Echo cancellation in digital data transmission system

• US 6,816,592 B1
• Filed: 11/14/2000
• Issued: 11/09/2004
• Est. Priority Date: 05/15/1998
• Status: Active Grant

• Current Assignee: Intellectual Ventures I LLC (Intellectual Ventures LLC)
• Original Assignee: Nokia Networks (Nokia Corporation)
• Inventors: Kirla, Olli
• Primary Examiner(s): TIEU, BINH KIEN
• Application Number:
  US09/700,334
• Time in Patent Office: 1,456 Days
• Field of Search: 379/406.01, 379/406.03, 379/406.05, 379/406.06, 379/406.08, 370/286, 370/289, 370/260
• US Class Current: 379/406.05
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers

Abstract

A method and an apparatus for echo cancellation in a digital data transmission system in which system the end of a transmission link to which sound returns as an echo is the far end and the end of the transmission link from which an echo is reflected back is the near end, and in which a speech coding method is used on the echo path at least for a far-end signal transmitted from the far end to the near end, the method comprising the following steps: the echo originating from the near end is estimated with an adaptive linear filter on the basis of the far-end signal, and the echo estimate is subtracted from the near-end signal transmitted from the near end to the far end, whereby the speech-encoded far-end signal is decoded in an echo canceller, and the echo originating from the near end is estimated on the basis of said decoded far-end signal.

Claims

1. A method for echo cancellation in a digital data transmission system in which system the end of a transmission link to which sound returns as an echo is the far end and the end of transmission link from which an echo is reflected back is the near end, and in which a speech coding method is used on the echo path at least for a far-end signal transmitted from the far end to the near end, the method comprising:

decoding the far-end speech-encoded signal with a speech decoder located on the far-end side of the transmission link;

estimating the echo originating from the near end using an adaptive linear filter based on the decoded far-end signal; and

subtracting the echo estimate from the near-end signal transmitted from the near end to the far end.

2. The method of claim 1, further comprising:

delaying the input or out signal of the adaptive linear filter to compensate for the transmission delays on the echo path.

3. The method of claim 2, further comprising:

delaying said input signal of the adaptive linear filter before the signal is decoded in the speech decoder.

4. The method of claim 1, further comprising:

cancelling residual echo with a non-linear processor or comfort noise generator from the signal coming from the near end, from which signal the echo estimate produced by the adaptive linear filter has already been subtracted.

5. The method of claim 1, further comprising encoding and decoding the echo estimate produced by the adaptive linear filter, before it is subtracted from the near-end signal, to compensate for the non-linear distortion caused by speech coding performed on the near-end signal on the echo path.

6. The method of claim 1, further comprising:

feeding said decoded signal also to a second adaptive linear filter parallel to said adaptive linear filter;

encoding and decoding the output signal of the second adaptive linear filter,

subtracting the thus obtained second echo estimate from the signal to be transmitted from the near end to the far end, and

selecting either the near-end signal, from which the first echo estimate has been subtracted, or the near-end signal, from which the second echo estimate has been subtracted, for transmitting on to the far end.

7. The method of claim 6, further comprising selecting the signal whose lever is lower.

8. The method of claim 6, further comprising delaying the input or output signal of the first adaptive linear filter to compensate for the delay caused by the encoding and decoding in the second filter branch.

9. The method of claim 6, further comprising cancelling the residual echo from the selected signal with a non-linear processor/comfort noise generator.

10. An apparatus for echo cancellation in a digital data transmission system in which system the end of a transmission link to which sound returns as an echo is the far end and the end of the transmission link from which an echo is reflected back is the near end, and in which a speech coding method is used on the echo path at least for a far-end signal transmitted from the far end to the near end, the apparatus comprising:

an adaptive linear filter, which is located on the far-end side of the transmission link, and configured to produce an echo estimate based on the far-end signal and subtract the echo estimate from the signal coming from the near end to cancel the echo originating from the near end; and

a speech decoder which is located on the far-end side of the transmission link and configured to decode the speech-encoded far-end signal and forward the decoded far-end signal to the adaptive linear filter for the purpose of producing an echo estimate.

11. The apparatus of claim 10, wherein the decoder is bit-exact with the decoder used in speech coding the far-end signal on the echo path.

12. The apparatus of claim 10, further comprising a non-linear processor or noise generator configured to cancel residual echo from the signal coming from the near end, from which signal, the echo estimate produced by the adaptive linear filter has already been subtracted.

13. The apparatus of claim 10, further comprising a delay line configured to delay the input or output signal of the adaptive linear filter to compensate for the transmission delays on the echo path.

14. The apparatus of claim 13, wherein the delay line is configured to cause a delay whose length is τ

r+τ

e+τ

s+τ

d, where;

τ

r=the transmission day of the far-end signal without speech coding delays;

τ

e=the encoder delay;

τ

s=the transmission delay of the near-end signal without speech coding delays; and

τ

d=the decoder delay.

15. The apparatus of claim 10, further comprising an encoder and a second decoder configured to encode and decode the output signal of the adaptive linear filter, before the output signal is subtracted from the near-end signal transmitted from the near end to the far end, to compensate for the non-linear distortion caused by the speech coding performed on the echo path on the near-end signal.

16. The apparatus of claim 15, wherein the encoder and second decoder are bit-exact with the encoder and, correspondingly, the decoder used in speech coding the near-end signal on the echo path.

17. The apparatus of claim 10, further comprising:

an addition to said adaptive linear filter, a second adaptive linear filter parallel to adaptive linear filter,

an encoder and a second decoder for encoding and decoding the output signal of the second adaptive linear filter, after which the thus obtained second echo estimate is subtracted from the near-end signal, and

a selector member configured to select either the near-end signal, from which the first echo estimate has been subtracted, or the near-end signal, from which the second echo estimate has been subtracted, and transmits it on to the far end.

18. The apparatus of claim 17, wherein the encoder and the second decoder are bit-exact with the encoder and, correspondingly, the decoder used in speech coding the near-end signal on the echo path.

19. The apparatus of claim 17, wherein the selector member is configured to select the signal whose level is lower.

20. The apparatus of claim 17, wherein the apparatus also comprises a non-linear processor/comfort noise generator configured to cancel residual echo from the signal selected by the selector member.

21. The apparatus of claim 17, further comprising a delay line configured to delay the input or output signal of the first adaptive linear filter to compensate for the delay caused by the encoding and decoding in the second filter branch.

22. The apparatus of claim 21, wherein the delay line, which delays the input or output signal of the first adaptive linear filter to compensate for the delay caused by the encoding and decoding in the second filter branch, is configured to cause a delay whose length is τ

e+τ

d, where;

τ

e=the encode delay; and

τ

d=the decoder delay.

23. The apparatus of claim 15, further comprising a delay line configured to delay the input signal of the first and the second adaptive linear filter to compensate for the transmission delays on the echo path.

24. The apparatus of claim 23, wherein the delay line, which delays the input signal of the first and the second adaptive linear filter to compensate for the transmission delays on the echo path, is configured to cause a delay whose length is τ

r+τ

s, where;

τ

r=the transmission delay of the far-end signal without speech coding delays; and

τ

s=the transmission delay of the near-end signal without speech coding delays.