  In this paper, we consider a single-cell multi-user orthogonal frequency
division multiple access (OFDMA) network with one unmanned aerial vehicle
(UAV), which works as an amplify-and-forward relay to improve the
quality-of-service (QoS) of the user equipments (UEs) in the cell edge. Aiming
to improve the throughput while guaranteeing the user fairness, we jointly
optimize the communication mode, subchannel allocation, power allocation, and
UAV trajectory, which is an NP-hard problem. To design the UAV trajectory and
resource allocation efficiently, we first decompose the problem into three
subproblems, i.e., mode selection and subchannel allocation, trajectory
optimization, and power allocation, and then solve these subproblems
iteratively. Simulation results show that the proposed algorithm outperforms
the random algorithm and the cellular scheme.
