MOTION TRACKING TECHNIQUES FOR RFID TAGS

• US 20120062381A1
• Filed: 09/13/2010
• Published: 03/15/2012
• Est. Priority Date: 09/13/2010
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Liu, Xu, Hull, Jonathan J.
• Granted Patent: US 8,325,019 B2
• Time in Patent Office: Days
• US Class Current: 340/572.1
• CPC Class Codes: G01S 11/06 using intensity measurements
• CPC Class Codes: G01S 5/02521 using a radio-map

Abstract

Techniques for tracking the motion of an RFID tag using signal strength information. A single antenna of an RFID reader may be used to take a sequence of readings from an RFID tag in motion. A signal strength indicator (e.g., received signal strength indicator (RSSI)) is determined for each reading. The sequence of RSSIs is then used to estimate a path of motion of the RFID tag and the direction of motion of the RFID tag along the path.

Claims

1. A method comprising:

taking, using a single antenna, a sequence of readings from a radio frequency identification (RFID) tag;

determining a received signal strength indicator (RSSI) for each reading in the sequence of readings;

generating a sequence of RSSIs based upon the RSSIs determined for the sequence of readings; and

determining motion-related information for the RFID tag based upon the sequence of RSSIs, the motion-related information comprising information indicative of a path of motion of the RFID tag and information indicative of a direction of motion of the RFID tag along the path.

2. The method of claim 1 wherein determining the motion-related information comprises using reference information and the sequence of RSSIs to determine the motion-related information.

3. The method of claim 2 wherein the reference information comprises information obtained using Hidden Markov Model (HMM) processing, the reference information comprising information identifying a plurality of locations and, for each location, an RSSI associated with the location.

4. The method of claim 2 wherein the reference information comprises a plurality of vectors, each vector comprising a sequence of RSSIs, each vector associated with information indicative of a path of motion and a direction of motion.

5. The method of claim 1 wherein determining the motion-related information comprises using a Hidden Markov Model (HMM).

6. The method of claim 1 wherein determining the motion-related information comprises performing a K-nearest neighbor analysis.

7. The method of claim 1 wherein the single antenna is stationary.

8. The method of claim 1 wherein the RFID tag is attached to an object, the method further comprising determining a path of motion and a direction of motion for the object based upon the path of motion and the direction of motion determined for the RFID tag.

9. A system comprising:

a reader comprising an antenna; and

a data processing system communicatively coupled with the reader;

wherein the reader is configured to;

take, using the antenna, a sequence of readings from an radio frequency identification (RFID) tag; and

determine a received signal strength indicator (RSSI) for each reading in the sequence of readings;

wherein the data processing system is configured to;

generate a sequence of RSSIs based upon the RSSIs determined for the sequence of readings; and

determine motion-related information for the RFID tag based upon the sequence of RSSIs, the motion-related information comprising information indicative of a path of motion of the RFID tag and information indicative of a direction of motion of the RFID tag along the path.

10. The system of claim 9 wherein the data processing system is configured to determine the motion-related information using reference information and the sequence of RSSIs.

11. The system of claim 10 wherein the reference information comprises information obtained using Hidden Markov Model (HMM) processing, the reference information comprising information identifying a plurality of locations and, for each location, an RSSI associated with the location.

12. The system of claim 10 wherein the reference information comprises a plurality of vectors, each vector comprising a sequence of RSSIs, each vector associated with information indicative of a path of motion and a direction of motion.

13. The system of claim 9 wherein the data processing system is configured to determine the motion-related information using a Hidden Markov Model (HMM).

14. The system of claim 9 wherein the data processing system is configured to determine the motion-related information by performing a K-nearest neighbor analysis.

15. The system of claim 9 wherein the antenna is stationary.

16. The system of claim 9 wherein:

the RFID tag is attached to an object; and

and the data processing system is configured to determine a path of motion and a direction of motion for the object based upon the path of motion and the direction of motion determined for the RFID tag.

17. A system comprising:

a memory configured to store a sequence of signal strength indicators (RSSIs) corresponding to a sequence of readings taken from a radio frequency identification (RFID) tag; and

a processor coupled with the memory, the processor configured to determine motion-related information for the RFID tag based upon the sequence of RSSIs, the motion-related information comprising information indicative of a path of motion of the RFID tag and information indicative of a direction of motion of the RFID tag along the path.

18. The system of claim 17 wherein:

the memory is configured to store reference information obtained using Hidden Markov Model (HMM) processing, the reference information comprising information identifying a plurality of locations and, for each location, an RSSI associated with the location; and

the processor is configured to determine the motion-related information using the reference information.

19. The system of claim 17 wherein:

the memory is configured to store reference information comprising a plurality of RSSI vectors, each vector comprising a sequence of RSSIs, each vector associated with information indicative of a path of motion and a direction of motion; and

the processor is configured to;

determine a vector from the plurality of vectors with smallest Euclidian distance to the sequence of RSSIs corresponding to the sequence of readings taken from the RFID tag; and

output the path of motion and direction of motion information associated with the determined vector as the path of motion and direction of motion of the RFID tag.

20. The system of claim 17 wherein:

the memory is configured to store reference information comprising a plurality of RSSI vectors, each vector comprising a sequence of RSSIs, each vector associated with a label indicative of a path of motion and a direction of motion; and

the processor is configured to;

determine a set of multiple vectors from the plurality of vectors with smallest Euclidian distances to the sequence of RSSIs corresponding to the sequence of readings taken from the RFID tag;

determine, from labels associated with the set of vectors, a label associated with most vectors in the set of vectors; and

output the path of motion and direction of motion information indicated by the determined label as the path of motion and direction of motion of the RFID tag.