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onboard regenerative switch subsystem (ABS: ATM Baseband Switch subsystem), and a multi-port amplier (MPA). e MBAs establish a communication line between the Japanese mainland and cities in Southeast Asia via 19 xed spot beams. e APAA establishes a communication line within the earth coverage of two spot beams by hop-ping.e adjacent xed beams are separated by polarization (vertical, horizontal). e APAA is vertically polarized. e same frequency band can be used for both beams and the SS-TDMA transmits a TDMA slot to each beam. WINDS has both a regenerative mode and a bent-pipe transponder mode. Figure 1 shows the specications of the WINDS transponder. e high-speed data transmission at 622/1244 Mbit/s using high-speed burst modem is operated by the bent-pipe TDMA mode.Both the regenerative transponder mode and the bent-pipe transponder mode are an SS-TDMA system that en-ables an Internet IP connection.ere are six routes in the bent-pipe TDMA mode of WINDS. Four routes transmit via a broad band-pass lter and the other two routes transmit via a narrow band-pass lter in transmission and reception. ere are six routes that pass band-pass lters (BPF-W1, W2, W3, W4, U1, and U2) from the communication pass of WINDS MBA-LNA/RX (or APAA) to MPA-MBA/TX (or APAA). e BPFs of BPF-W1 to BPF-W4 transmit over the entire frequency band of 1,100 MHz. e BPF-U1 and BPF-U2 transmit only the upper 600 MHz bandwidth of the 1,100 MHz frequency band. When using in the regenerative transpon-der mode, the upper band is used for the bent-pipe tran-sponder mode and the lower band is used for the regenerative transponder mode [3].SDR-VSAT and LET were developed for the purpose of establishing a high-speed network. SDR-VSAT consists of an earth terminal mounted on a vehicle (SDR-VSAT1) and a transportable mobile earth terminal (SDR-VSAT2). LET was constructed at Kashima Space Technology Center as a xed earth terminal.e views of LET, SDR-VSAT1 and SDR-VSAT2 are shown in Figs. 3, 4 and 5, respectively.e specications of the three earth terminals are shown in Table 2. e residual carrier of mission telemetry is used for antenna tracking of LET and SDR-VSAT1. SDRV-SAT2 does not have an antenna tracking system. e eect on level uctuation by tracking is not large and there is no eect on level uctuation by tracking in a short time experiment. e maximum power of HPA is 215 W. e bandwidth of transmission is 1,100 MHz and the center frequency of IF is 3,000 MHz.An example of link design of the bent-pipe TDMA mode is shown in Table 3. e C/No margin of the com-LETSDR-VSAT1SDR-VSAT2Antenna4.8 m Cassegrain reflector antenna2.4 m offset feed Gregorian reflec-tor antenna 2.4 m offset feed antenna Antenna gainTx: 60.2(dbi)Rx: 56.5(dBi)Tx: 53.9(dbi) Rx: 50.2(dBi)Tx: 54.7(dbi) Rx: 51.8(dBi)FrequencyTx:28.05 GHz ± 550 MHzmRx:18.25 GHz ± 550 MHzHPA output power215 WEIRP79.3 dBW73.1 dBW74.0 dBWG/T32.7 dB/K26.3 dB/K27.0 dB/KFlatnessRF loop back: 2.55 dBp-p (1.1 GHz BW)Spuriousless than -60 dBcTabT2　Earth station specificationsFiF3　LETFiF5　SDR-VSAT2FiF4　SDR-VSAT11033-4 622/1,244 Mbit/s Dual Rate High-Speed Burst Modem TDMA Satellite Communication Experiments