A STUDY ON TIME DURATION CHARCTERISTICS OF RAIN ATTENUATION AND DATA TRANSMISSION EFFCIENCY FOR SATELLITE COMMUNICATIONS

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The time duration characteristics of rain attenuation of Ka-band satellite radiowave are investigated related to the kinds of rain fronts, using CS-2, CS-3 and N-Star beacon signals (19., 45 GHz, Right-hand circular polarization, Elevation=49.5 deg) received at the Neyagawa earth station for the past 15 years. For the threshold levels less than 4 dB, warm, cold, and occluded fronts five large cumulative time distribution of rain attenuation, while for the threshold values of more than 5 dB, stationary fronts, shower, and typhoon give large distribution. The duration time distribution of rain attenuation becomes large in the order of cold fronts, stationary fronts, and shower-typhoon events for the threshold values of more than 5 dB, stationary fronts, shower, and typhoon give large distribution. The duration time distribution of rain attenuation becomes large in the order of cold fronts, stationary fronts, and shower-typhoon events for the threshold values of 3-10 dB, Rain attenuation … More ratio of Ka-to Ku-band satellite signals is similarly investigated related to the kinds of rain fronts, using BS (11.84 GHz) and N-Star (19.45 GHz) signals, which have been received in our university (Neyagawa, Osaka) for the past 13 years. A comparatively large attenuation ratio was primarily found, when the cold fronts passed over the earth station in Baiu season. In contrast, a comparatively small ratio was primarily obtained, when the earth station was located to the south of the stationary fronts in Akisame season. A small ratio was also found in summertime shower. This difference seems to be caused by a dominant kind of raindrop size distribution in each season. The effects of satellite diversity on Ka-band ranin attenuation were assessed in three propagation paths with the satellite orbital positions are 110, 132, and 150 E, respectively. The attenuation of each path was observed over the four years of 1995-1998 in our university. The up- and/or down-link Ku-band (14/12 GHz) attenuation was converted to the Ka-band down-link (19, 45 GHz) by the frequency attenuation methods, taking into account the kind of raindrop size distribution in each event. As for the attenuation of 20 dB, time percentage of the cumulative distribution is decreased down to about 60% and 40% of the original 0.01% in two-or three-path diversity systems, respectively.. The effects of satellite diversiyt, however, largely depend on the type of rainfall events Less