Motion tracking techniques for RFID tags

• US 8,325,019 B2
• Filed: 09/13/2010
• Issued: 12/04/2012
• Est. Priority Date: 09/13/2010
• Status: Expired due to Fees

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Liu, Xu, Hull, Jonathan J.
• Primary Examiner(s): HUNNINGS, TRAVIS R
• Application Number:
  US12/880,869
• Publication Number:
  US 20120062381A1
• Time in Patent Office: 813 Days
• Field of Search: 340/10.1, 340/572.1, 340/505
• US Class Current: 340/10.5
• 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:

receiving 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 first 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 first sequence of RSSIs and reference information, 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, the reference information comprising a plurality of RSSI vectors, each vector comprising a sequence of RSSIs and being associated with information indicative of a path of motion and a direction of motion;

wherein determining the motion-related information comprises;

determining, from the plurality of RSSI vectors, a RSSI vector having a smallest Euclidian distance to the first sequence of RSSIs; and

outputting a path of motion and a direction of motion associated with the determined RSSI vector as the path of motion and the direction of motion of the RFID tag.

2. The method of claim 1 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.

3. 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.

4. 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 and reference information, 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, the reference information comprising a plurality of RSSI vectors, each vector comprising a sequence of RSSIs and being associated with information indicative of a path of motion and a direction of motion;

wherein to determine the motion-related information, the data processing system is further configured to;

determine, from the plurality of RSSI vectors, a RSSI vector having a smallest Euclidian distance to the first sequence of RSSI; and

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

5. The system of claim 4 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.

6. The system of claim 4 wherein the antenna is stationary.

7. The system of claim 4 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.

8. 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.

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

the processer is configured to;

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

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

9. The system of claim 8 wherein:

the reference information is obtained using Hidden Markov Model (HMM) processing.

10. 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 motion of the RFID tag and information indicative of a direction of motion of the RFID tag alone the path,

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