Variable block size adaptation algorithm for noise-robust acoustic echo cancellation

• US 5,546,459 A
• Filed: 11/01/1993
• Issued: 08/13/1996
• Est. Priority Date: 11/01/1993
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sih, Gilbert C., Antonio, Franklin P.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): Hunter, Daniel S.
• Application Number:
  US08/146,644
• Time in Patent Office: 1,016 Days
• Field of Search: 379/410, 379/411, 379/406, 379/416, 370/32.1, 375/99, 375/121
• US Class Current: 379/406.09
• CPC Class Codes: H03H 21/0012 Digital adaptive filters
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers

Abstract

An apparatus that automatically adjusts the adaptation block size for a least-mean square (LMS) adaptive filter depending on the input signal-to-noise ratio (SNR) is disclosed. The apparatus monitors the instantaneous SNR and continually adjusts the block size to provide high noise immunity, thereby increasing the convergence speed of the filter and decreasing the asymptotic mean-square error. An exemplary embodiment of the present invention is presented in the context of acoustic echo cancellation, though it is noted that the adaptive filter of the present invention is useful in any environment in which the noise characteristics are subject to change.

Claims

1. An adaptive filter in a communications channel comprising:

noise computation means for monitoring noise content in the communications channel and for providing a monitor signal indicative of the noise content in the channel;

block size selection means for determining a variable adaptation block size value in response to said monitor signal;

filter coefficient computation means for receiving said variable adaptation block size value and for determining at least one filter tap correction value in response to said variable adaptation block size value; and

filter means for receiving at said least one filter tap correction value and for filtering a signal present in communications channel in accordance with said at least one filter tap correction value.

2. The apparatus of claim 1 wherein, said noise computation means monitors the signal to noise ratio in the communications channel and said monitor signal is indicative of the signal to noise ratio in the communications channel.

3. An echo canceller for canceling an echo signal of a far-end speech signal in a near-end speech signal in a communications channel, comprising:

block size selection means for determining a variable adaptation block size value;

filter coefficient computation means for receiving said variable adaptation block size value and for determining at least one filter tap correction value in response to said variable adaptation block size value;

filter means for receiving said at least one filter tap correction value and said far-end speech signal and for providing an estimate of said echo signal in accordance with said far-end speech signal and said at least one filter tap correction value; and

difference means for subtracting said estimate of said echo signal from said near-end speech signal to provide a filtered near-end speech signal.

4. The apparatus of claim 3 further comprising noise computation means for monitoring noise content in the communications channel and for providing a monitor signal indicative of the noise content in the communications channel;

and

wherein said block size selection means is responsive to said monitor signal.

5. The apparatus of claim 4 wherein, said noise computation means monitors the signal to noise ratio in the communications channel and said monitor signal is indicative of the signal to noise ratio in the communications channel.

6. The apparatus of claim 4 further comprising speech detection means for detecting said far-end speech signal and said near-end speech signal and for providing a control signal responsive to the presence of said far-end speech signal and said near-end speech signal;

and

wherein said noise computation means is responsive to said control signal.

7. The apparatus of claim 6 wherein, said noise computation means monitors the signal to noise ratio in the communications channel and said monitor signal is indicative of the signal to noise ratio in the communications channel.

8. A method for adaptively filtering a signal present in a communications channel comprising the steps of:

monitoring noise content in the communications channel and providing a monitor signal indicative of the noise content in the communications channel;

determining a variable adaptation block size value in response to said monitor signal;

determining at least one filter tap correction value in response to said variable adaptation block size value; and

filtering the signal present in the communications channel in accordance with said at least one filter tap correction value.

9. The apparatus of claim 8 wherein, said step of monitoring noise content in the communications channel comprises monitoring the signal to noise ratio in the communications channel;

and

wherein said monitor signal is indicative of the signal to noise ratio in the communications channel.

10. A method for canceling an echo signal of a far-end speech signal in a near-end speech signal in a communications channel, comprising:

determining a variable adaptation block size value;

determining at least one filter tap correction value in response to said variable adaptation block size value;

providing an estimate of said echo signal in accordance with said far-end speech signal and said at least one filter tap correction value; and

subtracting said estimate of said echo signal from said near-end speech signal to provide an echo canceled near-end speech signal in the communications channel.

11. The method of claim 10 further comprising the steps of monitoring noise content in the communications channel and providing a monitor signal indicative of the noise content in the communications channel;

and

wherein said step of determining said variable adaptation block size value determines said variable adaptation block size value in response to said monitor signal.

12. The apparatus of claim 11 wherein, said step of monitoring noise content in the communications channel comprises monitoring the signal to noise ratio in the communications channel;

and

wherein said monitor signal is indicative of the signal to noise ratio in the communications channel.

13. The method of claim 11 further comprising the step of providing a control signal responsive to the presence of said far-end speech signal and said near-end speech signal;

and

wherein said step of providing said monitor signal provides said monitor signal in response to said control signal.

14. An adaptive filter for filtering a signal present in a communications channel comprising:

averaging means for receiving the signal in the communications channel and for averaging a variable size block of samples of the signal to provide a sample average, wherein said bock size is varied as a function of noise content in the noise content in the communications channel;

filter coefficient computation means for receiving said sample average and for determining at least one filter tap correction value in response to said sample average; and

filter means for receiving said at least one filter tap correction value and for filtering the signal present in the communications channel in accordance with said at least one filter tap correction value.

15. The apparatus of claim 14 wherein, said noise content comprises signal to noise ratio.

16. A method for filtering a signal present in a communications channel comprising the steps of:

receiving the signal;

averaging a variable size block of samples of the signal to provide a sample average, wherein said block size is varied as a function of noise content in the communications channel;

determining at least one filter tap correction value responsive to said sample average; and

filtering the signal present in the communications channel in accordance with said at least one filter tap correction value.

17. The apparatus of claim 16 wherein, said noise content comprises signal to noise ratio.

18. An adaptive filter in a communications channel comprising:

a noise monitor coupled to the communications channel and having an output for providing a monitor signal indicative of noise content in the communications channel;

a block size selector having an output for providing a variable adaptation block size value in response to said monitor signal;

a filter coefficient calculator having an input coupled to said output of said block size selector and having an output for providing at least one filter tap correction value in response to said variable adaptation block size value; and

a filter in the communications channel having an input coupled to said output of said filter coefficient calculator and having a second input for receiving an input signal from the communications channel and an output for providing a filtered input signal.

19. The apparatus of claim 18 wherein, said noise content comprises signal to noise ratio.

20. An echo canceller for canceling an echo signal of a far-end speech signal in a near-end speech signal in a communications channel, comprising:

a noise monitor coupled to the communications channel and having an output for providing a monitor signal indicative of the noise content in the communications channel;

a block size selector having an output for providing a variable adaptation block size value, wherein said block size selector has an input coupled to said output of said signal to noise ratio monitor;

a filter coefficient calculator having an input coupled to said output of said block size selector and having an output;

a filter having an input coupled to said output of said filter coefficient calculator and having an output for providing an echo signal estimate in accordance with the far-end speech signal; and

a subtractor having a first input coupled to said output of said filter and having a second input for receiving said near-end speech signal, said subtractor subtracting said echo signal estimate from said near-end speech signal to produce an echo-canceled near-end speech signal.

21. The apparatus of claim 20 wherein, said noise content comprises signal to noise ratio.

22. The apparatus of claim 20 further comprising a speech detector having a first input for receiving said far-end speech signal and a second input for receiving said near-end speech signal and having an output for providing a control signal responsive to the presence of said far-end speech signal and said near-end speech signal;

and

wherein said noise monitor has a second input coupled to said output of said speech detector.

23. The apparatus of claim 22 wherein, said noise content comprises signal to noise ratio.