SPATIALLY LOCATING RADIO TAGS FOR ON DEMAND SYSTEMS

• US 20080165058A1
• Filed: 01/04/2007
• Published: 07/10/2008
• Est. Priority Date: 01/04/2007
• Status: Active Grant

• Current Assignee: Globalfoundries US Incorporated (GlobalFoundries, Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Ayachitula, Naga A., Chang, Shu-Ping, Lipscomb, James S., Brady, Stephen, Stein, Frank L.
• Granted Patent: US 7,616,113 B2
• Time in Patent Office: Days
• US Class Current: 342/359
• 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 7/4021 of receivers
• CPC Class Codes: H01Q 1/2208 associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems methods or arrangements for sensing record carriers, e.g. for reading patterns G06K7/00; record carrier for use with machines and with at least a part designed to carry digital markings G06K19/00
• CPC Class Codes: H01Q 21/28 Combinations of substantially independent non-interacting antenna units or systems multiple beam H01Q25/00

Abstract

An embodiment of the invention is a method of accurately determining the spatial location of an RFID tag in two-dimensions or three-dimensions. The method utilizes a plurality of RFID readers to make a plurality of distance, direction, and or time-of-flight determinations. Such determinations are made by sending a request signal from one of the plurality of RFID readers and listening for a response signal from an RFID tag received at each of the plurality of RFID readers. Correction factors are then determined and the time-of-flight factors adjusted. The adjusted time-of-flight factors are then used to determine more accurately the distances between the RFID tag and each of the plurality of RFID readers. These more accurate distance measurements are then used to determine the spatial location of the RFID tag.

Claims

1. A method of spatially locating RFID tags, said method comprising:

transmitting a request signal from at least one of a plurality of RFID readers;

receiving an RFID tag response signal at said plurality of RFID readers;

determining a plurality of time-of-flight factors;

determining a plurality of correction factors;

adjusting said plurality of time-of-flight factors by applying said plurality of correction factors to said plurality of time-of-flight factors;

determining based in part on said plurality of time-of-flight factors a plurality of distances between each of said plurality of RFID readers and said RFID tag; and

determining based in part on said plurality of distances the spatial location of said RFID tag.

2. The method in accordance with claim 1, wherein determining a plurality of time-of-flight factors includes determining the time period between sending said request signal from at least one of said plurality of RFID readers and receiving said RFID response signal at each of said plurality of RFID readers.

3. The method in accordance with claim 1, further comprising:

retrieving previously stored said plurality of correction factors.

4. The method in accordance with claim 1, further comprising:

measuring signal strength of said RFID tag response signal.

5. The method in accordance with claim 1, further comprising:

associating said plurality of correction factors with said RFID tag data.

6. The method in accordance with claim 5, wherein associating said plurality of correction factors with said RFID tag data includes storing said plurality of correction factors and said RFID tag data at a networked data processing resource.

7. The method in accordance with claim 1, further comprising:

decoding said RFID tag response signal to determine an identification code associated with said RFID tag.

8. The method in accordance with claim 7, further comprising:

retrieving previously stored said plurality of correction factors associated with said identification code.

9. The method in accordance with claim 8, wherein said identification code is at least one of the following:

i) said RFID tag serial number;

ii) said RFID tag model number;

iii) said RFID tag manufacturer number;

or

iv) said RFID tag data.

v) an implicit ID based on a record of a tag previously near this location suggesting that the tag now observed may be the same tag as the previous tag there.

10. The method in accordance with claim 1, further comprising:

calculating said plurality of correction factors based on said plurality of time-of-flight factors and said RFID tag response signal strength.

11. The method in accordance with claim 1, further comprising:

synthesizing valid said plurality of RFID readers data, when said plurality of RFID readers data is determined to be invalid, by replacing said plurality of RFID readers invalid data with previously valid said plurality of RFID readers data.

12. The method in accordance with claim 1, further comprising:

calibrating an uncalibrated RFID reader by using said RFID tag and data from said plurality of RFID readers, wherein said plurality of RFID readers are converged on the spatial location of said RFID tag..

13. The method in accordance with claim 1, wherein said RFID tag implements a two-axis non-planar antenna with the RFID tag using the antennas together at the same time or by switching successively between them to obtain the best send/receive signal strength to the reader.

14. The method in accordance with claim 1, wherein said RFID tag implements a three-axis non-planar antenna with the RFID tag using the antennas together at the same time or by switching successively between them to obtain the best send/receive signal strength to the reader.

15. The method in accordance with claim 1, wherein said RFID tag response signal is a precisely timed radio pulse.

16. The method in accordance with claim 1, wherein each of said plurality of RFID readers further comprising a directional antenna.

17. The method in accordance with claim 1, wherein said plurality of distances determinations is influenced by at least one of said plurality of RFID readers having a directional antenna.

18. The method in accordance with claim 1, wherein at least one on said plurality of RFID readers data communicate with a global network based data processing resource.

19. The method in accordance with claim 1, wherein each of the determining and adjusting is performed at a network based data processing resource.

20. A method of spatially locating RFID tags, said method comprising:

transmitting a request signal from at least one of a plurality of RFID readers;

receiving an RFID tag response signal at said plurality of RFID readers;

determining a plurality of time-of-flight factors;

determining a plurality of correction factors;

adjusting said plurality of time-of-flight factors by applying said plurality of correction factors to said plurality of time-of-flight factors;

determining based in part on said plurality of time-of-flight factors a plurality of distances between each of said plurality of RFID readers and said RFID tag;

determining based in part on said plurality of distances the spatial location of said RFID tag;

detecting disagreements between said plurality of readers as to the presumed spatial location of said RFID tag resultant from reflected signal paths; and

adjusting for spurious distances resultant from reflected signal paths by using mathematically modeled and saved RFID tag spatial location data near the determined said RFID tag spatial location.