Radio frequency identification tag location estimation and tracking system and method

• US 8,072,311 B2
• Filed: 04/14/2009
• Issued: 12/06/2011
• Est. Priority Date: 04/14/2008
• Status: Active Grant

• Current Assignee: Mojix Inc
• Original Assignee: Mojix Inc
• Inventors: Sadr, Ramin, Jones, Christopher, Stephens, Scott
• Primary Examiner(s): Pham, Toan N
• Assistant Examiner(s): GIRMA, FEKADESELASS
• Application Number:
  US12/423,796
• Publication Number:
  US 20100039228A1
• Time in Patent Office: 966 Days
• Field of Search: None
• US Class Current: 340/10.1
• 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: G01S 3/74 Multi-channel systems specially adapted for direction-finding, i.e. having a single antenna system capable of giving simultaneous indications of the directions of different signals systems in which the directions of different signals are determined sequentially and displayed simultaneously G01S3/04, G01S3/14
• CPC Class Codes: G01S 5/0278 involving statistical or probabilistic considerations G01S5/0252, G01S5/0294 take precedence
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
• CPC Class Codes: G06K 7/10366 the interrogation device being adapted for miscellaneous applications

Abstract

Systems and methods for locating one or more radio frequency identification (RFID) tags are provided. A phase difference of received information signals of illuminated RFID tags is utilized to locate the RFID tags. One or more exciters transmit interrogation signals to illuminate the RFID tags in which the exciters may have a plurality of antenna selectively configured to transmit through two or more antennas and to receive on one antenna. Multiple reads of the same RFID tag can also be performed to generate a probability model of the location of the RFID tag. An enhanced particle filter is applied to probability model to determine the exact location of the RFID.

Claims

1. A method of Locating one or more radio frequency identification [RFID] tags comprising:

transmitting an interrogation signal to an RFID tag using a transmit antenna of an exciter;

receiving an information signal from the RFID tag at a plurality of receive antennas Located a known distances from the exciter;

determining a phase derivate for the information signal received by each of the plurality of receive antennas; and

identifying the Location of the RFID tag based on the determined phase derivates of the received information signals by;

determining a path Length between the transmit antenna, the RFID tag and each of the plurality of receive antennas using the phase derivate for the information signal received by the receive antenna;

defining an ellipse for each of the plurality of receive antennas, where the receive antenna is Located at one focus of the ellipse and the transmit antenna is Located at the other focus and the distance between the two foci and the major diameter of the ellipse is equal to the path Length between the transmit antenna, the RFID tag and the receive antenna determined using the phase derivate of the information signal received by the receive antenna; and

observing the location of the RFID tag as the intersection of the plurality of ellipses.

2. The method of claim 1 further comprising transmitting an activation signal from a reader to an exciter.

3. The method of claim 1 wherein identifying the location of the at least one RFID tag is based on a frequency derivate of the received information signals.

4. The method of claim 1 wherein identifying the location of the at least one RFID tag is based on a ratio of the phase derivate versus the frequency derivate.

5. The method of claim 1 wherein identifying the location of the at least one RFID tag is based on a read rate derivate of the received information signals.

6. The method of claim 1, further comprising:

estimating a location of at least one RFID tag utilizing a probability model and the determined location measurements.

7. The method of claim 6 wherein the determining location measurements further comprises determining distance between the at least one transmitter to the at least one RFID tag based on a read rate derivate.

8. The method of claim 6 wherein estimating the location uses a sequential monte carlo process or particle filter.

9. The method of claim 8 wherein the particle filter determines a likelihood of a RFID tag location based on an observed read rate of the received information signals.

10. A radio frequency identification (RFID) system for Locating one or more RFID tags in which information is embedded, the system comprising:

at least one multiport exciter having a plurality of antennas and configured to selectively transmit interrogation signals through at least two of the plurality of antennas and to selectively receive information signals from an RFID tag through one of the plurality of antennas different from the at least two of the plurality of antennas; and

a separate reader in communication with the at least one multiport exciter and configured to activate the at least one exciter, where the reader comprises at least one antenna configured to receive information signals from the RFID tag and the reader is configured to detect data from the received information signals;

wherein the at least two of the plurality of antennas used to selectively transmit interrogation signals and the antenna used to selectively receive information signals are located known distances apart;

wherein the reader is configured to control the exciter to transmit a first interrogation signal using a first of the plurality of antennas and to receive an information signal from the RFID tag via the antenna used to selectively receive information signals and then to transmit at least a second interrogation signal using a second of the plurality of antennas and to receive an information signal from the RFID tag via the same antenna used to selectively receive information signals;

wherein the reader is configured to locate RFID tag based on a phase derivate of each of the received information signals and the known distances between the at least two of the plurality of antennas used to selectively transmit interrogation signals and the antenna use to selectively receive the information signals; and

wherein the plurality of antennas are positioned in pairs with each pair being foci for a substantially ellipsoid that identifies a locus of potential locations of the at least one RFID tag and each pair positioned to minimize overlapping of each substantially ellipsoid.

11. The system of claim 10 wherein the plurality of antennas are arranged in a uniform pattern.

12. The system of claim 10 wherein the plurality of antennas are positioned equidistant from each other.

13. The system of claim 10 wherein at least two of the plurality of antennas are positioned as foci for a substantially ellipsoid that identifies a locus of potential, locations of the at least one RFID tag.

14. The system of claim 10 wherein the plurality of antennas are positioned around the at least one multiport exciter, each location of each of the plurality of antennas differing from each other.

15. The system of claim 10 wherein the nnultiport exciter uses a carrier frequency to mix a reference signal, with the received information signals.

16. The system of claim 15 wherein the reference signal, is a pilot and a preamble signal.

17. The system of claim 10, wherein:

the reader is configured to generate a probability model based on information signals received from the repeated illumination of at least one RFID tag.

18. The system of claim 17 wherein:

the reader applies a particle filter on the generated probability model to determine a location of the at least one RFID tag based on a result of the applied particle filter; and

the particle filter further comprises computing weights for each location information of the at least one RFID tag based on each illumination.

19. The system of claim 18 wherein the particle filter further comprises normalizing the computed weights.

20. The system of claim 17 wherein the reader determines a likelihood of a RFID tag location based on a phase derivate of the received information signals.

21. The system of claim 17 wherein the particle filter determines a likelihood of a RFID tag location based on observed read rate of the received information signals.

23. The system of claim 17 wherein the reader is further configured to add an offset based on movement of the at least one RFID tag.

22. The system of claim wherein the reader replicates and randomizes likely location information and discards unlikely location information of the at least one RFID tag.