Pulse or digital communications – Transceivers – Modems
Patent
1995-06-07
1996-10-08
Tse, Young T.
Pulse or digital communications
Transceivers
Modems
455 385, H04B 138
Patent
active
055639089
ABSTRACT:
The invention provides a modulator and demodulator apparatus (modem) which modulates and demodulates a signal in a main channel, for main data, and a secondary channel, for secondary data obtained by frequency division, and which includes a carrier detection unit for detecting a carrier from a demodulation signal and executes a data processing sequence for the demodulation signal in accordance with a result of detection by the carrier detection unit. This apparatus can detect a carrier of a low roll-off ratio accurately and stably without a dispersion in detection time and, consequently, data of a demodulation signal can be processed with certainty. The modulator and demodulator apparatus comprises a filter having a characteristic wherein the time axis response is slow and it is provided at a stage preceding the carrier detection unit so that a demodulation signal which has passed through the filter is input to the carrier detection unit. The modulator and demodulator apparatus includes a modulation unit for modulating and transmitting data having a turnoff sequence with a last end and a demodulation unit for receiving and demodulating a receive signal to reproduce data. The modulation unit includes a tone signal generation unit for adding a tone signal to the last end of the turnoff sequence of the data to be transmitted.
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Kaku Takashi
Kawada Noboru
Fujitsu Limited
Tse Young T.
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