Location system and method that achieves time synchronized network performance with nodes divided into separate networks

• US 20050193149A1
• Filed: 11/03/2004
• Published: 09/01/2005
• Est. Priority Date: 11/07/2003
• Status: Active Grant

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Wherenet Corporation Corporation of The State of California
• Inventors: Boyd, Robert W.
• Granted Patent: US 7,218,229 B2
• Time in Patent Office: Days
• US Class Current: 709/248
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• 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

Abstract

A system for locating an object within a monitored environment includes receivers arranged in loosely coupled networks. A tag transmitter acts as a network node and bridge between the loosely coupled networks. A processor is operative with each receiver within each network for defining a clock timing for each network, a system time for all networks, and tracking its relationship to the clock timing for each network for time synchronizing all receivers. The processor is also operative for conducting differentiation of time of arrival signals received from a tag transmitter to locate an object associated with the tag transmitter.

Claims

1. A system for locating an object within a monitored environment comprising:

a plurality of receivers contained in the monitored environment and arranged in a plurality of loosely coupled networks such that receivers in each network are tightly coupled to each other allowing a timing signal that is received by receivers in the same network not to be received by receivers within the other loosely coupled network;

a tag transmitter positioned within the monitored environment at a location for transmitting an RF signal to receivers within each network and operative as a reference network node and bridge between loosely coupled networks; and

a processor operative with each receiver within each network for defining a clock timing for each network, a system time for all networks, and tracking its relationship to the clock timing for each network for time synchronizing all receivers, wherein the processor is operative for conducting differentiation of time of arrival signals received from a tag transmitter to locate an object associated with a tag transmitter.

2. A system according to claim 1, wherein the processor is operative for determining clock timing relationships between each clock at a receiver based on one of at least the propagation or processing delays in the receivers.

3. A system according to claim 1, wherein the tag transmitter is positioned at a known location.

4. A system according to claim 1, and further comprising a pair of tag transmitters which transmit RF signals to receivers with known propagation delay.

5. A system according to claim 1, wherein the processing delay within each receiver is substantially constant with each other.

6. A system according to claim 1, wherein the processor is operative for processing two time separated signals for determining a differential clock rate.

7. A system according to claim 6, wherein the processor is operative for processing three time separated signals to indicate differential rate change.

8. A system according to claim 7, wherein the processor is operative for maintaining a model of timing relationships of clocks at the receivers.

9. A system according to claim 1, wherein said receivers are positioned at known locations.

10. A system according to claim 1, wherein said RF signal includes data indentifying the object associated with the tag transmitter.

11. A system according to claim 1, wherein said RF signal further comprises a pseudo random spread spectrum RF signal.

12. A system according to claim 1, wherein said processor is operative for forming a tracking loop to track clock relationships that occur naturally over time.

13. A system according to claim 1, wherein the processor is operative for determining an equation relating the indicated time of one clock at a respective receiver to another clock at another receiver and tracking changes in that relationship over time.

14. A system for time synchronizing a network comprising:

a plurality of receivers arranged in a plurality of loosely coupled networks such that receivers in each network are tightly coupled to each other allowing a timing signal that is received by receivers in the same network not to be received by receivers within the other loosely coupled network;

a tag transmitter positioned within the monitored environment at a known location and operative as a network node and bridge for transmitting an RF signal to receivers within each network between loosely coupled networks; and

a processor operative with receivers within each network for defining clock timing for each network, a system time for all networks, and tracking its relationship to the clock timing for each network for time synchronizing all receivers.

15. A system according to claim 14, wherein the processor is operative for determining clock timing relationships between each clock at a receiver based on one of at least the propagation or processing delays in the receivers.

16. A system according to claim 14, and further comprising a pair of tag transmitters which transmit RF signals to receivers with known propagation delay.

17. A system according to claim 14, wherein the processor is operative for processing two time separated signals for determining a differential clock rate.

18. A system according to claim 17, wherein the processor is operative for processing three time separated signals to indicate differential rate change.

19. A system according to claim 18, wherein the processor is operative for maintaining a model of timing relationships of clocks at the receivers.

20. A system according to claim 14, wherein said receivers are positioned at known locations.

21. A system according to claim 14, wherein said RF signal includes data indentifying an object to be located and associated with the tag transmitter.

22. A system according to claim 14, wherein said RF signal further comprises a pseudo random spread spectrum RF signal.

23. A system according to claim 14, wherein said processor is operative for forming a tracking loop to track clock relationships that occur naturally over time.

24. A system according to claim 14, wherein the process or is operative for determining an equation relating the indicated time of one clock at a respective receiver to another clock at another receiver and tracking changes in that relationship over time.

25. A method for locating an object within a monitored environment, which comprises:

transmitting an RF signal from a tag transmitter operative as a reference network node and bridge between loosely coupled networks formed from a plurality of receivers contained in the monitored environment and arranged in a plurality of loosely coupled networks such that receivers in each network are tightly coupled to each other allowing a timing signal that is received by receivers in the same network not to be received by receivers within the other loosely coupled network;

receiving RF signals from the receivers and defining a clock timing for each network, a system time for all networks, and tracking its relationship to the clock timing for each network for time synchronizing all receivers; and

conducting differentiation of the time of arrival signals received from a tag transmitter to locate an object associated with the tag transmitter.

26. A method according to claim 25, which further comprises determining clock timing indications for each clock at a receiver based on one of at least the propagation or processing delays in the receivers to adjust an indicated arrival time of RF signals at each receiver.

27. A method according to claim 25, which further comprises transmitting RF signals from a pair of tag transmitters to receiver with known propagation delay.

28. A method according to claim 25, wherein the processing delay within each receiver is substantially constant with each other.

29. A method according to claim 25, which further comprises receiving two time separated signals for determining differential clock rate.

32. A method according to claim 25, which further comprises positioning the receivers at known locations.

33. A method according to claim 25, which further comprises transmitting an RF signal from the tag transmitter having data indentifying an object to which the tag is associated.

34. A method according to claim 25, which further comprises transmitting a pseudo random spread spectrum RF signal from the at least one tag.

35. A method according to claim 25, which further comprises processing first-to-arrive RF signals at each receiver.

36. A method according to claim 25, which further comprises forming a tracking loop to track clock relationships that occur naturally over time.

37. A method according to claim 25, which further comprises determining an equation relating the indicated time of one clock at a respective receiver to another clock at another receiver and tracking changes in that relationship over time.

38. A method for time synchronizing a network which comprises:

transmitting an RF signal from a tag transmitter positioned at a known location and operative as a reference network node and bridge between loosely coupled networks formed from a plurality of receivers contained in the monitored environment and arranged in a plurality of loosely coupled networks such that receivers in each network are tightly coupled to each other allowing a timing signal that is received by receivers in the same network not to be received by receivers within the other loosely coupled network; and

receiving RF signals from the receivers and defining a clock timing for each network, a system time for all networks, and tracking its relationship to the clock timing for each network for time synchronizing all receivers for time synchronizing all receivers.

30. A method according to claim 39, which further comprises receiving three time separated signals to indicate differential rate change.

31. A method according to claim 30, which further comprises maintaining a model of timing relationships of clocks at the receivers.

39. A method according to claim 38, which further comprises determining clock timing indications for each clock at a receiver based on one of at least the propagation or processing delays in the receivers to adjust an indicated arrival time of RF signals at each receiver.

40. A method according to claim 38, which further comprises transmitting RF signals from a pair of tag transmitters to receivers with known propagation delay.

41. A method according to claim 38, wherein the processing delay within each receiver is substantially constant with each other.

42. A method according to claim 38, which further comprises receiving two time separated signals for determining differential clock rate.

43. A method according to claim 42, which further comprises receiving three time separated signals to indicate differential rate change.

44. A method according to claim 43, which further comprises maintaining a model of timing relationships of clocks at the receivers.

45. A method according to claim 38, which further comprises positioning the receivers at known locations.

46. A method according to claim 38, which further comprises associating a tag with an object to be located.

47. A method according to claim 38, which further comprises transmitting an RF signal from the at least one tag having data indentifying the object to which the tag is associated.

48. A method according to claim 38, which further comprises transmitting a pseudo random spread spectrum RF signal from the at least one tag.

49. A method according to claim 38, which further comprises processing first-to-arrive RF signals at each receiver.

50. A method according to claim 38, which further comprises forming a tracking loop to track clock relationships that occur naturally over time.

51. A method according to claim 38, which further comprises determining an equation relating the indicated time of one clock at a respective receiver to another clock at another receiver and tracking changes in that relationship over time.