Echo canceller and method for controlling echo cancellation

• US 5,533,121 A
• Filed: 09/06/1994
• Issued: 07/02/1996
• Est. Priority Date: 09/07/1993
• Status: Expired due to Term

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Suzuki, Shigeaki, Naito, Yushi
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): Wolinsky, Scott
• Application Number:
  US08/301,344
• Time in Patent Office: 665 Days
• Field of Search: 379/410, 379/411, 379/406, 379/407, 370/32.1, 370/81, 370/110.1, 375/14
• US Class Current: 379/406.02
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers

Abstract

An echo canceller is disclosed which is capable of disabling its echo cancelling function when other echo cancellers are connected in tandem in a communications network. A pattern is inserted by extracting bits from a receiving side pulse code modulation (PCM) signal bit stream and replacing them with a predetermined bit-pattern sequence. When the predetermined bit-pattern sequence is detected at a transmission side input PCM signal bit stream, the echo cancelling function is disabled.

Claims

1. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a pattern inserting means for extracting a predetermined portion of a receiving side pulse code modulation (PCM) input signal and inserting a predetermined bit-pattern sequence into a receiving side PCM output signal in place of the extracted portion; and

(c) a pattern detecting means for detecting a predetermined bit pattern by monitoring a transmitting side input PCM signal, and disabling the echo cancelling function of the echo cancelling means when the predetermined bit-pattern is detected.

13. An echo canceller according to any one of claims 1-12, wherein

said pattern inserting means is arranged between exchanges of a channel associated signaling system and periodically extracts second bits from least significant bits of receiving side PCM signal code-words and inserts the predetermined bit-pattern into the receiving side PCM signal code-words in place of the extracted second bits.

14. An echo canceller according to any one of claims 1-12, wherein

said pattern inserting means is arranged between exchanges of a channel associated signaling system and extracts least significant bits of receiving side PCM signal code-words with a period which has a prime number relation to a period of a PCM robbed-bit signaling system and inserts the predetermined bit-pattern into the receiving side PCM signal code-words in place of the extracted bits.

2. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a first channel associated signal detecting means for determining whether a voice channel at the receiving side is in an idle state;

(c) a second channel associated signal detecting means for determining whether a voice channel at the transmitting side is in an idle state;

(d) a pattern detecting means for detecting a predetermined bit-pattern in a transmitting side input pulse code modulation (PCM) signal;

(e) a pattern inserting means for inserting a predetermined bit-pattern sequence into a receiving side PCM signal; and

(f) an operation controlling means for disabling echo cancelling function of the echo canceling means after detection of the predetermined bit-pattern in the transmitting side input PCM signal until the voice channel is in an idle state as detected by both the first and second channel associated signal detecting means, and for enabling the pattern inserting means for a predetermined duration when the voice channel status changes from the idle state to a busy state as detected by both the first and second channel associated signal detecting means.

3. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a first common channel signal detecting means for determining whether a voice channel at the receiving side is in an idle state;

(c) a second common channel signal detecting means for determining whether a voice channel at the transmitting side is in an idle state;

(d) a pattern detecting means for detecting a predetermined bit-pattern in a transmitting side input pulse code modulation (PCM) signal;

(e) a pattern inserting means for inserting a predetermined bit-pattern sequence into a receiving side PCM signal; and

(f) an operation controlling means for disabling echo cancelling function of the echo canceling means after detection of the predetermined bit-pattern in the transmitting side input PCM signal until the voice channel is in an idle state as detected by both the first and second common channel signal detecting means, and for enabling the pattern inserting means for a predetermined duration when the voice channel status changes from the idle state to a busy state as detected by both the first and second common channel signal detecting means.

4. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching, where a channel associated signaling signal or a common channel signaling signal is not included in receiving side or transmitting side input signal bit streams comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a signaling status input to obtain a channel status indicating whether a relevant voice channel is in an idle state or in a busy state.

(c) a pattern inserting means for inserting a predetermined bit-pattern into a receiving voice channel pulse code modulation (PCM) signal when the signaling status input indicates that the relevant voice channel status changed from an idle state to a busy state;

(d) a pattern detecting means for detecting a predetermined bit pattern by monitoring a transmitting side input PCM signal; and

(e) an operation controlling means for disabling echo cancelling function of the echo cancelling means after detection of the predetermined bit-pattern in the transmitting side input PCM signal until the voice channel status input changes from a busy state to an idle state, and for enabling the predetermined bit-pattern inserting means for a predetermined duration after the voice channel status changes from an idle state to a busy state.

5. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a first pattern detecting means for detecting a predetermined bit pattern in a transmitting side input pulse code modulation (PCM) signal, and disabling the echo cancelling function of the echo cancelling means when the predetermined bit-pattern is detected;

(c) a second pattern detecting means for detecting a predetermined bit pattern by monitoring receiving side input PCM signal bit stream; and

(d) a pattern inserting means for inserting a predetermined a bit pattern into a receiving side voice channel PCM signal when the second pattern detecting means does not detect the predetermined bit-pattern.

6. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo cancelling means for cancelling echo signal, which is disabled when a predetermined bit-pattern is detected in a transmitting side input pulse code modulation (PCM) signal, or while a data call is applied to a voice channel;

(b) a pattern inserting means for inserting a predetermined bit pattern in a receiving side PCM signal while the data call is not applied to the voice channel;

(c) a pattern detecting means for detecting the predetermined bit-pattern in the transmitting side input PCM signal;

(d) a tone detecting means for detecting a modem answering tone by monitoring the transmitting side PCM signal and a receiving side input PCM signal;

(e) a power detecting means for detecting an end of a data call by monitoring the absence of signal power for more than predetermined period in both the transmitting and receiving side input PCM signals; and

(f) a register for applying the data call to the voice channel after the modem answering tone signal is detected until the power detecting means detects the end of the data call.

7. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching, where a voice channel is not coded by low bit rate coding comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a first channel associated signal detecting means for determining whether the voice channel at the receiving side is in an idle state;

(c) a second channel associated signal detecting means for determining whether the voice channel at the transmitting side is in an idle state;

(d) a pattern inserting means for inserting a predetermined bit-pattern in the receiving side pulse code modulation (PCM) signal;

(e) a pattern detecting means for detecting a predetermined bit-pattern in a transmitting side input PCM signal;

(f) a tone detecting means for detecting a modem answering tone by monitoring both the transmitting side input PCM signal and a receiving side input PCM signals; and

(g) an operation controlling means for disabling an echo cancelling function of the echo cancelling means after detection of the predetermined bit-pattern in the transmitting side input PCM signal at the pattern detecting means or after detection of the modem answering tone, until the voice channel status changes from a busy state to an idle state as detected by both the first and the second channel associated signal detecting means, and for enabling the pattern inserting means for a predetermined duration when the voice channel status changes from an idle state to a busy state as detected by both the first and second channel associated signal detecting means, and disabling the pattern inserting means when the modem answering tone is detected.

8. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a first common channel signal detecting means for determining whether a voice channel at the receiving side is in an idle state;

(c) a second common channel signal detecting means for determining whether the voice channel at the transmitting side is in an idle state;

(d) a pattern inserting means for inserting a predetermined bit-pattern in a receiving side pulse code modulation (PCM) signal;

(e) a pattern detecting means for detecting a predetermined bit-pattern in a transmitting side input PCM signal;

(f) a tone detecting means for detecting a modem answering tone by monitoring both the transmitting side input PCM signal and a receiving side input PCM Signal; and

(g) an operation controlling means for disabling an echo cancelling function of the echo cancelling means after detection of the predetermined bit-pattern in the transmitting side input PCM signal at the pattern detecting means or after detection of the modem answering tone, until the voice channel status changes from a busy state to an idle state as detected by both the first and the second channel associated signal detecting means, and for enabling the pattern inserting means for a predetermined duration when the voice channel status changes from an idle state to a busy state as detected by both the first and second channel associated signal detecting means, and disabling the pattern inserting means when the modem answering tone is detected.

9. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo canceller circuit for cancelling echo signal;

(b) a signaling status input to obtain a channel status indicating whether a relevant voice channel is in an idle state or in a busy state;

(c) a pattern inserting means for inserting a predetermined bit-pattern into a receiving voice channel pulse code modulation (PCM) signal for a predetermined duration when the signaling status input indicates that the relevant voice channel status changed from an idle state to a busy state;

(d) a pattern detecting means for detecting a predetermined bit pattern by monitoring a transmitting side input PCM signal;

(e) a tone detecting means for detecting a modem answering tone by monitoring both transmitting side and receiving side input PCM signals; and

(f) an operation controlling means for disabling echo cancelling function of the echo cancelling means after detection of the predetermined bit-pattern in the transmitting side input PCM signal or after detection of the modem answering tone until the voice channel status input changes from a busy state to an idle state, for enabling the predetermined bit-pattern inserting means for a predetermined duration after the voice channel status changes from an idle state to a busy state, and for disabling the pattern inserting means when the modem answering tone is detected.

10. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo cancelling means for cancelling echo signal, which is disabled when a predetermined bit-pattern is detected in a transmitting side input pulse code modulation (PCM) signal, or while a data call is applied to a voice channel;

(b) a first pattern detecting means for detecting the predetermined bit-pattern in the transmitting side input PCM signal bit stream, and disabling the echo canceling function of the echo canceling means while the predetermined bit-pattern is detected;

(c) a second pattern detecting means for detecting a predetermined bit-pattern in the receiving side input PCM signal;

(d) a pattern inserting means for inserting a predetermined bit pattern in a receiving side PCM signal while the predetermined bit-pattern is not detected at the receiving side input PCM signal or while the data call is applied to the voice channel;

(e) a tone detecting means for detecting a modem answering tone by monitoring the transmitting side input PCM signal and a receiving side input PCM signal;

(f) a power detecting means for detecting an end of a data call by monitoring the absence of signal power for more than predetermined period in both the transmitting and receiving side input PCM signals; and

(g) a register for applying the data call to the voice channel after the modem answering tone signal is detected until the power detecting means detects the end of the data call.

11. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo cancelling means for cancelling echo signal, which is disabled when a predetermined bit-pattern is detected in a transmitting side input pulse code modulation (PCM) signal, or while a data call is applied to a voice channel;

(b) a first pattern detecting means for detecting the predetermined bit-pattern in the transmitting side input PCM signal;

(c) a second pattern detecting means for detecting a predetermined bit pattern in the receiving side input PCM signal;

(d) a pattern inserting means for inserting a predetermined bit pattern in a receiving side PCM signal while the predetermined bit-pattern is not detected at the receiving side input PCM signal or while the data call is applied to the voice channel;

(e) a modem signal detection input which receives detection information of a modem answering tone from an external tone detecting apparatus;

(f) a power detecting means for detecting an end of a data call by monitoring the absence of signal power for more than predetermined period in both the transmitting and receiving side input PCM signals; and

(g) a register for applying the data call for a duration after receipt of detection information by the modem signal detection input.

12. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a first common channel signal detecting means for determining whether the voice channel at the receiving side is in an idle state;

(c) a second common channel signal detecting means for determining whether the voice channel at the transmitting side is in an idle state;

(d) a pattern inserting means for inserting a predetermined bit-pattern in the receiving side pulse code modulations (PCM) signal;

(e) a pattern detecting means for detecting a predetermined bit-pattern in a transmitting side input PCM signal;

(f) a tone detecting means for detecting a modem answering tone by monitoring both the transmitting side input PCM signal and a receiving side input PCM signals; and

(g) an operation controlling means for disabling an echo cancelling function of the echo cancelling means after detection of the predetermined bit-pattern in the transmitting side input PCM signal at the pattern detecting means or after detection of the modem answering tone until the voice channel status changes from a busy state to an idle state as detected by both the first and the second common channel signal detecting means, for enabling the pattern inserting means for a predetermined duration when the voice channel status changes from an idle state to busy state as detected by both the first and second common channel signal detecting means, and for disabling the pattern inserting means when the modem answering tone is detected.

15. A method for controlling echo cancellation in an echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching, said method comprising the steps of:

(1) inserting a predetermined bit-pattern sequence in a receiving side pulse code modulation (PCM) signal; and

(2) disabling said echo cancellation when the predetermined bit-pattern is detected in a transmitting side input PCM signal.

16. The method of claim 15, further comprising the steps of:

(3) detecting whether a voice channel is in an idle state;

wherein said pattern is inserted upon detecting a change from an idle state to a busy state; and

wherein said echo cancellation is disabled until a change from a busy state to an idle state is detected.

17. The method of claim 15, wherein said insertion step includes periodically extracting least significant bits from the receiving side input PCM signal code-words and inserting the predetermined bit-pattern sequence.

18. The method of claim 15, wherein said inserting step includes periodically extracting second bits from least significant bits of the receiving side input PCM signal and inserting the predetermined bit-pattern sequence.

19. The method of claim 15, wherein said inserting step includes extracting least significant bits of the receiving side input PCM signal code-words with a period which has a prime number relation with a period of a PCM robbed bit signaling system.

20. The method of claim 15, further comprising the steps of:

(3) determining when a disable tone is present;

(4) stopping said inserting step when said disable tone is present; and

wherein said echo cancellation is disabled when said disable tone is present.

21. The method of claim 20, wherein said disable tone is a modem answering tone.

22. The method of claim 20, wherein said disable tone is a 2100 Hz sinusoidal signal.

23. The method of claim 20, wherein said disable tone is a 2100 Hz sinusoidal signal with periodical phase reversal.

24. The method of claim 15, further comprising the steps of:

(3) detecting the predetermined pattern by monitoring the receiving side input PCM signal;

(4) stopping said inserting step in response to said predetermined pattern being detected in the receiving side input PCM signal.

25. The method of claim 24, further comprising the steps of:

(5) determining when a disable tone is present;

(6) disabling said inserting step when said disable tone is present; and

wherein said echo cancellation is disabled when said disable tone is present.

26. An echo canceller which cancels echo generated at 2-wire/4-wire conversion portion by impedance mismatching comprising:

(1) an echo cancelling means for cancelling echo signal;

(2) a predetermined bit-pattern sequence insertion means for inserting a pattern in a receiving side pulse code modulation (PCM) signal; and

(3) operation control means for disabling said echo cancelling means when the pattern is detected in transmitting side input PCM signal.

27. The echo canceller of claim 26, further comprising:

(4) pattern detection means for detecting said predetermined bit-pattern in transmitting side input PCM signal.

28. The echo canceller of claim 26, wherein said pattern insertion means periodically extracts least significant bits from receiving side PCM signal code-words and inserts the predetermined bit-pattern sequence into the receiving side PCM signal code-words in place of the extracted bits.

29. The echo canceller of claim 26, wherein said pattern insertion means is arranged between exchanges of a channel associated signaling system and periodically extracts second bits from least significant bits of receiving side PCM signal code-words and inserts the predetermined bit-pattern sequence into the receiving side PCM signal code-words in place of the extracted second bits.

30. The echo canceller of claim 26 wherein said pattern insertion means is arranged between exchanges of a channel associated signaling system and extracts least significant bits of receiving side PCM signal code-words with a period which has a prime number relation with a period of a bit robbing PCM signaling system and inserts the predetermined bit-pattern sequence into the receiving side PCM signal code-words in place of the extracted bits.

31. The echo canceller of claim 26, further comprising pattern detecting means for detecting said predetermined pattern in a transmitting side input PCM signal.

32. The echo canceller of claim 26, further comprising:

(4) signaling detection means for determining whether a voice channel is in idle state; and

(5) pattern control means for controlling said pattern insertion means so that said pattern is inserted when said signaling detection means detects a change from busy state to idle state;

wherein said operation control means disables said echo cancelling means until said signaling detection means detects the status change from busy state to idle state.

33. The echo canceller of claim 32, wherein said signaling detection means includes channel associated signaling detection means.

34. The echo canceller of claim 32, wherein said signaling detecting means includes common signaling detection means.

35. The echo canceller of claim 32, wherein said signaling detecting means includes an input port indicating the signaling status of the voice channel.

36. The echo canceller of claim 35, further comprising:

(6) tone detecting means for determining when a disable tone is present;

(7) pattern control means for disabling said pattern insertion means when said disable tone is present; and

wherein said operation control means disables said echo cancellation circuit when said disable tone is present.

37. The echo canceller of claim 36, wherein said tone detecting means includes an input port for indicating modem signal detection.

38. The echo canceller of claim 36, wherein said tone detecting means includes means for detecting a disable tone by monitoring said transmitting side and receiving side PCM signals.

39. The echo canceller of claim 38, wherein said disable tone is a modem answering tone.

40. The echo canceller of claim 26, further comprising:

(4) second pattern detecting means for detecting said pattern by monitoring a receiving side input PCM signal; and

(5) pattern disabling means for disabling said pattern insertion means in response to pattern detection by said second pattern detecting means.

41. The echo canceller of claim 40, further comprising:

(6) tone detecting means for determining when a disable tone is present;

(7) pattern control means for disabling said pattern insertion means when said disable tone is present;

wherein said operation control means disables said echo cancellation of the echo cancelling means when said disable tone is present.

42. An echo canceller which cancels echo generated, comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a pattern inserting means for inserting a predetermined bit-pattern sequence into a receiving side pulse code modulation (PCM) output signal; and

(c) a pattern detecting means for detecting a predetermined bit-pattern by monitoring a transmitting side input PCM signal, and disabling the echo cancelling function of the echo cancelling means when the predetermined bit-pattern is detected.

43. An echo canceller which cancels echo generated, comprising:

(a) an echo cancelling means for cancelling echo signal;

(b) a pattern inserting means for extracting a portion of a receiving side pulse code modulation (PCM) input signal and inserting a predetermined bit-pattern sequence into a receiving side PCM output signal in place of the extracted portion; and

(c) a pattern detecting means for detecting a predetermined bit pattern by monitoring a transmitting side input PCM signal, and disabling the echo cancelling function of the echo cancelling means when the predetermined bit-pattern is detected.

44. A method for controlling echo cancellation in an echo canceller which cancels echo generated, said method comprising the steps of:

(1) inserting a predetermined bit-pattern sequence in a receiving side pulse code modulation (PCM) signal; and

(2) disabling said echo cancellation when the predetermined bit-pattern is detected in a transmitting side input PCM signal.