Apparatus and method for echo characterization of a communication channel

• US 5,577,116 A
• Filed: 09/16/1994
• Issued: 11/19/1996
• Est. Priority Date: 09/16/1994
• Status: Expired due to Fees

• Current Assignee: North Carolina State University (University of North Carolina System)
• Original Assignee: North Carolina State University (University of North Carolina System)
• Inventors: Duel-Hallen, Alexandra, Townsend, Keith, Alexander, Samuel T., Punjabi, Harish
• Primary Examiner(s): Zele, Krista M.
• Assistant Examiner(s): SAINT SURIN, JACQUES M
• Application Number:
  US08/307,257
• Time in Patent Office: 795 Days
• Field of Search: 379/410, 379/411, 379/406, 370/32.1, 370/32, 364/724.18, 364/724.19
• US Class Current: 379/406.12
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23

Abstract

An apparatus for echo characterization or measurement includes a frequency domain adaptive filter for converging a plurality of filter coefficients based upon transmit and receive frequency domain transforms. The frequency domain adaptive filter preferably determines least mean square differences between estimated receive frequency domain transforms and the respective corresponding actual receive frequency domain transforms. The apparatus also preferably includes an echo characterization output portion for generating an echo characterization value for the communications channel. The echo characterization value may be one or both of echo path loss and echo delay. The apparatus preferably includes a gain normalization portion operatively connected to the adaptive filter for generating normalized gains of respective filter coefficients based upon spectral power of the respective transmit frequency domain transforms. Moreover, the apparatus also preferably includes a gain normalization weighting portion operatively connected to the gain normalization portion for weighting the normalized gains based upon frequency. An associated method is also disclosed.

Claims

1. An apparatus for echo characterization of a communications channel, said apparatus comprising:

transmit sampling means for generating a series of sampled transmit values of a signal transmitted on the communications channel;

transmit frequency domain transform means operatively connected to said transmit sampling means for generating respective transmit frequency domain transforms of the sampled transmit values;

receive sampling means for generating a series of sampled receive values of a signal received on the communications channel based upon the signal transmitted on the communications channel;

receive frequency domain transform means operatively connected to said receive sampling means for generating respective receive frequency domain transforms of the sampled receive values;

frequency domain adaptive filter means operatively connected to said transmit and receive frequency domain transform means for converging a plurality of filter coefficients based upon the transmit and receive frequency domain transforms;

echo characterization output means operatively connected to said frequency domain adaptive filter means for generating an echo characterization value for the communications channel;

gain normalization means operatively connected to said frequency domain adaptive filter means for generating normalized gains of respective filter coefficients based upon spectral power of the respective transmit frequency domain transforms; and

gain normalization weighting means operatively connected to said gain normalization means for weighting the normalized gains based upon frequency;

wherein said gain normalization weighting means further comprises means for weighting the normalized gains as a predetermined function of frequency; and

wherein said gain weighting means further comprises means for determining an estimated average echo to return noise ratio based upon the signal received from the communications channel and for selecting a predetermined gain normalization weighting function based upon the ratio.

2. An apparatus according to claim 1 wherein said echo characterization output means comprises means for generating an echo path loss value.

3. An apparatus according to claim 1 wherein said echo path characterization means comprises means for generating an echo delay value.

4. An apparatus according to claim 1 wherein said frequency domain adaptive filter means comprises least means squares determining means for determining least mean square differences between estimated receive frequency domain transforms and the respective corresponding receive frequency domain transforms.

5. An apparatus according to claim 1 further comprising threshold selection means operatively connected to said transmit frequency domain transform means for selecting values above a predetermined spectral power threshold.

6. An apparatus for echo characterization of a communications channel, said apparatus comprising:

transmit sampling means for generating a series of sampled transmit values of a signal transmitted on the communications channel;

transmit frequency domain transform means operatively connected to said transmit sampling means for generating respective transmit frequency domain transforms of the sampled transmit values;

receive sampling means for generating a series of sampled receive values of a signal received on the communications channel based upon the signal transmitted on the communications channel;

receive frequency domain transform means operatively connected to said receive sampling means for generating respective receive frequency domain transforms of the sampled receive values;

frequency domain adaptive filter means operatively connected to said transmit and receive frequency domain transform means for converging a plurality of filter coefficients based upon the transmit and receive frequency domain transforms;

echo characterization output means operatively connected to said frequency domain adaptive filter means for generating an echo characterization value for the communications channel; and

display means operatively connected to said echo characterization output means for displaying the echo characterization value for the communications channel.

7. An apparatus according to claim 6 further comprising gain normalization means operatively connected to said frequency domain adaptive filter means for generating normalized gains of respective filter coefficients based upon spectral power of the respective transmit frequency domain transforms.

8. An apparatus according to claim 7 further comprising gain normalization weighting means operatively connected to said gain normalization means for weighting the normalized gains based upon frequency.

9. An apparatus according to claim 8 wherein said gain normalization weighting means further comprises means for weighting the normalized gains as a predetermined function of frequency.

10. An apparatus according to claim 8 wherein said gain normalization weighting means further comprises means for weighting the normalized gains so that normalized gains at a lower frequency have a greater weighting than normalized gains at higher frequencies.

11. An apparatus according to claim 6 further comprising logging means for recording the echo characterization value, a time the echo characterization was made, and a configuration of the communications channel at the time the echo characterization was made.

12. An apparatus for echo characterization of a communications channel, said apparatus comprising:

transmit sampling means for generating a series of sampled transmit values of a signal transmitted on the communications channel;

transmit frequency domain transform means operatively connected to said transmit sampling means for generating respective transmit frequency domain transforms of the sampled transmit values;

receive sampling means for generating a series of sampled receive values of a signal received on the communications channel based upon the signal transmitted on the communications channel;

receive frequency domain transform means operatively connected to said receive sampling means for generating respective receive frequency domain transforms of the sampled receive values;

frequency domain adaptive filter means operatively connected to said transmit and receive frequency domain transform means for converging a plurality of filter coefficients based upon the transmit and receive frequency domain transforms, said frequency domain adaptive filter means comprising least mean square determining means for determining least mean square differences between estimated receive frequency domain transforms and the respective corresponding receive frequency domain transforms;

gain normalization means operatively connected to said frequency domain adaptive filter means for generating normalized gains of respective filter coefficients based upon spectral power of the respective transmit frequency domain transforms;

gain normalization weighting means operatively connected to said gain normalization means for weighting the normalized gains based upon frequency; and

echo characterization output means operatively connected to said frequency domain adaptive filter means for generating an echo characterization value of the communications channel.

13. An apparatus according to claim 12 wherein said gain normalization weighting means further comprises means for weighting the normalized gains as a predetermined function of frequency.

14. An apparatus according to claim 12 wherein said gain normalization weighting means further comprises means for weighting the normalized gains so that normalized gains at a lower frequency have a greater weighting than normalized gains at higher frequencies.

15. An apparatus according to claim 13 wherein said gain normalization weighting means further comprises means for determining an estimated average echo to return noise ratio based upon the signal received from the communications channel and for selecting a predetermined gain normalization weighting function based upon the ratio.

16. An apparatus according to claim 12 wherein said echo path characterization means comprises means for generating at least one of an echo path loss signal and an echo delay signal.

17. An apparatus according to claim 12 further comprising threshold selection means operatively connected to said transmit frequency domain transform means for selecting values above a predetermined spectral power threshold.

18. An apparatus according to claim 12 further comprising logging means for recording an echo characterization value, a time the echo characterization was made, and a configuration of the communications channel at the time the echo characterization was made.

19. A telephone system comprising:

a plurality of telephone lines;

switch means connected to said plurality of telephone lines for selectively establishing connections between predetermined ones of said telephone lines to thereby establish a communications channel;

echo characterization means operatively connected to the communications channel established by said switch means for generating an echo characterization value of the communications channel, said echo characterization means comprising

transmit sampling means for generating a series of sampled transmit values of a signal transmitted on the communications channel,

transmit frequency domain transform means operatively connected to said transmit sampling means for generating respective transmit frequency domain transforms of the sampled transmit values,

receive sampling means for generating a series of sampled receive values of a signal received on the communications channel based upon the signal transmitted on the communications channel,

receive frequency domain transform means operatively connected to said receive sampling means for generating respective receive frequency domain transforms of the sampled receive values,

frequency domain adaptive filter means operatively connected to said transmit and receive frequency domain transform means for converging a plurality of filter coefficients based upon the transmit and receive frequency domain transforms, and

echo characterization output means operatively connected to said frequency domain adaptive filter means for generating the echo characterization value of the communications channel.

20. A telephone system according to claim 19 further comprising gain normalization means operatively connected to said frequency domain adaptive filter means for generating normalized gains of respective filter coefficients based upon spectral power of the respective transmit frequency domain transforms.

21. A telephone system according to claim 20 further comprising gain normalization weighting means operatively connected to said gain normalization means for weighting the normalized gains based upon frequency.

22. A telephone system according to claim 21 wherein said gain normalization weighting means further comprises means for weighting the normalized gains as a predetermined function of frequency.

23. A telephone system according to claim 21 wherein said gain normalization weighting means further comprises means for weighting the normalized gains so that normalized gains at a lower frequency have a greater weighting than normalized gains at higher frequencies.

24. A telephone system according to claim 22 wherein said gain normalization weighting means further comprises means for determining an estimated average echo to return noise ratio based upon the signal received from the communications channel and for selecting a predetermined gain normalization weighting function based upon the ratio.

25. A telephone system according to claim 19 wherein said echo path characterization means comprises means for generating one of an echo path loss signal and an echo delay value.

26. A telephone system according to claim 19 wherein said frequency domain adaptive filter means comprises least mean square determining means for determining least mean square differences between estimated receive frequency domain transforms and the respective corresponding receive frequency domain transforms.

27. A telephone system according to claim 19 further comprising threshold selection means operatively connected to said transmit frequency domain transform means for selecting values above a predetermined spectral power threshold.

28. A telephone system according to claim 19 further comprising logging means for recording an echo characterization value, a time the echo characterization was made, and a configuration of the communications channel at the time the echo characterization was made.

29. A telephone system according to claim 19 further comprising logging means for recording an echo characterization value, a time the characterization was made, and a configuration of the communications channel at the time the characterization was made.

30. A method for echo characterization of a communications channel, the method comprising the steps of:

generating a series of sampled transmit values of a signal transmitted on the communications channel;

generating respective transmit frequency domain transforms of the sampled transmit values;

generating a series of sampled receive values of a signal received on the communications channel based upon the signal transmitted on the communications channel;

generating respective receive frequency domain transforms of the sampled receive values;

converging a plurality of filter coefficients of a frequency domain adaptive filter based upon the transmit and receive frequency domain transforms;

generating an echo characterization value for the communications channel based upon convergence of the filter coefficients;

generating normalized gains of respective filter coefficients based upon spectral power of the respective transmit frequency domain transforms; and

weighting the normalized gains as a predetermined function of frequency;

wherein the step of weighting the normalized gains by determining an estimated average echo to return noise ratio based upon the signal received from the communications channel and selecting a predetermined gain weighting based upon the ratio.

31. A method according to claim 30 wherein the step of generating the echo characterization value comprises generating at least one of an echo path loss value and an echo delay value.

32. A method according to claim 30 wherein the step of converging filter coefficients further comprises the step of determining least mean square differences between estimated receive frequency domain transforms and the respective corresponding receive frequency domain transforms.

33. A method according to claim 30 further comprising the step of selecting values of the transmit frequency domain transform above a predetermined spectral power threshold.

34. A method for echo characterization of a communications channel, the method comprising the steps of:

generating a series of sampled transmit values of a signal transmitted on the communications channel;

generating respective transmit frequency domain transforms of the sampled transmit values;

generating a series of sampled receive values of a signal received on the communications channel based upon the signal transmitted on the communications channel;

generating respective receive frequency domain transforms of the sampled receive values;

converging a plurality of filter coefficients of a frequency domain adaptive filter based upon the transmit and receive frequency domain transforms;

generating an echo characterization value for the communications channel based upon convergence of the filter coefficients; and

displaying the echo characterization value.

35. A method according to claim 34 further comprising the step of logging a time and configuration for the communications channel along with the echo characterization value.

36. A method according to claim 34 further comprising the step of generating normalized gains of respective filter coefficients based upon spectral power of the respective transmit frequency domain transforms.

37. A method according to claim 36 further comprising the step of weighting the normalized gains based upon frequency.

38. A method according to claim 36 further comprising the step of weighting the normalized gains as a predetermined function of frequency.

39. A method according to claim 36 further comprising the step of weighting the normalized gains so that normalized gains at a lower frequency have a greater weighting than normalized gains at higher frequencies.