Collaborative Beamforming for Cognitive UAV Relaying System Coexisting with Satellite Networks

In this paper, we study a cognitive unmanned aerial vehicle (UAV) relaying system (CURS) which shares the downlink frequency of a satellite network. Specifically, we propose a collaborative beamforming (CBF) scheme that maximizes the signal-to-interference plus noise ratio (SINR) of CURS, subjects to the SINR requirements of the satellite network and the individual transmit power constraints of UAV relays. Since the original optimization problem is non-convex and mathematically intractable, we first transform it into an approximate convex one by means of the Charnes-Cooper transformation and the penalty function method as well as the difference of two-convex functions (D.C.) approach. Then a convergence proven iterative algorithm is designed to find the optimal CBF solution. Simulation results are provided to demonstrate the effectiveness of the proposed scheme and the impact of UAV transmit power and satellite network SINR requirements on the CURS.