METHOD AND APPARATUS FOR ECHO CANCELLATION

• US 20090136020A1
• Filed: 11/17/2008
• Published: 05/28/2009
• Est. Priority Date: 11/28/2007
• Status: Abandoned Application

• Current Assignee: Beken Corporation
• Original Assignee: Beken Corporation
• Inventors: Yu, Caogang, Wang, Weifeng
• Application Number:
  US12/272,282
• Publication Number:
  US 20090136020A1
• Time in Patent Office: Days
• US Class Current: 379/406.80
• CPC Class Codes: H04B 3/234 using double talk detection

Abstract

A method and apparatus for echo cancellation is disclosed. The apparatus includes an echo compensator and a double talk detector. The echo compensator compensates for associated feedback echo by filtering an echo component from a receiver input signal. The double talk detector provides a control signal based on comparisons of a receiver output signal to a threshold signal and to a transmit signal. The echo compensator also selectively updates filter parameters based on the control signal.

Claims

1. An apparatus for echo cancellation, comprising:

an echo compensator configured to receive a receiver input signal having at least an echo component and a received signal component, to receive an enable signal, to receive a transmit signal, and to provide a receiver output signal based on filtering the receiver input signal; and

a double talk detector configured to receive the receiver output signal, to receive the transmit signal, and to provide the enable signal based on the receiver output signal and the transmit signal.

2. The apparatus of claim 1, wherein the echo compensator is configured to estimate the echo component of the receiver input signal and to provide the receiver output signal based on subtracting the estimated echo component from the receiver input signal.

3. The apparatus of claim 1, wherein the echo compensator and the double talk detector are implemented as digital signal processor (DSP) code to be executed on a DSP.

4. The apparatus of claim 1, wherein the echo controller is configured to truncate one or more least significant bits and to perform a fixed point operation on one or more most significant bits.

5. The apparatus of claim 1, wherein the echo compensator includes:

a compensation controller configured to receive the enable signal, to receive the receiver output signal, and to provide filter coefficients based on the receiver output signal and the enable signal;

a filter configured to receive the filter coefficients, to receive the transmit signal, and to provide an estimated echo signal based on the transmit signal as an estimate of the echo component of the receiver input signal; and

a subtractor configured to receive the estimated echo signal, to receive the receiver input signal, and to provide the receiver output signal based on subtracting the estimated echo signal from the receiver input signal.

6. The apparatus of claim 5, wherein the filter is a finite impulse response (FIR) filter.

7. The apparatus of claim 6, wherein the FIR filter has a gain that is approximately equal to 6 decibels.

8. The apparatus of claim 5, wherein the compensation controller is configured to selectively update the filter coefficients if the enable signal is at a first value and to hold the filter coefficients unchanged if the enable signal is at a second value.

9. The apparatus of claim 5, wherein the compensation controller is configured to provide the filter coefficients based on a normalized least mean squares (NLMS) algorithm.

10. The apparatus of claim 9, wherein the NLMS algorithm is characterized by the equation:

$a_k<br><br>\left(n+1\right)=a_k<br><br>\left(n\right)+\frac{\mathrm{\mu <br><br>}<br><br><br><br>e<br><br>\left(n\right)}{P<br><br>\left(n\right)}*y<br><br>\left(n\right),$

wherein n represents an iteration number, a_k(n) represents the filter coefficients, μ

represents an iteration step size, e(n) represents the receiver output signal, P(n) represents a power of the receiver input signal, and y(n) represents the receiver input signal.

11. The apparatus of claim 1, wherein the double talk detector includes:

a first comparator configured to receive a threshold signal, to receive the receiver output signal, and to provide a double talk comparison signal based on a comparison of the receiver output signal to the threshold signal;

a second comparator configured to receive the transmit signal, to receive the receiver output signal, and to provide a feedback threshold signal based on a comparison of the receiver output signal to the transmit signal; and

a logic module configured to receive the feedback comparison signal, to receive the double talk comparison signal, and to provide the enable signal based on the feedback comparison signal and the double talk comparison signal.

12. The apparatus of claim 11, wherein the logic module includes:

an AND gate configured to provide the enable signal as a logically AND of the feedback comparison signal and the double talk comparison signal.

13. The apparatus of claim 1, further comprising:

an analog to digital converter configured to receive an analog receiver input signal and to provide the receiver input signal; and

a digital to analog converter configured to receive the transmit signal and to provide an analog transmit signal.

14. A method of echo cancellation, comprising:

receiving a receiver input signal having at least an echo component and a received signal component;

receiving a transmit signal; and

providing a receiver output signal, including;

estimating the echo component from the transmit signal based on selectively updated filter coefficients;

selectively updating the filter coefficients based on an enable signal, wherein the enable signal is based on a comparison of the transmit signal to the receiver output signal; and

subtracting the estimated echo component from the receiver input signal.

15. The method of claim 14, wherein estimating the echo component includes:

employing a finite impulse response (FIR) filter to provide the estimated echo component from the transmit signal.

16. The method of claim 14, wherein selectively updating the filter coefficients includes:

updating the filter coefficients if the enable signal is at a first value; and

holding the filter coefficients unchanged if the enable signal is at a second value.

17. The method of claim 14, wherein selectively updating the filter coefficients is further based on a normalized least mean squares (NLMS) algorithm.

18. The method of claim 17, wherein the NLMS algorithm is characterized by the equation:

$a_k<br><br>\left(n+1\right)=a_k<br><br>\left(n\right)+\frac{\mathrm{\mu <br><br>}<br><br><br><br>e<br><br>\left(n\right)}{P<br><br>\left(n\right)}*y<br><br>\left(n\right),$

wherein n represents an iteration number, a_k(n) represents the filter coefficients, μ

represents an iteration step size, e(n) represents the receiver output signal, P(n) represents a power of the receiver input signal, and y(n) represents the receiver input signal.

19. An apparatus for echo cancellation, comprising:

first means for receiving a receiver input signal having at least an echo component and a received signal component;

second means for receiving a transmit signal; and

third means for providing a receiver output signal, including;

fourth means for estimating the echo component from the transmit signal based on selectively updated filter coefficients;

fifth means for selectively updating the filter coefficients based on an enable signal, wherein the enable signal is based on a comparison of the transmit signal to the receiver output signal; and

sixth means for subtracting the estimated echo component from the receiver input signal.

20. The apparatus of claim 19, wherein the filter coefficients are further based on a normalized least mean squares (NLMS) algorithm characterized by the equation:

$a_k<br><br>\left(n+1\right)=a_k<br><br>\left(n\right)+\frac{\mathrm{\mu <br><br>}<br><br><br><br>e<br><br>\left(n\right)}{P<br><br>\left(n\right)}*y<br><br>\left(n\right),$

wherein n represents an iteration number, a_k(n) represents the filter coefficients, μ

represents an iteration step size, e(n) represents the receiver output signal, P(n) represents a power of the receiver input signal, and y(n) represents the receiver input signal.