Rain attenuation statistics useful for the design of mobile satellite communication systems

We have investigated how rain attenuation statistics, necessary to design fixed satellite systems working at frequencies greater than 10 GHz, are transformed to those applicable to the design of mobile satellite systems working in the same frequency bands and weather conditions in the special case of vehicles driven in zig-zag patterns to simulate city streets. The vehicles' speed has been modeled as a lognormal random variable, a mathematical model derived from measurements performed in freeways or in city traffic. We have used a large number of rain-rate time series collected in Italy (Gera Lario and Fucino) and in Canada (Montreal) to simulate rain-rate spatial fields and radio links at 19.77 GHz along a 30.6 degrees slant path. The simulations have shown that a receiving or transmitting terminal moving in zig-zag patterns may experience, in the long term and for a given attenuation, a smaller outage probability, compared to the fixed terminal. For a given rain attenuation, the ratio between the outage probability of the mobile system and that of the fixed system (probability extrapolation factor xi) is estimated to be around 0.2-0.3 in the optimistic case in which the probability of encountering rain is the same for all observers (fixed or in motion)-a less optimistic estimate shows that the probability of encountering rain might be twice as large and that, as a consequence, the values of xi mentioned must be doubled. Conservative values of xi can be calculated by using average values of rain storm speed and vehicles and average distances covered in the rain by fixed and mobile terminals. The results are less sensitive to changes in the geometrical or other parameters of the simulations.