  This paper discusses the problem of securing the transmissions of multiple
ground users against eavesdropping attacks. We propose and optimize the
deployment of a single unmanned aerial vehicle (UAV), which serves as an aerial
relay between the user cluster and the base station. The focus is on maximizing
the secrecy energy efficiency by jointly optimizing the uplink transmission
powers of the ground users and the position of the UAV. The joint optimization
problem is nonconvex; therefore we split it into two subproblems and solve them
using an iterative algorithm.
