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

Highlights

What are the main findings?

• A joint optimization algorithm is developed to maximize the covert rate by adjusting a fixed-wing drone’s transmit power and speed, and seeking the optimal central position and radius of its flight area.
• To maximize the covert rate, there exists a distance threshold between the receiver and the detector that is determined by the drone’s minimum flight speed and maximum bank angle. Below the threshold, the drone should fly as high as possible; above it, as low as possible.

What are the implications of the main findings?

• The proposed optimization algorithm can fully utilize the fixed-wing drone’s maneuverability to select both the flight area and altitude based on the distance from the detector.
• Within the derived flight area, the drone is capable of delivering covert data at the optimized covert rate while meeting the required level of quality of service.

Abstract

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 $r_{\mathrm{R}}$ meters and serves as a mobile transmitter to covertly deliver data to a ground receiver situated $d_0$ 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 $r_{\mathrm{R}}$, the larger the covert rate will be. The minimum value of $r_{\mathrm{R}}$ 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 $r_{\mathrm{R}}$ and $d_0$. If $2r_{\mathrm{R}}<d_0\le 4r_{\mathrm{R}}$, the FWD should fly as high as possible. Conversely, if $d_0>4r_{\mathrm{R}}$, the FWD should fly as low as possible so as to maximize the covert rate.