Abstract: A terminal apparatus for full duplex transmission of digital data comprising an echo canceler having FIR and IIR type filters and also comprising a filter convergence controller. The filter convergence controller performs its converging operation over both filters in a first duration of a communication starting sequence from the start of transmission from a local terminal to a remote terminal to the detection of the convergence of the echo canceller to a certain extent, stops the converging operation of the IIR type filter in a second duration of the communication starting sequence from the detection of the convergence to the detection of synchronization with the remote terminal, and again performs the converging operation of the both filters in a third duration after the detection of the synchronization.

Abstract: A signal processing method and system in a receiving apparatus including a receiving equalizer circuit are provided for extracting transmission data from a received signal inputted via a transmission path every transmission frame having a predetermined synchronization pattern and transmission data. A phase error is detected from the received signal extracted in synchronism with a sampling signal in the receiving equalizer circuit. The frequency of the sampling signal is controlled until the phase error becomes minimum. In parallel, it is detected whether the frame synchronization pattern is present in the received signal in a predetermined interval or not. When the presence of the frame synchronization pattern is not detected after the phase has been stabilized by frequency control of the sampling signal, the sampling phase of the received signal is judged to be in the quasi-convergence state. Then the frequency of the sampling signal is forcibly changed largely.

Abstract: A method for cancelling an echo in a network termination (NT) of a transmission system and an apparatus therefor are disclosed. The method comprises the steps of detecting an end of transmission of a specific data train in an up-going signal when the phase of the received clock is to be shifted for synchronization during the transmission of the up-going signal from the NT, shifting the phase of the receiving clock when the end of transmission is detected, sampling a residual echo signal of the echo of the specific data train not cancelled by the adaptive filter, determining a correction value for the output of the adaptive filter and storing the correction value and adding a sign corresponding to the direction of the phase shift to the correction value after the phase shift and adding the result to the output of the adaptive filter to cancel the echo of the specific data train.

Abstract: A method for cancelling an echo in a network termination (NT) of a transmission system and an apparatus therefor are disclosed. The method comprises the steps of detecting an end of transmission of a specific data train in an up-going signal when the phase of the received clock is to be shifted for synchronization during the transmission of the up-going signal from the NT, shifting the phase of the receiving clock when the end of transmission is detected, sampling a residual echo signal of the echo of the specific data train not cancelled by the adaptive filter, determining a correction value for the output of the adaptive filter and storing the correction value and adding a sign corresponding to the direction of the phase shift to the correction value after the phase shift and adding the result to the output of the adaptive filter to cancel the echo of the specific data train.

Abstract: An echo canceller which cancels an echo by generating a replica of echo from the transmit data when the signal from the transmit line appears as an echo signal on the receive line, and subtracting the replica of echo from the echo signal in a circuit for connecting a transmit line and receive line to the full duplex transmission line through a hybrid circuit. The echo canceller for generating a replica of echo is composed of the first circuit which generates a replica of echo of limited length and a second circuit in which generates a replica of echo for eliminating the residual echo that is not cancelled by the first circuit.