Sum Rate Maximization for UAV-Enabled Wireless Powered NOMA Systems

In this paper, we consider the sum rate maximization problem of uplink non-orthogonal multiple access (NOMA) system with unmanned aerial vehicle (UAV)-enabled wireless power transfer (WPT). The sum rate problem is a non-convex problem, which is difficult to handle directly because the energy harvesting time and position of UAV are coupled in the objective function. We propose an iterative algorithm to search the energy harvesting time and the position of UAV. The energy harvesting time problem is solved by the bisection search method. Then, the position optimization problem is solved by the quadratic transform method. Finally, based on the above two methods, we propose a two-tier iterative algorithm to jointly optimizing the energy harvesting time and position of the UAV. Simulation results show that the proposed algorithm has a better performance compared with the benchmark algorithms.