Method and apparatus for interference cancellation in communication signal processing

• US 20050254600A1
• Filed: 05/12/2004
• Published: 11/17/2005
• Est. Priority Date: 05/12/2004
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Chen, Dayong, Hui, Dennis
• Granted Patent: US 8,107,560 B2
• Time in Patent Office: Days
• US Class Current: 375/324
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation

Abstract

A method and apparatus blindly detects a received signal'"'"'s modulation type characterizing an impairment component of the received signal for each postulated modulation type by determining spatial correlations between In-phase and Quadrature components of the received signal. The blind detection circuit then detects the modulation type based on the characterized impairment component. A metric generator generates a postulation metric for each postulated modulation type based on the characterized impairment component. After evaluating the postulation metrics, an evaluation circuit identifies the postulated modulation type having the best postulation metric as the modulation type of the received signal. According to an exemplary embodiment, the blind detection circuit determines a whitened noise estimate for each postulated modulation type and generates the postulation metrics based on the whitened noise estimate to reduce interference effects in the postulation metrics.

Claims

1. A method of blindly detecting the modulation type of a received signal comprising:

generating a postulated received signal for each of two or more postulated modulation types based on the received signal;

characterizing an impairment component of each postulated received signal by determining spatial correlations between In-phase and Quadrature components of each postulated received signal; and

detecting the modulation type of the received signal based on the characterized impairment components.

2. The method of claim 1 wherein detecting the modulation type of the received signal based on the characterized impairment component comprises:

generating a metric for each postulated modulation type based on the characterized impairment component to thereby reduce interference effects in the metric; and

evaluating the metrics to identify the modulation type of the received signal.

3. The method of claim 2 wherein evaluating the metrics to identify the modulation type of the received signal comprises identifying the postulated modulation type corresponding to the best metric.

4. The method of claim 1 wherein generating the postulated received signal for each postulated modulation type comprises de-rotating the received signal by a different phase rotation for each postulated modulation type and wherein characterizing the impairment component of each postulated received signal comprises characterizing the impairment component of each de-rotated signal by determining spatial correlations between In-phase and Quadrature components of each de-rotated signal.

5. The method of claim 4 wherein de-rotating the received signal by a different phase rotation for each postulated modulation type further comprises applying an additional de-rotation to the previously de-rotated received signal for one of the postulated modulation types to make the interference stationary.

6. The method of claim 4 wherein de-rotating the received signal by a different phase rotation for each postulated modulation type comprises:

de-rotating the received signal by π

/2 for a postulated Gaussian minimum shift keying modulation type; and

de-rotating the received signal by 3π

/8 for a postulated 8-phase shift keying modulation type.

7. The method of claim 6 wherein characterizing the impairment component of the received signal for the postulated 8-phase shift keying modulation type further comprises de-rotating the characterized impairment component by π

/8.

8. The method of claim 1 wherein detecting the modulation type of the received signal based on the characterized impairment component comprises:

determining a whitened noise estimate for each postulated modulation type based on the characterized impairment component to thereby reduce interference effects in the characterized impairment component; and

detecting the modulation type of the received signal based on the whitened noise estimate.

9. The method of claim 8 wherein detecting the modulation type of the received signal based on the whitened noise estimate comprises:

generating a metric based on the whitened noise estimate for each postulated received signal; and

evaluating the metrics to identify the modulation type of the received signal.

10. The method of claim 8 further comprising generating a whitening filter for each postulated modulation type based on the characterized impairment component, wherein determining the whitened noise estimate for each postulated received signal comprises filtering a noise estimate for each postulated received signal with the corresponding whitening filter to reduce interference effects in the noise estimates.

11. The method of claim 10 wherein generating the whitening filter comprises generating the whitening filter according to a Whittle-Wiggins-Robinson algorithm.

12. The method of claim 8 wherein determining the whitened noise estimate for each postulated modulation type comprises generating whitened channel estimates while generating whitening filter coefficients based on the corresponding characterized impairment component to reduce interference effects from the whitened channel estimate and the whitening filter coefficients for each modulation type.

13. The method of claim 12 wherein generating the whitened channel estimate while generating the whitening filter coefficients comprises generating the whitened channel estimate while generating the whitening filter coefficients according to an indirect Generalized Least Squares algorithm.

14. The method of claim 1 wherein characterizing the impairment component of each postulated received signal comprises characterizing interference components of each postulated received signal for each postulated modulation type by determining spatial and temporal correlations between In-phase and Quadrature components of the received signal.

15. The method of claim 1 wherein characterizing the impairment component of each postulated received signal comprises:

de-rotating the received signal by a characteristic phase rotation value for each postulated modulation type to generate a de-rotated signal for each postulated modulation type; and

determining interference correlations for each de-rotated signal by spatially and temporally correlating In-phase and Quadrature components of each de-rotated signal.

16. The method of claim 15 wherein characterizing the impairment component of each postulated received signal further comprises:

using the interference correlations to reduce un-cancelled interference; and

calculating a metric for each de-rotated signal based on the interference correlations.

17. The method of claim 16 wherein detecting the modulation type comprises evaluating the metrics to identify the modulation type of the received signal.

18. The method of claim 1 wherein the postulated modulation types include 8-phase shift keying and Gaussian minimum shift keying.

19. The method of claim 1 further comprising determining a whitened channel estimate for each postulated received signal and providing the whitened channel estimate corresponding to the identified modulation type to a demodulator that demodulates the received signal using the detected modulation type and the whitened channel estimate.

20. A blind detection circuit in a wireless communication receiver to determine the modulation type of a received signal, the blind detection circuit comprising an impairment characterization unit configured to characterize an impairment component of the received signal for each of two or more postulated modulation types by spatially correlating In-phase and Quadrature components of the received signal for each postulated modulation type and configured to determine the modulation type of the received signal based on the characterized impairment component.

21. The blind detection circuit of claim 20 further comprising a metric generator configured to generate a postulation metric for each postulated modulation type based on the characterized impairment component to thereby reduce interference effects in the postulation metric.

22. The blind detection circuit of claim 20 wherein the impairment characterization unit comprises an interference characterization circuit configured to reduce interference effects in the postulation metrics based on the characterized impairment component.

23. The blind detection circuit of claim 22 wherein the interference characterization circuit comprises a whitening circuit for determining a whitened noise estimate of the received signal for each postulated modulation type based on the characterized impairment component and wherein the blind detection circuit detects the modulation type of the received signal based on the whitened noise estimate.

24. The blind detection circuit of claim 23 wherein the interference characterization circuit further comprises a filter generator to generate whitening filter coefficients while the whitening circuit determines a whitened channel estimate based on the characterized impairment component to reduce interference effects from the whitened channel estimate and the whitening filter coefficients for each modulation type.

25. The blind detection circuit of claim 23 wherein the interference characterization circuit further comprises a filter generator for generating a whitening filter based on the characterized impairment component and wherein the interference reduction circuit filters a noise estimate for the received signal with the whitening filter to reduce interference effects from the noise estimates for each postulated modulation type.

26. The blind detection circuit of claim 20 wherein the blind detection circuit further comprises an evaluation circuit configured to evaluate the postulation metrics and to identify the modulation type corresponding to the best postulation metric.

27. The blind detection circuit of claim 20 wherein the blind detection circuit further comprises a signal rotator to de-rotate the received signal by a different phase rotation for each postulated modulation type.

28. The blind detection circuit of claim 20 wherein the impairment characterization unit is configured to characterize the impairment component of the received signal for each of the two or more postulated modulation types by spatially and temporally correlating In-phase and Quadrature components of the received signal for each postulated modulation type.

30. The method of claim 28 wherein reducing the interference in the postulation metric determined for each postulated modulation type comprises determining a whitened noise estimate for each postulated modulation type based on the characterized interference and determining the postulation metric based on the whitened noise estimate for each postulated modulation type.

31. The method of claim 30 wherein detecting the modulation type of the received signal comprises evaluating the postulation metrics to identify the modulation type of the received signal.

32. The method of claim 30 wherein determining the whitened noise estimate for each postulated modulation type comprises generating a whitened channel estimate while generating whitening filter coefficients based on the characterized interference.

33. The method of claim 30 further comprising generating a whitening filter based on the characterized interference, wherein determining the whitened noise estimate for each postulated modulation type comprises filtering a noise estimate for the received signal with the whitening filter to reduce interference effects in the noise estimates.

29. A method of blindly detecting the modulation type of a received signal comprising:

characterizing interference in the received signal for each of two or more postulated modulation types by determining spatial and temporal In-phase and Quadrature correlations for the received signal;

reducing interference in a postulation metric determined for each postulated modulation type based on the characterized interference; and

detecting the modulation type of the received signal by identifying the modulation type corresponding to a best one of the postulation metrics.

34. The method of claim 29 wherein characterizing the interference in the received signal for each postulated modulation type comprises:

de-rotating the received signal by a characteristic phase rotation value for each postulated modulation type to generate a de-rotated signal for each postulated modulation type; and

determining interference correlations for each de-rotated signal by spatially and temporally correlating In-phase and Quadrature components of each de-rotated signal.

35. The method of claim 34 wherein reducing interference in the postulation metric determined for each postulated modulation type comprises using the interference correlations to reduce un-cancelled interference in the postulated metrics.

36. The method of claim 35 wherein detecting the modulation type of the received signal comprises evaluating the postulation metrics to identify the modulation type of the received signal.

37. The method of claim 34 wherein applying the characteristic phase rotation value to the received signal for each postulated modulation type comprises:

de-rotating the received signal by π

/2 for a postulated Gaussian minimum shift keying modulation type; and

de-rotating the received signal by 3π

/8 for a postulated 8-phase shift keying modulation type.

38. The method of claim 37 wherein characterizing interference in the received signal for the postulated 8-phase shift keying modulation type further comprises calculating an initial impairment component based on the 3π

/8 phase de-rotated signal and further de-rotating the initial impairment component by π

/8 to generate a modified impairment component.

39. The method of claim 29 further comprising generating a whitened channel estimate based on the characterized interference and providing the whitened channel estimate corresponding to the identified modulation type to a demodulator that demodulates the received signal using the identified modulation type and the whitened channel estimate.

40. A blind detection circuit configured to detect the modulation type of a received signal, the detector comprising:

an interference characterization circuit configured to characterize interference in the received signal for each of two or more postulated modulation types by determining spatial and temporal In-phase and Quadrature correlations for the received signal for each postulated modulation type;

a metric generator configured to reduce interference in a postulation metric determined for each postulated modulation type based on the characterized interference; and

an evaluation circuit configured to detect the modulation type of the received signal by identifying a best one of the postulation metrics.

41. The blind detection circuit of claim 40 wherein the interference characterization circuit comprises a whitening circuit for determining a whitened noise estimate of the received signal for each postulated modulation type based on the characterized impairment component and wherein the blind detection circuit detects the modulation type of the received signal based on the whitened noise estimate.

42. The blind detection circuit of claim 41 wherein the interference characterization circuit further comprises a filter generator to generate whitening filter coefficients while the whitening circuit determines a whitened channel estimate based on the characterized impairment component to reduce interference effects from the whitened channel estimate and the whitening filter coefficients for each modulation type.

43. The blind detection circuit of claim 41 wherein the interference characterization circuit further comprises a filter generator for generating a whitening filter based on the characterized impairment component and wherein the interference characterization circuit filters a noise estimate for the received signal with the whitening filter to reduce interference effects from the noise estimate for each postulated modulation type.

44. The blind detection circuit of claim 40 wherein the blind detection circuit further comprises a signal rotator to de-rotate the received signal by a different phase rotation for each postulated modulation type.

45. A method of processing a signal in a wireless network receiver comprising:

receiving the signal at the receiver; and

identifying the modulation type of the received signal by;

determining spatial correlations between In-phase and Quadrature components of the received signal for each postulated modulation type to characterize interference components of the received signal for each postulated modulation type;

reducing interference in a postulation metric determined for each postulated modulation type based on the characterized interference components; and

identifying the postulated modulation type corresponding to the best postulation metric as the modulation type of the received signal.

46. The method of claim 45 further comprising demodulating the received signal according to the identified modulation type.

47. The method of claim 45 wherein reducing interference in the postulation metric determined for each postulated modulation type comprises determining a whitened noise estimate for each postulated modulation type based on the characterized interference and determining the postulation metric based on the whitened noise estimate for each postulated modulation type.

48. The method of claim 47 wherein determining the whitened noise estimate for the received signal comprises generating a whitened channel estimate while generating whitening filter coefficients based on the characterized interference.

49. The method of claim 47 further comprising generating a whitening filter based on the characterized interference, wherein determining the whitened noise estimate comprises filtering a noise estimate for the received signal with the whitening filter to reduce interference effects in the noise estimates.

50. The method of claim 47 further comprising determining a whitened channel estimate based on the characterized interference and providing the whitened channel estimate corresponding to the identified modulation type to a demodulator that demodulates the received signal using the identified modulation type and the whitened channel estimate.

51. The method of claim 45 wherein characterizing the interference components of the received signal for each postulated modulation type comprises:

de-rotating the received signal by a characteristic phase rotation for each postulated modulation type to generate a de-rotated signal for each postulated modulation type; and

determining interference correlations for each de-rotated signal by spatially and temporally correlating In-phase and Quadrature components of each de-rotated signal.

52. The method of claim 45 wherein determining spatial correlations between In-phase and Quadrature components of the received signal for each postulated modulation type comprises determining spatial-temporal correlations between In-phase and Quadrature components of the received signal for each postulated modulation type.

53. A receiver for receiving a signal in a wireless network comprising:

a blind detection circuit configured to determine the modulation type of the received signal, the blind detection circuit comprising;

an impairment characterization unit configured to characterize an impairment component of the received signal for each of two or more postulated modulation types by spatially correlating In-phase and Quadrature components of the received signal for each postulated modulation type; and

a metric generator configured to generate a postulation metric for each postulated modulation type based on the characterized impairment component to thereby reduce interference effects in the postulation metric.

54. The receiver of claim 53 wherein the impairment characterization unit comprises an interference characterization circuit configured to reduce interference effects in the postulation metrics based on the characterized impairment component.

55. The receiver of claim 54 wherein the interference characterization circuit comprises a whitening circuit for determining a whitened noise estimate of the received signal for each postulated modulation type based on the characterized impairment component and wherein the blind detection circuit detects the modulation type of the received signal based on the whitened noise estimate.

56. The receiver of claim 55 wherein the interference characterization circuit further comprises a filter generator to generate whitening filter coefficients while the whitening circuit determines a whitened channel estimate based on the characterized impairment component to reduce interference effects from the whitened channel estimate and the whitening filter coefficients for each modulation type.

57. The receiver of claim 56 wherein an indirect Generalized Least Squares algorithm generates the whitened channel estimate and the whitening filter coefficients.

58. The receiver of claim 55 wherein the interference characterization circuit further comprises a filter generator for generating a whitening filter based on the characterized impairment component and wherein the interference reduction circuit filters a noise estimate for the received signal with the whitening filter to reduce interference effects from the noise estimate for each postulated modulation type.

59. The receiver of claim 58 wherein the filter generator generates the whitening filter based on a Whittle-Wiggins-Robinson algorithm.

60. The receiver of claim 53 wherein the blind detection circuit further comprises an evaluation circuit configured to evaluate the postulation metrics and to identify the modulation type corresponding to the best postulation metric.

61. The receiver of claim 53 wherein the blind detection circuit further comprises a signal rotator to de-rotate the received signal by a different phase rotation for each postulated modulation type.

62. The receiver of claim 61 wherein the signal rotator de-rotates the received signal by a π

/2 phase rotation for a postulated Gaussian minimum shift keying modulation type and wherein the signal rotator de-rotates the received signal by a 3π

/8 phase rotation for a postulated 8-phase shift keying modulation type.

63. The receiver of claim 62 wherein the signal rotator applies an additional π

/8 phase de-rotation to the characterized impairment component corresponding to the postulated 8-phase shift keying modulation type.

64. The receiver of claim 53 wherein the blind detection circuit determines the modulation type of the received signal based on spatial and temporal correlations between In-phase and Quadrature components of the received signal for each postulated modulation type.

65. The receiver of claim 53 further comprising a demodulator for demodulating the received signal based on the received signal'"'"'s modulation type.

66. The receiver of claim 65 wherein the impairment characterization unit comprises a whitening circuit for determining a whitened channel estimate for the received signal based on the characterized impairment component and wherein the blind detection circuit provides the whitened channel estimate corresponding to the received signal'"'"'s modulation type to the demodulator.

67. The receiver of claim 53 wherein the receiver is disposed in a mobile station.