HTML5 Webook

109/182

board. All of the boards consist of digital circuits using FPGAs. ATCA (Advanced Telecommunication Computing Architecture) is installed at the back plane.Quadrature Phase Shi Keying baseband signals are transformed to IF frequency band signals in the RF unit. e turbo product code (TPC: (128, 120) 2) for 4-bit so decision is used as FEC. e coding gain attained by simulation is 9 dB for the case of a coding rate of 0.879 and the BER=10-10. e transmission bit rate of QPSK modulation at the user rate of 1,244 Mbit/s is 1,648 Mbit/s (824 Msymbol/s).It is 824 Mbit/s (412 Msymbol/s) at the user rate of 622 Mbit/s.In order to correspond to the data rate of 1,244 Mbit/s, a D/A converter of 2 Gsample/s for a 4 × 1 multiplexer for a modulator was developed. In order to generate QPSK baseband signals of I and Q, a carrier frequency of 0 Hz is used for transmission at 1,244 Mbit/s, and both carrier frequencies of +273.6 MHz and -273.6 MHz are used for transmission at 622 Mbit/s. ese signals are converted to 3,000 MHz band IF signals in the RF unit.e demodulator and decoder boards were improved by correcting the FPGA program for the prototype modem board (breadboard model for 622 Mbit/s).e control board can be managed by Web application or telnet. A router is used for selection of routes. e TCP Accelerator is used to suppress the eect by transmission delay. In the experiment shown in this paper, the method to expand window size by Hybla/Reno is adopted.3Results of satellite communication experiment [8]–[11]3.1622 Mbit/s transmission experiment(1)Kanto Beam 622 Mbit/s 1 wave transmissione characteristics of bit error rate (BER) in 622 Mbit/s 1 wave continuous transmission are shown in Fig. 8. e transmission in the mode where a satellite switch of the satellite does not operate (normal bent-pipe mode) when using all frames of the modem TDMA is called 1 wave continuous transmission. e BER of 10-10 was achieved for 10 dB of Eb/No. e result of 10-10 means deterioration of 1-3 dB compared with the ground experiment (IF loop-back). e BER characteristic of this modem in ideal Gaussian noise channel obtained by simulation is 10-9 for 4 dB of Eb/N0 [3].e possible causes of deterioration of satellite lines are uctuations in the received signal level, frequency perfor-mance of the transmitter or non-linear characteristics. e received signal level of LET uctuates about 1 dBp-p, and 1.0E-101.0E-091.0E-081.0E-071.0E-061.0E-051.0E-041.0E-031.0E-021.0E-011.0E+00456789101112BEREb/No (dB)LET UpperLET LowerSDR-VSAT1 UpperSDR-VSAT1 LowerIF Loopback UpperIF Loopback Lower>10-10TabT4　Specification of 622/1244 Mbps Dual-Rate Burst ModemUser data rate622 Mbit/s1244 Mbit/sIF frequency2726.4, 3273.6 MHz3000.0 MHzModulationQPSKAccess methodSS-TDMAModulation rate (before FEC)724.2 Mbit/s1448.4 Mbit/sModulation rate824 Mbit/s1648 Mbit/sError correctionTurbo product code (128, 120)24bit soft decisionRoll offRoot raised cosineRoll off factor = 0.35User interfaceGiga bit EthernetRouter and TCP accelerator usedFiF7　622/1244 Mbps Dual-Rate Burst Modems (two sets)FiF8　BER result for 622 Mbit/s transmission test1053-4 622/1,244 Mbit/s Dual Rate High-Speed Burst Modem TDMA Satellite Communication Experiments