Patent ID: 6778595
Filing Date: 2004-08-17
Classification: H04M

Abstract:
An ADSL modem connected to a telephone line, comprising a detector for detecting whether another ADSL modem connected to the telephone line is using the ADSL frequency band and a control unit for suppressing the application of the signal energy to the ADSL frequency band upon detection that another ADSL modem is using the ADSL frequency band;wherein said detector includes a FFT demodulation unit for carrying out the FFT demodulation of one carrier in the input signal from the telephone line, a normalization circuit for generating a normalized demodulation signal by normalizing the output signal of the FFT demodulation unit, a symbol delay buffer for generating a one-symbol delay signal delayed one symbol behind the output signal of the normalization circuit, a complex conjugate unit for generating a complex conjugate of the output signal of the normalization circuit, a multiplier unit for multiplying the one-symbol delay signal with the complex conjugate and generating a difference signal, and a decision circuit for deciding that the ADSL band of the telephone line is occupied by another ADSL modem for communication in the case where the difference signal remains not more than a predetermined threshold value for a period corresponding to a specific number of symbols.