Proactive eavesdropping using UAV systems with full-duplex ground terminals

In addition of monitoring the environment of interest, an unmanned aerial vehicle (UAV) system can be utilized to actively monitor possible suspicious wireless communications in vicinity. To this end, we propose a proactive eavesdropping scheme wherein a full-duplex (FD) monitor eavesdrops suspicious communication while sending the collected information to the UAV. Our objective is to maximize the eavesdropping capability, while satisfying a certain quality-of- service requirement in a UAV network. In the case where FD monitor is equipped with single transmit/receive antennas, we propose semi- analytical solutions for the UAV altitude and monitor transmit power, whereas in the case of multiple transmit and single receive antennas, a joint optimization problem to determine the transmit beamformer, UAV altitude, and monitor transmit power is efficiently solved using semi- definite relaxation approach. Simulation results show that significant performance improvements can be achieved through optimization. Moreover, achievable performance gains highly depend on the system parameters such as the user zone, maximum monitor transmission power, and the strength of the residual self-interference.