Beam Tracking and Optimization for UAV Communications

Beam tracking for unmanned aerial vehicle (UAV) communications is an enabling technology that maintains the connection between UAV and ground base stations. In this paper, we propose an efficient training-based beam tracking scheme for UAV system. To track the beam, we need to answer how frequently the training should be performed. The proposed scheme uses joint beam training and angular velocity estimation, based on which the beam coherence time can be obtained. Accordingly, the training frequency can be adjusted based on the variation of beam coherence time to save the training overhead. Then, we study the maximization of flying range and speed of UAV. To this end, we optimize the beamwidth by choosing different codebook. For flying range maximization, we first propose an efficient algorithm that can obtain the optimal beamwidth and the corresponding maximal flying range at a given speed of UAV. To gain more insight, we then show that in most practical scenarios, the maximal flying range is achieved with the narrowest beamwidth. Furthermore, we show that when the flying range is small, broad beam should be used to support high speed of UAV, and vice versa.