Method of and apparatus for detecting impulsive noise, method of operating a demodulator, demodulator and radio receiver

• US 20030099287A1
• Filed: 10/30/2002
• Published: 05/29/2003
• Est. Priority Date: 10/31/2001
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Arambepola, Bernard
• Granted Patent: US 7,302,024 B2
• Time in Patent Office: Days
• US Class Current: 375/227
• CPC Class Codes: H03G 3/345 Muting during a short period of time when noise pulses are detected, i.e. blanking H03G3/348 takes precedence
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 1/1036 with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters H04B1/123 takes precedence; filter circuits H03H
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation

Abstract

In a digital receiver for receiving COFDM modulated television signals or the like, consecutive samples are compared with a detection threshold and the number of samples having amplitudes greater than the threshold is determined. This is compared with a further threshold and, if the number of such samples exceeds the further threshold, affected samples are blanked to zero. Similarly, an automatic gain control loop is disabled when the samples are blanked. A demodulator forms the difference in phase of pilot carriers from symbol to symbol. If the variance of the phase differences exceeds an averaged value, this indicates the presence of impulsive noise and is used to inhibit signal correction techniques within the demodulator. Noise energy is thus reduced and propagation of effects resulting from impulsive noise from symbol to symbol is substantially reduced.

Claims

1. A method of detecting impulsive noise in a stream of sets of signal samples in a radio receiver, wherein each of said sets comprises at least one of said samples, said method comprising the steps of:

(a) comparing a value based on an amplitude of said at least one sample of each said set with each of a number J of thresholds T_j, where J is greater than zero;

(b) determining each number n_j of said sets in each N_j consecutive ones of said sets for which said value is greater than T_j for each value of j such that 1≦

j≦

J; and

(c) indicating a noise impulse when each said number n_j is greater than a respective first number X_j.

2. A method as claimed in claim 1, in which said number J is equal to one.

3. A method as claimed in claim 1, in which each said set comprises one sample and said value comprises an amplitude of each said sample.

4. A method as claimed in claim 1, in which each said set comprises orthogonal first and second samples.

5. A method as claimed in claim 4, in which said value comprises a larger of amplitudes of said first and second samples.

6. A method as claimed in claim 1, in which said step (a) is performed for each said set Si of samples in turn in order of arrival with each said first threshold, where i indicates the order of arrival.

7. A method as claimed in claim 6, in which said step (b) comprises determining each said n_j from each said N_j consecutive sets, of which a most recent is Si.

8. A method as claimed in claim 7, in which said step (c) comprises indicating a start of said noise impulse when every said n_j rises above said respective first number X_j.

9. A method as claimed in claim 8, in which said step (c) comprises indicating an end of said noise impulse when every said n_j falls below a respective second number Y_j.

10. A method as claimed in claim 9, in which each said second number Yj is smaller than said respective first number X_j.

11. A method as claimed in claim 1, comprising the additional step (d) of performing an action in response to said step (c) indicating a noise impulse.

12. A method as claimed in claim 11, in which said step (d) comprises replacing each said sample of at least one of said sets with a replacement sample of reduced amplitude.

13. A method as claimed in claim 12, in which said replacement sample has zero amplitude.

14. A method as claimed in claim 12, in which:

said step (b) comprises determining each said n_j from each said N_j consecutive sets, of which a most recent is Si_j said step (c) comprises indicating a start of a noise impulse when every said n_j rises above said respective first number X_j and indicating an end of said noise impulse when every said n_j falls below a respective second number Y_j and said step (d) comprises replacing each said sample of each said set for which said step (c) indicates a presence of said noise impulse.

15. A method as claimed in claim 14, in which said step (d) comprises disabling said replacement after said samples of a third number of consecutive ones of said sets have been replaced.

16. A method as claimed in claim 11, in which said step (d) comprises acting on an automatic gain control arrangement of said receiver.

17. A method as claimed in claim 16, in which said automatic gain control arrangement controls a gain of said receiver based on a comparison between said samples and an average value based on said samples and said step (d) comprises preventing each said sample of at least one of said sets from contributing to said average value, in which said step (c) comprises.

18. A method as claimed in claim 17 in which:

said step (b) comprises determining each said n_j from each said N_j consecutive sets, of which a most recent is Si_j said step (c) comprises indicating a start of a noise impulse when every said n_j rises above said respective first number X_j and indicating an end of said noise impulse when every said n_j falls below a respective second number Y_j and said step (d) comprises preventing each said sample of each said set for which the step (c) indicates a presence of said noise impulse from contributing to said average value.

19. A method as claimed in claim 18, in which said step (d) comprises permitting a contribution to said average value after the said samples of a fourth number of consecutive ones of said sets have been prevented from contributing to said average value.

20. A method as claimed in claim 1, in which said samples are digital samples.

40. A method as claimed in claim 1, further comprising a method of operating a demodulator for demodulating a modulated signal, comprising the steps of:

(i) detecting noise in at least one pilot carrier of said modulated signal; and

(ii) preventing said detected noise from substantially influencing a signal correction within said demodulator.

21. A method of operating a demodulator for demodulating a modulated signal, comprising the steps of:

(i) detecting noise in at least one pilot carrier of said modulated signal; and

(ii) preventing said detected noise from substantially influencing a signal correction within said demodulator.

22. A method as claimed in claim 21, in which said modulated signal is a digital signal.

23. A method as claimed in claim 21, in which said modulated signal is a baseband signal.

24. A method as claimed in claim 21, in which said modulated signal is an orthogonal frequency division multiplexed signal.

25. A method as claimed in claim 24, in which said modulated signal is a coded orthogonal frequency division multiplexed signal.

26. A method as claimed in claim 24, in which said step (i) comprises forming the difference between a phase in a first symbol and a phase in a second symbol preceding said first symbol of said at least one pilot carrier.

27. A method as claimed in claim 26, in which said second symbol immediately precedes said first symbol.

28. A method as claimed in claim 26, in which said step (i) is repeated with each of at least some of said symbols of said at least one pilot carrier as said first symbol.

29. A method as claimed in claim 26, in which there is a plurality of said pilot carriers and said step (i) comprises forming a variance of said phase differences for each said first symbol.

30. A method as claimed in claim 29, in which each said variance is compared with a second threshold for determining a presence of a noise impulse.

31. A method as claimed in claim 30, in which said second threshold is formed by averaging said variances.

32. A method as claimed in claim 31, in which each said variance associated with said noise impulse is excluded from said averaging.

33. A method as claimed in claim 31, in which said second threshold comprises a sum of said variance average and a predetermined amount.

34. A method as claimed in claim 21, in which said step (ii) comprises preventing a portion of said modulated signal, detected in said step (i) as containing noise, from contributing to said signal correction.

35. A method as claimed in claim 34, in which said step (ii) comprises inhibiting a frequency response averaging in said demodulator.

36. A method as claimed in claim 34, in which said step (ii) comprises inhibiting a contribution to channel state information.

37. A method as claimed in claim 34, in which said step (ii) comprises inhibiting a carrier recovery loop in said demodulator.

38. A method as claimed in claim 34, in which said step (ii) comprises inhibiting a timing recovery loop in said demodulator.

39. A method as claimed in claim 21, in which said step (ii) is disabled when said step (i) detects noise for longer than a predetermined duration.

41. An apparatus for detecting impulsive noise in a stream of sets of samples in a radio receiver, wherein each of said sets comprises at least one of said samples, said apparatus comprising:

a comparator for comparing a value based on an amplitude of each said sample of each said set with each of a number J of thresholds T_j, where J is greater than zero;

determining means for determining each number n_j of said sets in each N_j consecutive ones of said sets for which the value is greater than T_j for each value of j such that 1≦

j≦

J; and

indicating means for indicating a noise umpulse when every said number n_j is greater than a respective first number X_j.

42. An apparatus as claimed in claim 41, in which said number J is equal to one.

43. An apparatus as claimed in claim 41, in which each said set comprises one sample and said value comprises an amplitude of each said sample.

44. An apparatus as claimed in claim 41, in which each said set comprises orthogonal first and second samples.

45. An apparatus as claimed in claim 44, in which said value comprises a larger of amplitudes of said first and second sample.

46. An apparatus as claimed in claim 41, in which said comparator is arranged to perform a comparison for each said set Si in turn in order of arrival with each said first threshold, where i indicates said order of arrival.

47. An apparatus as claimed in claim 46, in which said determining means is arranged to determine each said n_j from the or each said N_j consecutive sets of samples, of which a most recent is Si.

48. An apparatus as claimed in claim 47, in which said indicating means is arranged to indicate a start of said noise impulse when every said n_j rises above said respective first number X_j.

49. An apparatus as claimed in claim 48, in which said indicating means is arranged to indicate an end of said noise impulse when every said n_j falls below a respective second number Y_j.

50. An apparatus as claimed in claim 49, in which each said second number Yj is smaller than said respective first number X_j.

51. An apparatus as claimed in claim 41, comprising action performing means for performing an action in response to said indication by said indicating means of said noise impulse.

52. An apparatus as claimed in claim 51, in which said action performing means is arranged to replace each said sample of at least one of said sets with a replacement sample of reduced amplitude.

53. An apparatus as claimed in claim 52, in which said replacement sample has zero amplitude.

54. An apparatus as claimed in claim 52, in which:

said comparator is arranged to perform a comparison of each said set S_i in turn in order of arrival with each said first threshold, where i indicates said order of arrival;

said determining means is arranged to determine each said n_j from each said N_j consecutive ones of said sets, of which a most recent is S_i;

said indicating means is arranged to indicate a start of said noise impulse when every said n_j rises above said respective first number X_j and to indicate an end of said noise impulse when every said n_j falls below a respective second number Y_j; and

said action performing means is arranged to replace each said sample of each said set for which said indicating means indicates a presence of said noise impulse.

55. An apparatus as claimed in claim 54, in which said action performing means is arranged to be disabled after said samples of a third number of consecutive ones of said sets have been replaced.

56. A radio receiver comprising an apparatus as claimed in claim 41.

57. A receiver as claimed in claim 56, comprising an automatic gain control arrangement and action performing means for acting on said automatic gain control arrangement in response to said indication by said indicating means of said noise impulse.

58. A receiver as claimed in claim 57, in which said automatic gain control arrangement is arranged to control a gain of said receiver based on a comparison between said samples and an average value based on said samples and said action performing means is arranged to prevent each said sample of at least one of said sets from contributing to said average value.

59. A receiver as claimed in claim 58, in which:

said comparator is arranged to perform a comparison of each said set S_i in turn in order of arrival with each said first threshold, where i indicates said order of arrival;

said determining means is arranged to determine each said n_j from each said N_j consecutive ones of said sets, of which a most recent is S_i;

said indicating means is arranged to indicate a start of said noise impulse when every said n_j rises above said respective first number X_j and to indicate an end of said noise impulse when every said n_j falls below a respective second number Y_j; and

said action performing means is arranged to prevent each said sample of each said set for which said indicating means indicates a presence of said noise impulse from contributing to said average value.

60. A receiver as claimed in claim 59, in which said action performing means is arranged to permit a contribution to said average value after said samples of a fourth number of consecutive ones of said sets have been prevented from contributing to said average value.

61. A receiver as claimed in claim 56, comprising an analog-to-digital converter, said apparatus being arranged to receive said samples from said converter.

62. A receiver as claimed in claim 61, comprising an automatic gain control arrangement having a gain-controlled stage ahead of the converter.

83. A radio receiver as claimed in claim 56, further comprising a demodulator for demodulating a modulated signal, comprising a detector for detecting noise in at least one pilot carrier of said modulated signal, correcting means for performing signal correction, and preventing means for preventing said detected noise from substantially influencing said correcting means.

63. A demodulator for demodulating a modulated signal, comprising a detector for detecting noise in at least one pilot carrier of said modulated signal, correcting means for performing signal correction, and preventing means for preventing said detected noise from substantially influencing said correcting means.

64. A demodulator as claimed in claim 63, in which said modulated signal is a digital signal.

65. A demodulator as claimed in claim 63, in which said modulated signal is a baseband signal.

66. A demodulator as claimed in claim 63, in which said modulated signal is an orthogonal frequency division multiplexed signal.

67. A demodulator as claimed in claim 66, in which said modulated signal is a coded orthogonal frequency division multiplexed signal.

68. A demodulator as claimed in claim 66, in which said detector is arranged to form a difference between a phase in a first symbol and a phase in a second symbol preceding said first symbol of said at least one pilot carrier.

69. A demodulator as claimed in claim 68, in which said second symbol immediately precedes said first symbol.

70. A demodulator as claimed in claim 68, in which said detector is arranged to repeat said detection with each of at least some of said symbols of said at least one pilot carrier as said first symbol.

71. A demodulator as claimed in claim 68, in which there is a plurality of pilot carriers and said detector is arranged to form a variance of said phase differences for each said first symbol.

72. A demodulator as claimed in claim 71, in which said detector is arranged to compare each said variance with a second threshold for determining a presence of said noise impulse.

73. A demodulator as claimed in claim 72, in which said detector is arranged to form said second threshold by averaging said variances.

74. A demodulator as claimed in claim 73, in which the detector is arranged to exclude from the averaging the or each variance associated with a noise impulse.

75. A demodulator as claimed in claim 73, in which said detector is arranged to form said second threshold as a sum of said variance average and a predetermined amount.

76. A demodulator as claimed in claim 63, in which said preventing means is arranged to prevent a portion of said modulated signal, detected by said detector as containing noise, from contributing to said signal correction in said correcting means.

77. A demodulator as claimed in claim 76, in which said correcting means comprises frequency response averaging means.

78. A demodulator as claimed in claim 76, in which said the correcting means comprises channel state information generating means.

79. A demodulator as claimed in claim 76, in which said correcting means comprises a carrier recovery loop.

80. A demodulator as claimed in claim 76, in which said correcting means comprises a timing recovery loop.

81. A demodulator as claimed in claim 63, in which said preventing means is arranged to be disabled when said detecting means detects noise for longer than a predetermined duration.

82. A radio receiver comprising a demodulator as claimed in claim 63.