Energy efficiency maximization for WPT-enabled UAV-assisted emergency communication with user mobility

We investigate the energy efficient communication in the wireless power transfer (WPT)-enabled unmanned aerial vehicle (UAV)-assisted emergency communication system. Specifically, the UAV acts as a base station performs a two-phase task in each time-slot (TS). During the first phase of the TS, frequency division multiple access (FDMA) mode is used to serve multiple mobile users in the downlink. During the second phase, WPT technology is used to charge multiple mobile users on the ground. Due to the limited on-board energy of the UAV, our goal is to maximize the system energy efficiency (EE) by jointly optimizing the UAV trajectory, the information transmit power, the WPT power and the user bandwidth. However, the highly coupled nature of the optimization variables makes the nonconvex problem difficult to solve. In order to solve the problem, a low-complexity alternating iterative optimization algorithm is devised, utilizing block coordinate descent and successive convex approximation techniques. Through simulations, it is demonstrated that the proposed algorithm effectively achieves a balance between system throughput and UAV energy consumption, and can effectively improve the EE of the system compared to the benchmark schemes.