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G/T. In addition, Table 5 lists the estimated values of satel-lite maximum EIRP in dierent cities estimated using the distance of a city to its MBA beam center location, and the downlink estimated rain attenuation margin for a city—such a downlink estimated rain attenuation margin is ob-tained shiing the Kanto MBA 1 beam attenuation margin of 20.8 dB in Kashima by the dierence of the satellite estimated maximum EIRP at a city to the MBA Kanto satellite estimated maximum EIRP of 72.6 dBW. According to Table 5, the following downlink unavailability in dier-ent districts is expected: in the districts from Hokkaido to Tohoku, 0.01%; in the districts from Kanto to Kyushu, 0.03%; In Okinawa, 0.05%.6Measuring rain attenuation characteristicse rain attenuation in the Ka band is measured using the level TDMA reference burst (RB) used in the WINDS regenerative link and the level of the WINDS network information signal residual carrier.Figure 14 shows the downlink TDMA frame format—a super-frame consisting of 16 basic frames, and a basic frame consisting of 20 slots.e reference burst is satellite-generated, packed in the rst slot of each of the basic frames and transmitted with a constant level of satellite output power. Consequently, by observing the RB reception level, the satellite downlink rain attenuation can be measured independently of the uplink situation. e measurements were conducted at NICT Kashima Space Technology Center, NICT Headquarters (Koganei), and Hino Campus of Tokyo Metropolitan University, where the RB center frequency of the Kanto beam is 17.7925 GHz.FiF15　TDMA RB level measurement systemAt the same time, at Kashima Space Technology Center, 1 minute of rainfall is measured, studying the correlation between rain attenuation and rainfall.Figures 16 and 17 show examples of the measurements conducted at Kashima Space Technology Center. In Figure 16, a big attenuation can be observed between 15:11 and 15:38. Figure 17 shows an enlarged illustration of the corresponding time period. ese gures clearly show the correlation of rain attenuation and rainfall. Also, a time lag from the rainfall to the rain attenuation can be found. e time lag is likely to have been caused by wind owing, in most of the period, from the Kashima WINDS line of sight direction—the rain clouds causing rain attenuation on the slant transmission path to arrive in Kashima later by the delay time. In addition, those gures show that the rate of rain attenuation is about 0.5 dB/s at maximum.Also, the rain attenuation was measured by observing the WINDS network information signal residual carrier level at every second using spectrum analyzers. e fre-quency of the network information residual carrier is 18.9 GHz. e rain attenuation of the network information TabT4　Uplink rain attenuation versus satellite link unavailabilityUplink rain attenuation (ITU-R P.618-8)Satellite : WINDS143.0degrees EastUplink frequency28.05GHzUplink rain attenuation(dB)10.50.30.10.050.030.01NemuroHokkaidou East0.90.90.92.14.17.021.019.425.8SapporoHokkaidou South0.80.80.81.93.76.419.523.129.5MoriokaTouhoku0.80.80.81.83.97.126.223.029.4SendaiTouhoku0.70.70.71.73.97.329.019.425.8KashimaKantou3.85.98.014.219.724.637.120.326.7NagoyaCuubu5.78.711.620.528.034.651.324.430.8OosakaKinki4.87.510.017.724.430.144.921.027.4HiroshimaChuu-shikoku4.77.29.717.223.729.343.723.229.6KumamotoKyuusyuu5.07.810.518.525.231.145.920.226.6NahaOkinawa7.011.515.626.835.743.261.122.929.3City/AreaMBAEstimatedSatellite G/T(dB/K)Estimated Uplink RainAttenuationCompensation (dB)Unavailability (% of an average year)TabT5Downlink rain degradation versus satellite link unavailability　Satellite estimated maximum EIRPs are the values at MPA output power of 280 W.Required downlink rain marginSatellite : WINDS143.0degrees EastDownlink frequency18.25GHzDownlink rain degradation(dB)10.50.30.10.050.030.01NemuroHokkaidou East0.50.50.51.63.25.213.370.318.5SapporoHokkaidou South0.40.40.51.43.04.812.573.321.5MoriokaTouhoku0.30.30.31.33.05.316.071.419.6SendaiTouhoku0.30.30.31.33.05.517.569.918.1KashimaKantou2.74.25.59.112.114.621.472.620.8NagoyaCuubu3.95.97.612.316.319.728.672.220.4OosakaKinki3.55.26.711.014.517.525.472.620.8HiroshimaChuu-shikoku3.34.96.510.714.017.024.672.821.0KumamotoKyuusyuu3.55.36.911.314.817.925.872.120.3NahaOkinawa4.87.49.615.319.923.733.272.320.5City/AreaMBAMaximumEstimated SatelliteEIRP (dBW)DownlinkEstimated RainMargin (dB)Maximum estimated satellite EIRP is the case of MPA output power is 280W。Unavailability (% of an average year)LNCAntennaReceive SignalIDUGPSReceiverData GatheringPCReference TimeTDMA SlotSignalRain Attenuation MeasuringEquipmentGPS AntennaOutdoorIndoorSuper Frame (T=640ms)Frame #1Traffic SlotFrame #15Slot #2Slot #19Slot #1T=2msFrame (T=40ms)Frame #0報知Slot(T=2ms)Slot #0FiF14　Downlink TDMA frame format3 Ultra-High-Speed Satellite Communication Technology84　　　Journal of the National Institute of Information and Communications Technology Vol. 64 No. 2 (2017)