A STUDY ON NETWORK PERFORMANCE QUALITY AND DATA TRANSMISSION EFFCIENCY FOR SATELLITE COMMUNICATIONS IN RAINY CONDITIONS

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For the performance of satellite network operations related to the distributions of rain areas in rainy conditions, the effects of satellite diversities are numerically studied using the Ku- and Ku-band rain attenuation data obtained at our university (Neyagawa, Osaka) from the three satellites, SCC,N-Star, and BS, with each separated by 30 deg in azimuth. Using these satellites, the effects of site diversities are also numerically examined among three location, such as the Uji campus of Kyoto University Shigaraki MU observatory and our university with their distances of 20-50 km. The statistics are evaluated during the two years of 2003-2004, using the attenuation data aceumulated at each location. As a result, the yearly time percentages for Ku-band attenuation of 3-4 dB are shown to be reduced from 0.1% to 0.01% by switching operations between the two earth stations using the site diversity techniques. On the other hand, velocities and directions of rain area motions am estimated from the time difference of attenuation occurrence among the three locations. The results of more than 100 rainfall events are compared with those obtained from the cyclones and rainy fronts in weather charts for the past two years. A very good agreement is found between the velocities and directions inferred from the two methods with correlation coefficients of more than 0.9, indicating that the rain cloud motions are just perpendicular to the rain fronts in almost all cases over a horizontal scale of a few 10 km. This nature of rain cloud motions suggests that site and satellite diversity techniques are especially effective when the site or antenna beam locations am aligned in the direction perpendicular to the motion of rain fronts.