Impact of 6D Mobility on Doppler Characteristics of UAV-to-Vehicle Channels

Unmanned aerial vehicle (UAV) empowered vehicular networks are capable of providing flexible radio access, efficient data transmission, and secure driving operation. For this promising application, we focus on channel modeling for UAV-to-vehicle (U2V) communications in this paper. Based on six-dimensional (6D) mobility patterns, a semi-determined geometry-based model framework for U2V communications is studied. Multi-path Components (MPCs) are composed of a line-of-sight (LoS) path, a ground reflection (GR) path, and several scattering (SC) paths. Specifically, we consider the movement of a UAV in both 3D translational and 3D rotational directions, while a ground vehicle is capable of moving in any direction with varying velocity. Then, the expressions of Doppler shift in different paths are derived, considering a spatial angle, and eventually, Doppler power spectral density (PSD) is obtained by integrating Doppler shifts in each path. Simulation results demonstrate that the distinct impacts on Doppler characteristics led by linear velocity, angular velocity, the direction of the rotation axis when the UAV rotates, and the direction of translation.