Joint statistics of rain attenuation on terrestrial and earth‐space propagation paths

Abstract

Radar reflectivity data from the summer of 1975 were used to simulate the rain attenuation at 13 GHz on a network consisting of five earth terminals and six interconnecting terrestrial links. As rain echoes passed over the complex of terrestrial and earth‐space propagation paths, the attenuation over each of the eleven paths was calculated as a function of time with a resolution of a few minutes. Thirty‐four hours of data from twelve days were analyzed statistically to determine attenuation distributions for all paths in the network, separately and in various combinations. The five earth‐space paths were parallel, all at 18.5° elevation and 121.5° azimuth. The average attenuation distribution for these paths was essentially the same as that reported by Hodge for a network of eleven terminals located 35 km to the south of our network. Moreover, an analysis of the diversity gain achieved by using pairs of earth‐space paths revealed a dependence on terminal separation distance that was not significantly different from that of Hodge. A study of the attenuation distributions for the six terrestrial links of the network showed primarily a dependence on path length. For paths of equal length, however, moderate values of attenuation tended to occur less frequently on paths oriented perpendicular to the average direction of storm motion. Analyzed from the viewpoint of route diversity, data for the terrestrial links showed that the frequency of outages over a 40 km path could be reduced by an order of magnitude by adding a repeater along the route. Earth stations, defined as consisting of a main and an alternate earth terminal plus the terrestrial link between them, were found to have a reliability determined primarily by joint outages on the two earth‐space paths. Exceptions were cases with (1) baselines longer than about 30 km, (2) a low reference fade margin on the terrestrial link, (3) a terrestrial path leaving the main terminal in the same direction as the satellite azimuth. In these cases outages on the terrestrial link could further limit the overall system reliability.