Robust Hybrid Beamforming for Jittering UAV with MmWave Antenna Array

Unmanned aerial vehicle (UAV) communication systems with millimeter wave (mmWave) beamforming have good technical potential and wide applications. However, due to the directivity of mmWave beams, the jitter of the UAV platform may cause beam misalignment, and may cause severe loss of the channel gain, which has not been solved well yet. To this end, this paper considers data links between a jittering UAV base station (BS) equipped with a mmWave antenna array and multiple ground access points (APs). A robust hybrid beamforming scheme is proposed for the UAV-BS by formulating an optimization problem to maximize the minimum achievable rate of all the APs. First, we design analog beamforming (ABF) through generating wide beams towards the APs in the angle domain based on chirp sequence, which can flexibly adjust beam direction and beam width. Afterwards, equivalent downlink channel estimation is obtained with fixed ABF. Finally, digital beamforming is performed with zero-forcing algorithm and water-filling power allocation. Extensive simulation results demonstrate that the proposed robust hybrid beamforming solution can provide satisfactory quality of service against the UAV jitter.