HTML5 Webook

147/182

angle and received power level. As seen from the gure, during the ight test, the plane banked more steeply than usual and the antenna was no longer aligned with WINDS when the elevation angle was above 65° and below 25° so that the received power dropped out. e received power stabilized for elevation angles in the range of 25°–65°. Note that the plot is not shown in the vertical range between -52 dB and -57 dB. is was intentionally done to exclude the time zone where excessively low received power level is reported due to the following reason: received power of the communication signal is received at certain timings during the received level measurement, which is signicantly low as compared with the normal received power level. As described above, the data from the ight experiments veried that AES satised the required specications on tracking characteristics.Figure 13 shows the characteristics of the Doppler shi during ight in Fig. 8 patterns. e maximum Doppler shi was 7.9 kHz. e theoretical value during ight at a speed of 720 km/h is 8.2 kHz. e dierence between these values is 4%, which indicates that the actual value was approximately equal to the theoretical value. It can be concluded that when designing the frequency-tracking performance of a modem for a high-speed mobile earth station, the theoretical value can be calculated from the station’s speed. In this case, since we are using a geostation-ary satellite, we do not have to consider Doppler shi due to the satellite’s relative velocity. Note that the Doppler plot in the gure has missing sections near -4,000 Hz, which result from temporary incapability of the system to detect signal due to IDU’s local leak.(C)Data transmissionUp-link throughput characteristics from AES were in-vestigated, wherein the following two communication protocols were tested using iperf [9]: UDP (User Datagram Protocol) and TCP (Transmission Control Protocol). e measurements were made, while in a stable ight situation, using the regenerative 51 Mbps mode of WINDS. Figure 14 shows the throughput characteristics of UDP communica-tion. e gure indicates stable communication at the data rate of 38 Mbps.Figure 15 shows the throughput characteristics when TCP is used. ese results show that stable communication is possible at 31 Mbps. Since congestion is controlled be-tween terminals according to the state of the line with this protocol, the value uctuated when using TCP. is test showed that communication speed was recovered even aer an instantaneous interruption occurred, causing a delay time of over 500 ms.(d)Large-volume le transmissionTo evaluate the time required to upload large volume les, a high-resolution image captured by Pi-SAR (Polarimetric and Interferometric Airborne Synthetic Aperture Radar) was uploaded from AES to a web server. It took 1 minute, 18 seconds to upload the 192 MB le. is translates into a data communication rate of about FiF13Time variation of Doppler frequency during figure-of-eight flighttDoppler Frequency [Hz]FiF14　UDP based throughput characteristicsFiF15　TCP based throughput characteristics1433-8 Aeronautical Satellite Communications using WINDS