Importance

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Abstract

An on-hook/off-hook detection circuit (61) detects the voltage level of a telephone line C and thus detects whether the audio band communication using the telephone line C is in on-hook state or in off-hook state thereby to output a status detection signal (81). TEQ (63), FEQ (66) and a constellation encoder gain scaling (67), based on the particular status detection signal (81), conducts the data communication by the adaptive equalization, the bit allocation and the gain allocation in the time domain and the frequency domain using separate tables (75 to 80) for on-hook and off-hook states. In on-hook state where no telephone is used, the transmission subcarrier is extended or shifted up to the neighborhood of-the audio band and the communication is conducted using up to the audio band.

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First Claim