Secrecy-Energy-Efficiency Maximization for UAV-Enabled Two-Way Relay Systems

In wireless communication, unmanned-aerial-vehicle (UAV) relay seems to be an available paradigm to combat path-loss and expand signal coverage. Due to the openness of wireless channel and the inconvenient recharging, transmission security and energy efficiency are the most concerned issues for UAV-enabled communication. In this article, for an UAV-enabled two-way relay system, where two wireless terminals exchange their information assisted by a flying UAV and a malicious user tries to eavesdrop the transmitted information, the achievable secrecy energy-efficiency is formulated when the UAV speed, trajectory, allowable power and the time scheduling in the uplink and downlink transmission are considered in a comprehensive manner. To solve this non-convex problem, we decompose it into three subproblems based on the block coordinate descent (BCD) method. Then, the successive convex approximation (SCA) technique and the Dinkelbach algorithm are combined to obtain the global solution in an iterative manner. Simulation results show that the proposed schemes have higher secrecy energy-efficiency compared to the existing baseline schemes.