Experimental rain attenuation statistics estimated from radar measurements useful to design satellite communication systems for mobile terminals

Based on experimental data, we have reported a reliable method to scale the cumulative time T_F,T(A) that rain attenuation A (dB) is exceeded in a fixed satellite system to the time T_M,T(A) that it is exceeded in a satellite system for mobile terminals. Zigzag routes and ring-roads simulated city patterns; straight routes simulated freeways. In all cases, T_M,T(A) can be expressed as T_M,T(A)=ξT_F,T (A) with a probability scaling factor ξ independent of A. The simulations have been made at 19.77 GHz with satellite elevation angle θ of 30.6°, 45°, 60°, 80°, and 90°. For the horizontal structure of rain, we have used a very large number of rain-rate maps of rain storms randomly observed in 1989-1992 by a meteorological radar placed at Spine d´Adda (northern Italy). The vehicle speed was modeled as a log-normal random variable. We found: (a) in zigzag routes, T_M,T(A)<T_F,T(A), i.e., ξ<1, with results depending on vehicle speed modeling and starting conditions; (b) in a ring-road, there is no difference between fixed and mobile systems (ξ=1); and (c) in straight freeways, T_M,T(A)≪T_F,T (A)(ξ≪1); T_M,T(A) can change significantly in different straight lines and in opposite directions (anisotropy and asymmetry) for medium-large attenuation. When compared to zigzag routes or ring-roads, the performance in straight freeways is the most optimistic. For θ>30.6° and for the same pattern, ξ is fairly independent of θ. Since the radar rain maps are a reliable estimate of the horizontal structure of rain, the findings, which can be considered frequency-independent, stand as a very good prediction of the results obtainable by experiments