Method and apparatus for canceling echo accounting for delay variations

• US 5,675,644 A
• Filed: 09/26/1995
• Issued: 10/07/1997
• Est. Priority Date: 09/26/1995
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Sih, Gilbert C.
• Primary Examiner(s): Zele, Krista M.
• Assistant Examiner(s): KUMAR, DEVENDRA
• Application Number:
  US08/533,883
• Time in Patent Office: 742 Days
• Field of Search: 379/410, 379/411, 379/406, 379/3, 370/32.1
• US Class Current: 379/406.08
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers

Abstract

A method and apparatus for detecting and correcting for variations in the flat delay, which permits smooth echo canceller operation even under dynamic delay conditions. In a delay monitor, the received signal is compared against delayed versions of the echo estimate to determine whether a shift in the echo delay has occurred. If such a shift in delay has occurred then a signal indicating the amount of the shift is to the adaptive filter of the echo canceller and the filter taps are updated in accordance with the delay shift value.

Claims

1. An echo canceller comprising:

delay monitor means for receiving an echo estimate signal and a received signal and for monitoring an echo flat delay and providing a delay signal indicative of said monitored echo flat delay; and

adaptive filter means for generating an echo estimate responsive to said delay signal.

2. The apparatus of claim 1 wherein said delay monitor means comprises:

delay means for receiving said received signal and said echo estimate and delaying said received signal and said echo estimate by a delay according to a predetermined delay format; and

residual energy computation means for receiving said delayed received signal and said delayed echo estimate and for computing a plurality of residual energy values.

3. The apparatus of claim 2 further comprising selection means for receiving said plurality of residual energy values and for selecting a minimum residual energy value.

4. The apparatus of claim 2 wherein said delay means comprises:

at least one echo estimate delay subsystems wherein each of said echo estimate delay subsystems is for receiving said echo estimate and for delaying said echo estimate by a predetermined delay period; and

at least one received signal delay subsystems wherein each of said received signal delay subsystems is for receiving said received signal and for delaying said received signal by a predetermined delay period.

5. The apparatus of claim 2 wherein said residual energy computation means computes said residual energy values, E i!, in accordance with the equation:

##EQU4## wherein r(k) refers to the samples of said received signal and z(k) refers to the samples of said echo estimate signal.

6. The apparatus of claim 1 wherein said adaptive filter adapts at least one tap value in accordance with the equation:

##EQU5## wherein j is an index referring to said echo flat delay.

7. The apparatus of claim 1 further comprising speech detection means for detecting the presence of a far-end signal.

8. A method for echo cancellation comprising the steps of:

monitoring an echo flat delay based upon a received signal and an echo estimate signal;

providing a delay signal indicative of said monitored echo flat delay; and

generating an echo estimate responsive to said delay signal.

9. The method of claim 8 wherein said echo estimate is generated by an adaptive filter which adapts at least one tap value in accordance with the equation:

##EQU6## wherein j is an index referring to said echo flat delay.

10. The method of claim 8 further comprising the step of detecting the presence of a far-end signal.

11. The method of claim 8 wherein said step of monitoring an echo flat delay comprises the steps of:

delaying said received signal and said echo estimate by a delay according to a predetermined delay format; and

computing a plurality of residual energy values.

12. The method of claim 11 further comprising the step of selecting a minimum residual energy value.

13. The method of claim 11 wherein said step of delaying said received signal and said echo estimate comprises:

delaying said echo estimate by a predetermined delay period; and

delaying said received signal by a predetermined delay period.

14. The method of claim 11 wherein said step of computing a plurality of residual energy values computes said residual energy values, E i!, in accordance with the equation:

##EQU7## wherein r(k) refer the samples of said received signal and z(k) refers to the samples of said echo estimate signal.

15. An echo canceller comprising:

delay monitor having a first input for receiving a received signal and having a second input for receiving an echo estimate signal and having an output; and

adaptive filter means having an input coupled to said delay monitor output and having an output.

16. The apparatus of claim 15 wherein said delay monitor has a third input for receiving a far-end speech detection signal.

17. The apparatus of claim 16 further comprising a speech detector having an input for receiving a far-end signal and having an output coupled to said delay monitor third input.

18. The apparatus of claim 15 further comprising a double talk detector having a first input for receiving said received signal and having a second input for receiving said far-end signal and having an output coupled to a second input of said adaptive filter.