Apparatus for, and method of, reducing noise in a communications system

• US 6,236,645 B1
• Filed: 03/09/1998
• Issued: 05/22/2001
• Est. Priority Date: 03/09/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Agazzi, Oscar E.
• Primary Examiner(s): Patel, Ajit
• Application Number:
  US09/037,328
• Time in Patent Office: 1,170 Days
• Field of Search: 370/201, 370/286-292, 375/222, 375/229-235, 375/345, 375/254, 379/406, 379/410, 379/416, 379/417
• US Class Current: 370/286
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04B 3/32 Reducing cross-talk, e.g. by compensating
• CPC Class Codes: H04B 3/487 Testing crosstalk effects

Abstract

A communication line having a plurality of twisted wire pairs connects a plurality of transmitters, one transmitter at each end of each twisted wire pair, with a plurality of receivers, one receiver at each end of each twisted wire pair. Each receiver receives a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and a plurality of far-end crosstalk (FEXT) impairment signals, one from each of the remaining transmitters at the opposite end of the communications line. A plurality of FEXT cancellation systems, one associated with each receiver, provides a replica FEXT impairment signal. A device associated with each receiver is responsive to the combination signal received by the receiver and the replica FEXT impairment signal provided by the FEXT cancellation system associated with the receiver for substantially removing the FEXT impairment signals from the combination signal. If necessary, a skew adjuster delays the arrival of the combination signal at the device so that the combination signal and the FEXT impairment signal arrive at the device at substantially the same time. A sequential decoder operates on signals from each of the plurality of wire pairs simultaneously to produce receiver outputs. A plurality of near-end crosstalk (NEXT) cancellation systems and echo cancellers remove NEXT and echo impairment signals from the combination signal.

Claims

1. A communications system comprising:

a communication line having a plurality of twisted wire pairs;

a plurality of transmitters, one transmitter at each end of each twisted wire pair;

a plurality of receivers, one receiver at each end of each twisted wire pair, each receiver receiving a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and a plurality of far-end crosstalk (FEXT) impairment signals, one from each of the remaining transmitters at the opposite end of the communications line;

a plurality of FEXT cancellation systems, one associated with each receiver, each FEXT cancellation system for providing a replica FEXT impairment signal; and

a plurality of devices, one associated with each receiver, each device responsive to the combination signal received by such receiver and the replica FEXT impairment signal provided by the FEXT cancellation system associated with such receiver for substantially removing the FEXT impairment signals from the combination signal;

wherein each FEXT cancellation system is responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, the each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are applied to each of the plurality of devices to remove the FEXT impairment signals from the combination signal.

2. The communications system of claim 1, wherein the FEXT cancellation system comprises:

means for receiving the tentative decision signal from each of the receivers at the same end of the communications line except for the receiver with which the FEXT canceller is associated;

means for generating an individual replica FEXT impairment signal for each receiver signal; and

means for combining the individual replica FEXT impairment signals to generate the replica FEXT impairment signal.

3. The communications system of claim 2 further comprising a detector system responsive to the output signal of each device for providing, for each device, a detector output signal corresponding to the analog signal level closest in magnitude to the level of the device output signal.

4. The communications system of claim 3 wherein each device output signal is a soft decision signal comprising a plurality of bits, said detector system comprising a symbol-by-symbol decoder responsive to the signals to provide both a final decision signal and one of the receiver signals to each of the FEXT cancellation systems at the same end of the communications line, except for the FEXT cancellation system associated with such device.

5. The communications system of claim 4 further comprising a delay device for delaying the final decisions such that the final decisions are synchronized with each other.

6. The communications system of claim 3 wherein each device output signal is a soft decision signal comprising a plurality of bits, said detector system comprising:

a decoder which is responsive to the signals on a sequential basis to provide final decision signals; and

a symbol-by-symbol decoder which is responsive to the signals to provide one of the receiver signals to each of the FEXT cancellation systems at the same end of the communications line, except for the FEXT cancellation system associated with such device.

7. The communications system of claim 6 further comprising a delay device for delaying the final decisions such that the final decisions are synchronized with each other.

8. The communications system of claim 2 further comprising:

a plurality of analog to digital (A/D) converters, one associated with each receiver, each A/D converter responsive to the combination signal received by such receiver for providing a digital conversion of the combination signal;

a plurality of equalizer systems, one associated with each receiver, each equalizer system being part of the digital adaptive filter system and responsive to the digital conversion combination signal for providing an adaptive equalization of such digital conversion combination signal; and

a plurality of first-in-first-out (FIFO) devices, one associated with each receiver, each FIFO device receiving the output of the A/D converter and forwarding the output to the equalizer system on a FIFO basis.

9. The communications system of claim 8 further comprising a plurality of hybrids, one hybrid at each end of each twisted wire pair, each hybrid for isolating the transmitter associated with such twisted wire pair from the receiver associated with such twisted wire pair, each hybrid responsive to the combination signal for forwarding the combination signal to the A/D converter.

10. The communications system of claim 8 further comprising:

a detector system responsive to the output signal of each device for providing, for each device, a detector output signal; and

a plurality of timing recovery devices, one associated with each receiver, each timing recovery device responsive to at least one of the outputs of the detector system for regulating the rate of production of the A/D converter so that the digital conversions of the signals received by the A/D converter are at a particular rate and in a particular phase and for regulating the rate at which the FIFO forwards the output of the A/D converter to the equalizer system.

11. The communications system of claim 10 wherein the detector output signal corresponds to the analog signal level closest in magnitude to the level of the device output signal.

12. The communications system of claim 10 wherein the detector output signal corresponds to one of a discrete set of symbols.

13. The communications system of claim 12 wherein the detector system comprises a feedback filter, the discrete set of symbols is (−

2, −

1, 0, 1,

     2) and the symbol chosen is that symbol closest to the difference between the device output signal and the output of the feedback filter.

14. The communications system of claim 10 wherein each device output signal is a soft decision signal comprising a plurality of bits, said detector comprising a symbol-by-symbol decoder responsive to the signals to provide a final decision signal, one of the receiver signals to each of the FEXT cancellation systems at the same end of the communications line, except for the FEXT cancellation system associated with such device, and the input to the timing recovery device associated with such receiver.

15. The communications system of claim 14 further comprising a delay device for delaying the final decisions such that the final decisions are synchronized with each other.

16. The communications system of claim 10 wherein each device output signal is a soft decision signal comprising a plurality of bits, said detector system comprising:

a decoder which is responsive to the signals on a sequential basis to provide final decision signals; and

a symbol-by symbol decoder which is responsive to the signals to provide one of the tentative decision signals to each of the FEXT cancellation systems at the same end of the communications line, except for the FEXT cancellation system associated with such device and the input to the timing recovery device associated with such receiver.

17. The communications system of claim 16 further comprising a delay device for delaying the final decisions such that the final decisions are synchronized with each other.

18. The communications system of claim 1 wherein the combination signal further includes a plurality of near-end crosstalk (NEXT) impairment signals, one from each of the transmitters at the same end of the communications line, except for the transmitter at the same end of the twisted wire pair with which the receiver is associated, said communications system further comprising a plurality of NEXT cancellation systems, one associated with each receiver, each NEXT cancellation system for providing a replica NEXT impairment signal, wherein each said device is further responsive to the replica NEXT impairment signal for substantially canceling the plurality of NEXT impairment signals from the combination signal.

19. The communications system of claim 1 wherein the combination signal further includes an echo impairment signal received from the transmitter at the same end of the twisted wire pair with which the receiver is associated, said communications system further comprising a plurality of echo cancellers, one associated with each of receiver, each echo canceller for providing a replica echo impairment signal, wherein each said device is further responsive to the replica echo impairment signal for substantially canceling the echo impairment signal from the combination signal.

20. A communications system comprising:

a communication line having a plurality of twisted wire pairs;

a plurality of transmitters, one transmitter at each end of each twisted

a plurality of receivers, one receiver at each end of each twisted wire pair, each receiver receiving a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and a plurality of far-end crosstalk (FEXT) impairment signals, one from each of the remaining transmitters at the opposite end of the communications line;

a plurality of FEXT cancellation systems, one associated with each receiver, each FEXT cancellation system for providing a replica FEXT impairment signal;

a plurality of delay devices, one associated with each receiver, each delay device responsive to the combination signal received by such receiver for delaying the combination signal; and

a plurality of first devices, one associated with each receiver, each first device responsive to the output of the delay device associated with such receiver and the replica FEXT impairment signal provided by the FEXT cancellation system associated with such receiver for substantially removing the FEXT impairment signals from the combination signal;

wherein each FEXT cancellation system is responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, the each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are applied to each of the plurality of devices to remove the FEXT impairment signals from the combination signal.

21. The communications system of claim 20, wherein the FEXT cancellation system comprises:

a tentative decision signal receiver for receiving a tentative decision signal from each of the receivers at the same end of the communications line except for the receiver with which the FEXT canceller is associated and for generating an individual replica FEXT impairment signal for each received signal; and

a combiner which combines the individual replica FEXT impairment signals to generate the replica FEXT impairment signal.

22. The communications system of claim 21 wherein, when the direct signal arrives at the receiver after the FEXT impairment signals, the delay device delays the combination signal by an amount substantially equal to the time delay between the arrival, at the receiver, of the FEXT impairment signals and the direct signal.

23. The communications system of claim 21 wherein the delay device delays the combination signal so that such combination signal is synchronized with the combination signals from other receivers.

24. The communications system of claim 21 wherein, when the direct signal arrives at the receiver after the FEXT impairment signals, the delay device delays the combination signal by the greater of the following:

an amount substantially equal to the time delay between the arrival, at the receiver, of the FEXT impairment signals and the direct signal; and

an amount so that such combination signal is synchronized with the combination signals from other receivers.

25. The communications system of claim 21 wherein, when the direct signal arrives at the receiver after the FEXT impairment signals, the delay device delays the combination signal by an amount greater than the time delay between the arrival, at the receiver, of the FEXT impairment signals and the direct signal and the FEXT cancellation system, in turn, delays the replica FEXT impairment signal by an amount substantially equal to the greater amount.

26. The communications system of claim 21 wherein, when the FEXT impairment signals arrive at the receiver after the direct signal, the FEXT cancellation system delays the replica FEXT impairment signal by an amount substantially equal to the time delay between the arrival, at the receiver, of the direct signal and the FEXT impairment signals.

27. The communications system of claim 20, wherein the digital adaptive filter system includes:

a plurality of analog to digital (A/D) converters, one associated with each receiver, each A/D converter responsive to the combination signal received by such receiver for providing a digital conversion of the combination signal;

a plurality of equalizer systems, one associated with each receiver, each equalizer system responsive to the digital conversion combination signal for providing an adaptive equalization of such digital conversion combination signal; and

a plurality of first-in-first-out (FIFO) devices, one associated with each receiver, each FIFO device receiving the output of the A/D converter and forwarding the output to the equalizer system on a FIFO basis.

28. The communications system of claim 27 further comprising:

a first detector responsive to the output signal of each first device for providing a first detector output signal corresponding to the analog signal level closest in magnitude to the level of the first devise output signal; and

the tentative decision detector being responsive to the output signal of each equalizer system for providing a tentative decision detector output signal corresponding to the analog signal level closest in magnitude to the level of the equalizer output signal.

29. The communications system of claim 27 further comprising:

a first detector responsive to the output signal of each first device for providing a first detector output signal corresponding to one of a discrete set of symbols; and

the tentative decision detector being responsive to the output signal of each equalizer system for providing a tentative decision detector output signal corresponding to one of the discrete set of symbols.

30. The communications system of claim 29 wherein the first detector and the tentative decision detector each comprise a feedback filter, the discrete set of symbols is (−

2, −

1, 0, 1,

     2) and for the first detector, the symbol chosen is that symbol closest to the difference between the first device output signal and the output of a first detector feedback filter and for the tentative decision detector, the symbol chosen is that symbol closest to the difference between the output of the equalizer system and the output of a tentative decision detector filter.

31. The communications system of claim 28 wherein the first device output signal and the equalizer output signal are soft decision signals comprising a plurality of bits, the first detector and tentative decision detector are symbol-by-symbol decoders responsive to the signals, the first detector providing a final decision signal-and the tentative decision detector providing the tentative decision signal for each of the FEXT cancellation systems at the same end of the communications line, except for the FEXT cancellation system associated with such device.

32. The communications system of claim 28 wherein the first device output signal and the equalizer output signal are soft decision signals comprising a plurality of bits, the first detector is a decoder which is responsive to the signals on a sequential basis to provide a final decision signal and the tentative decision detector is a symbol-by symbol decoder which is responsive to the signals to provide the tentative decision signal for each of the FEXT cancellation systems at the same end of the communications line, except for the TEXT cancellation system associated with such device.

33. The communications system of claim 28 further comprising:

a plurality of timing recovery devices, one associated with each receiver, each timing recovery device responsive to at least one of the tentative decision detector outputs for regulating the rate of production of the A/D converter so that the digital conversions of the signals received by the A/D converter are at a particular rate and in a particular phase and for regulating the rate at which the FIFO forwards the output of the A/D converter to the equalizer system.

34. The communications system of claim 33, wherein the digital adaptive filter system includes:

a plurality of error devices, one associated with each receiver, each error device responsive to the output of the equalizer system associated with such receiver and one of the tentative decision detector output signals for providing an error signal to the timing recovery device associated with such receiver.

35. The communications system of claim 27 further comprising a plurality of hybrids, one hybrid at each end of each twisted wire pair, each hybrid for isolating the transmitter associated with such twisted wire pair from the receiver associated with such twisted wire pair, each hybrid responsive to the combination signal for forwarding the combination signal to the A/D converter.

36. The communications system of claim 28 wherein the combination signal further includes a plurality of near-end crosstalk (NEXT) impairment signals, one from each of the transmitters at the same end of the communications line, except for the transmitter at the same end of the twisted wire pair with which the receiver is associated, said communications system further comprising:

a plurality of NEXT cancellation systems, one associated with each receiver, each NEXT cancellation system for providing a replica NEXT impairment signal;

a plurality of second devices, one associated with each receiver, each second device responsive to the output of the equalizer system associated with such receiver and the replica NEXT impairment signal provided by the NEXT cancellation system associated with such receiver for substantially removing the NEXT impairment signals from the combination signal and providing the signal to the delay device and the tentative decision detector.

37. The communications system of claim 28 wherein the combination signal further includes an echo impairment signal received from the transmitter at the same end of the twisted wire pair with which the receiver is associated, said communications system further comprising:

a plurality of echo cancellers, one associated with each of receiver, each echo canceller for providing a replica echo impairment signal,

a plurality of second devices, one associated with each receiver, each second device responsive to the output of the equalizer system associated with such receiver and the replica echo impairment signal provided by the echo cancellation system associated with such receiver for substantially removing the echo impairment signals from the combination signal and providing the signal to the delay device and the tentative decision detector.

38. A method for reducing noise in a communications system including a communication line having a plurality of twisted wire pairs, a plurality of transmitters, one transmitter at each end of each of the twisted wire pairs, a plurality of receivers, one receiver at each end of each of the twisted wire pairs, each receiver receiving a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and a plurality of far-end crosstalk (FEXT) impairment signals, one from each of the remaining transmitters at the opposite end of the communications line;

said method comprising, for each receiver, the steps of;

generating a replica FEXT impairment signal; and

combining the replica FEXT impairment signal with the combination signal to produce an output signal substantially devoid of FEXT impairment signals;

wherein generating the replica FEXT impairment signal includes providing a FEXT cancellation system for each receiver, each FEXT cancellation system being responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are combined with combination signals to remove the FEXT impairment signals from the combination signals.

39. The method of claim 38 wherein the step of generating the replica FEXT impairment signal comprises the steps of:

receiving the tentative decision signal from each receiver, except for the receiver for which the replica FEXT impairment signal is being generated;

generating, based on each tentative decision signal, an individual replica FEXT impairment signal; and

combining the individual replica FEXT impairment signals to form the replica FEXT impairment signal.

40. The method of claim 38 wherein the step of combining the replica FEXT impairment signal with the combination signal comprises the step of subtracting the replica FEXT impairment signal from the combination signal.

41. The method of claim 38 wherein the communications system further includes a plurality of combining devices, one associated with each receiver, each combining device responsive to the combination signal and the replica FEXT impairment signal, wherein, when the direct signal arrives at the receiver after the FEXT impairment signals, the step of combining the replica FEXT impairment signal with the combination signal comprises the steps of:

delaying the arrival of the combination signal, at the combining device, by an amount substantially equal to the time delay between the arrival, at the receiver, of the FEXT impairment signals and the direct signal; and

subtracting the replica FEXT impairment signal from the combination signal.

42. The method of claim 38 wherein the communications system further comprises a plurality of combining devices, one associated with each receiver, each combining device responsive to the combination signal and the replica FEXT impairment signal, wherein, when the direct signal arrives at the receiver after the FEXT impairment signals, the step of combining the replica FEXT impairment signal with the combination signal comprises the steps of:

delaying the arrival of the combination signal, at the combining device, by an amount greater than the time delay between the arrival, at the receiver, of the FEXT impairment signals and the direct signal;

delaying the arrival of the replica FEXT impairment signal, at the combining device, by an amount substantially equal to the greater amount; and

subtracting the replica FEXT impairment signal from the combination signal.

43. The method of claim 38 wherein the communications system further includes a plurality of combining devices, one associated with each receiver, each combining device responsive to the combination signal and the replica FEXT impairment signal, wherein, when the FEXT impairment signals arrive at the receiver after the direct signal, the step of combining the replica FEXT impairment signal with the combination signal comprises the steps of:

delaying the arrival of the replica FEXT impairment, at the combining device, by an amount substantially equal to the time delay between the arrival, at the receiver, of the direct signal and the FEXT impairment signals; and

subtracting the replica FEXT impairment signal from the combination signal.

44. The method of claim 38 wherein the combination signal further includes a plurality of near-end crosstalk (NEXT) impairment signals, one from each of the transmitters located at the same end of the communications line, except for the transmitter at the same end of the twisted wire pair with which the receiver is associated;

said method further comprising the steps of;

generating a replica NEXT impairment signal; and

combining the replica NEXT impairment signal with the combination signal to produce an output signal substantially devoid of NEXT impairment signals.

45. The method of claim 38 wherein the combination signal further includes an echo impairment signal received from the transmitter at the same end of the twisted wire pair with which the receiver is associated;

said method further comprising the steps of;

generating a replica echo impairment signal; and

combining the replica echo impairment signal with the combination signal to produce an output signal substantially devoid of echo impairment signals.

46. The method of claim 38 wherein the combination signal further includes a plurality of near-end crosstalk (NEXT)impairment signals, one from each of the transmitters located at the same end of the communications line, except for the transmitter at the same end of the twisted wire pair with which the receiver is associated, and an echo impairment signal received from the transmitter at the same end of the twisted wire pair with which the receiver is associated;

said method further comprising the steps of;

generating a replica NEXT impairment signal;

generating a replica echo impairment signal; and

combining the replica NEXT impairment signal and the replica echo impairment signal with the combination signal to produce an output signal substantially devoid of noise.

47. A method for reducing noise in a communications system comprising a communication line having a plurality of twisted wire pairs, a plurality of transmitters, one transmitter at each end of each twisted wire pair, a plurality of receivers, one receiver al each end of each twisted wire pair, each receiver receiving a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receive. S associated and a plurality of noise signals including far-end crosstalk (FEXT), near-end crosstalk (NEXT), and en impairment signals, said method comprising the steps of:

generating a replica FEXT impairment signal;

generating a replica NEXT impairment signal;

generating a replica echo impairment signal; and

combining each replica impairment signal with the combination signal to produce an output signal substantially devoid of noise;

wherein generating the replica FEXT impairment signal includes providing a FEXT cancellation system for each receiver, each FEXT cancellation system being responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are combined with combination signals to remove the FEXT impairment signals from the combination signals.

48. The method of claim 47 wherein the communications system further comprises a plurality of second combining devices, one associated with each receiver, each second combining device responsive to the combination signal and the replica NEXT and echo impairment signals, and a plurality of first combining devices, one associated with each receiver, each first combining device responsive to the output of the second combining device and the replica FEXT impairment signals, wherein, when the direct signal arrives at the receiver after the FEXT impairment signals, the step of combining the replica impairment signal with the combination signal comprises the steps of:

subtracting, at the second combining device, the NEXT and echo impairment signals from the combination signal;

delaying the arrival of the output of the second combining device, at the first combining device, by an amount substantially equal to the time delay between the arrival, at the receiver, of the FEXT impairment signals and the direct signal; and

subtracting the replica FEXT impairment signal from the output of the second combining device.

49. The method of claim 47 wherein the communications system further comprises a plurality of second combining devices, one associated with each receiver, each second combining device responsive to the combination signal and the replica NEXT and echo impairment signals and a plurality of first combining devices, one associated with each receiver, each first combining device responsive to the output of the second combining device and the replica FEXT impairment signals, wherein, when the direct signal arrives at the receiver after the FEXT impairment signals, the step of combining the replica impairment signals with the combination signal comprises the steps of:

subtracting, at the second combining device, the NEXT and echo impairment signals from the combination signal;

delaying the arrival of the combination signal, at the first combining device, by an amount greater than the time delay between the arrival, at the receiver, of the FEXT impairment signals and the direct signal;

delaying the arrival of the replica FEXT impairment signal, at the first combining device, by an amount substantially equal to the greater amount; and

subtracting the replica FEXT impairment signal from the output of the second combining device.

50. The method of claim 47 wherein the communications system further comprises a plurality of second combining devices, one associated with each receiver, each second combining device responsive to the combination signal and the replica NEXT and echo impairment signals and a plurality of first combining devices, one associated with each receiver, each first combining device responsive to the output of the second combining device and the replica FEXT impairment signals, wherein, when the FEXT impairment signals arrive at the receiver after the direct signal, the step of combining the replica impairment signals with the combination signal comprises the steps of:

subtracting, at the second combining device, the NEXT and echo impairment signals from the combination signal;

delaying the arrival of the FEXT impairment signal, at the first combining device, by an amount substantially equal to the time delay between the arrival, at the receiver, of the direct signal and the FEXT impairment signals; and

subtracting the replica FEXT impairment signal from the output of the second combining device.

51. A noise reduction system for use in a communications system comprising a communication line having a plurality of twisted wire pairs, a plurality of transmitters, one transmitter at each end of each twisted wire pair, a plurality of receivers, one receiver at each end of each twisted wire pair, each receiver receiving a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and a plurality of noise signals including far-end crosstalk (FEXT), near-end crosstalk (NEXT), and echo impairment signals, said noise reduction system comprising:

a plurality of NEXT cancellation systems, one NEXT cancellation system associated with each receiver, said NEXT cancellation system including at least one NEXT canceller, said NEXT cancellation system responsive to the transmitted signals from the transmitters at the same end of the communications line as the receiver with which the NEXT cancellation system is associated, except for the transmitter at the same end of the twisted wire pair as the receiver with which the NEXT cancellation system is associated, the NEXT cancellation system responsive to the transmitted signals for generating a replica NEXT impairment signal;

a plurality of devices, one associated with each receiver, said device responsive to the combination signal and the replica NEXT impairment signal for providing an output signal substantially devoid of NEXT impairment signals; and

a plurality of FEXT cancellation systems, one FEXT cancellation system associated with each receiver, wherein each FEXT cancellation system is responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, the each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are applied to each of the plurality of devices to remove the FEXT impairment signals from the combination signal.

52. The noise reduction system of claim 51 wherein:

each FEXT cancellation system is responsive to the transmitted signals from the transmitters at the opposite end of the communications line as the receiver with which the NEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the NEXT cancellation system is associated, the FEXT cancellation system being responsive to the transmitted signals for generating a replica FEXT impairment signal; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

53. The noise reduction system of claim 51 further comprising a plurality of skew compensators, one associated with each receiver, said skew compensator responsive to the output of the device associated with such receiver, said skew compensator for adjusting the delay of the output signal from such device so that such delayed output signal is synchronized with other output signals from the other devices.

54. The noise reduction system of claim 53, wherein:

the FEXT cancellation system is responsive to the transmitted signals from the transmitters at the opposite end of the communications line as the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, the FEXT cancellation system responsive to the transmitted signals for generating a replica FEXT impairment signal; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

55. The noise reduction system of claim 51 further comprising a decoder responsive to the sequences of the output signals from each of the receivers for passing only acceptable sequences.

56. The noise reduction system of claim 55, wherein:

the FEXT cancellation system is responsive to the transmitted signals from the transmitters at the opposite end of the communications line as the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, the FEXT cancellation system responsive to the transmitted signals for generating a replica FEXT impairment signals; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

57. The noise reduction system of claim 51 further comprising a decoder responsive to the sequences of the output signals from each of the receivers for (1) passing only acceptable sequences of such signals, (2) discarding unacceptable sequences of such signals and (3) changing sequences of signals with minimal numbers of errors to sequences of signals in which the errors have been corrected to provide acceptable sequences closest to the sequences with the minimal number of errors.

58. The noise reduction system of claim 51 further comprising:

a plurality of skew compensators, one associated with each receiver, said skew compensator responsive to the output of the device associated with such receiver,

said skew compensator for adjusting the delay of the output signal from such device so that such delayed output signal is synchronized with other output signals from the other devices; and

a decoder responsive to the sequences of the output signals from each of the skew compensators for passing only acceptable sequences of the output sequences.

59. The noise reduction system of claim 58, wherein:

the FEXT cancellation system is responsive to the transmitted signals from the transmitters at the opposite end of the communications line as the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, the FEXT cancellation system responsive to the transmitted signals for generating a replica FEXT impairment signal; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

60. A noise reduction system for use in a communications system comprising a communication line having a plurality of twisted wire pairs, a plurality of transmitters, one transmitter at each end of each twisted wire pair, a plurality of receivers, one receiver at each end of each twisted wire pair, each receiver receiving a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and a plurality of noise signals including far-end crosstalk (FEXT), near-end crosstalk (NEXT), and echo impairment signals, said noise reduction system comprising

a plurality of echo cancellers, at least one of said echo cancellers associated with each receiver, said echo canceller for receiving the transmitted signals from the transmitter at the same end of the twisted wire pair as that of the receiver with which the echo canceller is associated, each echo canceller responsive to the transmitted signal for generating a replica of the echo impairment signal;

a plurality of devices, one associated with each receiver, said device responsive to the combination signal and the replica echo impairment signal for providing an output signal substantially devoid of noise; and

a plurality of FEXT cancellation systems, one FEXT cancellation system associated with each receiver, wherein each FEXT cancellation system is responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, the each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are applied to each of the plurality of devices to remove the FEXT impairment signals from the combination signal.

61. The noise reduction system of claim 60, wherein:

the FEXT cancellation system is responsive to the transmitted signals from the transmitters at the opposite end of the communications line as the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, the FEXT cancellation system responsive to the transmitted signals for generating a replica TEXT impairment signal; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

62. The noise reduction system of claim 60 further comprising a plurality of skew compensators, one associated with each receiver, said skew compensator responsive to the output of the device associated with such receiver, said skew compensator for adjusting the delay of the output signal from such device so that such delayed output signal is synchronized with other output signals from the other devices.

63. The noise reduction system of claim 62, wherein:

the FEXT cancellation system is responsive to the transmitted signals from the transmitters at the opposite end of the communications line as the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, the FEXT cancellation system responsive to the transmitted signals for generating a replica FEXT impairment signal; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

64. The noise reduction system of claim 60 further comprising a decoder responsive to the sequences of the output signals from each of the receivers for passing only acceptable sequences.

65. The noise reduction system of claim 64 wherein:

the FEXT cancellation system is responsive to the transmitted signals from the transmitters at the opposite end of the communications line the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, the FEXT cancellation system responsive to the transmitted signals for generating a replica FEXT impairment signal; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

66. The noise reduction system of claim 60 further comprising a decoder responsive to the sequences of the output signals from each of the receivers for (1) passing only acceptable sequences of such signals, (2) discarding unacceptable sequences of such signals and (3) changing sequences of signals with minimal numbers of errors to sequences of signals in which the errors have been corrected to provide acceptable sequences closest to the sequences with the minimal number of errors.

67. The noise reduction system of claim 60 further comprising:

a plurality of skew compensators, one associated with each receiver, said skew compensator responsive to the output of the device associated with such receiver, said skew compensator for adjusting the delay of the output signal from such device so that such delayed output signal is synchronized with other output signals from the other devices; and

a decoder responsive to the sequences of the output signals from each of the skew compensators for passing only acceptable sequences of the output sequences.

68. The noise reduction system of claim 67, wherein:

the FEXT cancellation system is responsive to the transmitted signals from the transmitters positioned at the opposite end of the communications line as the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, the FEXT cancellation system responsive to the transmitted signals for generating a replica FEXT impairment signal; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

69. A noise reduction system for use in a communications system comprising a communication line having a plurality of twisted wire pairs, a plurality of transmitters, one transmitter at each end of each twisted wire pair, a plurality of receivers, one receiver at each end of each twisted wire pair, each receiver receiving a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and a plurality of noise signals including far-end crosstalk (FEXT), near-end crosstalk (NEXT), and echo impairment signals, said noise reduction system comprising:

a plurality or devices, one associated with each receiver, said device responsive to the combination signal for providing an output signal;

a plurality of skew compensators, one associated with each receiver, said skew compensator responsive to the output of the device associated with such receiver, said skew compensator for adjusting the delay of the output signal from such device so that such delayed output signal is synchronized with other output signals from the other devices; and

a plurality of FEXT cancellation systems, one FEXT cancellation system associated with each receiver, wherein each FEXT cancellation system is responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, the each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are applied to each of the plurality of devices to remove the FEXT impairment signals from the combination signal.

70. The noise reduction system of claim 69, wherein:

the FEXT cancellation system is responsive to the transmitted signals from the transmitters at the opposite end of the communications line as the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, the FEXT cancellation system responsive to the transmitted signals for generating a replica FEXT impairment signal; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

71. The noise reduction system of claim 69 further comprising a decoder responsive to the sequences of the output signals from each of the receivers for passing only acceptable sequences.

72. The noise reduction system of claim 71, wherein:

the FEXT cancellation system is responsive to the transmitted signals from the transmitters at the opposite end of the communications line as the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, the FEXT cancellation system responsive to the transmitted signals for generating a replica FEXT impairment signal; and

said device is further responsive to the replica FEXT impairment signal for providing an output signal substantially devoid of FEXT impairment signals.

73. The noise reduction system of claim 69 further comprising a decoder responsive to the sequences of the output signals from each of the receivers for (1) passing only acceptable sequences of such signals, (2) discarding unacceptable sequences of such signals and (3) changing sequences of signals with minimal numbers of errors to sequences of signals in which the errors have been corrected to provide acceptable sequences closest to the sequences with the minimal number of errors.

74. A noise reduction system for use in a communications system comprising a communication line having a plurality of twisted wire pairs a plurality of transmitters, one transmitter at each end of each twisted wire pair, a plurality of receivers, one receiver at each end of each twisted wire pair, each receiver receiving a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and a plurality of noise signals including far-end crosstalk (FEXT), near-end crosstalk (NEXT), and echo impairment signals, said noise reduction system comprising:

a plurality of NEXT cancellation systems, one associated with each receiver, each NEXT cancellation system for receiving the transmitted signals from the transmitters at the same end of the communications line as the receiver with which the NEXT cancellation system is associated, except for the transmitter at the same end of the twisted wire pair as the receiver with which the NEXT cancellation system is associated, each NEXT cancellation system responsive to the transmitted signals for generating a replica NEXT impairment signal;

a plurality of echo cancellers, at least one of said echo cancellers associated with each receiver, each echo canceller for receiving the transmitted signals from the transmitter at the same end of the twisted wire pair as that of the receiver with which the echo canceller is associated, each echo canceller responsive to the transmitted signal for generating a replica echo impairment signal;

a plurality of FEXT cancellation systems, one associated with each receiver, each FEXT cancellation system for receiving the transmitted signals from the transmitters at the opposite end of the communications line as the receiver with which the FEXT cancellation system is associated, except for the transmitter at the opposite end of the twisted wire pair as the receiver with which the FEXT cancellation system is associated, each FEXT cancellation system responsive to the transmitted signals for generating a replica FEXT impairment signal;

a plurality of first summing devices, one associated with each receiver, said fist summing device responsive to the combination signal, the replica NEXT impairment signal and the replica echo impairment signal for providing an initial output signal substantially devoid of NEXT impairment signals and echo impairment signals;

a plurality of skew compensators, one associated with each receiver, said skew compensator responsive to the output of the first summing device associated with such receiver, said skew compensator for adjusting the delay of the initial output signal from such summing device so that such delayed initial output signal is synchronized with other output signals from the other first summing devices; and

a plurality of second summing devices, one associated with each receiver, said second summing device responsive to the delayed initial output signal and the replica FEXT impairment signal for providing a final output signal substantially devoid of FEXT impairment signal; and

wherein each FEXT cancellation system is responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, the each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are applied to each of the plurality of devices to remove the FEXT impairment signals from the combination signal.

75. The noise reduction system of claim 74 further comprising a decoder responsive to the sequences of the final output signals from each of the skew compensators for passing only acceptable sequences.

76. A method for reducing noise in a communications system comprising a communication mine having a plurality of twisted wire pairs, a plurality of transmitters, one transmitter at each end of each of the twisted wire pairs, a plurality of receivers, one receiver at each end of each of the twisted wire pairs, each receiver receiving a combination signal including a direct signal from the transmitter at the opposite end of the twisted wire pair with which the receiver is associated and a plurality of noise signal including far-end crosstalk (FEXT), near-end crosstalk (NEXT), and echo impairment signals;

said method comprising, for each receiver, the steps of;

generating a replica FEXT impairment signal;

combining the replica FEXT impairment signal with the combination signal to produce an output signal substantially devoid of FEXT impairment signals;

wherein generating the replica FEXT impairment signal includes providing a FEXT cancellation system for each receiver, each FEXT cancellation system being responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica TEXT impairment signals are combined with combination signals to remove the FEXT impairment signals from the combination signals; and

delaying the output signal from such receiver so that such delayed output signal is synchronized with other output signals from the other receivers.

77. The method of claim 76 further comprising the steps of:

monitoring a sequence of signals;

passing only acceptable sequences of such signals;

discarding unacceptable sequences of such signals;

changing sequences of signals with minimal numbers of errors to sequences of signals in which the errors have been corrected to provide acceptable sequences closest to the sequences with the minimal number of errors.

78. The method of claim 77 wherein the output signal is in the form of symbols, each comprising a plurality of bits, and the sequence is a series of symbols from an individual receiver.

79. The method of claim 77 wherein the output signal is in the form of symbols, each comprising a plurality of bits, and the sequence is a set of symbols comprising at least one symbol from each of the receivers.

80. A communications system comprising:

a communications line having a plurality of twisted wire pairs and having a transmitter and a receiver connected at each end of each twisted wire pair wherein transmitted signals are received from the opposite end of the twisted line pair connected to the receiver and wherein far-end crosstalk (NEXT) is generated at each receiver from noise passing to such receiver from the ends of the twisted line pairs opposite the receiver, other than from the opposite end of the twisted line pair connected to the receiver; and

a plurality of systems each associated with the receiver connected to the twisted line pair at one end of the twisted line pair for eliminating from combination signals, which include the transmitted signal and FEXT, at the receiver the FEXT at the receiver from the other end of the other twisted wire pairs by applying replica FEXT, impairment signals to the combination signals;

wherein each of the plurality of systems includes a plurality of devices including a FEXT cancellation system responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, the each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are applied to each of the plurality of devices to remove the FEXT from the combination signal.

81. The communications system as set forth in claim 80, wherein

noise is generated at each receiver from the other end of the twisted wire pair connected to the receiver; and

each of the systems in the plurality is operative to eliminate, from the signals at the receiver at the one end of the twisted wire pair, the noise generated at the receiver from the other end of the twisted wire pair.

82. The communications system as set forth in claim 80, wherein

noise is generated at each receiver, from the ends of the twisted wire pairs adjacent to the receiver other than the twisted wire pair connected at the other end of the receiver;

and

each of the systems in the plurality being operative to eliminate, from the signals at the receiver connected at the one end of the twisted wire pair, the noise generated at the receiver from the ends of the twisted wires adjacent to the receiver other than the twisted wire pair connected at the one end of the receiver.

83. The communications system as set forth in claim 80, further comprising a decoder responsive to the sequences of the signals from the receivers at the one end of the twisted wire pairs for determining whether such sequences of signals are acceptable and for processing such sequences of signals in accordance with such determinations.

84. The communications system as set forth in claim 80, wherein

noise is generated at each receiver from the other end of the twisted wire pair connected at the one end to the receiver and noise is generated at each receiver from the ends of the twisted wire pairs adjacent to the receiver other than the twisted wire pair connected to the receivers;

each of the systems in the plurality is operative to eliminate, from the signals at the receivers connected at the one end of the twisted wire pair, the noise generated at the receiver from the other end of the twisted wire pair,

each of the systems in the plurality is operative to eliminate, from the signals at the receiver connected at the one end to the twisted wire pair, the noise generated at the receiver from the ends of the twisted wires adjacent to the receiver other than the twisted wire pair connected at the one end to the receiver; and

a decoder is responsive to the sequences of the signals from the receivers at the same ends of the twisted pairs for determining whether such sequences are acceptable and for processing such sequences of signals in accordance with such determinations.

85. The communications system as set forth in claim 80, further comprising a skew compensator associated with each receiver and responsive to the signals from the receiver for delaying such signals so that such delayed signals are synchronized with the delayed signals from the other receivers before the signals are introduced to the plurality of systems.

86. The communications system as set forth in claim 84, further comprising a skew compensator associated with each receiver and responsive to the signals from the receiver far delaying such signals so that such delayed signals are synchronized with the delayed signals from the other receivers before the signals are introduced to the plurality of systems.

87. A communications system comprising:

a communication line having a plurality of twisted wire pairs and having a transmitter and a receiver connected at each end of each twisted wire pair to transmit and receive sequences of signals; and

a decoder responsive to the sequences of the signals from the receivers at the same ends of the twisted wire pairs for determining whether such sequences of signals are acceptable and for processing such sequences of signals in accordance with such determinations;

wherein the receivers apply replica FEXT impairment signals to the sequence of signals received, each receiver including a FEXT cancellation system responsive to a tentative decision signal from a tentative decision detector in a digital adaptive filter system in each receiver, the each tentative decision detector being coupled to receive and derive the tentative decision signal from the combination signal before replica FEXT impairment signals are applied in the receiver to remove noise from the sequence of signals.

88. The communications system as set forth in claim 87 wherein:

the decoder determines whether the sequences of the signals at the receivers are acceptable or unacceptable and if unacceptable, whether the unacceptability is minor or major; and

the decoder passes the acceptable sequences of signals, the decoder converting the unacceptable sequences of signals to acceptable sequences of signals when the unacceptability is minor and the decoder rejects the unacceptable sequences of signals when the unacceptability is major.

89. The communications system as set forth in claim 87 wherein:

the system removes the noise from the signals in the sequences before the sequences of signals are introduced to the decoder.

90. The communications system as set forth in claim 87, wherein:

the noise passes to the receiver from the other ends of the twisted line pairs other than from the other end of the twisted line pair connected to the receiver; and

the system is operative to eliminate such noise from the signals at each receiver before the signals pass to the decoder.

91. The communications system as set forth in claim 87, wherein:

the noise is generated at the receiver from the other end of the twisted wire pair connected to the receiver; and

the system is operative to eliminate, from the signals at the receiver connected to the twisted wire pair, the noise generated at the receiver from the other end of the twisted wire pair.

92. The communications system as set forth in claim 87, wherein:

the noise is generated at each receiver from the ends of the twisted wire pairs adjacent to the receiver other than from the twisted wire pair connected to the receiver; and

the system is operative to eliminate, from the signals at the receiver connected to the twisted wire pair, the noise generated at the receiver from the ends of the twisted wire pairs adjacent to the receiver other than from the twisted wire pair connected to the receiver.

93. The communication system as set forth in claim 88, wherein

the noise includes noise which:

passes to the receiver from the other ends of the twisted line pairs other than from the other end of the twisted line pair connected to the receiver;

is generated at the receiver from the other end of the twisted wire pair connected to the receiver; and

is generated at each receiver from the ends of the twisted wire pairs adjacent to the receiver other than from the twisted wire pair connected to the receiver.

94. The communications system as set forth in claim 87, further comprising a compensator responsive to the signals in the sequences from the receivers for adjusting the times of such signals to provide for the introduction of such signals to the decoder in time synchronization.