  Jittering effects significantly degrade the performance of UAV communications
especially in millimeter-wave (mmWave) band. To investigate and mitigate the
impacts of UAV jitter to mmWave communications, we firstly model UAV mmWave
channel based on the geometric relationship between element antennas of the
uniform planar arrays (UPAs) in receiver side and transmitter side, and we
incorporate the jittering effects to our channel model through extracting the
relationship between UAV attitude & position and angle of arrival (AoA) & angle
of departure (AoD) of the UPAs. Then, based on the extracted relationship, we
propose to utilize UAV navigation information to obtain a rough estimation of
AoA and AoD, and we also analyze the impact of AoA and AoD estimation error to
UAV beamforming. Finally, we propose a direction-constrained beam training
scheme to refine the AoA/AoD estimation. Particularly, we construct a partially
random sensing matrix to measure the channel within a narrow angle range that
is centered at the aforementioned rough estimate of AoA/AoD. Numerical results
show that our proposed UAV beam training scheme with navigation information is
able to fast and accurately estimate the AoA/AoD fluctuation caused by UAV
jitter.
