Joint Placement and Resources Optimization for Multi-User UAV-Relaying Systems With Underlaid Cellular Networks

In this paper, we focus on a multi-user UAV-relaying system, where an unmanned aerial vehicle (UAV) act as a relay for pairs of ground users that coexist with a cellular user. We aim at maximizing the instantaneous sum rate of all ground pairs, while ensuring the rate requirements of the cellular user, by jointly optimizing the UAV placement and transmit power allocation. Due to the non-convex nature of the original problem, we employ block coordinate decent and successive convex optimization (SCO) techniques by decomposing it into two sub-problems, which are alternately solved to iteratively improve the achievable sum rate. Numerical results show that using UAV as relay has remarkable advantages compared to direct ground communications in case of highly unfavorable channels and sparsely distributed ground devices.