Method and apparatus for localization of RFID tags

• US 20070115137A1
• Filed: 11/21/2005
• Published: 05/24/2007
• Est. Priority Date: 11/21/2005
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Pradhan, Salil, Lyon, Geoff
• Granted Patent: US 9,285,471 B2
• Time in Patent Office: Days
• US Class Current: 340/825.490
• CPC Class Codes: G01S 13/767 Responders; Transponders teaching or practice apparatus for gun-aiming or gun-laying using reflecting targets or active targets F41G3/26

Abstract

A method and apparatus for an RFID tag to facilitate the determination of its location while at the same time minimizing the energy drain on the tag'"'"'s battery. At predetermined intervals, the tag transmits its identifier along with status information. If the status indicates that the tag is in a new location, the tag will then expend additional battery energy by participating in the determination of its location. The distance from an interrogator to the tag is determined by transmitting two signals from the interrogator that propagate at different velocities. By determining the difference in arrival times at the tag of the two signals, the distance from the interrogator to the tag can be determined.

Claims

1. A method for a tag to facilitate the determination of its location, comprising:

transmitting at a predetermined time interval from the tag an identifier associated with the tag;

determining if tag has been moved to a different position using one or more sensors associated with the tag; and

expending energy from the tag responsive to the movement determination as the tag participates in an operation that locates the tag in the different position.

2. The method of claim 1 wherein the determination of tag movement further comprises:

receiving an indication of movement from a movement sensor associated with the tag; and

determining that the tag has ceased movement when a subsequent indication from the movement sensor has not occurred for a predetermined time interval.

3. The method of claim 2 wherein the determination of movement cessation further comprises:

receiving a first indication of movement from one or more movement sensors;

receiving a time interval signal measured from the most recently received first indication of movement;

receiving a second indication that movement is occurring;

receiving a third indication that movement has not occurred for a predetermined time interval; and

determining that the tag has ceased movement according to the second indication that movement is occurring and the third indication that movement has not occurred for a predetermined time interval.

4. The method of claim 1 wherein, in addition to the identifier, an indication of movement is communicated to the interrogator when the tag is in motion.

5. The method of claim 1 wherein, in addition to the identifier, an indication of no movement is communicated to the interrogator when the tag is not in motion.

6. The method of claim 1 wherein the operation that locates the tag comprises:

receiving by the tag having the identifier a first signal transmitted from the interrogator having a first velocity that arrives at the tag at a first time;

receiving by the tag having the identifier a second signal transmitted from the interrogator having a second velocity that arrives at the tag at a second time; and

transmitting to the interrogator a third signal indicative of the distance from the tag to the interrogator based upon from the arrival times of the first and second signals.

7. The method of claim 6 wherein the first signal is a radio signal and the second signal is an ultrasound signal.

8. The method of claim 6 wherein the difference in arrival times between the first signal and the second signal is indicative of the tag'"'"'s distance from the interrogator.

9. The method of claim 1 wherein a high-visibility mode can be set so that tag location can be determined while the tag is moving.

10. The method of claim 1 wherein the tag is attached to an object to monitor the object'"'"'s position for inventory control.

11. A method for an interrogator to determine a tag location, comprising:

receiving at a predetermined time interval from the tag an identifier associated with the tag;

receiving an indication that the tag has changed position; and

performing a location operation in response to the indication that the tag has changed position.

12. The method of claim 11 wherein the determination of the tag location comprises:

transmitting to the tag having the identifier a first signal having a first velocity that will arrive at the tag at a first time;

transmitting to the tag having the identifier a second signal having a second velocity that will arrive at the tag at a second time; and

receiving at the interrogator a third signal from the tag in response to first and second signal transmissions that is indicative of the distance from the tag to the interrogator.

13. The method of claim 12 wherein the first signal is a radio signal and the second signal is an ultrasound signal.

14. The method of claim 12 wherein the first and second signals are transmitted at predetermined times.

15. The method of claim 12 wherein the difference in arrival times between the first signal and the second signal is indicative of the tag'"'"'s distance from the interrogator.

16. The method of claim 12 wherein the distance from the tag to the interrogator is calculated by the tag and transmitted to the interrogator.

17. The method of claim 12 wherein the distance from the tag to the interrogator is calculated by the interrogator and is determined by the arrival time of the third signal at the interrogator sent by the tag upon the arrival of the second signal from the interrogator.

18. A computer program product for use by a tag to facilitate the determination of its location, tangibly stored on a computer readable medium, comprising instructions operable to cause a programmable processor to:

transmit at a predetermined time interval from the tag an identifier associated with the tag;

determine if tag has been moved to a different position using one or more sensors associated with the tag; and

expend energy from the tag responsive to the movement determination as the tag participates in an operation that locates the tag in the different position.

19. A computer program product for use by an interrogator to determine a tag location, tangibly stored on a computer readable medium, comprising instructions operable to cause a programmable processor to

receive at a predetermined time interval from the tag an identifier associated with the tag;

receive an indication that the tag has changed position; and

perform a location operation in response to the indication that the tag has changed position.

20. A tag capable of assisting in the determination of its location, comprising:

a first transmitter capable of sending an identifier associated with the tag at a predetermined time interval from the tag;

a motion sensor and timer capable of determining if tag has been moved to a different position within a predetermined interval measured by the timer; and

a second transmitter that receives signals traveling at a second velocity compared with a first velocity of signals received by the first transmitter that determines a location of the tag in a new position responsive to the motion sensor.