Method and system for calibrating wireless location systems

• US 20020196186A1
• Filed: 06/25/2001
• Published: 12/26/2002
• Est. Priority Date: 06/25/2001
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Holt, Brian
• Granted Patent: US 6,522,296 B2
• Time in Patent Office: Days
• US Class Current: 342/453
• 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

Abstract

This invention relates to a method for calibrating a wireless location system (WLS) to enable the system to make highly accurate differential measurements such as time difference of arrival (TDOA) and frequency difference of arrival (FDOA). Calibration is accomplished by transmitting a signal from an unknown location and measuring at each of two receivers the parameter to be calibrated from that part of the received signal reflected or refracted from an object at a known location in the area. A differential measurement error is determined by comparing the expected difference in the parameter measurements with the actual difference in the parameter measurements. The expected difference is known, a priori, based on the locations of the receivers and the location of the object.

Claims

1. A system for calibrating receivers used for locating a transmitter comprising:

a transmitter at an unknown location that transmits a signal;

a proxy receiver that reflects and/or refracts the signal;

a plurality of spatially oriented receivers that receive the signal from the proxy receiver, each receiver having a clock for determining Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival of signals, wherein the clocks are calibrated based on the clock offset.

2. A system according to claim 1, and further comprising a processor associated with each receiver for calculating Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival and clock offset.

3. A system according to claim 1, wherein said transmitter comprises a mobile unit.

4. A system according to claim 1, wherein said signal comprises a radio frequency signal.

5. A system according to claim 1, wherein said proxy receiver comprises a natural landmark.

6. A system according to claim 5, wherein said proxy receiver comprises an earth elevation.

7. A system according to claim 1, wherein said proxy receiver comprises a man-made structure.

8. A system according to claim 7, wherein said proxy receiver comprises a building.

9. A system according to claim 1, wherein said plurality of receivers comprise two receivers.

10. A system according to claim 1, wherein each clock comprises a stable local clock.

11. A system for calibrating receivers used for locating a transmitter determination comprising:

a transmitter at an unknown location that transmits a signal;

a proxy receiver that reflects and/or refracts the signal;

a plurality of spatially oriented receivers each having an antenna directed at the proxy receiver for receiving the signal from the proxy receiver, each receiver having a clock for determining Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival of signals, wherein the clocks are calibrated based on the clock offset.

12. A system according to claim 11, wherein each antenna comprises a focused beam antenna.

13. A system according to claim 11, and further comprising a processor associated with each receiver for calculating at least one of Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival and clock offset.

14. A system according to claim 11, wherein said transmitter comprises a mobile unit.

15. A system according to claim 11, wherein said signal comprises a radio frequency signal.

16. A system according to claim 11, wherein said proxy receiver comprises a natural landmark.

17. A system according to claim 16, wherein said proxy receiver comprises an earth elevation.

18. A system according to claim 11, wherein said proxy receiver comprises a man-made structure.

19. A system according to claim 18, wherein said proxy receiver comprises a building.

20. A system according to claim 11, wherein said plurality of receivers comprise two receivers.

21. A system according to claim 11, wherein each clock comprises a stable local clock.

22. A method of calibrating spatially oriented receivers used in a location determination system comprising the steps of:

transmitting a signal from an unknown location;

receiving within each spatially oriented receiver the signal after having reflected and/or refracted from a proxy receiver having a known location, each receiver having a clock for determining at least Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival of signals;

calculating the Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival for the signal at each receiver;

determining the clock offset between the plurality of receivers based on the Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival of the signal within each receiver; and

calibrating the clocks based on the clock offset.

23. A method according to claim 22, and further comprising the step of transmitting the signal from a mobile unit.

24. A method according to claim 22, wherein said signal comprises a radio frequency signal.

25. A method according to claim 22, wherein said proxy receiver comprises a natural landmark.

26. A method according to claim 25, wherein said proxy receiver comprises an earth elevation.

27. A method according to claim 22, wherein said proxy receiver comprises a man-made structure.

28. A method according to claim 27, wherein said proxy receiver comprises a building.

29. A method according to claim 27, wherein each clock comprises a stable local clock.

30. A method according to claim 27, wherein said plurality of receivers comprise two receivers.

31. A method of calibrating spatially oriented receivers used in a location determination system comprising the steps of:

transmitting a signal from an unknown location;

reflecting and/or refracting the signal from a proxy receiver having a known location;

directing an antenna of each receiver at the proxy receiver for receiving the signal within each spatially oriented receiver;

calculating the Time of Arrival, Time Difference of Arrival, or Frequency Difference of Arrival for the signal at each receiver;

determining the clock offset between the plurality of receivers; and

calibrating the clocks based on the clock offset.

32. A method according to claim 31, wherein each antenna comprises a narrow beam antenna.

33. A method according to claim 31, and further comprising the steps of transmitting the signal from a mobile transmitter unit.

34. A method according to claim 31, wherein said signal comprises a radio frequency signal.

35. A method according to claim 31, wherein said proxy receiver comprises a natural landmark.

36. A method according to claim 35, wherein said proxy receiver comprises an earth elevation.

37. A method according to claim 31, wherein said proxy receiver comprises a man-made structure.

38. A method according to claim 35, wherein said proxy receiver comprises a building.

39. A method according to claim 31, wherein each clock comprises a stable local clock.

40. A method according to claim 31, wherein said plurality of receivers comprise two receivers.

41. A method for calibrating a wireless location system comprises the steps of:

transmitting a signal from the unknown location;

receiving the signal and measuring at each of first and second receivers a parameter of that portion of the signal reflected or refracted to each of the two receivers by a proxy reference transmitter comprising one of a natural or man-made object;

determining an error value based on the difference between the expected difference between parameter values and the actual difference between measured parameter values; and

using the error value to apply corrections to any wireless location system equipment to minimize the errors in subsequent measurements and/or apply corrections to any prior, concurrent or subsequent measurements of the parameter.

42. A method according to claim 41 and further comprising the step of determining the expected difference using information from a database.