  This paper investigates the secrecy energy efficiency (SEE) maximization
problem for unmanned aerial vehicle enabled mobile relaying system, where a
high-mobility UAV is exploited to assist delivering the confidential
information from a ground source to a legitimate ground destination with the
direct link blocked, in the presence of a potential eavesdropper. We aim to
maximize SEE of the UAV by jointly optimizing the communication scheduling,
power allocation, and UAV trajectory over a finite time horizon. The formulated
problem is a mixed-integer non-convex optimization problem that is challenging
to be solved optimally. To make the problem tractable, we decompose the problem
into three subproblems, and propose an efficient iterative algorithm that
alternately optimizes the subproblems. In addition, two special cases are
considered as benchmarks in this paper. Simulation results show that the
proposed design significantly improves the SEE of the UAV, as compared to the
benchmarks
