Throughput Maximization for UAV-Enabled Wireless Powered Communication Networks

This paper studies an unmanned aerial vehicle (UAV)-enabled wireless powered communication network (WPCN), in which a UAV is dispatched as a mobile access point (AP) to serve a set of ground users periodically. The UAV employs the radio frequency (RF) wireless power transfer (WPT) to charge the users in the downlink, and the users use the harvested RF energy to send independent information to the UAV in the uplink. Unlike the conventional WPCN with fixed APs, the UAV-enabled WPCN can exploit the mobility of the UAV via periodic trajectory design, jointly with the transmission resource allocation optimization, to improve the system performance. In particular, we aim to maximize the uplink common (minimum) throughput among all ground users over a finite UAV’s flight period, subject to its maximum speed constraint and the users’ energy neutrality constraints. The resulting problem is nonconvex and thus difficult to be solved optimally. To tackle this challenge, we first consider an ideal case without the maximum UAV speed constraint, and obtain the optimal solution to the relaxed problem. The optimal solution shows that the UAV should successively hover above a finite number of ground locations for downlink WPT, as well as above each of the ground users for uplink communication. Next, based on the above multilocation-hovering solution, we propose a successive hover-andfly trajectory, jointly with the downlink and uplink power allocations, to find an efficient suboptimal solution to the problem with the maximum UAV speed constraint. Numerical results show that the proposed UAV-enabled WPCN achieves significant common throughput gain over the conventional WPCN with a fixed-location AP.