Adaptive array antenna nulling

• US 6,486,828 B1
• Filed: 07/26/2000
• Issued: 11/26/2002
• Est. Priority Date: 07/26/2000
• Status: Expired due to Fees

• Current Assignee: Proxim Wireless Corporation
• Original Assignee: Western Multiplex Corporation
• Inventors: Leimer, Donald, Cahn, Charles R.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US09/626,203
• Time in Patent Office: 853 Days
• Field of Search: 342/363, 342/365, 342/362, 342/380, 342/383, 455/278.1, 455/63, 455/562, 455/276.1, 455/295, 455/296
• US Class Current: 342/363
• CPC Class Codes: H01Q 21/24 Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction circularly polarised patch antennas H01Q9/0428; circularly polarised horns H01Q13/0241; cross-polarised horns H01Q13/0258; polarisation converters H01Q15/242; cross-polarised rear feeds H01Q19/136; crossed polarisation dual antenna H01Q25/001
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling
• CPC Class Codes: H04B 7/0857 using maximum ratio combining techniques, e.g. signal-to- interference ratio [SIR], received signal strenght indication [RSS]
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04K 3/228 Elimination in the received signal of jamming or of data corrupted by jamming interference suppression in receivers H04B1/10

Abstract

An adaptive antenna array employs selective polarization nulling and spatial nulling to receive desired signals in the presence of jamming signals. The desired signals have the same circular polarization, and the array includes at least one antenna element having an opposite circular polarization to null jamming signals having an opposite circular polarization. A gain pattern for the array is selected to minimize signals having the same circular, or linear, polarization. The gain pattern is computed based on jamming signals received when no desired signals are transmitted, or selected based on measured desired signals.

Claims

1. A method of processing received signals, comprising:

forming a first output signal from transmitted signals received at a first antenna from a plurality of directions of arrival, said received signals including desired signals having a first circular polarization and interfering signals, said first antenna having said first circular polarization;

forming a second output signal from said transmitted signals received at a second antenna, said second antenna having a second circular polarization distinguishably different from said first circular polarization;

selecting an initial first gain to substantially reduce one or more of said interfering signals received at said first antenna during a quiet time in which said interfering signals can be distinguished from said desired signals;

varying said initially selected first gain by a predetermined amount to derive alternative first gains;

computing a performance value for each said alternative first gain at different predetermined directions of arrival of said desired signals;

selecting the first gain from among said initially selected first gain and said alternative first gains that provides the highest number of performance values over a selected threshold value;

selecting a second gain to substantially reduce one or more of said interfering signals received at said second antenna during a quiet time in which said interfering signals can be distinguished from said desired signals;

deriving complex weights corresponding to said selected first gain and second gain; and

applying said complex weights to said respective first and second output signals; and

combining said first and second output signals to form a third output signal having enhanced gain over the directions of arrival of said desired signals for processing said desired signals.

2. The method of claim 1, further comprising:

increasing said selected threshold value if said highest number of performance values is above a first preselected number; and

decreasing said selected threshold value if said highest number of performance values is below a second preselected number.

3. The method of claims 1 or 2, wherein said performance value is the ratio of a desired signal to the sum of said interfering signals and background noise.

4. The method of claim 2, wherein selecting said first gain comprises:

selecting said first gain to substantially enhance the performance value for one or more of said desired signals.

5. The method of claim 4, wherein said performance value is selected from the group comprising signal-to-noise ratio, amplitude, and bit error rate.

6. The method of claim 4, wherein selecting said first gain further comprises:

varying an initially selected first gain by a predetermined amount to derive alternative first gains;

measuring said performance values for each said alternative first gain; and

selecting the first gain from among said initially selected first gain and said alternative first gains that provides the highest number of performance values over a selected threshold value.

7. The method of claim 6, further comprising:

increasing said selected threshold value if said highest number of performance values is above a first preselected number; and

decreasing said selected threshold value if said highest number of performance values is below a second preselected number.

8. The method of claims 6 or 7, wherein said performance value is the ratio of said desired signals to the sum of said interfering signals and background noise.

9. A method of processing received signals, comprising:

forming a first output signal from transmitted signals received at an antenna array from a plurality of directions of arrival, said received signals including desired signals having a first circular polarization and interfering signals, said antenna array comprising a plurality of first antennas having said first circular polarization, said first output signal formed from signals received during a quiet time in which said interfering signals can be distinguished from said desired signals;

forming a second output signal from said transmitted signals received at a second antenna, said second antenna having a second circular polarization distinguishably different from said first circular polarization, said second output signal formed from signals received during a quiet time in which said interfering signals can be distinguished from said desired signals;

selecting an initial complex steering vector;

deriving an array gain pattern corresponding to said initial steering vector;

varying each real value and each imaginary value of said initial steering vector by a predetermined amount to derive alternative steering vectors;

computing an array performance value for each said alternative steering vector over said range of directions;

selecting the gain pattern corresponding to the steering vector that provides array performance values over a selected threshold value for the highest number of directions of arrival

selecting a second gain to substantially reduce one or more of said interfering signals received at said second antenna;

deriving complex weights corresponding to said selected gain pattern and second gain;

applying said complex weights to said respective output signals; and

combining said weighted first and second output signals to form a third output signal having enhanced gain over the directions of arrival of said desired signals for processing said desired signals.

10. The method of claim 9, further comprising:

increasing said selected threshold value if said highest number of directions of arrival is above a first preselected number; and

decreasing said selected threshold value if said highest number of directions of arrival is below a second preselected number.

11. The method of claims 9 or 10, wherein said array performance value is a signal-to-noise ratio.

12. The method of claim 11, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.

13. The method of claim 9, wherein selecting said gain pattern further comprises:

varying each real value and each imaginary value of an initially selected gain pattern by a predetermined amount to derive alternative gain patterns;

measuring an array performance value for each received desired signal for each said alternative gain pattern; and

selecting the gain pattern from among said initially selected gain pattern and said alternative gain patterns that provides array performance values over a selected threshold value for the highest number of received desired signals.

14. The method of claim 13, further comprising:

increasing said selected threshold value if said highest number of received desired signals is above a first preselected number; and

decreasing said selected threshold value if said highest number of received desired signals is below a second preselected number.

15. The method of claims 13 or 14, wherein said array performance value is a signal-to-noise ratio.

16. The method of claim 15, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.

17. A receiver, comprising:

a first antenna for forming a first output signal from signals received from a plurality of directions of arrival, said received signals including interfering signals and desired signals having a first circular polarization, said first antenna having said first circular polarization, said first antenna for forming said first output signal from signals received during a quiet time in which said interfering signals can be distinguished from said desired signals;

a second antenna for forming a second output signal from said received signals, said second antenna having a second circular polarization distinguishably different from said first circular polarization, said second antenna for forming said second output signal from signals received during a quiet time in which said interfering signals can be distinguished from said desired signals; and

a processor connected to said first and second antennas for substantially reducing one or more of said received interfering signals in a third output signal by varying an initially selected first gain by a predetermined amount to derive alternative first gains, computing performance values for each alternative first gain at different predetermined directions of arrival of said desired signals, and selecting the first gain from among said initially selected first gain and said alternative first gains that provides the highest number of array performance values over a selected threshold value, selecting a second gain related to said interfering signals received at said second antenna, deriving complex weights corresponding to said selected first gain and second gain, applying said complex weights to said respective first and second output signal, and linearly combining said weighted first and second output signals to form said third output signal having enhanced gain over the directions of arrival of said desired signals.

18. The receiver of claim 17, wherein said processor further comprises:

a processor for increasing said selected threshold value if said highest number of performance values is above a first preselected number, and decreasing said selected threshold value if said highest number of performance values is below a second preselected number.

19. The receiver of claims 17 or 18, wherein said performance value is the ratio of a desired signal to the sum of said interfering signals and background noise.

20. The receiver of claim 17, wherein said processor further comprises:

a processor for varying an initially selected first gain by a predetermined amount to derive alternative first gains, measuring a performance value for each said alternative first gain, and selecting the first gain from among said initially selected first gain and said alternative first gains that provides the highest number of array performance values over a selected threshold value.

21. The receiver of claim 20, wherein said processor further comprises:

a processor for increasing said selected threshold value if said highest number of performance values is above a first preselected number, and decreasing said selected threshold value if said highest number of performance values is below a second preselected number.

22. The receiver of claims 20 or 21, wherein said performance value is the ratio of said desired signals to the sum of said interfering signals and background noise.

48. The method of claim 17, wherein selecting said gain pattern comprises:

selecting said gain pattern to substantially enhance the performance value of one or more of said received desired signals.

49. The method of claim 48, wherein said performance value is selected from the group of values comprising signal-to-noise ratio, amplitude, and bit error rate.

23. A receiver, comprising:

an antenna array comprising a plurality of first antennas for forming a first output signal from signals received from a plurality of directions of arrival, said received signals including desired signals having a first circular polarization and interfering signals, said first antennas having said first circular polarization, said first antennas for forming said first output signal from signals received during a quiet time in which no desired signals are transmitted;

a second antenna for forming a second output signal from said received signals, said second antenna having a second circular polarization distinguishably different from said first circular polarization, said second antenna for forming said second output signal from signals received during a quiet time in which no desired signals are transmitted; and

a processor connected to said first and second antennas for selecting a gain pattern for said antenna array to substantially reduce one or more of said received interfering signals by selecting an initial complex steering vector, deriving the array gain pattern corresponding to said selected steering vector, varying each real value and each imaginary value of said selected steering vector by a predetermined amount to derive alternative steering vectors, computing array performance values for each said alternative steering vector over said range of directions, and selecting the gain pattern of the steering vector that provides array performance values over a selected threshold value for the highest number of directions of arrival, selecting a second gain for said second antenna to substantially reduce one or more of said received interfering signals, deriving complex weights for each antenna corresponding to said selected gain pattern and second gain, applying said complex weights to said respective first and second output signals, and linearly combining said weighted first and second output signals to form a third output signal having enhanced gain over the directions of arrival of said desired signals.

24. The receiver of claim 23, wherein said processor further comprises:

a processor for increasing said selected threshold value if said highest number of directions of arrival is above a first preselected number, and decreasing said selected threshold value if said highest number of directions of arrival is below a second preselected number.

25. The receiver of claims 23 or 24, wherein said array performance value is a signal-to-noise ratio.

26. The receiver of claim 25, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.

27. The receiver of claim 23, wherein said processor comprises:

a processor for measuring a performance value for each received desired signal and selecting said gain pattern to substantially enhance the performance value of one or more of said received desired signals.

28. The receiver of claim 27, wherein said performance value is selected from the group of values comprising signal-to-noise ratio, amplitude, and bit error rate.

29. The receiver of claim 23, wherein said processor further comprises:

a processor for varying each real value and each imaginary value of an initially selected gain pattern by a predetermined amount to derive alternative gain patterns, measuring an array performance value for each received desired signal at each alternative gain pattern, and selecting the gain pattern from among said initially selected gain pattern and said alternative gain patterns that provides array performance values over a selected threshold value for the highest number of received desired signals.

30. The receiver of claim 29, wherein said processor further comprises:

a processor for increasing said selected threshold value if said highest number of received desired signals is above a first preselected number, and decreasing said selected threshold value if said highest number of received desired signals is below a second preselected number.

31. The receiver of claims 29 or 30, wherein said array performance value is a signal-to-noise ratio.

32. The receiver of claim 31, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.

33. A method of processing received signals, comprising sequentially:

forming a first output signal from transmitted signals received at a first antenna, said received signals including desired signals having a first circular polarization and interfering signals, said first antenna having said first circular polarization;

forming a second output signal from said transmitted signals received at a second antenna, said second antenna having a second circular polarization distinguishably different from said first circular polarization;

selecting first and second gains related to said interfering signals received at said first and second antenna, respectively, during a quiet time in which said interfering signals can be distinguished from said desired signals, said first and second gains selected to substantially reduce one or more of said interfering signals received at said first and second antennas;

varying an initially selected first gain by a predetermined amount to derive alternative first gains;

computing a performance value for each said alternative first gain at different predetermined directions of arrival of said desired signals;

selecting the first gain from among said initially selected first gain and said alternative first gains that provides the highest number of performance values over a selected threshold value;

deriving complex weights corresponding to said selected first gain and second gain;

applying said complex weights to said respective first and second output signals; and

then

minimizing said interfering signals by combining said first and second output signals to form a third output signal for processing said desired signals.

34. The method of claim 33, wherein said performance value is the ratio of a desired signal to the sum of said interfering signals and background noise.

35. The method of claim 33, further comprising:

increasing said selected threshold value if said highest number of performance values is above a first preselected number; and

decreasing said selected threshold value if said highest number of performance values is below a second preselected number.

36. The method of claim 35, wherein said performance value is the ratio of a desired signal to the sum of said interfering signals and background noise.

37. The method of claim 35, wherein selecting said first gain comprises:

selecting said first gain to substantially enhance the performance value for one or more of said desired signals.

38. The method of claim 37, wherein selecting said first gain further comprises:

varying an initially selected first gain by a predetermined amount to derive alternative first gains;

measuring said performance values for each said alternative first gain; and

selecting the first gain from among said initially selected first gain and said alternative first gains that provides the highest number of performance values over a selected threshold value.

39. The method of claim 38, wherein said performance value is the ratio of said desired signals to the sum of said interfering signals and background noise.

40. The method of claim 38, further comprising:

increasing said selected threshold value if said highest number of performance values is above a first preselected number; and

decreasing said selected threshold value if said highest number of performance values is below a second preselected number.

41. The method of claim 40, wherein said performance value is the ratio of said desired signals to the sum of said interfering signals and background noise.

42. The method of claim 33, wherein forming said first output signal further comprises:

measuring a performance value for each of said desired signals.

43. A method of processing received signals, comprising sequentially:

forming a first output signal from transmitted signals received at an antenna array during a quiet time in which interfering signals can be distinguished from desired signals, said received signals including at least said interfering signals, said desired signals having a first circular polarization and said antenna array comprising a plurality of first antennas having said first circular polarization;

forming a second output signal from said transmitted signals received at a second antenna during a quiet time in which said interfering signals can be distinguished from said desired signals, said second antenna having a second circular polarization distinguishably different from said first circular polarization;

selecting an initial complex steering vector to substantially reduce the array gain in the direction of arrival of one or more of said interfering signals received at said first antenna over a predetermined range of directions;

deriving an array gain pattern corresponding to said initial steering vector;

varying each real value and each imaginary value of said initial steering vector by a predetermined amount to derive alternative steering vectors;

computing an array performance value for each said alternative steering vector over said range of directions;

selecting the gain pattern corresponding to the steering vector that provides array performance values over a selected threshold value for the highest number of directions of arrival;

selecting a second gain for said second antenna to substantially reduce one or more of said interfering signals;

deriving complex weights corresponding to said selected gain pattern and second gain;

applying said complex weights to said respective output signals; and

minimizing said interfering signals by combining said weighted first and second output signals to form a third output signal for processing said desired signals.

44. The method of claim 43, wherein said array performance value is a signal-to-noise ratio.

45. The method of claim 44, further comprising:

increasing said selected threshold value if said highest number of directions of arrival is above a first preselected number; and

decreasing said selected threshold value if said highest number of directions of arrival is below a second preselected number.

46. The method of claim 45, wherein said array performance value is a signal-to-noise ratio.

47. The method of claim 46, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.

50. The method of claim 43, wherein forming said first output signal further comprises:

measuring a performance value for each received desired signal.

51. The method of claim 50, wherein selecting said gain pattern further comprises:

varying each real value and each imaginary value of an initially selected gain pattern by a predetermined amount to derive alternative gain patterns;

measuring an array performance value for each received desired signal for each said alternative gain pattern; and

selecting the gain pattern from among said initially selected gain pattern and said alternative gain patterns that provides array performance values over a selected threshold value for the highest number of received desired signals.

52. The method of claim 51, wherein said array performance value is a signal-to-noise ratio.

53. The method of claim 52, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.

54. The method of claim 51, further comprising:

increasing said selected threshold value if said highest number of received desired signals is above a first preselected number; and

decreasing said selected threshold value if said highest number of received desired signals is below a second preselected number.

55. The method of claim 54, wherein said array performance value is a signal-to-noise ratio.

56. The method of claim 55, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.

57. A receiver, comprising:

a first antenna for forming a first output signal from received signals, said received signals including interfering signals and desired signals having a first circular polarization, said first antenna having said first circular polarization;

a second antenna for forming a second output signal from said received signals, said second antenna having a second circular polarization distinguishably different from said first circular polarization; and

a circuit connected to said first and second antennas for minimizing said interfering signals by selecting a first gain related to said interfering signals received at said first antenna and a second gain related to said interfering signals received at said second antenna, respectively, during a quiet time in which said interfering signals can be distinguished from said desired signals, said first and second gains selected to substantially reduce one or more of said interfering signals received at said first and second antennas, said circuit further for varying an initially selected first gain by a predetermined amount to derive alternative first gains, computing performance values for each alternative first gain at different predetermined directions of arrival of said desired signals, selecting the first gain from among said initially selected first gain and said alternative first gains that provides the highest number of array performance values over a selected threshold value, and then deriving complex weights corresponding to said selected first gain and second gain, applying said complex weights to said respective first and second output signal, and linearly combining said weighted first and second output signals to form a third output signal.

58. The receiver of claim 57, wherein said performance value is the ratio of a desired signal to the sum of said interfering signals and background noise.

59. The receiver of claim 57, wherein said circuit further comprises:

a circuit for increasing said selected threshold value if said highest number of performance values is above a first preselected number, and decreasing said selected threshold value if said highest number of performance values is below a second preselected number.

60. The receiver of claim 59, wherein said performance value is the ratio of a desired signal to the sum of said interfering signals and background noise.

61. The receiver of claim 57, wherein said circuit further comprises:

a circuit for measuring a performance value for each of said desired signals and selecting said first gain to substantially enhance said performance value for one or more of said received desired signals.

62. The receiver of claim 61, wherein said performance value is selected from the group comprising signal-to-noise ratio, amplitude, and bit error rate.

63. The receiver of claim 61, wherein said circuit further comprises:

a circuit for varying an initially selected first gain by a predetermined amount to derive alternative first gains, measuring the performance value for each said alternative first gain, and selecting the first gain from among said initially selected first gain and said alternative first gains that provides the highest number of array performance values over a selected threshold value.

64. The receiver of claim 63, wherein said performance value is the ratio of said desired signals to the sum of said interfering signals and background noise.

65. The receiver of claim 63, wherein said circuit further comprises:

a circuit for increasing said selected threshold value if said highest number of performance values is above a first preselected number, and decreasing said selected threshold value if said highest number of performance values is below a second preselected number.

66. The receiver of claim 65, wherein said performance value is the ratio of said desired signals to the sum of said interfering signals and background noise.

67. A receiver, comprising:

an antenna array comprising a plurality of first antennas for forming a first output signal from transmitted signals received during a quiet time in which interfering signals can be distinguished from desired signals, said received signals including at least said interfering signals, said desired signals having a first circular polarization and said antenna array comprising a plurality of first antennas having said first circular polarization;

a second antenna for forming a second output signal from said transmitted signals received during a quiet time in which said interfering signals can be distinguished from said desired signals, said second antenna having a second circular polarization distinguishably different from said first circular polarization; and

a circuit connected to said first and second antennas for minimizing said interfering signals by selecting an initial complex steering vector to substantially reduce the array gain in the direction of arrival of one or more of said interfering signals received at said first antenna over a predetermined range of directions, deriving an array gain pattern corresponding to said initial steering vector, varying each real value and each imaginary value of said initial steering vector by a predetermined amount to derive alternative steering vectors, computing an array performance value for each said alternative steering vector over said range of directions, selecting the gain pattern corresponding to the steering vector that provides array performance values over a selected threshold value for the highest number of directions of arrival, selecting a second gain for said second antenna to substantially reduce one or more of said interfering signals, and then deriving complex weights corresponding to said selected gain pattern and second gain, applying said complex weights to said respective first and second output signals, and linearly combining said weighted first and second output signals to form a third output signal for processing said desired signals.

68. The receiver of claim 67, wherein said array performance value is a signal-to-noise ratio.

69. The receiver of claim 67, wherein said circuit comprises:

a circuit for increasing said selected threshold value if said highest number of directions of arrival is above a first preselected number, and for decreasing said selected threshold value if said highest number of directions of arrival is below a second preselected number.

70. The receiver of claim 69, wherein said array performance value is a signal-to-noise ratio.

71. The receiver of claim 70, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.

72. The receiver of claim 67, wherein said circuit comprises:

a circuit for measuring a performance value for each received desired signal.

73. The receiver of claim 72, wherein said circuit for selecting said gain pattern comprises:

a circuit for selecting said gain pattern to substantially enhance the performance value of one or more of said received desired signals.

74. The receiver of claim 73, wherein said performance value is selected from the group of values comprising signal-to-noise ratio, amplitude, and bit error rate.

75. The receiver of claim 72, wherein said circuit for selecting said gain pattern further comprises:

a circuit for varying each real value and each imaginary value of an initially selected gain pattern by a predetermined amount to derive alternative gain patterns, measuring an array performance value for each received desired signal for each said alternative gain pattern, and selecting the gain pattern from among said initially selected gain pattern and said alternative gain patterns that provides array performance values over a selected threshold value for the highest number of received desired signals.

76. The receiver of claim 75, wherein said array performance value is a signal-to-noise ratio.

77. The receiver of claim 76, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.

78. The receiver of claim 75, wherein said circuit further comprises:

a circuit for increasing said selected threshold value if said highest number of received desired signals is above a first preselected number, and for decreasing said selected threshold value if said highest number of received desired signals is below a second preselected number.

79. The receiver of claim 78, wherein said array performance value is a signal-to-noise ratio.

80. The receiver of claim 79, wherein said array performance value is the ratio of said desired signal to the sum of said interfering signals and background noise.