Orbital and site diversity systems in rain environment: Radar-derived results

During the summers of 1981 and 1982, an experiment was carried out in the Po River Valley with the scope of evaluating the statistical performance of diversity systems for earth to satellite links experiencing rain attenuation. The data were collected by an
S
-band meteorological radar scanning a
32\deg
inclined plane having the SIRIO path as its highest radial. Attenuation values directly measured through the satellite beacon at 11.6 GHz were used to "calibrate" the radar on event basis, in order to properly convert reflectivity into specific attenuation. In a previous paper the performance of site diversity (SD) systems was presented for earth terminals spaced from 1 to 20 km. In this paper, the same set of data is processed to simulate orbital diversity (OD) systems, which employ two satellites angularly spaced and one earth terminal. Aperture angles
\theta
up to
95\deg
have been considered. The results show that this diversity scheme already has a significant gain with
\theta = 30\deg
where at 10 dB single link attentuation the gain (as defined by Hodge) is 2.5 dB and it increases steadily as
\theta
increases. The comparison between orbital diversity and site diversity performances shows that the site separation is linearly related to the orbital diversity aperture angle for any single link attenuation of the site diversity configuration.