  This paper investigates an unmanned aerial vehicle (UAV)-enabled wireless
communication system with energy harvesting, where the UAV transfers energy to
the users in half duplex or full duplex, and the users harvest energy for data
transmission to the UAV. We minimize the total energy consumption of the UAV
while accomplishing the minimal data transmission requests of the users. The
original optimization problem is decomposed into two subproblems: path planning
subproblem and energy minimization subproblem with fixed path planning. For
path planning subproblem, the optimal visiting order is obtained by using the
dual method and the trajectory is optimized via the successive convex
approximation technique. For energy minimization subproblem with fixed path
planning, we firstly obtain the optimal portion of data transmission time
within the entire procedure and the optimal transmission power of each user.
Then, the the energy minimization subproblem is greatly simplified and it is
efficiently solved via a one-dimensional search method. Simulation results are
illustrated to verify the theoretical findings.
