PREDICTION OF SITE DIVERSITY PERFORMANCE IN SATELLITE-COMMUNICATIONS SYSTEMS AFFECTED BY RAIN ATTENUATION - EXTENSION OF THE 2-LAYER RAIN MODEL

Site diversity is a classical countermeasure to rain attenuation in sa tellite communications systems at frequencies above 10 GHz. The paper has extended the Two-Layer Rain Model to predict site diversity perfor mance. Simple physical and statistical hypotheses have been assumed fr om which the formulae to calculate the bivariate probability distribut ion of the diversity link have been derived (it is not a best fit mode l) by standard calculations. The model has been then tested against a large experimental data set of direct (beacon+radiometer) and indirect (radar) experiments, with frequencies up to 30 GHz and distances from 2 km to 48 km. Defining the error epsilon = g(pre) - g(mea), where g = G/A is the ratio between the diversity gain and the single link atte nuation (at a given probability), we have obtained [epsilon] = 0.037 a nd square-root < epsilon2 > = 0.129. The model is thus not biased. Sim ilar results have been obtained when E is conditioned to frequency or site separation. The predictions have been then compared to those obta ined from Hodge's well-known formula. The two methods give about the s ame statistical errors: this means that the simple physical and statis tical hypotheses of the Two-Layer Rain Model hold on average. As the p resent model needs only a meteorological quantity (i.e. the rain-rate distribution) and gives a complete ''picture'' of the statistical proc ess of attenuation, its applicability is more general than Hodge's for mula.