This article investigates the intelligent reflecting surface (IRS)-aided multi-antenna covert communications. In particular, with the help of an IRS, a favorable communication environment can be established via controllable intelligent signal reflection, which facilitates the covert communication between a multi-antenna transmitter (Alice) and a legitimate full-duplex receiver (Bob) in the existence of a watchful warden (Willie). In order to shelter the desired communication, Bob generates jamming signals with a varying power to confuse Willie. The beamforming vector employed by Alice and the passive phase shifts of the IRS are optimized jointly to maximize the covert rate under the constraints of the successful detection probability at Willie and the communication outage experienced by Bob. We focus on the worst case by characterizing the minimum successful detection probability at Willie. The formulated problem is non-convex, due to the coupling between the beamforming vector of Alice and the phase shifts of the IRS, and the unit modulus constraint on the phase shifts of the IRS. To tackle the above issues, we first employ the penalty dual decomposition (PDD) method to handle the coupling effect. After that, we apply the successive convex approximation (SCA) method to develop an iterative algorithm for locating a Karush-Kuhn-Tucker (KKT) solution of the joint design problem. Moreover, we show that our proposed iterative algorithm can be adapted to handle the multi-antenna Willie case. Simulation results validate the effectiveness of the proposed iterative algorithm and show the great potential brought by the IRS for covert communications.

中文翻译：

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智能反射表面辅助多天线隐蔽通信：主动和被动联合波束形成优化


本文研究了智能反射表面 (IRS) 辅助的多天线隐蔽通信。特别是，在IRS的帮助下，可以通过可控的智能信号反射建立良​​好的通信环境，这有利于现有的多天线发射器（Alice）和合法的全双工接收器（Bob）之间的隐蔽通信。一个警惕的典狱长（威利）。为了掩盖所需的通信，鲍勃产生不同功率的干扰信号来迷惑威利。 Alice 采用的波束形成向量和 IRS 的无源相移被联合优化，以在 Willie 成功检测概率和 Bob 经历的通信中断的约束下最大化隐蔽率。我们通过描述威利的最小成功检测概率来关注最坏的情况。由于 Alice 的波束成形矢量与 IRS 相移之间的耦合以及 IRS 相移的单位模数约束，公式化的问题是非凸的。为了解决上述问题，我们首先采用惩罚对偶分解（PDD）方法来处理耦合效应。之后，我们应用逐次凸逼近（SCA）方法开发一种迭代算法来定位联合设计问题的Karush-Kuhn-Tucker（KKT）解。此外，我们表明我们提出的迭代算法可以适用于处理多天线威利情况。仿真结果验证了所提出的迭代算法的有效性，并显示了IRS为隐蔽通信带来的巨大潜力。