Apparatus for, and method of, reducing power dissipation in a communications system

• US 6,304,598 B1
• Filed: 08/28/1998
• Issued: 10/16/2001
• Est. Priority Date: 08/28/1998
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Hatamian, Mehdi, Creigh, John L., Agazzi, Oscar E.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Ha, Dac V.
• Application Number:
  US09/143,476
• Time in Patent Office: 1,145 Days
• Field of Search: 375/232, 375/348, 375/350, 375/346, 375/285, 708/322, 708/323
• US Class Current: 375/232
• CPC Class Codes: H04B 3/32 Reducing cross-talk, e.g. by compensating
• CPC Class Codes: H04B 3/487 Testing crosstalk effects

Abstract

A method is provided for reducing power dissipation within a communications system having a plurality of adaptive filters with a plurality of taps, each tap is switchable between an active and an inactive state, each tap also has a coefficient. An acceptable error for the system is specified. This error is typically the mean squared error of the system. A tap threshold is set for each active tap. Those taps having a coefficient with an absolute value less than the tap threshold set for the active tap are deactivated. The error of the system is computed and compared to the acceptable system error. If the computed system error is less than the acceptable system error, the tap threshold for each active tap is increased. The process of comparing the tap coefficients to the tap thresholds, deactivating taps with a coefficient less than the tap threshold and computing the resulting system error is repeated until the computed system error approaches the acceptable system error without exceeding the acceptable system error. In addition, the previously deactivated taps may be periodically activated and their coefficients once again compared to the tap threshold. If a coefficient is less than the tap threshold the tap is again deactivated. If a coefficient is greater than the tap threshold, the tap remains active.

Claims

1. A method of reducing power dissipation in a communications system having a plurality of adaptive filters each having a plurality of taps, said method comprising the steps of:

defining a prespecified acceptable communications system target error;

setting a tap threshold for each of the taps; and

dynamically adjusting the tap threshold to allow the taps to be selectively activated or deactivated to converge an error of the communications system to the prespecified acceptable communications system target error.

2. The method of claim 1 wherein the step of dynamically adjusting the tap threshold includes determining whether to deactivate a tap based upon an adjusted tap threshold.

3. The method of claim 2 wherein the step of determining whether to deactivate a tap comprises the steps of:

computing a tap error produced by deactivating such tap; and

if the tap error is less than a prespecified acceptable level of tap error, deactivating the tap.

4. The method of claim 2 wherein the step of determining whether to deactivate a tap comprises the steps of:

computing a filter error produced by deactivating such tap; and

if the filter error is less than the prespecified acceptable level of filter error, deactivating the tap.

5. The method of claim 4 wherein the step of computing the filter error comprises the steps of:

determining a tap error of each individual tap; and

summing the individual tap errors.

6. The method of claim 2 wherein the step of determining whether to deactivate a tap comprises the steps of:

computing a system error produced by deactivating such tap; and

if the system error is less than the prespecified acceptable communications system target error, deactivating the tap.

7. The method of claim 6 wherein the step of computing the system error comprises the steps of:

determining a filter error of each adaptive filter; and

summing the individual filter errors.

8. The method of claim 7 wherein the step of computing the filter error comprises the steps of:

determining the tap error of each individual tap; and

summing the individual tap errors.

9. The method of claim 1 wherein the step of dynamically adjusting the tap threshold includes determining whether to activate a previously deactivated tap based upon an adjusted tap threshold.

10. The method of claim 9 wherein the step of determining whether to activate a previously deactivated tap comprises the steps of:

periodically activating previously deactivated taps;

computing the tap error produced by deactivating such taps; and

if the tap error is less than a prespecified acceptable level of tap error, deactivating the tap.

11. The method of claim 1 wherein the at least one of the adaptive filters has a sufficient number of taps to accommodate for delay due to the length of the communications line.

12. The method of claim 11 wherein a select plurality of taps positioned at the input end of the at least one of the adaptive filters are not subject to deactivation.

13. The method of claim 11 further comprising the step of partitioning the taps into a plurality of blocks each having at least one tap and wherein activation and deactivation of adaptive filters is performed on a block-by-block basis.

14. The method of claim 13 wherein the blocks are adjusted in a sequential manner starting at the input end of at least one of the adaptive filters.

15. The method of claim 1 wherein the communications system comprises at least one echo canceller having at least one adaptive filter.

16. The method of claim 1 wherein the communications system comprises at least one NEXT canceller having at least one adaptive filter.

17. The method of claim 1 wherein the communications system comprises at least one FEXT canceller having at least one adaptive filter.

18. A method for reducing power dissipation within a communications system having at least one adaptive filter with a plurality of taps, each tap switchable between an active and an inactive state, each tap having a tap coefficient, said method comprising the steps of:

a) defining a prespecified acceptable communications system target error;

b) setting a tap threshold for each of the taps; and

c) dynamically adjusting the tap threshold to allow the taps to be selectively activated or deactivated to converge an error of the communications system to the prespecified acceptable communications system target error by;

for each active tap, deactivating those taps having a coefficient with an absolute value less than the tap threshold set for the active tap;

computing a filter error;

comparing the computed filter error to the prespecified acceptable communications system target error;

if the computed filter error is less than the prespecified acceptable communications system target error, increasing, the tap threshold for each active tap; and

repeating step c) until the computed filter error approaches the prespecified acceptable communications system target error.

19. The method of claim 18 wherein a determination of whether to deactivate a tap is done in a sequential manner starting at the input end of the at least one adaptive filter.

20. The method of claim 18 further comprising the steps of:

periodically activating previously deactivated taps;

and repeating steps b) and c).

21. The method of claim 20 wherein the previously deactivated taps are activated in a sequential manner starting at the input end of at least one adaptive filter.

22. The method of claim 18 wherein each tap threshold is substantially the same.

23. The method of claim 18 wherein each tap threshold is initially set equal to the tap coefficient having the minimum absolute value.

24. The method of claim 18 wherein each tap threshold has a different value.

25. The method of claim 18 wherein the taps are partitioned into a plurality of blocks, each block having at least one tap and the tap threshold for each tap within each of the blocks is substantially the same.

26. The method of claim 18 wherein the step of computing the filter error comprises the steps of:

determining the error of each individual tap; and

summing the individual errors.

27. The method of claim 26 wherein the error of each individual tap is the mean square error for the tap and is determined by multiplying the absolute value of the tap coefficient by the average energy signal.

28. A method for reducing power dissipation within a communications system having a plurality of adaptive filters with a plurality of taps, each tap switchable between an active and an inactive state, each having a coefficient, said method comprising the steps of:

a) defining a prespecified acceptable level communications system target error;

b) setting a tap threshold for each of the taps; and

c) dynamically adjusting the tap threshold to allow the taps to be selectively activated or deactivated to converge an error of the communications system to the prespecified acceptable communications system target error by;

for each active tap, deactivating those taps having a coefficient with an absolute value less than the tap threshold set for the active tap;

computing a system error;

comparing the computed system error to the prespecified acceptable communications system target error;

if the computed system error is less than the prespecified acceptable filter error, increasing the tap threshold for each active tap; and

repeating step c) until the computed system error approaches the prespecified acceptable communications system target error.

29. The method of claim 28 wherein a determination of whether to deactivate a tap is done in a sequential manner starting at the input end of each of the adaptive filters.

30. The method of claim 28 further comprising the steps of:

periodically activating previously deactivated taps; and

repeating steps b) and c).

31. The method of claim 30 wherein the previously deactivated taps are activated in a sequential manner starting at the input end of each of the adaptive filters.

32. The method of claim 28 wherein the step of computing the system error comprises the steps of:

determining the error of each individual adaptive filter; and

summing the individual filter errors.

33. The method of claim 32 wherein the step of computing the filter error comprises the steps of:

determining the error of each individual tap; and

summing the individual tap errors.

34. The method of claim 33 wherein the error of each individual tap is the mean square error for the tap and is determined by multiplying the absolute value of the tap coefficient by the average energy signal.

35. The method of claim 28 further comprising the steps of:

i) specifying an acceptable level of error for the taps;

ii) for each active tap, calculating the error of deactivating the tap; and

iii) if the calculated error is less than the acceptable error, deactivating the tap.

36. The method of claim 35 wherein steps i), ii) and iii) are performed prior to steps a) through c).

37. A method for reducing power dissipation within a communications system having at least one adaptive filter with a plurality of taps, each tap switchable between an active and an inactive state, each tap having a tap coefficient, said method comprising the steps of:

a) computing an initial system error;

b) for each active tap, setting a tap threshold; and

c) dynamically adjusting the tap threshold to allow the taps to be selectively activated or deactivated to converge an error of the communications system to the prespecified acceptable communications system target error by;

for each active tap, deactivating those taps having a coefficient with an absolute value less than the tap error threshold set for the active tap;

computing a subsequent system error;

if the difference between the subsequent system error and the initial system error is less than the prespecified acceptable communciations system target error, increasing the tap threshold for each active tap; and

repeating step c) until the difference between the subsequent system error and the initial system error approaches the prespecified acceptable communications system target error.

38. The method of claim 37 wherein a determination of whether to deactivate a tap is done in a sequential manner starting at the input end of the at least one adaptive filter.

39. The method of claim 37 wherein each tap threshold is initially set equal to the tap coefficient having the minimum absolute value.

40. The method of claim 37 wherein the tap threshold is the substantially the same for each tap in the at least one adaptive filter.

41. A communications system comprising:

a communications line;

a plurality of adaptive filters responsive to signals carried by the communications line, each adaptive filter having a plurality of taps each having a coefficient, each tap switchable between an active and an inactive state;

means for defining a prespecified acceptable communications system target error;

means for setting a tap threshold of each tap;

means for calculating a present error for the communications system;

means for comparing the present error to the prespecified acceptable communications system target error; and

means for dynamically adjusting the tap threshold to allow the taps to be selectively activated or deactivated to converge an error of the communications system to the prespecified acceptable communications system target error.

42. The communications system of claim 41 wherein the means for setting a tap threshold of each tap comprises:

means for specifying the tap threshold for each tap;

means for comparing for each tap the absolute value of the tap coefficient with the tap threshold; and

means for deactivating those taps having a coefficient with an absolute value less than the tap threshold.

43. The communications system of claim 42 wherein the means for setting a tap threshold of each tap further comprises:

means for periodically activating previously deactivated taps.

44. The communications system of claim 42 further comprising means for increasing the tap threshold when the present error is less than the prespecified acceptable communications system target error.

45. The communications system of claim 42 wherein a select plurality of taps positioned at the input end of each adaptive filter are not subject to deactivation.

46. The communications system of claim 41 wherein each adaptive filter has a sufficient number of taps to accommodate for signal delay due to the length of the communications line.

47. The communications system of claim 41 wherein the taps are equally spaced within each adaptive filter such that the time between successive sampling of the input signal is substantially equal.

48. The communications system of claim 41 wherein the communications system comprises at least one echo canceller having at least one adaptive filter.

49. The communications system of claim 41 wherein the communications system comprises at least one NEXT canceller having at least one adaptive filter.

50. The communications system of claim 41 wherein the communications system comprises at least one FEXT canceller having at least one adaptive filter.

51. A power dissipation reduction system for use in a communications system having at least one adaptive filter having a plurality of taps each having a coefficient, each tap switchable between an active and an inactive state, said power dissipation reduction system comprising:

means for defining a prespecified acceptable communications system target error;

means for setting a tap threshold of each tap;

means for calculating a present error for the communications system;

means for comparing the present error to the prespecified acceptable communciations system target error; and

means for dynamically adjusting the tap threshold to allow the taps to be selectively activated or deactivated to converge an error of the communications system to the prespecified acceptable communications system target error.

52. The communications system of claim 51 wherein the means for setting a tap threshold of each tap comprises:

means for specifying the tap threshold for each tap;

means for comparing for each tap the absolute value of the tap coefficient with the tap threshold; and

means for deactivating those taps having a coefficient with an absolute value less than the tap threshold.

53. The communications system of claim 52 wherein the means for setting a tap threshold of each tap further comprises:

means for periodically activating previously deactivated taps.

54. The communications system of claim 52 further comprising means for increasing the tap threshold when the present error is less than the prespecified acceptable communications system target error.

55. The communications system of claim 52 wherein a select plurality of taps positioned at the input end of the at least one adaptive filter are not subject to deactivation.

56. The communications system of claim 51 wherein the taps are equally spaced within the at least one adaptive filter such that the time between successive sampling of the input signal is substantially equal.