In this paper, we consider a challenging secure wireless sensing scenario where a legitimate radar station (LRS) intends to detect a target at unknown location in the presence of an unauthorized radar station (URS). We aim to enhance the sensing performance of the LRS and in the meanwhile prevent the detection of the same target by the URS. Under this setup, conventional stealth-based approaches such as wrapping the target with electromagnetic wave absorbing materials are not applicable, since they will disable the target detection by not only the URS, but the LRS as well. To tackle this challenge, we propose in this paper a new target-mounted IRS approach, where intelligent reflecting surface (IRS) is mounted on the outer/echo surface of the target and by tuning the IRS reflection, the strength of its reflected radar signal in any angle of departure (AoD) can be adjusted based on the signal's angle of arrival (AoA), thereby enhancing/suppressing the signal power towards the LRS/URS, respectively. To this end, we propose a practical protocol for the target-mounted IRS to estimate the LRS/URS channel and waveform parameters based on its sensed signals and control the IRS reflection for/against the LRS/URS accordingly. Specifically, we formulate new optimization problems to design the reflecting phase shifts at IRS for maximizing the received signal power at the LRS while keeping that at the URS below a certain level, for both the cases of short-term and long-term IRS operations with different dynamic reflection capabilities. To solve these non-convex problems, we apply the penalty dual decomposition method to obtain high-quality suboptimal solutions for them efficiently. Finally, simulation results are presented that verify the effectiveness of the proposed protocol and algorithms for the target-mounted IRS to achieve secure wireless sensing, as compared with various benchmark schemes.

翻译：本文考虑一种具有挑战性的安全无线感知场景，其中合法雷达站（LRS）意图在存在未授权雷达站（URS）的情况下，检测未知位置的目标。我们旨在提升LRS的感知性能，同时防止URS对同一目标的检测。在此设置下，传统的隐身方法（如用电磁波吸收材料包裹目标）不适用，因为这会同时阻碍URS和LRS对目标的检测。为应对这一挑战，本文提出一种新型目标搭载IRS方法，即在外置于目标表面或回波反射面上安装智能反射表面（IRS）。通过调节IRS的反射特性，可根据信号到达角（AoA）调整其在任意离角（AoD）方向上的反射雷达信号强度，从而分别增强/抑制面向LRS/URS的信号功率。为此，我们针对目标搭载IRS提出一种实用协议：基于其感知信号估计LRS/URS的信道与波形参数，并相应控制IRS的反射以支持/对抗LRS/URS。具体而言，针对具备不同动态反射能力的短期与长期IRS运行场景，我们构建新颖的优化问题，通过设计IRS的反射相位偏移，最大化LRS接收信号功率，同时将URS接收功率控制在阈值以下。为解决这些非凸优化问题，我们采用惩罚对偶分解法高效获得高质量次优解。最后，仿真结果验证了所提协议与算法相较于多种基准方案在实现目标搭载IRS安全无线感知方面的有效性。