Passive tracking system and method

• US 6,618,010 B2
• Filed: 11/14/2001
• Issued: 09/09/2003
• Est. Priority Date: 11/14/2001
• Status: Expired due to Fees

• Current Assignee: Administrator of The National Aeronautics and Space Administration, National Aeronautics and Space Administration US Government As Represented By The Administrator of The, US Government As Represented By The Director National Security Agency
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Ngo, Phong H., Bourgeois, Brian A., Hill, Brent W., Phan, Chau T., Chen, Henry A., Dusl, John, Arndt, G. Dickey
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): MULL, FRED H
• Application Number:
  US09/994,989
• Publication Number:
  US 20030103004A1
• Time in Patent Office: 664 Days
• Field of Search: 342/465, 342/463, 342/423, 342/442, 342/368
• US Class Current: 342/465
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G01S 5/0205 Details
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop

Abstract

System and methods are disclosed for passively determining the location of a moveable transmitter utilizing a pair of phase shifts at a receiver for extracting a direction vector from a receiver to the transmitter. In a preferred embodiment, a phase difference between the transmitter and receiver is extracted utilizing a noncoherent demodulator in the receiver. The receiver includes an antenna array with three antenna elements, which preferably are patch antenna elements spaced apart by one-half wavelength. Three receiver channels are preferably utilized for simultaneously processing the received signal from each of the three antenna elements. Multipath transmission paths for each of the three receiver channels are indexed so that comparisons of the same multipath component are made for each of the three receiver channels. The phase difference for each received signal is determined by comparing only the magnitudes of received and stored modulation signals to determine a winning modulation symbol.

Claims

1. A passive system for locating a transmitter, said transmitter having a transmitter frequency, said transmitter producing a transmitter signal, said system comprising:

at least one antenna array having a first antenna element, a second antenna element and a third antenna element, said first antenna element being operable for receiving a first received signal from said transmitter, said second antenna element being operable for receiving a second received signal from said transmitter, and said third antenna being operable for receiving a third signal from said transmitter; and

electronic circuitry for said antenna array to determine a first phase difference Φ

₁ and a second phase difference Φ

₂ between said first received signal, said second received signal, and said third received signal, said electronic circuitry being operable for utilizing said first phase difference and said second phase difference for determining location information using the equations $\mathrm{\phi <br><br>}=\arctan <br><br>\left(\frac{{\mathrm{\Phi <br><br>}}_2}{{\mathrm{\Phi <br><br>}}_1}\right)$

and $\mathrm{\theta <br><br>}=\arcsin \left(\frac{\sqrt{{\mathrm{\Phi <br><br>}}_1^2+{\mathrm{\Phi <br><br>}}_2^2}}{\mathrm{\pi <br><br>}}\right)$

which are related to a vector (sin θ

cos Φ

, sin θ

sin Φ

, cos θ

) oriented in a direction of said transmitter with respect to said at least one antenna array.

2. The passive system of claim 1, further comprising:

said second antenna element being spaced apart from said first antenna element by one-half wavelength or integer multiple thereof and said third antenna element being spaced apart from said first antenna element by one-half wavelength or integer multiple thereof.

3. The passive system of claim 1, wherein said at least one antenna array comprises only three antenna elements consisting of said first antenna element, said second antenna element, and said third antenna element.

4. The passive system of claim 1, further comprising a geometrical configuration of said first antenna element, said second antenna element, and said third antenna element such that a first leg between said first antenna element and said second antenna element and a second leg between said first antenna element and said third antenna element have a first angle therebetween less than one hundred eighty degrees.

5. The passive system of claim 4, wherein said first angle is ninety degrees.

6. The passive system of claim 1, wherein said first antenna element, said second antenna element, and said third antenna element each comprise a microstrip patch antenna.

7. The passive system of claim 1, wherein said electronic circuitry further comprises:

a local oscillator, said local oscillator being frequency locked with respect to said transmitter frequency but not being phase locked with respect to said transmitter frequency.

8. The passive system of claim 1, wherein said electronic circuitry is operable for determining said first phase difference between said first received signal and said second received signal, and said electronic circuitry is operable for determining said second phase difference between said first received signal and said third received signal.

9. The passive system of claim 1, wherein said electronic circuitry further comprises:

a spread spectrum receiver with a first receiver channel for processing said first received signal from said first antenna element, a second receiver channel for processing said second received signal from said second antenna element, and a third receiver channel for processing said third received signal from said third antenna element.

10. The passive system of claim 9, wherein said electronic circuitry comprises:

a first finger for said first receiver channel, a second finger for said second receiver channel, and a third finger for said third receiver channel, each of said first finger, said second finger, and said third finger being operable for performing a Fast Walsh Transform to determine a winning Walsh symbol based on magnitude and not phase of a Walsh vector.

11. A method for passively detecting the location of a transmitter, said transmitter being operable for transmitting a transmitter signal, said transmitter having a transmitter frequency, said method comprising:

receiving said transmitter signal with a first antenna array comprising a first antenna element that produces a first received signal, a second antenna element that produces a second received signal, and a third antenna element that produces a third received antenna signal;

determining a first phase difference and a second phase difference between said first received signal, said second received signal, and said third received signal; and

utilizing said first phase difference Φ

₁ and said second phase difference Φ

₂ to determine location information using the equations $\mathrm{\phi <br><br>}=\arctan <br><br>\left(\frac{{\mathrm{\Phi <br><br>}}_2}{{\mathrm{\Phi <br><br>}}_1}\right)$

and $\mathrm{\theta <br><br>}=\arcsin \left(\frac{\sqrt{{\mathrm{\Phi <br><br>}}_1^2+{\mathrm{\Phi <br><br>}}_2^2}}{\mathrm{\pi <br><br>}}\right)$

which are related to a first vector (sin θ

cos Φ

, sin θ

sin Φ

, cos θ

) oriented in a direction of said transmitter with respect to said first antenna array.

12. The method of claim 11, further comprising:

receiving said transmitter signal with a second antenna array spaced from said first antenna array by a known distance, said second antenna array comprising a fourth antenna element that produces a fourth received signal, a fifth antenna element that produces a fifth received signal, and a sixth antenna element that produces a sixth received antenna signal;

determining a third phase difference and a fourth phase difference between said fourth received signal, said fifth received signal, and said sixth received signal; and

utilizing said third phase difference and said fourth phase difference to determine additional location information related to a second vector oriented in a second direction of said transmitter with respect to said second antenna array.

13. The method of claim 12, further comprising utilizing an orientation of said first vector and an orientation of said second vector for locating said transmitter.

14. The method of claim 12, further comprising providing a local oscillator which is frequency locked with respect to said transmitter frequency but not phase locked with respect to said transmitter frequency.

15. The method of claim 14, further comprising processing said first received signal, and said second received signal, and said third received signal in a spread spectrum receiver.

16. The method of claim 15, further comprising downconverting and despreading said first received signal, said second received signal and said third received signal in said spread spectrum receiver.

17. The method of claim 16, further comprising tracking multiple transmitter paths of said first received signal, said second received signal, and said third received signal.

18. The method of claim 17, further comprising separately time multiplexing said multiple transmitter paths for each of said first received signal, said second received signal, and said third received signal.

19. The method of claim 18, further comprising indexing multipath components for said first received signal, said second received signal, and said third received signal with respect to timing of a locally generated PN sequence.

20. The method of claim 19, further comprising comparing an indexed multipath signal of said first received signal to a corresponding indexed multipath signal of said second received signal and a corresponding indexed multipath signal of said third received signal to produce a multipath comparison.

21. The method of claim 20, further comprising utilizing said multipath comparison to determine said first phase difference and said second phase difference.

22. The method of claim 16, further comprising storing a plurality of modulation symbols, and performing a Fast Walsh Transform on said plurality of modulation symbols to determine a winning symbol.

23. The method of claim 22, further comprising comparing said winning signal to said plurality of symbols to determine a signal to noise ratio.

24. The method of claim 23, further comprising utilizing said signal to noise ratio to determine whether a local PN-generator is aligned with respect to said transmitted signal.

25. A method for passively detecting the location of a transmitter, said transmitter being operable for transmitting a transmitter signal, said transmitter having a transmitter frequency, said method comprising:

providing a noncoherent receiver whereby a local oscillator is frequency locked with respect to said transmitter frequency but is not phase locked with respect to said transmitter frequency;

determining a first phase difference between said transmitter and said noncoherent receiver; and

utilizing said first phase difference to produce location information related to a vector which is oriented in a direction of said transmitter.

26. The method of claim 25, further comprising providing that said receiver is a spread spectrum receiver operable for orthogonal symbol modulation.

27. The method of claim 26, further comprising detecting bits at any arbitrary angle between the transmitter and receiver.

28. The method of claim 27, further comprising obtaining a plurality of modulation symbols, and selecting a winning modulation symbol from said plurality of modulation symbols based solely on respective magnitudes related to said plurality of modulation symbols.

29. The method of claim 28, further comprising utilizing a phase related to said winning modulation symbol to represent said phase difference between said transmitter and said noncoherent receiver.

30. The method of claim 29, further comprising utilizing an antenna array having a first antenna element, a second antenna element, and a third antenna element.

31. The method of claim 30, further comprising wherein said second antenna element is spaced from said first antenna element by a distance of an integer multiple of one-half wave length of said transmitter signal, and said third antenna element is spaced from said first antenna element by an integer multiple of one-half wavelength of said transmitter signal.

32. A method for detecting the location of a transmitter, said transmitter being operable for transmitting a transmitter signal, said transmitter having a transmitter frequency, said transmitter sending a transmitted PN code signal, said method comprising:

receiving a plurality of modulation symbols with a receiver;

determining a magnitude and phase related to each of said modulation symbols;

comparing said plurality of modulation symbols with respect only to said magnitude to determine a winning modulation symbol from said plurality of modulation symbols; and

utilizing a phase of said winning modulation symbol for representing a relative phase between said transmitter and said receiver.

33. The method of claim 32, further comprising producing a local PN code signal which corresponds to said transmitted PN code signal of said transmitter, producing a floor from said magnitude of said plurality of modulation symbols, comparing said floor with a magnitude of said winning symbol to produce a value related to signal to noise, utilizing said value to determine if said local PN signal is aligned with said transmitted PN code signal of said transmitter.

34. The method of claim 33, further comprising if said value is outside of a desired range, then shifting said local PN signal for alignment with said transmitted PN code signal.

35. The method of claim 33, further comprising if said value is within a desired range, then utilizing said phase of said winning symbol to determine early and late modulation symbols.

36. The method of claim 35, further comprising comparing said early and late modulation symbols to previously stored early and late modulation signals.

37. The method of claim 36, further comprising utilizing three antenna elements for said receiver to provide a first received signal, a second received signal, and a third received signal.

38. The method of claim 37, further comprising tracking multiple transmitter paths of said first received signal, said second received signal, and said third received signal.

39. The method of claim 38, further comprising indexing said multiple transmitter paths for said first received signal, said second received signal, and said third received signal with respect to said local PN signal.

40. The method of claim 39, further comprising comparing an indexed multipath signal of said first received signal to a corresponding indexed multipath signal of said second received signal and of said third received signal to produce a multipath comparison.

41. The method of claim 40, further comprising utilizing said multipath comparison to determine said relative phase between said transmitter and said receiver for each of said first received signal, said second received signal, and said third received signal.

42. The method of claim 40, further comprising determining location information related to a vector oriented in a direction of said transmitter utilizing said relative phase between said transmitter and said receiver for each of said first received signal, said second received signal, and said third received signal.

43. A method for determining a phase between a spread spectrum transmitter and spread spectrum receiver, said method comprising:

receiving a plurality of modulation symbols with said receiver;

determining a magnitude and phase related to each of said modulation symbols;

comparing said plurality of modulation symbols with respect only to said magnitude to determine a winning modulation symbol from said plurality of modulation symbols; and

utilizing a phase of winning symbol for representing a relative phase between said transmitter and said receiver.

44. A method for a passive system operable for determining location characteristics of a plurality of moveable transmitters, each of said plurality of moveable transmitters producing a transmitter signal, said plurality of moveable transmitters having a transmitter frequency, said system comprising:

providing a plurality of receivers spaced apart wherein each of said plurality of moveable transmitters is receivable by at least one of said plurality of receivers;

providing each receiver with an antenna array having three separate antenna elements;

determining two transmitter signal phase shifts (Φ

₁ and Φ

₂) at said three separate antenna elements with respect to a first moveable transmitter and a first receiver; and

utilizing said two transmitter signal phase shifts to determine information using the equations $\mathrm{\phi <br><br>}=\arctan <br><br>\left(\frac{{\mathrm{\Phi <br><br>}}_2}{{\mathrm{\Phi <br><br>}}_1}\right)$

and $\mathrm{\theta <br><br>}=\arcsin \left(\frac{\sqrt{{\mathrm{\Phi <br><br>}}_1^2+{\mathrm{\Phi <br><br>}}_2^2}}{\mathrm{\pi <br><br>}}\right)$

which are related to a vector (sin θ

cos Φ

, sin θ

sin Φ

, cos θ

) oriented in a first direction of said first moveable transmitter with respect to said first receiver.

45. The system of claim 44, further comprising utilizing a receiver generated PN signal to determine a distance from said first receiver to said first moveable transmitter, and utilizing said distance with said information related to said first direction to determine a position of said first moveable transmitter.

46. The system of claim 44, further comprising determining a second of two transmitter signal phase shifts at a second of said three separate antenna elements with respect to said first moveable transmitter and a second receiver, utilizing said second of two transmitter signal phase shifts to determine information related to a second direction of said first moveable transmitter with respect to said second receiver, and utilizing said information related to first direction and said second direction to determine a position of said first moveable transmitter.

47. The system of claim 44, further comprising obtaining a possible path of travel of said first moveable transmitter, and utilizing said first direction and said possible path of travel for determining a position of said first moveable transmitter.

48. The system of claim 44, further comprising displaying a position of one or more of said plurality of moveable transmitters on a map.

49. The system of claim 48, further comprising displaying said map in a vehicle to which said moveable transmitter is affixed.

50. The system of claim 44, wherein each of said plurality of receivers comprises a noncoherent receiver.

51. A method for modifying an existing communication system comprising a plurality of moveable transceivers and a plurality of affixed transceivers to provide location information related to said plurality of moveable transceivers, said existing communication system being operable for transmitting a data modulated signal via an electromagnetic wave from said plurality of moveable transceivers to said plurality of affixed transceivers, said electromagnetic wave having a wavelength and a transmitter frequency, said method comprising:

mounting an antenna array at each of said affixed transceivers, each antenna array having three antenna elements spaced apart by an integer times one-half of said wavelength, said three antenna elements being operable for producing a first received data modulated signal, a second received data modulated signal, and a third received data modulated signal in response to said data modulated signal from a first moveable transceiver of said plurality of moveable transceivers;

providing a receiver with each antenna array for receiving said data modulated signal from said first of said plurality of moveable transceivers, said receiver being operable for measuring a first phase difference Φ

₁ and a second phase difference Φ

₂ between said first received data modulated signal, said second received data modulated signal, and said third received data modulated signal;

determining information using the equations $\mathrm{\phi <br><br>}=\arctan <br><br>\left(\frac{{\mathrm{\Phi <br><br>}}_2}{{\mathrm{\Phi <br><br>}}_1}\right)$

and $\mathrm{\theta <br><br>}=\arcsin \left(\frac{\sqrt{{\mathrm{\Phi <br><br>}}_1^2+{\mathrm{\Phi <br><br>}}_2^2}}{\mathrm{\pi <br><br>}}\right)$

which are related to a vector (sin θ

cos Φ

, sin θ

sin Φ

, cos θ

) oriented in a first direction of said first moveable transceiver from said first phase difference and said second phase difference; and

utilizing said information related to said first direction for determining a first location of said first moveable transceiver.

52. The method of claim 51, further comprising utilizing a second receiver for producing information related to a second direction of said first moveable transmitter with respect to said second receiver, and determining said first location of said first moveable transceiver by utilizing said information related to first direction and said second direction.

53. The method of claim 51, further comprising determining a distance from said receiver to said first moveable transceiver, and determining said first location of said first moveable transceiver by utilizing said first direction and said distance.

54. The method of claim 51, wherein said first received data modulated signal, said second received data modulated signal, and said third received data modulated signal each comprise multipath signals, providing circuitry in said receiver for tracking said multipath signals such that said first phase difference and said second phase difference are determined from respective multipath signals received by said three antenna elements.

55. The method of claim 51, wherein said step of providing a receiver further comprises providing a noncoherent receiver such that a local oscillator of said receiver has a local oscillator frequency which is frequency locked with respect to said transmitter frequency but which is not phase locked with respect to said transmitter frequency.