On Cylinder- vs. Sphere-Based Stochastic Modeling of Space-Time Correlated UAV-to-UAV Channels

The two-cylinder model and the two-sphere model are two widely-used geometrical channel models that are both the generalizations of the two-ring model; however, a comparative study between them seems to be missing in literature. In this paper, under the background of unmanned aerial vehicle (UAV) air-to-air propagation modeling, similarities and differences between the two geometry-based stochastic models (GBSMs) are analyzed by reviewing their respective closed-form space-time correlation functions (ST-CFs). Notably, some interesting properties of the ST-CFs are analytically obtained, which reveals the behaviors of the ST-CF with respect to several UAV-related parameters, including the moving directions and the antenna orientations.