Covert communication is one of the most promising ways in 6G due to its high concealment, diverse forms, and strong compatibility. In traditional covert communication, high-gain antennas, signal amplifiers, and multipath transmission methods are commonly used to expand communication distance. However, the current research on covert communication is mostly limited to fixed receivers or fixed detection parties. In order to solve the above problems, we propose a covert communication countermeasure model in which the maximum covert transmission rate is achieved by introducing the unmanned aerial vehicle (UAV) as a typical high-flexibility relay under a movable detection party. Specifically, we obtain the optimal detection threshold and its corresponding total error probability through binary hypothesis testing and the monotonicity of the function at first. Then, we derive the optimal expressions for the covert constraint and transmission outage constraint in our model under the optimal detection threshold and total error probability. In addition, we optimize the position of the UAV based on the covert constraint and transmission outage through the Lagrange multiplier method. The numerical results reinforce the validity of our proposed approach and showcase the enhanced performance of the covert transmission rate.

中文翻译：

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基于主动对抗的无人机中继辅助隐蔽通信最优阵位设计

隐蔽通信因其隐蔽性高、形式多样、兼容性强等特点，成为6G最有前途的方式之一。传统的隐蔽通信中，通常采用高增益天线、信号放大器、多径传输等方式来扩大通信距离。然而，目前对隐蔽通信的研究大多局限于固定接收方或固定检测方。为了解决上述问题，我们提出了一种隐蔽通信对抗模型，其中通过引入无人机（UAV）作为可移动检测方下的典型高灵活性中继来实现最大隐蔽传输速率。具体来说，我们首先通过二元假设检验和函数的单调性来获得最佳检测阈值及其相应的总错误概率。然后，我们在最佳检测阈值和总错误概率下推导了模型中隐蔽约束和输电中断约束的最佳表达式。此外，我们通过拉格朗日乘子法，基于隐蔽约束和传输中断来优化无人机的位置。数值结果增强了我们提出的方法的有效性，并展示了隐蔽传输速率的增强性能。