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

为了在多雨条件下与降雨区域分布相关的卫星网络运行性能，利用我校（大阪Neyagawa）从三颗卫星（SCC、N-Star和BS）获得的Ku波段和Ku波段雨衰减数据，对卫星多样性的影响进行了数值研究，每颗卫星在方位角上间隔30度。利用这些卫星，数值分析了地点多样性对三个地点的影响，如京都大学的宇治校区，志垣MU天文台和我们大学，它们的距离为20-50公里。利用每个地点累积的衰减数据，对2003-2004年的统计数据进行了评估。结果表明，通过使用站点分集技术在两个地面站之间切换操作，每年3-4 dB的ku波段衰减时间百分比从0.1%降低到0.01%。另一方面，根据三个地点之间衰减发生的时间差估计雨区运动的速度和方向。将过去两年的100多个降雨事件的结果与天气图上的气旋和雨锋的结果进行了比较。两种方法推断的速度和方向的相关系数均大于0.9，表明在10公里的水平尺度上，雨云运动在几乎所有情况下都与雨锋垂直。雨云运动的这种性质表明，当站点或天线波束的位置垂直于雨锋运动的方向时，站点和卫星分集技术特别有效。

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.