Secrecy Energy Efficiency Maximization for UAV-Enabled Mobile Relaying

This paper investigates the secrecy energy efficiency (SEE) maximization problem for unmanned aerial vehicle (UAV) enabled mobile relaying system, where a high-mobility UAV is exploited to assist transmitting confidential information from a ground source to a legitimate ground destination, in the presence of a potential eavesdropper. We aim to maximize the SEE of the UAV by jointly optimizing the communication scheduling, power allocation, and UAV trajectory over a given time horizon. The formulated problem is non-convex that is challenging to be optimally solved. To make the problem more tractable, we decompose the problem into three subproblems, and propose an efficient iterative algorithm that alternately optimizes each block of the variables with the others fixed. Moreover, the practical scenario with uncertain eavesdropper location is investigated to evaluate the performance of the proposed solution. Double circular flight and running track shape flight cases are considered to drawn more insights. Simulation results show that the proposed design significantly improves the SEE of the UAV, as compared to the benchmark schemes.