Article tracking system

• US 6,483,427 B1
• Filed: 03/09/2000
• Issued: 11/19/2002
• Est. Priority Date: 10/17/1996
• Status: Expired due to Term

• Current Assignee: RF Technologies, Inc. (Microwave Techniques LLC)
• Original Assignee: RF Technologies, Inc. (Microwave Techniques LLC)
• Inventors: Werb, Jay
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): Dalencourt, Yves
• Application Number:
  US09/522,128
• Time in Patent Office: 985 Days
• Field of Search: 340/10.1, 340/5.8, 340/573.1, 340/573.4, 340/825.49, 342/42, 342/44
• US Class Current: 340/10.1
• CPC Class Codes: G01S 13/84 for distance determination by phase measurement
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G06K 17/00 Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations
• CPC Class Codes: G06K 19/0724 the arrangement being a circuit for communicating at a plurality of frequencies, e.g. for managing time multiplexed communication over at least two antennas of different types
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10059 transponder driven
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: G07C 9/28 the pass enabling tracking or indicating presence

Abstract

System for tracking mobile tags. Cell controllers with multiple antenna modules generate a carrier signal which is received by the tags. Tags shift the frequency of the carrier signal, modulate an identification code onto it, and transmit the resulting tag signal at randomized intervals. The antennas receive and process the response, and determine the presence of the tags by proximity and triangulation. Distance of a tag from an antenna is calculated by measuring the round trip signal time. The cell controllers send data from the antenna to a host computer. The host computer collects the data and resolves them into positional estimates. Data are archived in a data warehouse, such as an SQL Server.

Claims

1. A tag comprising:

a receiver for receiving a first signal in a first frequency range;

a discriminator that operates on the first signal to provide a second signal that can be discriminated from the first signal;

a digital logic device that generates tag-specific data;

a modulator that modulates the tag-specific data onto the second signal to generate a tag signal;

a transmitter that transmits the tag signal; and

an enabling device that periodically enables the tag to receive the first signal and transmit the second signal at times that are independent of the first signal.

2. The tag as claimed in claim 1, wherein the discriminator comprises a device that frequency translates the first signal to provide the second signal in a second frequency range.

3. The tag as claimed in claim 1, wherein the discriminator comprises a circuit that introduces a time delay into the first signal to provide the second the signal.

4. The tag as claimed in claim 1, wherein the enabling device is a microprocessor.

5. The tag as claimed in claim 1, wherein the enabling device maintains the tag in a low power state between consecutive transmissions of the tag signal.

6. The tag as claimed in claim 1, wherein the tag-specific data comprises a unique identification code that uniquely identifies the tag.

7. The tag as claimed in claim 6, wherein the tag signal comprises synchronization bits to reliably determine where the unique identification code ends.

8. The tag as claimed in claim 6, wherein the unique identification code associated with the tag is used by the enabling device to generate times at which the tag is periodically enabled.

9. The tag as claimed in claim 6, wherein the digital logic device changes the unique identification code in response to a received signal.

10. The tag as claimed in claim 1, wherein the tag specific data comprises a header.

11. The tag as claimed in claim 1, wherein the tag specific data comprises a validity check.

12. The tag as claimed in claim 1, wherein the tag specific data comprises an error correction code.

13. The tag as claimed in claim 1, wherein the digital logic device changes the times at which the tag is enabled in response to a received signal.

14. The tag as claimed in claim 1, further comprising:

a random number generator coupled to the enabling device to generate the times at which the tag is periodically enabled by the enabling device.

15. The tag as claimed in claim 1, wherein the enabling device uses the tag-specific data to generate times at which the tag is periodically enabled.

16. The tag as claimed in claim 1, wherein the modulator modulates the second signal using amplitude modulation.

17. The tag as claimed in claim 1, wherein the modulator modulates the second signal using binary phase-shift keyed modulation.

18. The tag as claimed in claim 1, wherein the modulator modulates the second signal using multiple phase-shift keyed modulation.

19. The tag as claimed in claim 1, wherein the modulator modulates the second signal using quadrature amplitude modulation.

20. The tag as claimed in claim 1, wherein multiple first signals are received by the tag simultaneously, and wherein the tag simultaneously generates multiple tag signals corresponding to each first signal received.

21. The tag as claimed in claim 1, further comprising an object associated with the tag, and wherein the tag signal comprises data derived from the object associated with the tag.

22. The tag as claimed in claim 1, wherein the tag specific data comprises data obtained from a person associated with the tag.

23. The tag as claimed in claim 1, wherein the first signal has a center frequency substantially in a range of 902-928 MHz and the second signal has a center frequency substantially in a range of 2400-2483 MHz.

24. The tag as claimed in claim 1, wherein the first signal has a center frequency substantially in a range of 902-928 MHz and the second signal has a center frequency substantially in a range of 5725-5875 MHz.

25. The tag as claimed in claim 1, wherein the first signal has a center frequency substantially in a range of 2400-2483 MHz and the second signal has a center frequency substantially in a range of 5725-5875 MHz.

26. The tag as claimed in claim 1, wherein the first signal has a center frequency substantially in a range of 2400-2483 MHz and the second signal has a center frequency substantially in a range of 902-928 MHz.

27. The tag as claimed in claim 1, wherein the first signal has a center frequency substantially in a range of 5725-5875 MHz and the second signal has a center frequency substantially in a range of 2400-2483 MHz.

28. The tag as claimed in claim 1, wherein the first signal has a center frequency substantially in a range of 5725-5875 MHz and the second signal has a center frequency substantially in a range of 902-928 MHz.

29. The tag as claimed in claim 1, wherein the enabling device is an RC circuit that comprises a resistor and a capacitor.

30. The tag as claimed in claim 1, incorporated into a system for detecting the tag, the system further comprising:

at least one tag reader comprising at least one antenna for receiving tag signals transmitted by the tag.

31. The system as claimed of claim 30, the tag reader further comprising a transmitter for transmitting the first signal.

32. The system as claimed in claim 30,

the tag reader further comprising a calculation unit for calculating a location of the tag based on a time of reception of the tag signal by the at least one antenna.

33. The system as claimed in claim 32,

the tag reader further comprising:

a quadrature demodulator for extracting inphase and quadrature components of the tag signal; and

a digitizer for digitizing the inphase and quadrature components of the tag signal for subsequent processing.

34. The system as claimed in claim 30, wherein the tag reader comprises a cell controller that is coupled to a plurality of antennas to receive the tag signal.

35. The system as claimed in claim 34, wherein the cell controller is configured to calculate a distance from the tag to each antenna that receives the tag signal based on a time of transmission of the tag signal and a time of reception of the tag signal at each such antenna.

36. The system as claimed in claim 32, wherein the tag reader is configured to modify operating characteristics of a piece of equipment coupled to the tag reader based on the location of the tag.

37. The system as claimed in claim 36, wherein the piece of equipment comprises a computer screen.

38. The system as claimed in claim 30,

the tag reader further comprising a microprocessor that derives information from the tag signal.

39. The system as claimed in claim 38, further comprising:

a computer-readable storage medium coupled to the tag reader for storing the information derived from the tag signal.

40. The system as claimed in claim 30, wherein the tag reader comprises a device for determining from the tag signal received, a time at which the tag will next transmit a tag signal.

41. A method for providing a tag signal, comprising acts of:

receiving at a tag a first signal;

operating with the tag on the first signal to provide a second signal that can be discriminated from the first signal;

generating with the tag, tag-specific data;

modulating with the tag, the tag-specific data onto the second signal to generate a tag signal;

transmitting with the tag, the tag signal; and

periodically enabling the tag to receive and transmit at times independent of any received first signal.

42. The method as claimed in claim 41, wherein the act of operating on the first signal to provide the second signal comprises:

mixing the first signal with a local oscillator signal to generate the second signal at a second frequency.

43. The method as claimed in claim 41, wherein the act of operating on the first signal to provide the second signal comprises:

delaying the first signal to provide the second signal.

44. The method as claimed in claim 41, further comprising an act of maintaining the tag in a low-power state between consecutive acts of transmitting the tag signal.

45. The method as claimed in claim 41, wherein the act of generating tag specific data comprises generating a unique identification code that uniquely identifies the tag.

46. The method as claimed in claim 45, further comprising acts of:

receiving a third signal; and

modifying the unique identifying code in response to the third signal.

47. The method as claimed in claim 41, further comprising acts of:

simultaneously receiving at the tag, multiple first signals;

simultaneously generating with the tag, multiple tag signals corresponding to the first signals received.

48. The method as claimed in claim 41, wherein the act of generating tag-specific data, further comprises acts of:

deriving data from an object associated with the tag; and

generating tag specific data comprising the data derived from the object associated with the tag.

49. The method as claimed in claim 41, wherein the act of generating tag-specific data, further comprises an act of generating tag specific data comprising data obtained from a person associated with the tag.

50. The method as claimed in claim 41 further comprising an act of transmitting the first signal.

51. The method as claimed in claim 50, wherein the act of transmitting the first signal further comprises:

transmitting a pseudonoise sequence on the first signal.

52. The method as claimed in claim 50, wherein act of transmitting the first signal further comprises:

transmitting a direct sequence spread spectrum signal.

53. The method as claimed in claim 41, wherein:

the act of receiving the first signal comprises an act of receiving at the tag a first signal having a center frequency substantially in a frequency range of 902-928 MHz; and

the act of operating on the first signal to provide a second signal comprises an act of providing a second signal having a center frequency substantially in a range of 2400-2483 MHz.

54. The method as claimed in claim 41, wherein:

the act of receiving the first signal comprises an act of receiving at the tag a first signal having a center frequency substantially in a frequency range of 902-928 MHz; and

the act of operating on the first signal to provide a second signal comprises an act of providing a second signal having a center frequency substantially in a frequency range of 5345-5875 MHz.

55. The method as claimed in claim 41, wherein:

the act of receiving the first signal comprises an act of receiving at the tag a first signal having a center frequency substantially in a frequency range of 2400-2483 MHz; and

the act of operating on the first signal to provide a second signal comprises an act of providing a second signal having a center frequency substantially in a frequency range of 5345-5875 MHz.

56. The method as claimed in claim 41, wherein:

the act of receiving the first signal comprises an act of receiving at the tag a first signal having a center frequency substantially in a frequency range of 2400-2483 MHz; and

the act of operating on the first signal to provide a second signal comprises an act of providing a second signal having a center frequency substantially in a frequency range of 902-928 MHz.

57. The method as claimed in claim 41, wherein:

the act of receiving the first signal comprises an act of receiving at the tag a first signal having a center frequency substantially in a frequency range of 5345-5875 MHz; and

the act of operating on the first signal to provide a second signal comprises an act of providing a second signal having a center frequency substantially in a frequency range of 2400-2483 MHz.

58. The method as claimed in claim 41, wherein:

the act of receiving the first signal comprises an act of receiving at the tag a first signal having a center frequency substantially in a frequency range of 5345-5875 MHz; and

the act of operating on the first signal to provide a second signal comprises an act of providing a second signal having a center frequency substantially in a frequency range of 902-928 MHz.

59. A method for detecting a tag, comprising acts of:

receiving at a tag a first signal;

operating with the tag on the first signal to provide a second signal that can be discriminated from the first signal;

generating with the tag, tag-specific data;

modulating with the tag, the tag-specific data onto the second signal to generate a tag signal;

transmitting with the tag, the tag signal;

receiving the tag signal with a tag reader;

detecting a presence of the tag based on receipt of the tag signal at the tag reader; and

wherein the tag is periodically enabled to receive and transmit at times independent of any received first signal.

60. The method as claimed in claim 59, further comprising an act of determining an identity of the tag from the tag-specific data encoded in the tag signal.

61. The method as claimed in claim 59, further comprising acts of

receiving the tag signal with a plurality of antennas coupled to the tag reader; and

determining a location of the tag with respect to the plurality of antennas.

62. The method as claimed in claim 61, further comprising acts of:

receiving the tag signal at three locations; and

determining a location of the tag using triangulation techniques.

63. The method as claimed in claim 61, further comprising an act of determining a distance from the tag to each antenna of the plurality of antennas that receives the tag signal, based on a time of transmission of the tag signal and a time of reception of the tag signal at each antenna.

64. The method as claimed in claim 61, further comprising an act of providing the location of the tag to a user interface.

65. The method as claimed in claim 61, further comprising an act of modifying with the tag reader a piece of equipment coupled to the tag reader based on the location of the tag.

66. The method as claimed in claim 61, further comprising an act of placing the tag at a known location for performing a system calibration.

67. The method as claimed in claim 66, wherein the act of performing the system calibration comprises:

separating the received tag signal into inphase and quadrature components;

repeatedly correlating the inphase and quadrature components with a pseudonoise sequence;

determining a phase difference between successive correlations; and

calibrating a tag clock based on the phase difference.

68. The method as claimed in claim 59, further comprising an act of determining from the received tag signal, a time at which the tag will next transmit a tag signal.

69. The method as claimed in claim 59, further comprising an act of obtaining information from the received tag signal.

70. The method as claimed in claim 67, further comprising an act of modifying a piece of equipment based on information obtained from the received tag signal.

71. The method as claimed in claim 67, further comprising an act of storing information obtained from the received tag signal.