Dual-processing interference cancelling system and method

• US 6,332,028 B1
• Filed: 04/07/1998
• Issued: 12/18/2001
• Est. Priority Date: 04/14/1997
• Status: Expired due to Term

• Current Assignee: Andrea Electronics Corporation
• Original Assignee: Andrea Electronics Corporation
• Inventors: Marash, Joseph
• Primary Examiner(s): Isen, Forester W.
• Assistant Examiner(s): PENDLETON, BRIAN T
• Application Number:
  US09/055,709
• Time in Patent Office: 1,351 Days
• Field of Search: 381/92, 381/94.7, 381/94.1, 367/119, 367/121
• US Class Current: 381/92
• CPC Class Codes: H03H 21/0012 Digital adaptive filters
• CPC Class Codes: H04R 25/407 Circuits for combining signals of a plurality of transducers
• CPC Class Codes: H04R 3/005 for combining the signals of two or more microphones specially adapted for hearing aids H04R25/407

Abstract

A dual-processing interference cancelling system and method for processing a broadband input in a computationally efficient manner. Dual processing divides the input into higher and lower frequency bands and applies adaptive filter processing to the lower frequency band while applying non-adaptive filter processing to the higher frequency band. Various embodiments are shown including those based on sub-bands, broadband processing with band-limited adaptation, and broadband processing with an external main-channel generator.

Claims

1. A dual-processing interference canceling system for processing an input signal containing a target signal component originating from a target source and an interference signal component originating from one or more interference sources and for producing an output signal representing the target signal component with a substantially reduced interference signal component, comprising:

a main-channel generator capable of receiving said input signal and for generating therefrom a broadband main channel having said target signal component and said interference component;

a reference-channel generator capable of receiving said input signal and for generating one or more broadband reference channels representing signals received from said one or more interference sources;

a first low-pass filter, connected to the reference-channel generator, for filtering said one or more broadband reference channels into one or more low-frequency reference channels;

an adaptive filter, connected to the first low-pass filter and having filter weights, for filtering said one or more low-frequency reference channels into one or more low-frequency canceling signals approximating the low-frequency interference signal component present in the broadband main channel;

an interpolator, connected to the adaptive filter, for interpolating said one or more low-frequency canceling signals into one or more broadband canceling signals;

a subtractor, connected to the main-channel generator and the interpolator, for generating a broadband output by subtracting said one or more broadband canceling signals from the broadband main channel;

a second low-pass filter for filtering the broadband output to produce a low-frequency output; and

said adaptive filter having filter-weight-updating means for determining updated filter weight values for the adaptive filter such that the difference between the low-frequency output and said one or more low-frequency canceling signals is substantially minimized;

said adaptive filter also having weight constraining means for truncating said updated filter weight values to predetermined threshold values when the updated filter weight value exceeds the corresponding threshold value.

2. The system of claim 1, wherein the adaptive filter further comprises:

inhibiting means, connected to receive signals from the first low-pass filter and the second low-pass filter, for estimating the power of the low-frequency output and the power of the low-frequency reference channels and for generating an inhibit signal to said filter-weight-updating means when a normalized power difference between the low-frequency output and the low-frequency reference channels is positive.

3. A dual-processing interference canceling system for processing an input signal containing a target signal component originating from a target source and an interference signal component originating from one or more interference sources and for producing an output signal representing the target signal component with a substantially reduced interference signal component, comprising:

a main-channel generator capable of receiving said input signal and for generating therefrom a broadband main channel having said target signal component and said interference component;

a reference-channel generator capable of receiving said input signal and for generating one or more broadband reference channels representing signals received from said one or more interference sources;

a first low-pass filter, connected to the reference-channel generator, for filtering said one or more broadband reference channels into one or more low-frequency reference channels;

an adaptive filter, connected to the first low-pass filter and having filter weights, for filtering said one or more low-frequency reference channels into one or more low-frequency canceling signals approximating the low-frequency interference signal component present in the broadband main channel;

an interpolator, connected to the adaptive filter, for interpolating said one or more low-frequency canceling signals into one or more broadband canceling signals;

a subtractor, connected to the main-channel generator and the interpolator, for generating a broadband output by subtracting said one or more broadband canceling signals from the broadband main channel;

a second low-pass filter for filtering the broadband output to produce a low-frequency output; and

said adaptive filter having filter-weight-updating means for determining updated filter weight values for the adaptive filter such that the difference between the low-frequency output and said one or more low-frequency canceling signals is substantially minimized;

said adaptive filter also having weight constraining means for converting the updated filter weight values to frequency representation values, truncating the frequency representation values at predetermined threshold values, and converting the truncated frequency representation values back to adaptive filter weights.

4. The system of claim 3, wherein the weight constraining means comprises:

a Fast Fourier Transform unit for generating frequency representation values of the updated filter weight values;

a set of frequency bins, each frequency bin for storing the frequency representation values for a frequency band assigned to each frequency bin;

a set of truncating means, each connected to the corresponding frequency bin, for truncating the frequency representation values stored in each frequency bin to a predetermined threshold value if the frequency representation values exceed the threshold value associated with each frequency bin; and

an Inverse Fast Fourier Transform unit, connected to the set of truncating means, for converting values from the set of truncating means back to adaptive filter weights.

5. A dual-processing interference canceling system for processing an array of input signals containing a target signal component originating from a target source and an interference signal component originating from one or more interference sources and for producing an output signal representing the target signal component with a substantially reduced interference signal component, comprising:

a main-channel matrix capable of receiving said array of input signals and for generating therefrom a broadband main channel having said target signal component and said interference component;

a reference-channel matrix capable of receiving said array of input signals and for generating one or more broadband reference channels representing signals received from said one or more interference sources;

a first low-pass filter, connected to the reference-channel matrix, for filtering said one or more broadband reference channels into one or more low-frequency reference channels;

an adaptive filter, connected to the first low-pass filter and having filter weights, for filtering said one or more low-frequency reference channels into one or more low-frequency canceling signals approximating the low-frequency interference signal component present in the broadband main channel;

an interpolator, connected to the adaptive filter, for interpolating said one or more low-frequency canceling signals into one or more broadband canceling signals;

a subtractor, connected to the main-channel matrix and the interpolator, for generating a broadband output by subtracting said one or more broadband canceling signals from the broadband main channel;

a second low-pass filter for filtering the broadband output to produce a low-frequency output; and

said adaptive filter having filter-weight-updating means for determining updated filter weight values for the adaptive filter such that the difference between the low-frequency output and said one or more low-frequency canceling signals is substantially minimized;

said adaptive filter also having weight constraining means for truncating said updated filter weight values to predetermined threshold values when the updated filter weight value exceeds the corresponding threshold value.

6. The system of claim 5, wherein the adaptive filter further comprises:

inhibiting means, connected to receive signals from the first low-pass filter and the second low-pass filter, for estimating the power of the low-frequency output and the power of the low-frequency reference channels and for generating an inhibit signal to said filter-weight-updating means when a normalized power difference between the low-frequency output and the low-frequency reference channels is positive.

7. A dual-processing interference canceling system for processing an array of input signals containing a target signal component originating from a target source and an interference signal component originating from one or more interference sources and for producing an output signal representing the target signal component with a substantially reduced interference signal component, comprising:

a main-channel matrix capable of receiving said array of input signals and for generating therefrom a broadband main channel having said target signal component and said interference component;

a reference-channel matrix capable of receiving said array of input signals and for generating one or more broadband reference channels representing signals received from said one or more interference sources;

a first low-pass filter, connected to the reference-channel matrix, for filtering said one or more broadband reference channels into one or more low-frequency reference channels;

an adaptive filter, connected to the first low-pass filter and having filter weights, for filtering said one or more low-frequency reference channels into one or more low-frequency canceling signals approximating the low-frequency interference signal component present in the broadband main channel;

an interpolator, connected to the adaptive filter, for interpolating said one or more low-frequency canceling signals into one or more broadband canceling signals;

a subtractor, connected to the main-channel matrix and the interpolator, for generating a broadband output by subtracting said one or more broadband canceling signals from the broadband main channel;

a second low-pass filter for filtering the broadband output to produce a low-frequency output; and

said adaptive filter having filter-weight-updating means for determining updated filter weight values for the adaptive filter such that the difference between the low-frequency output and said one or more low-frequency canceling signals is substantially minimized;

said adaptive filter also having weight constraining means for converting the updated filter weight values to frequency representation values, truncating the frequency representation values at predetermined threshold values, and converting the truncated frequency representation values back to adaptive filter weights.

8. The system of claim 7, wherein the weight constraining means comprises:

a Fast Fourier Transform unit for generating frequency representation values of the updated filter weight values;

a set of frequency bins, each frequency bin for storing the frequency representation values for a frequency band assigned to each frequency bin;

a set of truncating means, each connected to the corresponding frequency bin, for truncating the frequency representation values stored in each frequency bin to a predetermined threshold value if the frequency representation values exceed the threshold value associated with each frequency bin; and

an Inverse Fast Fourier Transform unit, connected to the set of truncating means, for converting values from the set of truncating means back to adaptive filter weights.

9. A dual-processing interference canceling system for processing an input signal containing a target signal component originating from a target source and an interference signal component originating from one or more interference sources and for producing an output signal representing the target signal component with a substantially reduced interference signal component, comprising:

an external main-channel generator capable of receiving said input signal and for generating therefrom a broadband main channel having said target signal component and said interference component;

a reference-channel generator capable of receiving said input signal and for generating one or more broadband reference channels representing signals received from said one or more interference sources;

a first low-pass filter, connected to the reference-channel generator, for filtering said one or more broadband reference channels into one or more low-frequency reference channels;

an adaptive filter, connected to the first low-pass filter and having filter weights, for filtering said one or more low-frequency reference channels into one or more low-frequency canceling signals approximating the low-frequency interference signal component present in the broadband main channel;

an interpolator, connected to the adaptive filter, for interpolating said one or more low-frequency canceling signals into one or more broadband canceling signals;

a subtractor, connected to the external main-channel generator and the interpolator, for generating a broadband output by subtracting said one or more broadband canceling signals from the broadband main channel;

a second low-pass filter for filtering the broadband output to produce a low-frequency output; and

said adaptive filter having filter-weight-updating means for determining updated filter weight values for the adaptive filter such that the difference between the low-frequency output and said one or more low-frequency canceling signals is substantially minimized;

said adaptive filter also having weight constraining means for truncating said updated filter weight values to predetermined threshold values when the updated filter weight value exceeds the corresponding threshold value.

10. The system of claim 9, wherein the adaptive filter further comprises:

inhibiting means, connected to receive signals from the low-pass filter and the low-frequency reference-channel generator, for estimating the power of the broadband main channel and the power of the broadband reference channels and for generating an inhibit signal to said filter-weight-updating means when a normalized power difference between the low-frequency output and the low-frequency reference channels is positive.

11. A dual-processing interference canceling system for processing an input signal containing a target signal component originating from a target source and an interference signal component originating from one or more interference sources and for producing an output signal representing the target signal component with a substantially reduced interference signal component, comprising:

an external main-channel generator capable of receiving said input signal and for generating therefrom a broadband main channel having said target signal component and said interference component;

a reference-channel generator capable of receiving said input signal and for generating one or more broadband reference channels representing signals received from said one or more interference sources;

a first low-pass filter, connected to the reference-channel generator, for filtering said one or more broadband reference channels into one or more low-frequency reference channels;

an adaptive filter, connected to the first low-pass filter and having filter weights, for filtering said one or more low-frequency reference channels into one or more low-frequency canceling signals approximating the low-frequency interference signal component present in the broadband main channel;

an interpolator, connected to the adaptive filter, for interpolating said one or more low-frequency canceling signals into one or more broadband canceling signals;

a subtractor, connected to the external main-channel generator and the interpolator, for generating a broadband output by subtracting, said one or more broadband canceling signals from the broadband main channel;

a second low-pass filter for filtering the broadband output to produce a low-frequency output; and

said adaptive filter having filter-weight-updating means for determining updated filter weight values for the adaptive filter such that the difference between the low-frequency output and said one or more low-frequency canceling signals is substantially minimized;

said adaptive filter also having weight constraining means for converting the updated filter weight values to frequency representation values, truncating the frequency representation values at predetermined threshold values, and converting the truncated frequency representation values back to adaptive filter weights.

12. The system of claim 11, wherein the weight constraining means comprises:

a Fast Fourier Transform unit for generating frequency representation values of the updated filter weight values;

a set of frequency bins, each frequency bin for storing the frequency representation values for a frequency band assigned to each frequency bin;

a set of truncating means, each connected to the corresponding frequency bin, for truncating the frequency representation values stored in each frequency bin to a predetermined threshold value if the frequency representation values exceed the threshold value associated with each frequency bin; and

an Inverse Fast Fourier Transform unit, connected to the set of truncating means, for converting values from the set of truncating means back to adaptive filter weights.

13. A dual-processing interference canceling system for processing an array of input signals containing a target signal component originating from a target source and an interference signal component originating from one or more interference sources and for producing an output signal representing the target signal component with a substantially reduced interference signal component, comprising:

an external main-channel matrix capable of receiving said array of input signals and for generating therefrom a broadband main channel having said target signal component and said interference component;

a reference-channel matrix capable of receiving said array of input signals and for generating one or more broadband reference channels representing signals received from said one or more interference sources;

a first low-pass filter, connected to the reference-channel matrix, for filtering said one or more broadband reference channels into one or more low-frequency reference channels;

an adaptive filter, connected to the first low-pass filter and having filter weights, for filtering said one or more low-frequency reference channels into one or more low-frequency canceling signals approximating the low-frequency interference signal component present in the broadband main channel;

an interpolator, connected to the adaptive filter, for interpolating said one or more low-frequency canceling signals into one or more broadband canceling signals;

a subtractor, connected to the external main-channel matrix and the interpolator, for generating a broadband output by subtracting said one or more broadband canceling signals from the broadband main channel;

a second low-pass filter for filtering the broadband output to produce a low-frequency output; and

said adaptive filter having filter-weight-updating means for determining updated filter weight values for the adaptive filter such that the difference between the low-frequency output and said one or more low-frequency canceling signals is substantially minimized;

said adaptive filter also having weight constraining means for truncating said updated filter weight values to predetermined threshold values when the updated filter weight value exceeds the corresponding threshold value.

14. The system of claim 13, wherein the adaptive filter further comprises:

inhibiting means, connected to receive signals from the low-pass filter and the low-frequency reference-channel matrix, for estimating the power of the broadband main channel and the power of the broadband reference channels and for generating an inhibit signal to said filter-weight-updating means when a normalized power difference between the low-frequency output and the low-frequency reference channels is positive.

15. A dual-processing interference canceling system for processing an array of input signals containing a target signal component originating from a target source and an interference signal component originating from one or more interference sources and for producing an output signal representing the target signal component with a substantially reduced interference signal component, comprising:

an external main-channel matrix capable of receiving said array of input signals and for generating therefrom a broadband main channel having said target signal component and said interference component;

a reference-channel matrix capable of receiving said array of input signals and for generating one or more broadband reference channels representing signals received from said one or more interference sources;

a first low-pass filter, connected to the reference-channel matrix, for filtering said one or more broadband reference channels into one or more low-frequency reference channels;

an adaptive filter, connected to the first low-pass filter and having filter weights, for filtering said one or more low-frequency reference channels into one or more low-frequency canceling signals approximating the low-frequency interference signal component present in the broadband main channel;

an interpolator, connected to the adaptive filter, for interpolating said one or more low-frequency canceling signals into one or more broadband canceling signals;

a subtractor, connected to the external main-channel matrix and the interpolator, for generating a broadband output by subtracting said one or more broadband canceling signals from the broadband main channel;

a second low-pass filter for filtering the broadband output to produce a low-frequency output; and

said adaptive filter having filter-weight-updating means for determining updated filter weight values for the adaptive filter such that the difference between the low-frequency output and said one or more low-frequency canceling signals is substantially minimized;

said adaptive filter also having weight constraining means for converting the updated filter weight values to frequency representation values, truncating the frequency representation values at predetermined threshold values, and converting the truncated frequency representation values back to adaptive filter weights.

16. The system of claim 15, wherein the weight constraining means comprises:

a Fast Fourier Transform unit for generating frequency representation values of the updated filter weight values;

a set of frequency bins, each frequency bin for storing the frequency representation values for a frequency band assigned to each frequency bin;

a set of truncating means, each connected to the corresponding frequency bin, for truncating the frequency representation values stored in each frequency bin to a predetermined threshold value if the frequency representation values exceed the threshold value associated with each frequency bin; and

an Inverse Fast Fourier Transform unit, connected to the set of truncating means, for converting values from the set of truncating means back to adaptive filter weights.