Gridless Compressed Sensing Based Channel Estimation for UAV Wideband Communications With Beam Squint

Unmanned aerial vehicle (UAV) has become an appealing solution for a wide range of commercial and civilian applications thanks to its high mobility and flexible deployment. Due to the continuous UAV navigation, the channels between UAV based arial base station (BS) and the ground users are subject to the Doppler effect. Meanwhile, when UAV is equipped with massive number of antennas in high frequency band such as mmWave and Tera Hertz (THz), the non-negligible propagation delay across the array aperture would cause
beam squint
effect. In this paper, we first investigate the channel under both Doppler effect and beam squint effect for UAV communications with large antenna array and high frequency band. Then, we design a gridless compressed sensing (GCS) based channel tracking method, where the high dimension uplink channel can be derived by estimating a few physical parameters such as the direction of arrival (DOA), Doppler shift, and the complex gain information. Besides, with the Doppler shift reciprocity and angular reciprocity, the downlink channel can be derived by only one pilot symbol, which greatly decreases the downlink channel training overhead. Various simulation results are provided to verify the effectiveness of the proposed methods.