Optimal Position Design for Unmanned Aerial Vehicle Relay-Assisted Covert Communication Based on Active Countermeasures

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.