Joint Optimization on Energy Efficiency for UAV-Enabled Two-Way Relay Systems.

To combat the severe path fading between two users/access points and obtain enough signal gain for demodulation, a three-terminal cooperative communication system with a UAV operating as a two-way relay is presented in this paper, and then its optimal energy efficiency is investigated. Specifically, considering the time slot pairing between multiple access (MA) and broadcast (BC) phases, the energy efficiency of the UAV is maximized by optimizing the transmit power of the three terminals and the UAV trajectory jointly. For such a non-convex problem, to obtain its optimal solution, it is decomposed into three subproblems based on the block coordinate descent (BCD) method. Then, after the optimal solutions of the subproblems have been derived based on the successive convex approximation (SCA) techniques, the overall solution of the original optimization problem is obtained in an alternative manner. Simulation results show that the proposed optimization scheme can enhance energy efficiency significantly compared to other existing schemes while considering the reduction system power consumption.