Methods and apparatus for estimating accuracy of measurement signals

• US 6,486,831 B1
• Filed: 04/23/2001
• Issued: 11/26/2002
• Est. Priority Date: 04/23/2001
• Status: Expired due to Fees

• Current Assignee: Exelis Incorporated (L3Harris Technologies, Inc.)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: Martorana, Marc J., Galgano, Steven, Martorana, Scott C.
• Primary Examiner(s): Phan, Dao
• Application Number:
  US09/839,576
• Publication Number:
  US 20020171586A1
• Time in Patent Office: 582 Days
• Field of Search: 342/118, 342/357.02, 342/457, 342/458, 455/456, 455/457
• US Class Current: 342/458
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/0273 using multipath or indirect path propagation signals in position determination
• CPC Class Codes: G01S 5/0294 Trajectory determination or predictive filtering, e.g. target tracking or Kalman filtering
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

Range measurements useful for determining a device'"'"'s position are screened to eliminate unacceptable measurements. A two-stage range measurement screening technique involves a coarse screening stage that includes comparing the range measurement to an estimated expected range and a fine screening stage that includes comparing the range measurement to the computed fading-average range. Range measurements that fall within both coarse and fine screening windows are deemed acceptable and are supplied to a position tracking filter together with their estimated measurement accuracies. Range measurements that do not fall within either the coarse or fine screening window are discarded and do not corrupt the position solution. The accuracies of acceptable range measurements are determined from multiple factors including the measurement offset from a fading-average of previous range measurements and the standard deviation of the previous range measurements.

Claims

1. A method of determining whether a measurement is acceptable for use in a tracking system, the method comprising:

(a) determining a measurement value from a detected signal;

(b) computing an average and standard deviation of previous acceptable measurements;

(c) generating a window of acceptability as a function of the average and standard deviation of the previous acceptable measurements; and

(d) if the measurement value is within the window of acceptability, supplying the measurement value to the tracking system for updating a state tracked by the tracking system.

2. The method of claim 1, wherein the average is a fading average of previous acceptable measurements, wherein more recent measurements are weighted more heavily in determining the fading average.

3. The method of claim 1, wherein the measurement value is a range measurement and the tracking system determines the position of an object from a plurality of range measurements.

4. The method of claim 3, wherein:

the measurement value represents a range between a mobile communication device and a reference communication device determined from a round-trip signal propagation time of ranging signals exchanged between the mobile communication device and the reference communication device.

5. The method of claim 1, further comprising:

(e) calculating an error between the measurement and the average of the previous acceptable measurements;

(f) determining the accuracy of the measurement value as a function of the error between the measurement and the average of the previous acceptable measurements and the standard deviation of the previous acceptable measurements; and

(g) supplying the accuracy to the tracking system for updating the state tracked by the tracking system.

6. The method of claim 5, wherein the detected signal is detected using a rake filter, and wherein (f) further includes determining the accuracy of the measurement value as a function of a number of rake taps used by the rake filter in detecting the signal.

7. The method of claim 5, wherein detecting the detected signal includes curve fitting the detected signal to a stored signal replica, and wherein (f) further includes determining the accuracy of the measurement value as a function of a quality of fit of the curve fitting.

8. The method of claim 5, wherein (f) further includes determining the accuracy of the measurement value as a function of a signal-to-noise ratio of the detected signal.

9. The method of claim 5, wherein the measurement value is a range measurement of a range between a mobile communication device and a reference communication device and the tracking system estimates the position of the mobile communication device from a plurality of range measurements, the method further comprising:

(h) computing a predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device; and

(i) estimating the accuracy of the predicted range based on estimated accuracies of the tracked positions of the reference communication device and the mobile communication device;

wherein (f) further includes determining the accuracy of the range measurement as a function of the estimated accuracy of the predicted range.

10. The method of claim 1, wherein the measurement value is a range measurement of a range between a mobile communication device and a reference communication device and the tracking system estimates the position of the mobile communication device from a plurality of range measurements, the method further comprising:

(e) computing a predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device;

(f) estimating the accuracy of the predicted range based on estimated accuracies of the tracked positions of the reference communication device and the mobile communication device;

(g) generating a coarse window of acceptability as a function of the predicted range and the estimated accuracy of the predicted range;

(h) supplying the range measurement to the tracking system for updating the estimated position of the mobile communication device if the range measurement is within said coarse window of acceptability and said window of acceptability.

18. The method of claim 5, wherein (i) further includes determining the accuracy of the range measurement as a function of the estimated accuracy of the predicted range.

11. A method of determining whether a range measurement is acceptable for use in updating an estimated position of a mobile communication device, comprising:

(a) measuring a range between the mobile communication device and a reference communication device;

(b) computing a predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device;

(c) estimating the accuracy of the predicted range based on estimated accuracies of the tracked positions of the reference communication device and the mobile communication device;

(d) generating a first window of acceptability as a function of the predicted range and the estimated accuracy of the predicted range;

(e) computing an average and standard deviation of previous range measurements;

(f) generating a second window of acceptability as a function of the average and standard deviation of the previous measurements;

(g) if the range measurement is within both the first and second windows of acceptability, supplying the range measurement to a tracking system for updating the estimated position of the mobile communication device.

12. The method of claim 11, wherein the average is a fading average of previous range measurements, wherein more recent range measurements are weighted more heavily in determining the fading average.

13. The method of claim 11, wherein the range measurement is determined from a round-trip signal propagation time of ranging signals exchanged between the mobile communication device and the reference communication device.

14. The method of claim 11, further comprising:

(h) calculating an error between the range measurement and the average of the previous range measurements;

(i) determining the accuracy of the range measurement as a function of the error between the range measurement and the average of the previous range measurements and the standard deviation of the previous range measurements; and

(j) supplying the accuracy to the tracking system for updating the estimated position of the mobile communication device.

15. The method of claim 14, wherein the range measurement is detected using a rake filter, and wherein (i) further includes determining the accuracy of the range measurement as a function of a number of rake taps used by the rake filter in detecting the range measurement.

16. The method of claim 14, wherein measuring the range includes curve fitting the detected signal to a stored signal replica, and wherein (i) further includes determining the accuracy of the range measurement as a function of a quality of fit of the curve fitting.

17. The method of claim 14, wherein (i) further includes determining the accuracy of the range measurement as a function of a signal-to-noise ratio of the range measurement.

19. A method of estimating the accuracy of a measurement to be used in a tracking system, the method comprising:

(a) determining a measurement value from a detected signal;

(a) computing an average and standard deviation of previous measurements;

(b) calculating an error between the measurement value and the average of the previous measurements;

(c) determining the accuracy of the measurement value as a function of the error and the standard deviation of the previous measurements; and

(d) supplying the measurement value and the accuracy to the tracking system for updating a state tracked by the tracking system.

20. The method of claim 19, wherein the detected signal is detected using a rake filter, and wherein (c) further includes determining the accuracy of the measurement value as a function of a number of rake taps used by the rake filter in detecting the signal.

21. The method of claim 19, wherein detecting the detected signal includes curve fitting the signal to a stored signal replica, and wherein (c) further includes determining the accuracy of the measurement value as a function of a quality of fit of the curve fitting.

22. The method of claim 19, wherein (c) further includes determining the accuracy of the measurement value as a function of a signal-to-noise ratio of the detected signal.

23. The method of claim 19, wherein the measurement value is a range measurement of a range between a mobile communication device and a reference communication device and the tracking system estimates the position of the mobile communication device from a plurality of range measurements, the method further comprising:

(e) computing a predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device; and

(f) estimating the accuracy of the predicted range based on estimated accuracies of the tracked positions of the reference communication device and the mobile communication device;

wherein (c) further includes determining the accuracy of the measurement value as a function of the estimated accuracy of the predicted range.

24. The method claim 19, wherein the average is a fading average of previous measurements, wherein more recent measurements are weighted more heavily in determining the fading average.

25. A mobile communication device capable of estimating its position by determining ranges to a plurality of reference communication devices having known positions, comprising:

a receiver configured to receive ranging signals from reference communication devices, said receiver generating a range measurement from a detected ranging signal;

a processor configured to receive the range measurement, said processor generating a window of acceptability as a function of an average and a standard deviation of previous range measurements and finding the range measurement to be acceptable if the range measurement is within the window of acceptability; and

a tracking system configured to receive acceptable range measurements from said processor, said tracking system updating an estimated position of the mobile communication device from the acceptable range measurements.

26. The device of claim 25, wherein the average is a fading average of previous range measurements, wherein more recent range measurements are weighted more heavily in determining the fading average.

27. The device of claim 25, wherein said receiver determines the range measurement from a round-trip signal propagation time of ranging signals exchanged between the mobile communication device and the reference communication device.

28. The device of claim 25, wherein said processor:

calculates an error between the range measurement and the average of the previous range measurements;

determines the accuracy of the range measurement as a function of the error between the range measurement and the average of the previous range measurements and the standard deviation of the previous range measurements; and

supplies the accuracy to the tracking system for updating the estimated position of the mobile communication device.

29. The device of claim 28, wherein said receiver includes a rake filter, and wherein said processor determines the accuracy of the range measurement as a function of a number of rake taps used by the rake filter.

30. The device of claim 28, wherein said receiver performs curve fitting of the detected ranging signal to a stored signal replica, and wherein said processor determines the accuracy of the range measurement as a function of a quality of fit of the curve fitting.

31. The device of claim 28, wherein said processor determines the accuracy of the range measurement as a function of a signal-to-noise ratio of the range measurement.

32. The device of claim 28, wherein said processor computes a predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device, and estimates the accuracy of the predicted range based on estimated accuracies of the tracked positions of the reference communication device and the mobile communication device, said processor determining the accuracy of the range measurement as a function of the estimated accuracy of the predicted range.

33. The device of claim 25, wherein said processor:

computes a predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device;

estimates the accuracy of the predicted range based on estimated accuracies of the tracked positions of the reference communication device and the mobile communication device;

generates a coarse window of acceptability as a function of the predicted range and the estimated accuracy of the predicted range; and

supplies the range measurement to the tracking system for updating the estimated position of the mobile communication device if the range measurement is within said coarse window of acceptability and said window of acceptability.

34. A mobile communication device capable of estimating its position by determining ranges to a plurality of reference communication devices having known positions, comprising:

a receiver configured to receive ranging signals from reference communication devices, said receiver generating a range measurement from a detected ranging signal;

a processor configured to receive the range measurement, said processor generating a coarse window of acceptability as a function of a predicted range and an estimated accuracy of the predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device, said processor generating a fine window of acceptability as a function of an average and a standard deviation of previous range measurements, said processor finding the range measurement to be acceptable if the range measurement is within both the coarse window of acceptability and the fine window of acceptability; and

a tracking system configured to receive acceptable range measurements from said processor, said tracking system updating an estimated position of the mobile communication device from the acceptable range measurements.

35. The device of claim 34, wherein the average of previous range measurements is a fading average of previous range measurements, wherein more recent range measurements are weighted more heavily in determining the fading average.

36. The device of claim 34, wherein said processor determines the range measurement from a round-trip signal propagation time of ranging signals exchanged between the mobile communication device and the reference communication device.

37. The device of claim 34, wherein said processor:

calculates an error between the range measurement and the average of the previous range measurements;

determines the accuracy of the range measurement as a function of the error between the range measurement and the average of the previous range measurements and the standard deviation of the previous range measurements; and

supplies the accuracy to the tracking system for updating the estimated position of the mobile communication device.

38. The device of claim 37, wherein said receiver includes a rake filter, and wherein said processor determines the accuracy of the range measurement as a function of a number of rake taps used by the rake filter.

39. The device of claim 37, said receiver performs curve fitting of the detected ranging signal to a stored signal replica, and wherein said processor determines the accuracy of the range measurement as a function of a quality of fit of the curve fitting.

40. The device of claim 37, wherein said processor determines the accuracy of the range measurement as a function of a signal-to-noise ratio of the range measurement.

41. The device of claim 37, wherein said processor determines the accuracy of the range measurement as a function of the estimated accuracy of the predicted range.

42. A mobile communication device capable of estimating its position by determining ranges to a plurality of reference communication devices having known positions, comprising:

a receiver configured to receive ranging signals from reference communication devices, said receiver generating a range measurement from a detected ranging signal;

a processor configured to receive the range measurement, said processor computing an average and standard deviation of previous range measurements and determining the accuracy of the range measurement as a function of the standard deviation of the previous range measurements and the difference between the range measurement and the average of the previous range measurements; and

a tracking system configured to receive acceptable range measurements and corresponding accuracies from said processor, said tracking system updating an estimated position of the mobile communication device from the acceptable range measurements.

43. The device of claim 42, wherein said receiver includes a rake filter, and wherein said processor determines the accuracy of the range measurement as a function of a number of rake taps used by the rake filter.

44. The device of claim 42, wherein said receiver performs curve fitting of the detected ranging signal to a stored signal replica, and wherein said processor determines the accuracy of the range measurement as a function of a quality of fit of the curve fitting.

45. The device of claim 42, wherein said processor determines the accuracy of the range measurement as a function of a signal-to-noise ratio of the range measurement.

46. The device of claim 42, wherein said processor computes a predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device, and estimates the accuracy of the predicted range based on estimated accuracies of the tracked positions of the reference communication device and the mobile communication device, said processor determining the accuracy of the range measurement as a function of the estimated accuracy of the predicted range.

47. The device claim 42, wherein the average of the previous range measurements is a fading average of previous range measurements, wherein more recent range measurements are weighted more heavily in determining the fading average.

48. A method of determining whether a measurement is acceptable for use in a tracking system, the method comprising:

(a) determining a measurement value from a detected signal;

(b) determining a variability of previous acceptable measurements;

(c) forming a window of acceptability whose size is based upon the variability of the previous acceptable measurements; and

(d) if the measurement value is within the window of acceptability, supplying the measurement value to the tracking system for updating a state tracked by the tracking system.

49. A The method of claim 48, wherein the window of acceptability is a function of a fading average of the previous acceptable measurements, wherein more recent measurements are weighted more heavily in determining the fading average.

50. The method of claim 48, wherein the measurement value is a range measurement and the tracking system determines the position of an object from a plurality of range measurements.

51. The method of claim 48, further comprising:

(e) calculating an error between the measurement and an average of the previous acceptable measurements;

(f) determining the accuracy of the measurement value as a function of the error between the measurement and the average of the previous acceptable measurements and the variability of the previous acceptable measurements; and

(g) supplying the accuracy to the tracking system for updating the state tracked by the tracking system.

52. A mobile communication device capable of estimating its position by determining ranges to a plurality of reference communication devices having known positions, comprising:

a receiver configured to receive ranging signals from the reference communication devices, said receiver generating a range measurement from a detected ranging signal;

a processor configured to generate a window of acceptability whose size is based on a variability of previous acceptable range measurements, said processor determining the range measurement to be acceptable if the range measurement is within the window of acceptability; and

a navigation system configured to receive acceptable range measurements from said processor, said navigation system updating an estimated position of the mobile communication device based on the acceptable range measurements.

53. The device of claim 52, wherein the window of acceptability is a function of a fading average of the previous acceptable measurements, wherein more recent measurements are weighted more heavily in determining the fading average.

54. The device of claim 52, wherein said receiver determines the range measurement from a round-trip signal propagation time of ranging signals exchanged between the mobile communication device and the reference communication device.

55. The device of claim 52, wherein said processor:

calculates an error between the range measurement and an average of the previous acceptable range measurements;

determines the accuracy of the range measurement as a function of the error between the range measurement and the average of the previous acceptable range measurements and a variability of the previous acceptable range measurements; and

supplies the accuracy to the navigation system for updating the estimated position of the mobile communication device.

56. The device of claim 52, wherein said processor computes a predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device, and estimates the accuracy of the predicted range based on estimated accuracies of the tracked positions of the reference communication device and the mobile communication device, said processor determining the accuracy of the range measurement as a function of the estimated accuracy of the predicted range.

57. The device of claim 54, wherein said processor:

computes a predicted range between the mobile communication device and the reference communication device based on tracked positions of the mobile communication device and the reference communication device;

estimates the accuracy of the predicted range based on estimated accuracies of the tracked positions of the reference communication device and the mobile communication device;

generates a coarse window of acceptability as a function of the predicted range and the estimated accuracy of the predicted range; and

supplies the range measurement to the navigation system for updating the estimated position of the mobile communication device if the range measurement is within said coarse window of acceptability and said window of acceptability.

58. An apparatus for determining whether a measurement is acceptable for use in a tracking system, the method comprising:

means for determining a measurement value from a detected signal;

means for forming a window of acceptability whose size is based upon the variability of previous acceptable measurements; and

means for supplying the measurement value to the tracking system for updating a state tracked by the tracking system in response to the measurement value being within the window of acceptability.

59. The apparatus of claim 58, further comprising:

means for forming another window of acceptability based upon a state tracked by the tracking system, wherein the means for supplying supplies the measurement value to the tracking system in response to the measurement value being within the window of acceptability and said another window of acceptability.

60. A method of determining whether a measurement is acceptable for use in a tracking system, comprising:

(a) determining a measurement value from a detected signal;

(b) generating a first window of acceptability based on a state tracked by the tracking system;

(c) generating a second window of acceptability whose size is based on a variability of previous acceptable measurements;

(d) supplying the measurement value to the tracking system for updating the state tracked by the tracking system in response to the measurement value being within both the first and second windows of acceptability.

61. The method of claim 60, further comprising:

(e) calculating an error between the range measurement and the average of the previous range measurements;

(f) determining an accuracy of the measurement value as a function of a difference between the measurement value and an average of the previous acceptable measurements; and

(g) supplying the accuracy to the tracking system for updating the state tracked by the tracking system.

62. The method of claim 60, wherein the first window of acceptability is based on an accuracy of the state tracked.

63. The method of claim 60, wherein the second window of acceptability is based on a standard deviation of the previous acceptable measurements.

64. A mobile communication device capable of estimating its position by determining ranges to a plurality of reference communication devices having known positions, comprising:

a receiver configured to receive ranging signals from the reference communication devices, said receiver generating a range measurement from a detected ranging signal;

a processor configured to generate;

a first window of acceptability whose size is based on a tracked range between the mobile communication device and the reference communication device; and

a second window of acceptability based on a variability of previous acceptable range measurements, said processor determining the range measurement to be acceptable if the range measurement is within the first and second windows of acceptability; and

a navigation system configured to receive acceptable range measurements from said processor, said navigation system updating an estimated position of the mobile communication device based on the acceptable range measurements.

65. The device of claim 64, wherein said processor:

calculates an error between the range measurement and the average of the previous acceptable range measurements;

determines the accuracy of the range measurement as a function of the error between the range measurement and the average of the previous acceptable range measurements and the standard deviation of the previous acceptable range measurements; and

supplies the accuracy to the navigation system for updating the estimated position of the mobile communication device.

66. The device of claim 64, wherein the first window of acceptability is based on an estimated accuracy of the tracked range.

67. The device of claim 64, wherein the second window of acceptability is based on a standard deviation of the previous acceptable range measurements.