On the Physical Layer Security of UAV-Aided Backscatter Communications

In this letter, we investigate the issue of physical layer security in unmanned aerial vehicle (UAV)-assisted backscatter communication. The scenario involves a single UAV, a single passive backscatter device (BD), in the presence of a single eavesdropper (ED) attempting to intercept the backscattered information from the BD. To counteract the ED's efforts, we propose an artificial noise (AN) injection scheme to degrade the ED link. We aim to maximize the secrecy rate of the BD by optimizing three key factors: the UAV's hovering position, the power allocation factor, and the reflection coefficient of the BD. For this system setting, we derive the secrecy rate and formulate an optimization problem to optimize these variables. Due to the non-convex nature of the problem, we design an iterative algorithm based on the alternating optimization (AO) algorithm for maximizing the secrecy rate. Additionally, we provide insights into the impact of various system parameters on the overall performance. Notably, we demonstrate that the power allocation factor and the hovering altitude of the UAV play important roles for achieving secure communication.