Joint 3D Beamforming and Trajectory Design for UAV-Enabled Mobile Relaying System

The goal of this paper is to investigate the security performance of the multi-antenna unmanned aerial vehicle (UAV)-enabled mobile relaying system with a multi-antenna destination in the presence of a multi-antenna eavesdropper. To improve the secrecy outage probability performance, we propose a location-based three dimensional (3D) beamforming scheme without the channel state information of the destination and the eavesdropper. To this end, we first derive the expression of the secrecy outage probability for uniform linear arrays (ULAs) and uniform circular arrays (UCAs), which is valid for arbitrary values of system parameters. The expression is practicable in the UAV-enabled mobile relaying system as the system parameters are time-variant with the movement of the UAV. Using this expression, we study the secrecy outage probability minimization problem by optimizing the 3D beamforming direction along with the trajectory of the UAV, subject to the mobility constraint and location constraint. To solve this problem, an efficient iterative algorithm is proposed. The numerical results demonstrate the effectiveness of our algorithms by comparing to other benchmark schemes, they also show the system with UCAs outperforms the system with ULAs on secrecy outage probability performance.