF) towards all possible locations in the authorized area, subject to the constraints on the maximum reflection gains over the undesired CSFs towards those in the unauthorized and authorized areas. To reduce the optimization complexity, we decouple the original problem into two subproblems corresponding to two dimensions, respectively. Although each subproblem is still difficult to solve due to the semi-infinite and non-convex constraints, we transform the semiinfinite constraints into a finite form. The resultant problem is then solved via the successive convex approximation algorithm. Simulation results are presented to verify the effectiveness of the proposed system and algorithm, as compared to the benchmark schemes