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

• US 20010055335A1
• Filed: 08/15/2001
• Published: 12/27/2001
• Est. Priority Date: 08/28/1998
• Status: Active Grant

• 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.
• Granted Patent: US 6,898,238 B2
• Time in Patent Office: Days
• 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:

specifying a threshold error for the system; and

periodically adjusting the transfer function of at least one of the adaptive filters by selectively deactivating taps while ensuring that the error of the communications system does not exceed the threshold error.

2. The method of

claim 1

wherein the step of periodically adjusting the transfer function of at least one of the adaptive filters comprises the step of determining whether to deactivate a tap.

3. The method of

claim 2

wherein the step of determining whether to deactivate a tap comprises the steps of:

computing the 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 the filter error produced by deactivating such tap; and

if the filter error is less than a 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 the 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 the system error produced by deactivating such tap; and

if the system error is less than the threshold error, deactivating the tap.

7. The method of

claim 6

wherein the step of computing the system error comprises the steps of:

determining the 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 periodically adjusting the transfer function of at least one of the adaptive filters further comprises the step of determining whether to activate a previously deactivated tap.

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 filter 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 filter 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 the step of adjusting the transfer function of the adaptive filter 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 the filter.

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 coefficient, said method comprising the steps of:

a) specifying an acceptable level of error for the filter;

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

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

d) computing a filter error;

e) comparing the computed filter error to the acceptable filter error;

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

g) repeating steps c) through f) until the computed filter error approaches the acceptable filter error without exceeding the acceptable filter error.

19. The method of

claim 18

wherein the determination of whether to deactivate a tap is done in a sequential manner starting at the input end of the filter.

20. The method of

claim 18

further comprising the steps of:

periodically activating previously deactivated taps; and

repeating steps b) through g).

21. The method of

claim 20

wherein the previously deactivated taps are activated in a sequential manner starting at the input end of the 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) specifying an acceptable error for the system;

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

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

d) computing a system error;

e) comparing the computed system error to the acceptable system error;

f) the computed system error is less than the acceptable system error, increasing the tap threshold for each active tap; and

g) repeating steps c) through f) until the computed system error approaches the acceptable system error without exceeding the acceptable system error.

29. The method of

claim 28

wherein the determination of whether to deactivate a tap is done in a sequential manner starting at the input end of the filter.

30. The method of

claim 28

further comprising the steps of:

periodically activating previously deactivated taps;

repeating steps b) through g).

31. The method of

claim 30

wherein the previously deactivated taps are activated in a sequential manner starting at the input end of the filter.

32. The method of

claim 28

wherein the step of computing the system error comprises the steps of:

determining the error of each individual 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:

specifying an acceptable level of error for the taps;

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

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

36. The method of

claim 35

wherein said steps are performed prior to steps a) through g).

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 coefficient, said method comprising the steps of:

a) computing an initial system error

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

c) 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;

d) computing a subsequent system error;

e) if the difference between the subsequent system error and the initial system error is less than a prespecified value, increasing the tap error threshold for each active tap; and

f) repeating steps c) through e) until the difference between the subsequent system error and the initial system error exceeds the prespecified value.

38. The method of

claim 37

wherein the determination of whether to deactivate a tap is done in a sequential manner starting at the input end of the 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 error threshold is the substantially the same for each tap in the filter.

41. 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 coefficient, said method comprising the steps of:

specifying an acceptable error for each tap;

selectively deactivating those taps which, if deactivated, would produce an error less than the specified acceptable error;

specifying an acceptable error for the system;

calculating a system error;

selectively deactivating those taps which, if deactivated, would result in the calculated system error being less than the acceptable system error.

42. The method of

claim 41

wherein the step of selectively deactivating those taps which, if deactivated, would produce an error less than the specified acceptable error comprises the steps of:

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

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

43. The method of

claim 42

wherein the step of calculating the error of deactivating the tap comprises the step of multiplying the absolute value of the tap coefficient by the average energy signal.

44. A method

claim 41

wherein the step of selectively deactivating those taps which, if deactivated, would cause the calculated system error to remain below the acceptable system error comprises the steps of:

a) setting a tap threshold;

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

c) computing a system error;

d) comparing the computed system error to the acceptable system error;

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

f) repeating steps b) through e) until the computed system error approaches the acceptable system error without exceeding the acceptable system error.

45. 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 specifying a threshold error for the system;

means for setting the state of each tap;

means for calculating a present error for the system; and

means for comparing the present error to the threshold error.

46. The communications system of

claim 45

wherein the means for setting the state of each tap comprises:

means for specifying a 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.

47. The communications system of

claim 46

wherein the means for setting the state of each tap further comprises:

means for periodically activating previously deactivated taps.

48. The communications system of

claim 46

further comprising means for increasing the tap threshold when the present error is less than the threshold error.

49. The communications system of

claim 46

wherein a select plurality of taps positioned at the input end of the adaptive filter are not subject to deactivation.

50. The communications system of

claim 45

wherein the adaptive filter has a sufficient number of taps to accommodate for signal delay due to the length of the communications line.

51. The communications system of

claim 45

wherein the taps are equally spaced within the adaptive filter such that the time between successive sampling of the input signal is substantially equal.

52. The communications system of

claim 45

wherein the communications system comprises at least one echo canceller having at least one adaptive filter.

53. The communications system of

claim 45

wherein the communications system comprises at least one NEXT canceller having at least one adaptive filter.

54. The communications system of

claim 45

wherein the communications system comprises at least one FEXT canceller having at least one adaptive filter.

55. A power dissipation reduction system for use in a communication 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 specifying a threshold error for the system;

means for setting the state of each tap;

means for calculating a present error for the system; and

means for comparing the present error to the threshold error.

56. The communications system of

claim 55

wherein the means for setting the state of each tap comprises:

means for specifying a 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.

57. The communications system of

claim 56

wherein the means for setting the state of each tap further comprises:

means for periodically activating previously deactivated taps.

58. The communications system of

claim 56

further comprising means for increasing the tap threshold when the present error is less than the threshold error.

59. The communications system of

claim 56

wherein a select plurality of taps positioned at the input end of the adaptive filter are not subject to deactivation.

60. The communications system of

claim 55

wherein the taps are equally spaced within the adaptive filter such that the time between successive sampling of the input signal is substantially equal.