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

• US 20030206579A1
• Filed: 06/06/2003
• Published: 11/06/2003
• Est. Priority Date: 10/01/2001
• Status: Abandoned Application

• Current Assignee: Chaos Telecom, Inc.
• Original Assignee: Chaos Telecom, Inc.
• Inventors: Bryant, Paul Henry
• Application Number:
  US10/456,270
• Publication Number:
  US 20030206579A1
• Time in Patent Office: Days
• US Class Current: 375/219
• CPC Class Codes: H03F 1/02 Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H03G 7/007 of digital or coded signals
• CPC Class Codes: H04B 1/04 Circuits
• CPC Class Codes: H04B 2001/045 with means for improving efficiency
• CPC Class Codes: H04L 25/03885 adaptive
• CPC Class Codes: H04L 27/367 using predistortion

Abstract

In a digital communication system where digitally modulated signals are transmitted in a signal path including a bi-directional channel, a multistage echo-canceller has two or more stages connected in a sequence to remove the linear and nonlinear echo of the outgoing signal from the incoming signal. Results are of importance both to systems with overlapping outgoing and incoming frequency bands and to those with separated bands (for which only the nonlinear echo is of concern). The two or more stages are each characterized by a respective function, and the sequence is characterized by alternation of the functions of the two or more stages between linear and nonlinear.

Claims

1. 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 first stage characterized by a first function to produce first results modeling linear 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 nonlinear distortion in the echo of the transmitted digitally-modulated signal; 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.

2. The combination of claim 1, the multistage echo canceller comprising:

three or more stages;

each stage having an input and an output, the input of any stage following another stage in the sequence being connected to the output of the other stage;

each stage being characterized by a respective function that, in response to an input digital time series x₁, x₂, x₃, . . . , produces an output digital time series y₁, y₂, y₃, . . . , the value of any element of the output time series depending on the values of one or more of the elements of the input series; and

the sequence causing the stages to alternate in their respective functions between linear functions and nonlinear functions.

3. The combination of claim 2, wherein the sequence continues with one or more stages following the third stage, the respective functions of the one or more stages alternating in the sequence (nonlinear, linear, nonlinear, . . . ).

4. The combination of claim 2, in which the linear functions include the function:

5. The combination of claim 2 in which one or more of the nonlinear functions are functions in the group including:

a one-dimensional power series function;

an inverse of a known non-linear function;

an inverse of a known piecewise linear function;

a one-dimensional, difference-based power series function of degree P;

a one-dimensional function depending on k parameters;

a two-dimensional power series of degree P; and

, a D-dimensional function, depending on k parameters.

6. 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.

7. The transmit/receive apparatus of claim 6, the multistage echo canceller comprising:

three or more stages connected in a sequence;

each stage having an input and an output, the input of any stage following another stage in the sequence being connected to the output of the other stage;

each stage being characterized by a respective function that, in response to an input digital time series x₁, x₂, x₃, . . . , produces an output digital time series y₁, y₂, y₃, . . . , the value of any element of the output time series depending on the values of one or more of the elements of the input series; and

the sequence causing the stages to alternate in their respective functions between linear functions and nonlinear functions.

8. The transmit/receive apparatus of claim 7, wherein the sequence continues with one or more stages following the third stage, the respective functions of the one or more stages alternating in the sequence (nonlinear, linear, nonlinear, . . . ).

9. The transmit/receive apparatus of claim 6, in which the linear functions include the function:

10. The transmit/receive apparatus of claim 6 in which one or more of the nonlinear functions are functions in the group including:

a one-dimensional power series function;

an inverse of a known non-linear function;

an inverse of a known piecewise linear function;

a one-dimensional, difference-based power series function of degree P;

a one-dimensional function depending on k parameters;

a two-dimensional power series of degree P; and

, a D-dimensional function, depending on k parameters.

11. 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.

12. The method of claim 11, wherein producing a corrected echo signal includes:

correcting the model of the distorted echo of the first digitally-modulated signal in a sequence of functions;

each function having an input and an output, the input of any function following another function in the sequence receiving the output of the other function;

each function being characterized by a response to an input digital time series x₁, x₂, x₃, . . . , that produces an output digital time series y₁, y₂, y₃, . . . , the value of any element of the output time series depending on the values of one or more of the elements of the input series; and

the sequence causing the functions to alternate between linear functions and nonlinear functions.

13. The method of claim 12, in which the linear functions include the function:

14. The method of claim 12 in which one or more of the nonlinear functions are functions in the group including:

a one-dimensional power series function;

an inverse of a known non-linear function;

an inverse of a known piecewise linear function;

a one-dimensional, difference-based power series function of degree P;

a one-dimensional function depending on k parameters;

a two-dimensional power series of degree P; and

, a D-dimensional function, depending on k parameters.

15. 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.

16. The method of claim 15, wherein producing a corrected echo includes:

correcting the model of the distorted echo of the first digitally-modulated signal in a sequence of functions;

each function having an input and an output, the input of any function following another function in the sequence receiving the output of the other function;

each function being characterized by a response to an input digital time series x₁, x₂, x₃, . . . , that produces an output digital time series y₁, y₂, y₃, . . . , the value of any element of the output time series depending on the values of one or more of the elements of the input series; and

the sequence causing the functions to alternate between linear functions and nonlinear functions.

17. The method of claim 16, wherein the sequence continues with one or more functions following the third function, the one or more functions alternating in the sequence (nonlinear, linear, nonlinear, . . . ).

18. The method of claim 16, in which the linear functions include the function:

19. The method of claim 16, in which one or more of the nonlinear functions are functions in the group including:

a one-dimensional power series function;

an inverse of a known non-linear function;

an inverse of a known piecewise linear function;

a one-dimensional, difference-based power series function of degree P;

a one-dimensional function depending on k parameters;

a two-dimensional power series of degree P; and

, a D-dimensional function, depending on k parameters.

20. 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.

21. The transmit/receive apparatus of claim 20, the multistage echo canceller comprising:

three or more stages connected in a sequence;

each stage having an input and an output, the input of any stage following another stage in the sequence being connected to the output of the other stage;

each stage being characterized by a respective function that, in response to an input digital time series x₁, x₂, x₃, . . . , produces an output digital time series y₁, y₂, y₃, . . . , the value of any element of the output time series depending on the values of one or more of the elements of the input series; and

the sequence causing the stages to alternate in their respective functions between linear functions and nonlinear functions.

22. The transmit/receive apparatus of claim 21, wherein the sequence continues with one or more stages following the third stage, the respective functions of the one or more stages alternating in the sequence (nonlinear, linear, nonlinear, . . . ).

23. The transmit/receive apparatus of claim 21, in which the linear functions include the function:

24. The transmit/receive apparatus of claim 21 in which one or more of the nonlinear functions are functions in the group including:

a one-dimensional power series function;

an inverse of a known non-linear function;

an inverse of a known piecewise linear function;

a one-dimensional, difference-based power series function of degree P;

a one-dimensional function depending on k parameters;

a two-dimensional power series of degree P; and

, a D-dimensional function, depending on k parameters.

25. 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.

26. The method of claim 25, wherein producing a corrected echo includes:

correcting the model of the distorted echo of the first digitally-modulated signal in a sequence of functions;

each function having an input and an output, the input of any function following another function in the sequence receiving the output of the other function;

each function being characterized by a response to an input digital time series x₁, x₂, x₃, . . . , that produces an output digital time series y₁, y₂, y₃, . . . , the value of any element of the output time series depending on the values of one or more of the elements of the input series; and

the sequence causing the functions to alternate between linear functions and nonlinear functions.

27. The method of claim 26, wherein the sequence continues with one or more functions following the third function, the one or more functions alternating in the sequence (nonlinear, linear, nonlinear, . . . ).

28. The method of claim 26, in which the linear functions include the function:

29. The method of claim 26, in which one or more of the nonlinear functions are functions in the group including:

a one-dimensional power series function;

an inverse of a known non-linear function;

an inverse of a known piecewise linear function;

a one-dimensional, difference-based power series function of degree P;

a one-dimensional function depending on k parameters;

a two-dimensional power series of degree P; and

, a D-dimensional function, depending on k parameters.

30. 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.

31. The combination of claim 30, the multistage echo canceller comprising:

three or more stages;

each stage having an input and an output, the input of any stage following another stage in the sequence being connected to the output of the other stage; and

each stage being characterized by a respective function that, in response to an input digital time series x₁, x₂, x₃, . . . , produces an output digital time series y₁, y₂, y₃, . . . , the value of any element of the output time series depending on the values of one or more of the elements of the input series.

32. The combination of claim 31, wherein the sequence continues with one or more stages following the third stage, the respective functions of the one or more stages alternating in the sequence (nonlinear, linear, nonlinear, . . . ).

33. The combination of claim 31, in which the linear functions include the function:

34. The combination of claim 31, in which one or more of the nonlinear functions are functions in the group including:

a one-dimensional power series function;

an inverse of a known non-linear function;

an inverse of a known piecewise linear function;

a one-dimensional, difference-based power series function of degree P;

a one-dimensional function depending on k parameters;

a two-dimensional power series of degree P; and

, a D-dimensional function, depending on k parameters.

35. The combination of claim 31, in which one or more of the linear functions are implemented in the frequency domain.

36. The combination of claim 30, further including:

a linear echo canceller having an input connected in common with an input of one of the stages, and an output; and

an adder having a first input connected to the output of the linear echo canceller and having a second input connected to the output of one stage of the plurality of stages, the adder for providing a combined output as an input to another stage of the plurality of stages, or as the output of the multistage echo canceller.

37. The combination of claim 36, wherein:

the plurality of stages further includes a last stage;

the input of the linear echo canceller is connected in common with the input of the first stage; and

the output of the linear echo canceller is connected to the first input of the adder and the output of the last stage is connected to the second input of the adder.

38. The combination of claim 36, wherein:

the multistage echo canceller comprises three or more stages in a sequence and the linear echo canceller comprises a single stage;

each stage having an input and an output; and

each stage being characterized by a respective function that, in response to an input digital time series x₁, x₂, x₃, . . . , produces an output digital time series y₁, y₂, y₃, . . . , the value of any element of the output time series depending on the values of one or more of the elements of the input series

39. The combination of claim 38, in which the linear functions include the function:

40. The combination of claim 38, in which one or more of the nonlinear functions are functions in the group including:

a one-dimensional power series function;

an inverse of a known non-linear function;

an inverse of a known piecewise linear function;

a one-dimensional, difference-based power series function of degree P;

a one-dimensional function depending on k parameters;

a two-dimensional power series of degree P; and

, a D-dimensional function, depending on k parameters.

41. The combination of claim 38 in which one or more of the linear functions are implemented in the frequency domain.

42. 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.

43. The apparatus of claim 42, wherein the first, second, and final sequences each includes a single linear stage, each linear stage having an input and an output, each linear stage being characterized by a respective function that, in response to an input digital time series x₁, x₂, x₃, . . . , produces an output digital time series y₁, y₂, y₃, . . . , the value of any element of the output time series depending on the values of one or more of the elements of the input series, and the coupling stage being characterized by a function that, in response to input digital time series x₁, x₂, x₃, . . . and y₁, y₂, y₃, . . . , produces an output digital time series z₁, z₂, z₃, K, the value of any element of the output time series produced by the coupling stage depending on the values of one or more of the elements of each of the input series.

44. The apparatus of claim 43, in which the linear functions include the function:

45. The apparatus of claim 43, wherein the coupling stage is characterized by a nonlinear function from the group including:

a two-dimensional power series function depending on one element from each input;

a two-dimensional function depending on k parameters and on one element from each of the two inputs; and

, a D-dimensional function, depending on k parameters and on A elements from the first input and on B elements from the second input, where A+B=D.

46. The apparatus of claim 43 in which one or more of the linear functions are implemented in the frequency domain.