Multi-UAV Interference Coordination via Joint Trajectory and Power Control

Recently, unmanned aerial vehicles (UAVs) have found growing applications in wireless communications and sensor networks. One of the key challenges for UAV-based wireless networks lies in managing the strong cross-link interference caused by the line-of-sight dominated propagation conditions. In this article, we address this challenge by studying a UAV-enabled interference channel (UAV-IC), where each of the $K$ UAVs communicates with its associated ground terminal. To exploit the new degree of freedom of UAV mobility, we formulate a joint trajectory and power control (TPC) problem for maximizing the aggregate sum rate of the UAV-IC for a given flight interval, under practical constraints on the UAV flying speed, altitude, and collision avoidance. These constraints couple the TPC variables across different time slots and UAVs, leading to a challenging large-scale and non-convex optimization problem. We show that the optimal TPC solution follows the fly--hover--fly strategy, based on which the problem can be handled first by finding optimal hovering locations followed by solving a dimension-reduced TPC problem. For the reduced TPC problem, we propose a successive convex approximation algorithm. To further reduce the computation time, we develop a parallel TPC algorithm that is efficiently implementable over multi-core CPUs. We also propose a segment-by-segment method that decomposes the TPC problem into sequential TPC subproblems each with a smaller problem dimension. Simulation results demonstrate the superior computation time efficiency of the proposed algorithms, and also show that the UAV-IC can yield higher network sum rate than the benchmark orthogonal schemes.