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Low-Overhead Beam Alignment for High-Speed UAV Communications

Owing to the merit of mobility and dynamic deployment, the unmanned aerial vehicle (UAV) can be widely used as aerial users, base stations (BS) or even relays for various tasks such as surveillance, aerial photography and remote sensing. Moreover, millimeter-wave (mmWave) communication with large spectrum resource can meet the vast demand of data transmission for various UAV application scenarios. In this paper, considering mmWave-UAV communication system, we study the low-overhead beam alignment to enable reliable link between the UAV and the ground BS. We focus on uplink capacity and overhead for high-speed UAVs without the motion restriction. Firstly, we study the beam training stage where we collect the initial estimation of steering angle, thus predict the angular velocity of UAV and beam coherence time. Then, we propose a low-overhead beam tracking algorithm to predict the beam direction in the subsequent time slot. Moreover, we exploit the beam coherence time to adaptively adjust tracking frequency to save tracking overhead. Simulation results show that our proposed scheme outperforms the conventional training-based tracking scheme in terms of overhead, and it is superior to the mixed search scheme for uplink capacity in both high-speed and low-speed scenarios.