Optimal Height of UAV in Covert Visible Light Communications

Abstract

This letter focuses on an unmanned aerial vehicle (UAV)-based covert visible light communication system. In the system, the UAV (Alice) sends information to a legitimate user (Bob) covertly while avoiding being detected by a warden (Willie). We analyze the mutual information of the communication channel and the covertness constraint of the detection channel. To improve system performance, we optimize the UAV’s height by maximizing the mutual information between Alice and Bob under the UAV’s height constraint. Without considering the covertness constraint, we first obtain the optimal height of the UAV, and prove the existence and uniqueness of such an optimal height. Moreover, considering the covertness constraint, we obtain the covert optimal heights under different conditions according to the relationship between the UAV’s height and the covertness constraint, and verify the existence of the solutions. Finally, we verify the theoretical analysis by numerical results.