Occluded Scatterers and the Urban Ground-to-ground Channel at Low UHF

Ground-to-ground radio links in urban environments rarely enjoy direct line-of-sight between terminals, and therefore in-canyon, over-rooftop, and scattering from distant structures become primary propagation modes. Because both rooftop diffraction and canyon propagation losses can be severe, and because the walls of deep urban canyons often occlude distant scatterers, the relative importance of these three propagation modes to a given urban channel is unclear. We present results of channel sounding measurements at 437 MHz for ground-to-ground links in Boston, Massachusetts, USA to quantify the importance of each propagation mode. Occupancy curves derived from our measured channels suggest that while canyon-mode propagation is dominant for short range urban links, the importance of the distant scatterer propagation mode increases with terminal separation distance, even when those scatterers are occluded from transmitter and/or receiver view. We present an urban channel model which evaluates the vertical profile of incident power on distant scatterers, even those that are occluded, and find that reasonable agreement can be obtained between measured and modeled channels only when occluded buildings are considered.