SYSTEM AND METHOD FOR DETECTION AND DISCRIMINATION OF TARGETS IN THE PRESENCE OF INTERFERENCE

• US 20090027257A1
• Filed: 06/06/2006
• Published: 01/29/2009
• Est. Priority Date: 06/06/2005
• Status: Active Grant

• Current Assignee: Signal Labs Incorporated
• Original Assignee: Signal Labs Incorporated
• Inventors: Gumas, Donald Spyro, Arikan, Orhan
• Granted Patent: US 7,474,258 B1
• Time in Patent Office: Days
• US Class Current: 342/159
• CPC Class Codes: G01S 13/22 using irregular pulse repetition frequency G01S13/12 takes precedence
• CPC Class Codes: G01S 13/325 using transmission of coded signals, e.g. P.S.K. signals
• CPC Class Codes: G01S 13/52 Discriminating between fixed and moving objects or between objects moving at different speeds
• CPC Class Codes: G01S 13/723 by using numerical data
• CPC Class Codes: G01S 7/292 Extracting wanted echo-signals
• CPC Class Codes: G01S 7/295 Means for transforming co-ordinates or for evaluating data, e.g. using computers

Abstract

Systems and method of detection and discrimination of targets in the presence of interference are disclosed. A system transmits a signal and then receives signals including interference and reflections of transmitted signals. The system processes the received signals and transmitted signals to generate a 2D representation of the STAP cube with one of the dimensions collapsed. The system then reduces the interference contributions and identifies angle and Doppler component of potential targets. The system then computes slices, which are one dimensional representation of cross-ambiguity functions of the received and transmitted signals. It reduces the interference contributions in the slices and determines range components of the targets.

Claims

1. A method for detecting one or more targets comprising:

receiving signals including reflections of a from the one or more targets and interference;

computing one or more projections of cross-ambiguity functions of processed or unprocessed received signals and a reference signal;

processing the one or more computed projections to reduce interference contribution(s), wherein the processing comprises performing a mathematical operation on a value of the one or more computed projections, said value having angle-Doppler component coordinates;

determining an angle and a Doppler component for at least one target based on the processed computed projections; and

for the determined angle and Doppler component, determining a corresponding range component for the at least one target.

2. The method of claim 1, wherein the Doppler component is a Doppler shift.

3. The method of claim 1, wherein the Doppler component is a velocity.

4. The method of claim 1, wherein the range component is a time delay.

5. The method of claim 1, wherein the range component is a distance.

6. The method of claim 1, wherein the step of receiving is performed by multiple antenna elements.

7. The method of claim 1 further comprising the step of processing the received signals.

8. The method of claim 7, wherein the step of processing the received signals comprises multiplying the received signals by one or more complex quantities.

9. The method of claim 1, wherein interference is one or more of:

clutter, noise, and signals from electronic countermeasure.

10. The method of claim 1, wherein interference is a signal generated by an electronic device.

11. The method of claim 1, wherein the reference signal is modulated using one or more of:

continuous wave modulation, linear frequency modulation, pseudorandom number coded modulation, and frequency stepped COSTAS modulation.

12. The method of claim 11, wherein modulation type of the reference signal is selected adaptively.

13. The method of claim 1 further comprising the step of transmitting a signal.

14. The method of claim 1, wherein computing the one or more projections is based on the following equation:

P_φ

(u)=∫

|A_rs(u cos φ

−

v sin φ

, u sin φ

+v cosφ

)|²dv,

where A_rs(τ

, v) is the cross-ambiguity function evaluated at time delay τ and

Doppler shift v, φ

is the projection angle, v is the projection path, at an angle φ

with respect to the delay axis of the cross-ambiguity function, and u is projection axis, perpendicular to the projection path.

15. The method of claim 1 further comprising estimating interference contribution(s) in angle-Doppler component domain.

17. The method of claim 15, wherein the mathematical operation is subtraction and a subtrahend is based on a value of estimated interference contribution(s) for the angle-Doppler component coordinates.

18. The method of claim 15, wherein the mathematical operation is division and a divisor is based on a value of estimate interference contribution(s) for the angle-Doppler component coordinates.

19. The method of claim 1, wherein the interference contribution(s) are previously known.

20. The method of claim 15, wherein estimating interference contribution(s) is based on prior knowledge.

21. The method of claim 20, wherein modulation of the reference signal is orthogonal to at least some interference.

22. The method of claim 1, wherein the step of determining the angle and the Doppler component comprises comparing values of the processed computed projections to a threshold.

23. The method of claim 22, wherein the step of determining the angle and the Doppler component further comprises detecting one or more peaks of the processed computed projections.

24. The method of claim 1, wherein determining the corresponding range component comprises computing a slice of the cross-ambiguity function of the processed or unprocessed received signals and the reference signal.

25. The method of claim 24, wherein the slice is computed through cross-ambiguity function associated with the determined angle and at the determined Doppler component.

26. The method of claim 24, wherein computing the one or more slices is based on the following equation:

A_rs(τ

₀+λ

sin φ

, v₀+λ

cos φ

)=∫

{circumflex over (r)}<sub>2φ

/π</sub>

(μ

)ŝ

*<sub>2φ

/π</sub>

(μ

)exp[j2π

μ

]dμ

,

where τ

₀ is the starting delay time of the slice, v₀ is the starting Doppler shift of the slice, λ

is the distance of the computed slice sample from the starting point, φ

is the angle of the slice, and where {circumflex over (r)}(t)=r(t+τ

₀/2)exp[jπ

v₀t] and ŝ

(t)=r(t−

τ

₀/2)exp[jπ

v₀t] are the fractional Fourier transforms of the shifted and modulated received and reference radar waveforms, and where X<sub>2φ

/π</sub>

(t)=∫

K<sub>2φ

/π</sub>

(t,t′

)×

(t′

)dt′

defines the fractional Fourier transformation and where φ

is the transformation angle K<sub>2φ

/π</sub>

is the transformation kernel defined as K<sub>2φ

/π</sub>

(t,t′

)=k_φ

exp[jπ

(t²cotφ

−

2tt′

cscφ

+t′

²cotφ

] with complex scaling k_φ

defined as

$k_{\mathrm{\phi <br><br>}}=\frac{\exp <br><br>\left\{\mathrm{j\phi <br><br>}/2-\mathrm{\pi <br><br>}/4<br><br>\mathrm{sgn}<br><br><br><br>\mathrm{\phi <br><br>}\right\}}{\sqrt{<br><br>\sin <br><br><br><br>\mathrm{\phi <br><br>}<br><br>}}.$

27. The method of claim 24 further comprising processing the computed slice to reduce interference contribution(s).

28. The method of claim 27 further comprising estimating interference contribution(s) in a range component domain.

29. The method of claim 28, wherein processing the computed slice comprises performing a mathematical operation on a value of the computed slice, said value associated with a range component coordinate.

30. The method of claim 29, wherein the mathematical operation is subtraction and a subtrahend is based on a value of estimated interference contribution(s) for the range component coordinate.

31. The method of claim 29, wherein the mathematical operation is division and a divisor is based on a value of estimated interference contribution(s) for the range component coordinates.

32. The method of claim 27, wherein the interference contribution(s) are previously known.

33. The method of claim 32, wherein estimating interference contribution(s) is based on prior knowledge.

34. The method of claim 27, wherein the step of determining the range component comprises comparing values of the processed computed slice to a threshold.

35. The method of claim 34, wherein the step of determining the range component further comprises detecting one or more peaks of the processed computed slice.

36. The method of claim 1 further comprising generating a target report based on the one or more angles, one or more Doppler components, and one or more range components at which the one or more targets are present.

84. The method of claim 13, wherein the transmitted signal is the reference signal.

16. (canceled)

37. A system for detecting one or more targets comprising:

a receiver operable to receive signals including reflections from the one or more targets and interference; and

a signal processor comprising;

a projection computation module operable to compute one or more projections of cross ambiguity functions corresponding to processed or unprocessed received signals and a reference signal,

a projection target estimation module operable to process the one or more computed projections to reduce interference contributions(s) in the one or more computed projections,

a projection threshold comparator operable to determine an angle and a Doppler component of at least one target based on the processed one or more projections, and

a slice threshold comparator operable to determine a corresponding range component for the at least one target corresponding to the determined angle and Doppler component.

38. The system of claim 37, wherein the receiver comprises multiple antenna elements.

39. The system of claim 37, wherein the interference is one or more of:

clutter, noise, and signals from electronic countermeasures.

40. The system of claim 37, wherein the interference is generated by an electronic device.

41. The system of claim 37 further comprising a transmitter operable to transmit a modulated signal.

42. The system of claim 85 further comprising a waveform generator operable to generate waveforms of the transmitted signal.

43. The system of claim 42, wherein the waveform generator is operable to generate the waveforms with one or more modulation types:

continuous wave modulation, linear frequency modulation, pseudorandom number coded modulation, and frequency stepped COSTAS modulation.

44. The system of claim 43, wherein a type of modulation of the generated waveform is selected adaptively.

45. The system of claim 42, wherein a modulation of the transmitted signal is orthogonal to at least some interference.

46. The system of claim 37, wherein the signal processor further comprises a interference projection estimation module operable to estimate interference in an angle-Doppler component domain.

47. The system of claim 46, wherein the signal processor further comprises an interference projection normalization module operable to perform a mathematical operation on values of the estimated interference in the angle-Doppler component domain.

48. The system of claim 37, wherein the signal processor further comprises a slice computation module operable to compute a slice of a cross ambiguity surface.

49. The system of claim 48, wherein the signal processor further comprises a interference slice estimation module operable to estimate interference in a range component domain.

50. The system of claim 49, wherein the signal processor further comprising a slice target estimation module operable to process the computed slice to reduce interference contributions(s) in the slice.

51. The system of claim 37 further comprising a reporting module operable to generate a report comprising one or more of:

the determined angle, the determined Doppler component, and the determined range component.

52. The system of claim 51 further comprising a tracker operable to compute trajectories of the detected targets.

53. The system of claim 37 further comprising one or more memories operable to store instructions executed by the signal processor.

54. The system of claim 37 further comprising one or more memories operable to store results of intermediate computations of the signal processor.

55. The system of claim 37, wherein the projection computation module, the projection target estimation module, the projection threshold comparator, and the slice threshold comparator are at different processors.

56. The system of claim 37, wherein the projection computation module, the projection target estimation module, the projection threshold comparator, and the slice threshold comparator are at a single processor.

85. The system of claim 41, wherein the transmitted modulated signal is the reference signal.

57. A machine readable medium having stored thereon data representing sequences of instructions, which when executed by a computer system cause the computer system to perform the steps of:

computing one or more projections of cross-ambiguity functions of (1) processed or unprocessed received signals that include reflections from one or more targets and interference, and (2) a reference signal;

processing the one or more computed projections to reduce interference contribution(s), wherein the processing comprises performing a mathematical operation on a value of the one or more computed projections, said value having angle-Doppler component coordinates;

determining an angle and a Doppler component for at least one target based on the processed computed projections; and

for the determined angle and Doppler component, determining a corresponding range component for the at least one target.

58. The machine readable medium of claim 57 further having stored thereon data representing sequences of instructions, which when executed by the computer system cause the computer system to perform the step of processing the received signals.

59. The machine readable medium of claim 58 further having stored thereon data representing sequences of instructions, which when executed by the computer system causes the computer system to perform the step of processing the received signals by multiplying the signals by one or more complex quantities.

60. The machine readable medium of claim 58, wherein interference is one or more of:

clutter, noise, and signals from electronic countermeasure.

61. The machine readable medium of claim 58 further having stored thereon data representing sequences of instructions, which when executed by the computer system causes the computer system to perform the step of generating a waveform of the reference signal.

62. The machine readable medium of claim 58 further having stored thereon data representing sequences of instructions, which when executed by the computer system causes the computer system to perform the step of selecting a modulation type of the waveform.

63. The machine readable medium of claim 61, wherein the execution of the step of computing the one or more projections is based on the following equation:

P_φ

(u)=∫

|A_rs(u cos φ

−

v sin φ

, u sin φ

+v cos®

)|²dv,

where A_rs(τ

, v) is the cross-ambiguity function evaluated at time delay τ and

Doppler shift v, φ

is the projection angle, v is the projection path, at an angle φ

with respect to the delay axis of the cross-ambiguity function, and u is projection axis, perpendicular to the projection path.

64. The machine readable medium of claim 58 further having stored thereon data representing sequences of instructions, which when executed by the computer system causes the computer system to perform the step of estimating interference contribution(s) in angle-Doppler component domain.

66. The machine readable medium of claim 57, wherein the mathematical operation is subtraction and a subtrahend is based on a value of estimated interference contribution(s) for the angle-Doppler component coordinates.

67. The machine readable medium of claim 57, wherein the mathematical operation is division and a divisor is based on a value of estimate interference contribution(s) for the angle-Doppler component coordinates.

68. The machine readable medium of claim 64, wherein instructions causing the computer to perform the step of estimating interference contribution(s) use prior knowledge.

69. The machine readable medium of claim 62, wherein the modulation of the waveform is orthogonal to at least some interference.

70. The machine readable medium of claim 57, wherein instructions, which when executed by the computer system causing the computer system to perform the step of determining the angle and the Doppler component comprise instructions which when executed by the computer system cause the computer system to perform the step of comparing values of the processed computed projections to a threshold.

71. The machine readable medium of claim 70, wherein instructions, which when executed by the computer system causing the computer system to perform the step of determining the angle and the Doppler component comprise instructions which when executed by the computer system cause the computer system to perform the step of detecting one or more peaks of the processed computed projections.

72. The machine readable medium of claim 70, wherein instructions, which when executed by the computer system cause the computer system to perform the step of determining the corresponding range component comprise instructions, which when executed by the computer system cause the computer system to perform the step of computing a slice of the cross-ambiguity functions of to the processed or unprocessed received signals and the reference signal.

73. The machine readable medium of claim 72, wherein instructions cause the computer to compute the slice through cross-ambiguity function associated with the determined angle and at the determined Doppler component.

74. The machine readable medium of claim 73, wherein the execution of the step of computing the slice is based on the following equation:

A_rs(τ

₀+λ

sin φ

, v₀+λ

cos φ

)=∫

{circumflex over (r)}<sub>2φ

/π</sub>

(μ

)ŝ

*<sub>2φ

/π</sub>

(μ

)exp[j2π

μ

]dμ

,

where τ

₀ is the starting delay time of the slice, v₀ is the starting Doppler shift of the slice, λ

is the distance of the computed slice sample from the starting point, φ

is the angle of the slice, and where {circumflex over (r)}(t)=r(t+τ

₀/2)exp[jπ

v₀t] and ŝ

(t)=r(t−

τ

₀/2)exp[jπ

v₀t] are the fractional Fourier transforms of the shifted and modulated received and reference radar waveforms, and where X<sub>2φ

/π</sub>

(t)=∫

K<sub>2φ

/π</sub>

(t,t′

)×

(t′

)dt′

defines the fractional Fourier transformation and where φ

is the transformation angle K<sub>2φ

/π</sub>

is the transformation kernel defined as K<sub>2φ

/π</sub>

(t,t′

)=k_φ

exp [jπ

(t²cotφ

−

2tt′

cscφ

+t′

²cotφ

] with complex scaling k_φ

defined as

$k_{\mathrm{\phi <br><br>}}=\frac{\exp <br><br>\left\{\mathrm{j\phi <br><br>}/2-\mathrm{\pi <br><br>}/4<br><br>\mathrm{sgn}<br><br><br><br>\mathrm{\phi <br><br>}\right\}}{\sqrt{<br><br>\sin <br><br><br><br>\mathrm{\phi <br><br>}<br><br>}}.$

75. The machine readable medium of claim 72 further having stored thereon data representing sequences of instructions, which when executed by the computer system cause the computer system to perform the step of processing the computed slice to reduce interference contribution(s).

76. The machine readable medium of claim 75 further having stored thereon data representing sequences of instructions, which when executed by the computer system cause the computer system to perform the step of estimating interference contribution(s) in a range component domain.

77. The machine readable medium of claim 76, wherein instructions, which when executed by the computer system cause the computer system to perform the step of processing the computed slice comprise instructions causing the computer system to perform a mathematical operation on a value of the computed slice, said value associated with a range component coordinate.

78. The machine readable medium of claim 77, wherein the mathematical operation is subtraction and a subtrahend is based on a value of estimated interference contribution(s) for the range component coordinate.

79. The machine readable medium of claim 77, wherein the mathematical operation is division and a divisor is based on a value of estimated interference contribution(s) for the range component coordinates.

80. The machine readable medium of claim 76, wherein instructions causing the computer to perform the step of estimating interference contribution(s) use prior knowledge.

81. The machine readable medium of claim 76, wherein instructions, which when executed by the computer system cause the computer system to perform the step of determining the range component comprise instructions causing the computer system to perform the step of comparing values of the processed computed slice to a threshold.

82. The machine readable medium of claim 81, wherein instructions, which when executed by the computer system cause the computer system to perform the step of determining the range component further comprise instructions causing the computer system to perform the step of detecting one or more peaks of the processed computed slice.

83. The machine readable medium of claim 57 having further stored thereon data representing sequences of instructions, which when executed by a computer system cause the computer system to perform the step of generating a target report based on the one or more angles, one or more Doppler components, and one or more range components at which the one or more targets are present.

65. (canceled)