Method and apparatus for geolocating a wireless communications device

• US 20030176196A1
• Filed: 11/12/2002
• Published: 09/18/2003
• Est. Priority Date: 03/18/2002
• Status: Active Grant

• Current Assignee: Christopher J. Hall, Clay S. Turner, Jimmy C. Ray
• Original Assignee: Christopher J. Hall, Clay S. Turner, Jimmy C. Ray
• Inventors: Hall, Christopher J., Ray, Jimmy C., Turner, Clay S.
• Granted Patent: US 6,891,500 B2
• Time in Patent Office: Days
• US Class Current: 455/456.1
• CPC Class Codes: G01S 5/0205 Details
• 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: H04M 2207/18 wireless networks
• CPC Class Codes: H04M 2242/30 Determination of the location of a subscriber
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

The time difference of arrival for a signal received at two or more receiving sites as transmitted from a wireless communications device, is determined by a frequency domain technique. The constituent frequencies of the signals received at the two or more receiving sites are determined, including the phase, or a value representative of the phase, of each frequency component. The phase values for the same frequency are subtracted to yield a phase difference values as a function of frequency. The slope of the function represents the time difference of arrival for the wireless communications device signal as received at the two receiving sites. To determine the mobile location based on the determined time difference of arrival values, a seed or initial location is first assumed for the wireless communications device and the distance difference of arrival (the time difference of arrival multiplied by the speed of light) is calculated. The calculated time difference of arrival is then used to adjust the distance difference of arrival by continuously iterating the position of the wireless communications device until the calculated distance of arrival and the calculated time difference of arrival (as multiplied by the speed of light) are within a predetermined margin.

Claims

1. For a transmitting unit transmitting a signal, a method for determining the time difference of arrival of the signal received at two or more receiving sites, said method comprising:

(a) for the signal received at the two or more receiving sites, determining a frequency domain representation of the signal, wherein the frequency domain representation comprises a two dimensional number for each of a plurality of frequencies; and

(b) determining the time difference of arrival using the two-dimensional numbers for like-frequency component pairs from at least two frequency domain representations.

2. The method of claim 1 wherein the transmitting unit is selected from among a mobile communications device, a portable communications device, a personal communications device, a cellular communications device, a push-to-talk communications device and a trunked radio.

3. The method of claim 1 wherein the plurality of receiving sites comprises N receiving sites, and wherein the time difference of arrival is determined pairwise among N receiving sites.

4. The method of claim 1 wherein the step (a) further comprises determining the frequency domain representation of the time domain signal using a transformation process that relates the time and frequency duality of a signal.

5. The method of claim 1 wherein the step (a) further comprises determining the frequency domain representation of the time domain signal using a process selected from among, a Fourier transform integral, a fast Fourier transform algorithm, a discrete Fourier transform, a Hartley transform, a Hilbert transform and a Laplace transform.

6. The method of claim 1 further comprising a step (c) determining the location of the transmitting unit from the determined time difference of arrival.

7. The method of claim 6 wherein the two-dimensional number comprises a phase and a magnitude, and wherein the step (c) further comprises generating a phase angle versus like-frequency function and determining the location from the slope of the function.

8. The method of claim 7 wherein the step (c) further comprises utilizing a regression analysis or a weighted regression analysis to determine the slope of the phase angle versus like-frequency function.

9. The method of claim 7 wherein the y-intercept of the phase angle versus like-frequency function represents the frequency offset between the signal received by at least two of the plurality of receiving sites.

10. The method of claim 9 wherein each receiving site comprises signal receiving apparatuses and further comprising a step (d) retuning the signal receiving device at the receiving sites to reduce the frequency offset.

11. The method of claim 9 further comprising, for a plurality of transmitting units, determining the transmitting unit of interest using radio frequency signature parameters including frequency offset.

12. The method of claim 1 wherein the transmitting unit comprises a cellular telephone and the two or more receiving sites comprise two or more cellular base stations.

13. The method of claim 1 wherein the transmitting unit comprises a cellular telephone and the two or more receiving sites are selected from among two or more cellular base stations, two or more cellular monitoring stations, and a combination of cellular base stations and cellular monitoring stations.

14. The method of claim 1 wherein the time domain signal is selected from among a cell access attempt signal, a response to an incoming call, a registration signal, a control channel signal and a call requesting the dispatch of emergency or other position-relevant services.

15. The method of claim 1 wherein the step (a) further comprises determining the signal arrival time at the one or more receiving sites relative to a common time reference and determining an identification of the transmitting unit.

16. The method of claim 1 wherein the step (a) is executed at each of the two or more receiving sites.

17. The method of claim 1 wherein the frequency domain representation is provided from each of the two or more receiving sites to a processing site, and wherein the step (b) is executed at the processing site.

18. The method of claim 17 wherein the frequency domain representation is provided to the processing site over a narrow bandwidth transmission medium.

19. The method of claim 17 wherein at the processing site the time difference of arrival is used for determining the location of the transmitting unit, and wherein the location is provided by the processing site.

20. The method of claim 1 wherein the two-dimensional number comprises a magnitude and a phase, and wherein the step (a) further comprises determining the difference in phase angles by forming the Hermetian product for each like-frequency component.

21. The method of claim 20 wherein the result of forming the Hermetian product is a vector comprising a plurality of elements, and wherein each element comprises a value representing the phase angle difference for a like-frequency component.

22. The method of claim 21 wherein the number of vectors is less than or equal to the number of pairwise combinations of receiving sites.

23. The method of claim 22 wherein the step (a) further comprises determining the pairwise phase angle difference for the like-frequency components in at least two vectors.

24. The method of claim 1 wherein the same time domain signal is received at the two or more receiving sites, further comprising sampling the time domain signal and providing the sampled time domain signal to a processing site, wherein the steps (a) and (b) are executed at the processing site.

25. The method of claim 1 wherein the time domain signal has a known format, and wherein the time difference of arrival as determined for the time domain signal received at the two or more receiving sites is based on a reference point within the known format.

26. The method of claim 1 further comprising:

(c) determining an estimated location of the transmitting unit from the time difference of arrival;

(d) determining the actual location of the transmitting unit relative; and

(e) determining the difference between the estimated location and the actual location.

27. The method of claim 1 wherein the step (a) further comprises filtering the frequency domain representation to control the effect of certain frequency domain components on the time difference of arrival determination.

28. The method of claim 27 wherein the step of filtering further comprises determining a signal quality metric for the frequency domain components, determining a signal quality metric threshold, and removing the frequency components having a signal quality metric below the signal quality metric threshold.

29. The method of claim 27 wherein the step of filtering further comprises determining a signal quality metric for frequency domain components and weighting the like-frequency components in accordance with the signal quality metric.

30. The method of claim 1 wherein the two-dimensional number is selected from among a magnitude and a phase value, and a real and an imaginary part of a complex number.

31. The method of claim 1 wherein the two-dimensional number represents the phase angle associated with each of the plurality of frequencies.

32. The method of claim 31 wherein the step (a) further comprises determining the difference in the phase angles for like-frequency component pairs in two of the two or more frequency domain representations.

34. The method of claim 30 wherein the step (c) further comprises determining the derivative of the phase function with respect to frequency, wherein the time difference of arrival is determined from the derivative.

35. The method of claim 34 wherein the step (c) further comprises determining the time difference of arrival by performing a linear regression operation on the derivative of the phase function.

36. The method of claim 35 wherein the linear regression operation further comprises a weighted linear regression operation.

33. For a transmitting unit transmitting a signal, a method for determining the time difference of arrival of a signal received at two or more receiving sites, said method comprising:

(a) determining a frequency domain representation of the signal as received at the two or more receiving sites, wherein each frequency domain representation comprises a plurality of frequency domain components;

(b) determining a phase function from two or more like-frequency components in the signal as received at the two or more receiving sites, wherein the phase function is representative of phase angles of the two or more like-frequency components; and

(c) determining the time difference of arrival from the phase function.

37. The method of claim 33 wherein the phase function comprises the phase difference for the two or more like-frequency components, as a function of the like-frequency.

38. The method of claim 33 wherein the step (b) of determining the phase function comprises determining the Hermetian product pairs for like-frequency components.

39. The method of claim 38 wherein the step (c) further comprises:

(d1) separating the Hermetian product pairs into real and imaginary parts; and

(d2) determining the derivative with respect to frequency of the arctangent of the ratio of the imaginary part to the real part, wherein the derivative is the time difference of arrival as a function of frequency.

40. The method of claim 33 wherein the transmitting unit is selected from among a mobile communications device, a portable communications device, a personal communications device, a cellular communications device, a push-to-talk communications device and a trunked radio.

41. The method of claim 33 wherein the plurality of receiving sites comprises N receiving sites, and wherein the time difference of arrival is determined pairwise among the N receiving sites.

42. The method of claim 33 further comprising a step (d) determining the location of the transmitting unit from observed time differences of arrival.

43. The method of claim 33 wherein the transmitting unit comprises a cellular telephone and the two or more receiving sites comprise two or more cellular base stations.

44. The method of claim 33 wherein the transmitting unit comprises a cellular telephone and the two or more receiving sites are selected from among two or more cellular base stations, two or more cellular monitoring stations, and a combination of cellular base stations and cellular monitoring stations.

45. The method of claim 33 wherein the step (a) is executed at each of the two or more receiving sites.

46. The method of claim 33 wherein the frequency domain representation is provided from each of the two or more receiving sites to a processing site, and wherein the steps (b) and (c) are executed at the processing site.

47. The method of claim 33 wherein the result of the step (b) comprises a vector comprising a plurality of elements, and wherein each element comprises a value representing the phase angle difference for a like-frequency component.

48. The method of claim 47 wherein the number of vectors is less than or equal to the number of pairwise combinations of receiving sites.

49. The method of claim 33 wherein the step (a) further comprises filtering the frequency domain representation to control the effect of certain frequency domain components on the time difference of arrival determination.

50. The method of claim 49 wherein the step of filtering further comprises determining a signal quality metric for the frequency domain components, and weighting the frequency components in response to the signal quality metric.

51. The method of claim 33 wherein the step (a) further comprises determining the frequency domain representation of the time domain signal using a process selected from among, a Fourier transform integral, a fast Fourier transform algorithm, a discrete Fourier transform, a Hartley transform, a Hilbert transform and a Laplace transform.

52. A method for determining the location of a transmitting unit transmitting a signal, in response to the time difference of arrival of the signal at two or more receiving sites, comprising:

(a) selecting a location estimate for the transmitting unit;

(b) determining the pairwise distance difference of arrival from the location estimate to at least two of the two or more receiving sites;

(c) determining the error in the location estimate in response to the distance difference of arrival value determined at the step (b); and

(d) updating the location estimate in response to the error.

53. The method of claim 52 further comprising determining a predetermined threshold value and a step (e), repeating the steps (b) through (d) until the error is less than the threshold value.

54. The method of claim 52 wherein the distance difference of arrival value is the product of the time difference of arrival and the speed of light.

55. The method of claim 52 wherein the initial location is the geographic center of the two or more receiving sites.

56. The method of claim 52 wherein the step (c) further comprises:

(c1) determining a linear differential equation relating the distance difference of arrival, the geographic location of the two or more receiving sites, the location estimate and the error in the location estimate; and

(c2) solving the linear differential equation to determine the error in the location estimate.

57. The method of claim 55 wherein the step (c2) further comprises solving the linear differential equation according to a least squared error process.

58. The method of claim 55 wherein the step (b) further comprises determining the distance difference of arrival for the pairwise combinations of the receiving sites, wherein the error in the location estimate according to the step (c) further comprises the error in the location estimate with respect to each of the pairwise combinations of receiving sites.

59. The method of claim 55 wherein the location estimate includes a location estimate in three dimensions.

60. An apparatus for determining the location of a transmitting unit transmitting a signal received at two or more receiving sites, the apparatus comprising:

an antenna at each of the two or more receiving sites responsive to the signal;

a processor responsive to the antenna for determining a frequency domain representation for the signal as received at the two or more receiving sites, wherein each frequency domain representation comprises a plurality of frequency domain components, and wherein each frequency domain component comprises a two-dimensional number for each of the a plurality of frequency domain components;

the processor for determining the time difference of arrival of the signal as received at the two or more receiving sites in response to the two-dimensional numbers, wherein the time difference of arrival represents the difference in the arrival time of the signal as received at the two or more receiving sites; and

the processor for determining the location of the transmitting unit in response to the time difference of arrival.