Multistage nonlinear echo-canceller for digital communication systems with or without frequency division duplexing

A transmit/receive apparatus for a digital modulation transmission system, comprising:

• a digital-to-analog converter (DAC) with an input coupled to receive a digitally-modulated signal;
• a filter coupled to the DAC for filtering a digitally-modulated analog signal produced by the DAC;
• a hybrid coupled to the filter for providing the digitally-modulated analog signal produced by the DAC and filtered by the filter to a dispersive channel for transmission therein, and for receiving a digitally-modulated analog signal from the dispersive channel;
• an analog-to-digital converter (ADC) coupled to receive the digitally-modulated analog signal received from the dispersive channel, the ADC having an output for providing a converted digitally-modulated signal;
• a multistage echo canceller having an input coupled to the source of a digitally-modulated signal and an output;
• the multistage echo canceller having a first stage characterized by a first function to produce first results modeling first linear distortion in an echo of the digitally-modulated signal, a second stage coupled in series with the first stage, the second stage characterized by a second function to produce from the first results second results modeling nonlinear distortion in the echo of the digitally-modulated signal, and at least a third stage, the third stage characterized by a third function to produce from the second results third results modeling second linear distortion in the echo of the digitally-modulated signal;
• and
• a subtracter coupled to the output of the ADC and to the output of the multistage echo canceller for subtracting the modeled echo of the transmitted digitally-modulated signal, corrected for linear and non-linear distortion, from the converted received digitally-modulated signal.

In a digital transmission system, a method for modeling and canceling the echo of a digitally-modulated signal to be transmitted through a dispersive medium from a digitally-modulated signal received from the dispersive medium, comprising:

• providing a first digitally-modulated signal;
• converting the first digitally-modulated signal to a first digitally modulated analog signal;
• providing the first digitally-modulated analog signal to a hybrid for transmission through a dispersive channel;
• providing from the hybrid a second digitally-modulated analog signal received from the dispersive channel having an echo of the first digitally modulated analog signal;
• converting the second digitally-modulated analog signal to a second digitally-modulated signal;
• modeling a distorted echo of the first digitally modulated signal;
• producing a corrected echo of the first digitally-modulated signal by correcting the model of the distorted echo of the first digitally-modulated signal for linear distortion using a first function, at least followed by correcting the model of the echo of the first digitally-modulated signal using a second function for nonlinear distortion;
• and
• subtracting the corrected echo from the second digitally-modulated signal.

An echo cancellation method for a transmitter/receiver, comprising:

• converting a first digitally-modulated signal to analog form;
• filtering the analog form of the first digitally-modulated signal;
• coupling the filtered analog form of the first digitally-modulated signal to an end of a dispersive channel for transmission therein;
• receiving a second digitally-modulated analog signal from the end of the dispersive channel;
• converting the second digitally-modulated analog signal to a second digitally-modulated signal;
• modeling a distorted echo of the first digitally modulated signal;
• producing a corrected echo by using a first function to produce first results correcting first linear distortion in the model of the distorted echo of the first digitally-modulated signal, using a second function to produce from the first results second results correcting nonlinear distortion in the model of the distorted echo of the first digitally-modulated signal, and using at least a third function to produce third results from the second results correcting second linear distortion in the model of the distorted echo of the first digitally-modulated signal;
• and subtracting the corrected echo from the second digitally-modulated signal.

A transmit/receive apparatus for a digital subscriber line (DSL) system, comprising:

• a digital-to-analog converter (DAC) with an input coupled to receive a digitally-modulated signal;
• a filter coupled to the DAC for filtering a digitally-modulated analog signal produced by the DAC;
• a hybrid coupled to the filter for providing the digitally-modulated analog signal produced by the DAC and filtered by the filter to a DSL channel for transmission therein, and for receiving a digitally-modulated analog signal from the DSL channel;
• an analog-to-digital converter (ADC) coupled to receive the digitally-modulated analog signal received from the DSL channel, the ADC having an output for providing a converted digitally-modulated signal;
• a multistage echo canceller having an input coupled to the source of a digitally-modulated signal and an output;
• the multistage echo canceller having a first stage characterized by a first function to produce first results modeling first linear distortion in an echo of the digitally-modulated signal, a second stage coupled in series with the first stage, the second stage characterized by a second function to produce from the first results second results modeling nonlinear distortion in the echo of the digitally-modulated signal, and at least a third stage, the third stage characterized by a third function to produce from the second results third results modeling second linear distortion in the echo of the digitally-modulated signal;
• and
• a subtracter coupled to the output of the ADC and to the output of the multistage echo canceller for subtracting the modeled echo of the transmitted digitally-modulated signal, corrected for linear and non-linear distortion, from the converted received digitally-modulated signal.

An echo cancellation method for a transmitter/receiver in a digital subscriber line (DSL) system, comprising:

• converting a first digitally-modulated signal to analog form;
• filtering the analog form of the first digitally-modulated signal;
• coupling the filtered analog form of the first digitally-modulated signal to an end of a DSL channel for transmission therein;
• receiving a second digitally-modulated analog signal from the end of the DSL channel;
• converting the second digitally-modulated analog signal to a second digitally-modulated signal;
• modeling a distorted echo of the first digitally modulated signal;
• producing a corrected echo by using a first function to produce first results correcting first linear distortion in the model of the distorted echo of the first digitally-modulated signal, using a second function to produce from the first results second results correcting nonlinear distortion in the model of the distorted echo of the first digitally-modulated signal, and using at least a third function to produce third results from the second results correcting second linear distortion in the model of the distorted echo of the first digitally-modulated signal;
• and
• subtracting the corrected echo from the second digitally-modulated signal.

In a digital transmission system, a combination for canceling an echo of a digitally-modulated signal to be transmitted through a dispersive medium from a digitally-modulated signal received from the dispersive medium, comprising:

• a source of a digitally-modulated signal;
• a digital-to-analog converter (DAC) with an input coupled to receive the digitally-modulated signal;
• a hybrid with an input coupled to receive a digitally-modulated analog signal produced by the DAC and to provide the digitally-modulated analog signal for transmission in a dispersive channel, the hybrid having an output for providing a digitally-modulated analog signal received from the dispersive channel;
• an analog-to-digital converter (ADC) coupled to receive the digitally-modulated signal received from the dispersive channel, the ADC having an output;
• a multistage echo canceller having an input coupled to the source of the transmitted digitally-modulated signal and an output;
• the multistage echo canceller having a plurality of stages connected in a sequence, the plurality of stages including first stage characterized by a first function to produce first results modeling distortion in an echo of the transmitted digitally-modulated signal, and at least a second stage, the second stage characterized by a second function to produce from the first results second results modeling distortion in the echo of the transmitted digitally-modulated signal;
• the sequence including at least one linear stage and one nonlinear stage;
• and
• a subtracter with a first input connected to the output of the multistage echo canceller, a second input connected to the output of the ADC, and an output.

In a digital transmission system, an apparatus for canceling an echo of a digitally-modulated signal to be transmitted through a dispersive medium from a digitally-modulated signal received from the dispersive medium, and for removing effects of nonlinear coupling between the transmitted and received signals and for equalizing the received signal, the apparatus comprising:

• a source of a digitally-modulated signal;
• a digital-to-analog converter (DAC) with an input coupled to receive the digitally-modulated signal;
• a hybrid with an input coupled to receive a digitally-modulated analog signal produced by the DAC and to provide the digitally-modulated analog signal for transmission in a dispersive channel, the hybrid having an output for providing a digitally-modulated analog signal received from the dispersive channel;
• an analog-to-digital converter (ADC) coupled to receive the digitally-modulated signal received from the dispersive channel, the ADC having an output;
• a multistage combination having a first input coupled to the source of the transmitted digitally-modulated signal and a second input coupled to the output of the ADC and an output;
• the multistage combination having a first sequence of zero or more stages having an output and an input connected to the first input, a second sequence of zero or more stages having an output and an input connected to the second input, a coupling stage having two inputs and one output, the first input connected to the output of the first sequence, the second input connected to the output of the second sequence, and a third sequence of zero or more stages having an output and an input, the input of the third sequence connected to the output of the coupling stage;
• and
• the first sequence for producing first results modeling distortion in the transmitted signal, the second sequence for producing second results correcting distortion in the received signal, the coupling stage for producing third results correcting coupling between transmitted and received signals and canceling echo, and the third sequence for producing fourth results correcting distortion in the received signal;
• the multistage combination including at least one nonlinear stage.