Security enhancement of UAV swarm enabled relaying systems with joint beamforming and resource allocation

The high mobility of unmanned aerial vehicles (UAVs) could bring abundant degrees of freedom for the design of wireless communication systems, which results in that UAVs, especially UAV swarm, have attracted considerable attention. This paper considers a UAV Swarm enabled relaying communication system, where multiple UAV relays are organized via coordinated multiple points (CoMP) as a UAV swarm to enhance physical layer security of the system in the presence of an eavesdropper. In order to maximize achievable secrecy rate of downlink, we jointly optimize the beamforming vector of the virtual array shaped by the UAV swarm and bandwidth allocation on it for receiving and forwarding, and both amplify-and-forward (AF) and decode-and-forward (DF) protocols are considered on the UAV swarm. Due to the non-convexity of the joint optimization problem, we propose an alternating optimization (AO) algorithm to decompose it into two subproblems utilizing block coordinate descent technique, then each subproblem is solved by successive convex optimization method. Simulation results demonstrate that DF has competitive performance advantage compared with AF and the superiority of the proposed secure transmission strategy with optimal beamforming and bandwidth allocation compared with benchmark strategies.