Effects of Terrain on 3.5 GHz Propagation Modeling of Diffraction in an Urban Environment

Urban propagation models are almost exclusively empirical or semi-empirical with a strong focus on signal strength and direct line-of-sight distances suitable for commercial broadband deployment scenarios. Military systems, by contrast, operate over significantly longer distances where the effects of terrain diffraction and diurnal/synoptic variability in atmospheric refractivity begin to dominate. Parabolic Equation (PE) models offer deterministic approaches for incorporating terrain and atmospheric effects, but their use has been largely limited to oceanic and littoral areas where the need to represent refractive effects associated with maritime gradients outweighs the added computational cost and complexity. In this manuscript, we evaluate the performance of semi-empirical and PE models in predicting propagation loss in a long-distance over-land urban scenario. Measurement data were recorded from 17 km and 45 km long drive routes that included terrain features and urban clutter. Comparisons with measured data show that PE models demonstrated up to a 14.4 dB improvement in median difference between measurement and predictions compared to semi-empirical models.