Power and Trajectory Optimization for UAV-Enabled Amplify-and-Forward Relay Networks

Unmanned aerial vehicle (UAV) is suitable to improve connectivity of wireless communication networks in harsh environment due to its flexible deployment and high mobility. In this paper, we consider the case that a UAV is employed as a mobile relay to ferry data between two disconnected ground nodes. The amplify-and-forward mobile relay technique is studied. By exploiting the channel state variation induced by the movement of UAV, we consider maximizing the end-to-end throughput of this mobile relay system by optimizing the source/relay power allocation, as well as the UAV's trajectory. However, the formulated problem is non-convex and intractable to solve. To address this non-convex problem, we propose two iterative algorithms to optimize the source/relay power allocation with the fixed UAV's trajectory and the UAV's trajectory with fixed power allocation, by successive convex optimization, respectively. Then, an iterative algorithm is proposed to optimize the source/relay power allocation and UAV's trajectory in an alternate manner. By exploiting the predictable channel variation via the proposed power and trajectory optimization scheme, numerical results show that significant throughput gains can be achieved.