Article tracking system

• US 6,150,921 A
• Filed: 10/17/1997
• Issued: 11/21/2000
• Est. Priority Date: 10/17/1996
• Status: Expired due to Term

• Current Assignee: RF Technologies (Actaris Capital SA)
• Original Assignee: Pinpoint Incorporated (Altitude Capital Partners)
• Inventors: McKinney, Kenelm, Lanzl, Colin, Werb, Jay
• Primary Examiner(s): Horabik, Michael
• Assistant Examiner(s): Dalencourt, Yves
• Application Number:
  US08/953,755
• Time in Patent Office: 1,131 Days
• Field of Search: 340/825.54, 340/825.34, 340/825.49, 340/573.1, 340/573.4, 340/10.1, 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 for transponding a radio frequency interrogator signal, comprising:

a receiver for receiving the interrogator signal at a first frequency, said receiver being enabled for receiving only at pseudo-random intervals that are independent of generation times of said first frequency;

a frequency mixer for generating from the received interrogator signal a radio frequency transmit signal at a second frequency;

a microprocessor for generating a tag-specific data signal;

a modulator for modulating the tag data signal onto the transmit signal to generate a first tag signal; and

a transmitter for transmitting the first tag signal at selected times.

2. A tag for transponding a radio frequency interrogator signal, comprising:

a receiver for receiving the interrogator signal at a first frequency, said receiver being enabled for receiving only at pseudo-random intervals that are independent of generation times of said first frequency;

a time delay for generating from the received interrogator signal a radio frequency transmit signal;

a microprocessor for generating a tag-specific data signal;

a modulator for modulating the tag data signal onto the transmit signal to generate a first tag signal; and

a transmitter for transmitting the first tag signal at selected times.

3. A tag for transponding a radio frequency interrogator signal, comprising:

a receiver for receiving the interrogator signal at a first frequency, said receiver being enabled for receiving said interrogator signal at pseudo-random times that are independent of generation times of said interrogator signal;

a signal transmission discriminator for generating from the received interrogator signal using a frequency mixer a radio frequency transmit signal that is distinguishable at the interrogator, from the interrogator signal;

a microprocessor for generating a tag-specific data signal;

a modulator for modulating the tag signal onto the transmit signal to generate a first tag signal; and

a transmitter for transmitting the first tag signal at selected times.

4. The tag of claim 3, wherein:

the signal transmission discriminator is a frequency mixer.

5. The tag of claim 3, wherein:

the signal transmission discriminator is a time delay.

6. The tag of claim 3, wherein:

the selected times are generated pseudorandomly.

7. The tag of claim 3, wherein:

a difference between two of the selected times is a function of the contents of the tag data signal.

8. The tag of claim 3, wherein:

the tag data signal uniquely identifies the tag.

9. The tag of claim 3, wherein:

the tag data signal comprises a header and a unique tag identifier.

10. The tag of claim 8, further wherein:

the tag data signal includes a validity check.

11. The tag of claim 8, wherein:

the tag data signal additionally includes error correction bits.

12. The tag of claim 8, wherein:

the tag data signal includes data derived from an object associated with the tag.

13. The tag of claim 8, wherein:

the tag is in a low power state between consecutive transmissions of first tag signals.

14. The tag of claim 9, further wherein:

said microprocessor, in response to a user input, changes the unique tag identifier.

15. The tag of claim 4, further wherein:

said microprocessor changes the selected times in response to user input.

16. The tag of claim 4, wherein said modulator comprises:

a modulator for modulating said transmit signal using on/off keyed modulation.

17. The tag of claim 4, wherein said modulator comprises:

a modulator for modulating using binary phase-shift keyed modulation.

18. The tag of claim 4, wherein said modulator comprises:

a modulator for modulating using multiple phase-shift keyed modulation.

19. The tag of claim 4, wherein said modulator comprises:

a modulator for modulating using quadrature amplified modulation.

20. The tag of claim 7, further comprising:

said microprocessor causing a second tag signal to be transmitted periodically.

21. The tag of claim 4, wherein:

the tag receives and responds to multiple interrogator signals simultaneously.

22. A method for estimating the location of an object, comprising:

transmitting an interrogator signal;

receiving said transmitted interrogator signal with a receiver enabled for receiving only at pseudo-random intervals that are independent of generation times of said interrogator signal;

transmitting a tag signal from a tag associated with the object;

receiving the transmitted tag signal at one or more of the reception antennas, the transmitted tag signal being received at a respective reception antenna at a time of arrival for that reception antenna;

deriving the identity of a tag from the tag signal received at said one or more reception antennas; and

estimating the location of the tag as a function of the locations of a subset of the reception antennas receiving the tag signal and of the times of arrival of the tag signal at the subset of reception antennas.

23. The method of claim 22, wherein receiving the tag signal comprises the steps of:

for each antenna among a set of at least one antenna, determining whether the antenna is receiving a tag signal; and

if the antenna is receiving a tag signal, identifying the antenna as a reception antenna for that tag signal.

24. The method of claim 22, said transmitting step further comprises the steps of:

modulating a pseudo-noise sequence onto a carrier signal for generating said interrogator signal; and

extending the pseudo-noise sequence after identifying the antenna as a reception antenna for the tag signal.

25. A method for estimating the location of an object, comprising:

transmitting an interrogator signal at a transmission time;

receiving said transmitted interrogator signal with a receiver being enabled for receiving said interrogator signal only at pseudo-random intervals that are independent of generation times of said interrogator signal;

transmitting a tag signal from a tag associated with the object;

receiving the transmitted tag signal at one or more reception antenna, the transmitted tag signal being received at a respective reception antenna at a time of arrival for that reception antenna;

deriving the identity of a tag from the tag signal received at one or more of the reception antennas;

at a cell controller, determining a distance from each of the reception antennas to the tag based on the transmission time and the time of arrival of that reception antenna; and

estimating the location of the tag as a function of the distances from a subset of the reception antennas to the tag.

26. A method for detecting the presence of a tag, comprising:

at a cell controller, transmitting a first signal at a first frequency;

at the tag, receiving the first signal and transponding the first signal, at selected times, at a second frequency as a second signal, said selected times being pseudo-random intervals that are independent of generation times of said first frequency;

at the cell controller, receiving the second signal; and

at the cell controller, detecting the presence of the tag based on the receipt of the second signal.

27. A method for measuring the distance from an antenna to a tag, comprising:

at the antenna, transmitting a pseudonoise sequence on a first signal at a first frequency at a transmission time;

at the tag, receiving the first signal and transponding the first signal at a second frequency as a second signal only at pseudo-random intervals that are independent of generation times of said first frequency;

at the antenna, receiving the second signal at a time of arrival; and

at the cell controller, determining a distance from the antenna to the tag based on the transmission time and the time of arrival.

28. A cell controller comprising:

an antenna for transmitting a cell controller signal on a first frequency and for receiving a tag signal from a transponding tag on a second frequency at pseudo-random intervals that are independent of generation times of said first frequency;

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

digitizing the inphase and quadrature components for subsequent processing.

29. A cell controller, comprising:

circuitry for transmitting a cell controller signal modulated onto a carrier signal;

circuitry for receiving a tag signal transmitted at selected times by a tag, said circuitry for receiving being enabled for receiving said tag signal only at pseudo-random time intervals that are independent of generation times of said cell controller signal.

30. The cell controller of claim 29, further comprising:

circuitry for determining, from the received tag signal, the identity of the tag.

31. The cell controller of claim 30, further comprising:

circuitry for determining, from the received tag signal, the time at which the tag will next transmit a tag signal.

33. The system of claim 31, wherein:

the cell controller is configurable to be connected to a variable number of additional antennas.

32. A system for monitoring the location of objects, comprising:

at least one cell controller unit connected to at least one transmission antenna for transmitting a cell controller signal modulated onto a carrier signal at a first frequency and at a selected transmission time, and connected to at least one reception antenna for receiving a responding tag signal containing a tag datagram at a second frequency and at a time of arrival, said responding tag signal being generated at pseudo-random time intervals that are independent of generation times of said cell controller signal;

at least one tag unit having a translation circuitry for translating each received cell controller signal into the tag signal; and

at least one calculation unit connected to each cell controller for calculating the location of each tag unit based on the time of arrival of at least one reception antenna.

34. A system for monitoring the location of objects, wherein:

at least one reception antenna connected to a cell controller is mounted near a piece of equipment; and

the cell controller is configured to modify the operating characteristics of the piece of equipment based on the identity of a responding object near said piece of equipment, said responding object including a tag that transponds a tag signal only at pseudo-random intervals that are independent of generation times of an interrogator signal.

35. The system of claim 34, wherein:

the reception antenna is mounted near a computer screen so that the reception antenna'"'"'s input is directed at the computer screen'"'"'s field of vision.

36. A system for monitoring the location of objects, comprising:

at least one cell controller unit connected to at least one antenna module for transmitting a cell controller signal and for receiving a tag signal;

at least one tag unit for receiving the cell controller signal, for translating the received cell controller signal into the tag signal, and for transmitting the tag signal at selected times, said selected times being pseudo-random intervals that are independent of generation times of said cell controller signal;

at least one calculation unit connected to each cell controller unit for determining the location of each tag unit based on the received tag signals, and for storing information derived from the received tag signals in a computer-readable storage medium.

37. The system of claim 36, further comprising:

tag units located at known fixed locations for performing system calibration.

38. A method for calibrating a tag clock of a tag in a system for monitoring the location of objects, comprising:

separating a tag signal transmitted by a tag at pseudo-random times that are independent of generation times of a cell controller signal into inphase and quadrature components;

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

determining a phase difference between successive correlations;

calibrating the tag clock based on the phase difference.