Doppler Characteristics of UAV-to-Vehicle Channel Based on Twin-Cluster Model

With the advantages of low cost， ease of operation， and high mobility， Unmanned Aerial Vehicles （UAVs） have become a crucial component of air-to-ground communication systems. For the multiple-input multiple-output channel derived from real-world propagation scenarios in the context of UAV-to-Vehicle （U2V） communication link， this study proposed a twin-cluster U2V channel model incorporating UAV fuselage scattering effects and three-dimensional （3D） rotation. In this model， the channel consisted of a line-of-sight path， a single-bounce reflection path， and some randomly scattered paths. In the scattering path， the scattering effects introduced by both the ground scatterers and UAV itself were simultaneously taken into account. Consequently， the propagation process of the signal along the random scattering path was decomposed into three segments： from the transmitting antenna to the fuselage scatterer， from the fuselage scatterer to the ground scatterer， and from the ground scatterer to the receiving antenna. We investigated the six-dimensional （6D） motion of UAVs， including 3D translation and rotation， as well as scenarios where ground vehicles moved at arbitrary speeds and in arbitrary directions. We introduced a time-varying attitude matrix to update the position vectors of fuselage scatterers and antennas in real time. Additionally， we analyzed the Doppler shifts and channel statistical characteristics of various paths， including the Time Autocorrelation Function （TCF） and Doppler Power Spectral Density （DPSD）. The study findings indicated that fuselage scattering and 6D motion significantly affected the Doppler effect on the transmitted signal and stationarity of system performance. The UAV’s 3D translation and rotation led to macro- and micro-Doppler shifts in the transmitted signal， respectively， with macro-Doppler shifts being dominant. The greater the 3D translation velocity， the faster the decay of the transmission signal TCF， and accordingly， the poorer the signal stability. The micro-Doppler frequency shift introduced by the 3D rotation caused periodic fluctuations in the DPSD. Thus， to ensure reliable communication under dynamic operating conditions， integrating the UAV’s 6D motion model into the U2V channel framework is essential.