Development of variable-rate digital modem for digital satellite communication systems

The authors present the configuration of a continuously variable-rate digital modem that has been developed using a digital signal processing technology based on custom LSIs. The modem covers the operating baud rate range from 40 Kbauds to 6 Mbauds, and the bit error rate degradation for any baud rate is within 0.5 dB of the theoretical value. Seven custom-designed LSIs have been developed for the modem to realize a compact construction unit and low power consumption. The selection of the cutoff frequency of pre- and postfilters is discussed.<
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