A Novel 3D MIMO GBSM for UAV Air-To-Air Communications

Abstract

In the sixth generation (6G) era, the vision of integrated space-air-ground-sea communication networks stresses the importance of unmanned aerial vehicle (UAV) communications. This paper proposes a general three-dimensional (3D) multipleinput multiple-output (MIMO) geometry-based stochastic model (GBSM) for UAV air-to-air (A2A) channels at different altitudes. The proposed channel model is the first to incorporate a dynamically adaptive dual-cluster non-line-of-sight (NLoS) framework, which introduces rooftop clusters to capture the influence of highrise buildings on propagation in mid-to-high altitude scenarios, while retaining the general scattering clusters to ensure accuracy in low-altitude scenarios. Building on this, we introduce a specular reflection (SR) path for ground and rooftop single reflections and establish separate existence probability models for SR and line-of-sight (LoS) components. These probabilities are employed in both the channel impulse response (CIR) generation process and the LoS probability-weighted path loss model. Channel statistical properties, including the time autocorrelation function (TACF), root mean square (RMS) delay spread, and RMS angular spread, are derived and analyzed. Comparisons between simulation results and measurement data validate the accuracy and generality of the proposed channel model.