Sum-Rate Maximization for UAV Aided Wireless Power Transfer in Space-Air-Ground Networks

The Internet of things (IoT) has become a prominent platform which bridges diverse technologies in order to meet the ever-increasing application requirements of various industries. However, the IoT devices, especially in remote areas that lack infrastructures, are featured by the restricted energy and pose great challenges on network access and sustainable communication. In this paper, we investigate the unmanned aerial vehicle (UAV) aided wireless power transfer under a space-air-ground (SAG) network, where the UAV is exploited as an aerial relay to assist in uploading information generated by ground nodes (GNs), and mounted with energy transmitter to deliver wireless energy for GNs. The goal is to maximize the system sum rate while satisfying the proportional rate for GNs and the sustainability of the ground network. To this end, by adopting decode and forward (DF) and amplify and forward (AF) protocols, two sum rate maximization problems are formulated via jointly optimizing power control, time allocation as well as UAV trajectory. The resource allocation problems are both nonconvex, which are difficult to solve directly. To tackle them, two near-optimal iterative algorithms are proposed by leveraging the successive convex approximation technology and the alternating optimization method. Extensive simulations are provided to demonstrate the effectiveness of the proposed algorithms and evaluate the impacts of various parameters on DF and AF relays.