In this paper, we propose a robust secrecy transmission scheme for intelligent reflecting surface (IRS) aided communication systems. Different from all the existing works where IRS has already been deployed at a fixed location, we take the location of IRS as a variable to maximize the secrecy rate (SR) under the outage probability constraint by jointly optimizing the location of IRS, transmit beamformer and IRS phase shifts with imperfect channel state information (CSI) of Eve, where we consider two cases: a) the location of Eve is known; b) only a suspicious area of Eve is available. We show a critical observation that CSI models are different before and after IRS deployment, thus the optimization problem could be decomposed and solved via a two-stage framework. For case a), in the first stage, universal upper bounds of outage probabilities only related to the location of IRS are derived which can be optimized via successive convex approximation (SCA) method. In the second stage, we develop an alternative optimization (AO) algorithm to optimize beamformer and phase shifts iteratively. For case b), we propose a Max-Min SR scheme based on two-stage framework, where the location of IRS is optimized based on the worst location of Eve. Simulation results indicate the importance of the location of IRS optimization.

中文翻译：

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具有位置优化功能的稳健 IRS 辅助保密传输


在本文中，我们提出了一种用于智能反射面（IRS）辅助通信系统的鲁棒保密传输方案。与所有现有的IRS已经部署在固定位置的工作不同，我们将IRS的位置作为变量，通过联合优化IRS、发射波束形成器和IRS的位置，在中断概率约束下最大化保密率（SR）。 IRS 相移与 Eve 的不完美信道状态信息 (CSI) 相关，我们考虑两种情况：a) Eve 的位置已知； b) 只有 Eve 的可疑区域可用。我们展示了一个关键的观察结果，即 CSI 模型在 IRS 部署之前和之后是不同的，因此优化问题可以通过两阶段框架分解和解决。对于情况a），在第一阶段，导出仅与IRS位置相关的停电概率的通用上限，可以通过逐次凸逼近（SCA）方法对其进行优化。在第二阶段，我们开发了一种替代优化（AO）算法来迭代优化波束形成器和相移。对于情况b），我们提出了一种基于两阶段框架的Max-Min SR方案，其中IRS的位置根据Eve的最差位置进行优化。仿真结果表明了IRS优化位置的重要性。