On Fixed-Wing Drone-Enabled Covert Transmission with Mobility Restrictions and QoS Requirement

This article examines a fixed-wing drone (FWD)-enabled covert transmission, where the FWD performs a level flight within a circular area with a radius of rR meters and serves as a mobile transmitter to covertly deliver data to a ground receiver situated d0 meters away from a ground detector. First, the conditions for satisfying the covertness constraint and meeting the transmission's quality of service (QoS) requirement are derived, imposing additional mobility restrictions on the FWD beyond the predefined speed and altitude limits. Considering the FWD's mobility and transmit power limits, an optimization problem maximizing the covert rate is solved, leading to a joint optimization algorithm that adjusts the FWD's transmit power and speed while seeking the optimal central position and radius of the circular area. Within this area, the FWD is capable of performing an unrestricted level flight and delivering covert data at the optimized covert rate while meeting the required QoS level. Computer simulation results demonstrate that the smaller the radius rR, the larger the covert rate will be. The minimum value of rR is twice the FWD's minimum turning radius, which is determined by the minimum flight speed and the maximum bank angle. The FWD's flight altitude exhibits a strong correlation with both rR and d0. If 2rR4rR, the FWD should fly as low as possible so as to maximize the covert rate.