Throughput Maximization for UAV-Enabled Wireless Powered Communication Networks
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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. The UAV employs the radio frequency (RF) signals based wireless power transfer (WPT) to charge the users in the downlink, and the users use the harvested RF energy to send individual information back 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 trajectory optimization, jointly with the wireless resource allocation, to improve the system performance. In particular, we aim to maximize the uplink common throughput among all ground users over a particular finite time period, subject to the UAV's maximum speed constraint and the users' energy harvesting constraints. The decision variables include the UAV's trajectory design, as well as the UAV's downlink power allocation for WPT and the users' uplink power allocation for wireless information transfer (WIT). This problem is non-convex and thus very difficult to be solved optimally. To overcome this issue, we first consider a special case when the maximum UAV speed constraint is ignored, and obtain the optimal solution to this relaxed problem. The optimal solution shows that the UAV should hover above a finite number of ground locations over time for downlink WPT, and then hover above each user at different time for uplink WIT. Next, based on the optimal multi-location-hovering solution to the relaxed problem, we propose the successive hover-and-fly trajectory, jointly with the downlink and uplink power allocation, to efficiently solve the original problem with the maximum UAV speed constraint. Numerical results show that the proposed UAV-enabled WPCN achieves much higher uplink common throughput than the conventional WPCN with fixed-location AP.
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