Power Allocation in UAV-Enabled Relaying Systems for Secure Communications

Unmanned aerial vehicle (UAV)-enabled mobile relaying technique is a promising approach in providing high data rate transmission. Limitations of the UAV's hardware and the line-of-sight link of the air-to-ground channel make UAV ground communication more vulnerable to wiretap and spoof threats. This paper tackles the secure transmission problem with physical layer security (PLS) technologies. A four-node wiretap channel with UAV-enabled relay is considered and eavesdroppers' location information is partially known that they are in a certain area with variable densities. We put forward the secrecy rate maximization problem aiming at optimizing the source/relay transmission power. The objective function and constraints are proved to be non-convex and we convert the non-convex problem to a convex one by introducing the difference-of-concave (DC) programming and slack variables. For a special case, a closed-form solution is obtained which greatly reduces the complexity of the algorithm. The simulation result shows that with the proposed algorithm, the system with partial eavesdroppers' location information can achieve a pretty good secrecy performance close to that in the case with perfect location information.