Method and apparatus for localization of RFID tags

• US 9,285,471 B2
• Filed: 11/21/2005
• Issued: 03/15/2016
• 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: Lyon, Geoff M., Pradhan, Salil
• Primary Examiner(s): Khan, Omer S
• Application Number:
  US11/285,370
• Publication Number:
  US 20070115137A1
• Time in Patent Office: 3,767 Days
• Field of Search: 340/825.49
• US Class Current: 1/1
• 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. An RFID tag capable of assisting in a determination of its location, comprising:

a timer to periodically generate a signal at a predetermined time interval;

a controller to be powered up upon receiving the periodically generated signal from the timer;

a radio frequency (RF) transceiver to send an identifier associated with the RFID tag at the predetermined time interval from the RFID tag in response to the powering of the controller by the periodically generated signal from the timer;

a motion sensor to determine whether the RFID tag has been moved to a different position, wherein to determine whether the RFID tag has been moved comprises;

receiving a first indication of movement from the motion sensor;

receiving a time interval signal measured according to the 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 period; and

determining that the RFID tag has ceased movement according to the second indication that movement is occurring and the third indication that movement has not occurred for the predetermined time period; and

an ultrasound receiver to receive signals traveling at a second velocity compared with a first velocity of signals received by the transceiver that determines a location of the RFID tag in a new position responsive to the motion sensor.

2. The RFID tag of claim 1, further comprising:

a tag movement flag to indicate a stationary status or in-motion status of the RFID tag, wherein when there is an indication of movement from the motion sensor, the RFID tag movement flag is set to indicate the in-motion status of the RFID tag and a time interval measurement is started by the timer.

3. The RFID tag of claim 2, wherein when the time interval measurement is greater than a time threshold, the RFID tag movement flag is reset to indicate the stationary status of the RFID tag.

4. The RFID tag of claim 1, wherein when the RFID tag is in motion, the transceiver is to send, to an interrogator, an indication of movement of the RFID tag.

5. The RFID tag of claim 2, wherein when the RFID tag movement flag indicates the stationary status of the RFID tag, the RF transceiver is to send, to an interrogator, the stationary status of the RFID tag.

6. The RFID tag of claim 1, wherein the RF transceiver is to

receive from an interrogator a first signal having a first velocity that arrives at the RFID tag at a first time,

receive from the interrogator a second signal having a second velocity that arrives at the RFID tag at a second time, and

transmit to the interrogator a third signal indicative of the distance between the RFID tag and the interrogator based upon a difference between the arrival times of the first and second signals.

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

8. A method for an RFID tag to facilitate a determination of its location, wherein the RFID tag includes a timer, a controller, a radio frequency (RF) transceiver, a motion sensor, and an ultrasound receiver, the method comprising:

periodically generating, by the timer, a signal at a predetermined time interval;

powering up the controller in response to the periodically generated signal from the timer;

sending, by the RF transceiver, an identifier associated with the RFID tag at the predetermined time interval from the RFID tag in response to the powering of the controller;

determining, by the motion sensor, if the RFID tag has been moved to a different position, wherein the determining comprises;

receiving a first indication of movement from the motion sensor;

receiving a time interval signal measured according to the 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 period; and

determining that the RFID tag has ceased movement according to the second indication that movement is occurring and the third indication that movement has not occurred for the predetermined time period; and

receiving, by the ultrasound receiver, signals traveling at a second velocity compared with a first velocity of signals received by the RF transceiver that determines a location of the RFID tag in a new position responsive to the motion sensor.

9. The method of claim 8, further comprising:

setting a tag movement flag to indicate an in-motion status of the RFID tag when there is an indication of movement from the motion sensor, and

starting, by the timer, a time interval measurement.

10. The method of claim 9, further comprising:

resetting the RFID tag movement flag to indicate a stationary status of the RFID tag when the time interval measurement is greater than a time threshold.

11. The method of claim 8, further comprising:

sending to an interrogator an indication of movement of the RFID tag when the RFID tag is in motion.

12. The method of claim 8, further comprising:

sending to an interrogator an indication of stationary status of the RFID tag in response to a determination by the motion sensor that the RFID tag is stationary.

13. The method of claim 8, further comprising:

receiving from an interrogator a first signal having a first velocity that arrives at the RFID tag at a first time; and

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

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

14. An RFID tag device comprising:

a timer to periodically generate a signal at a predetermined time interval;

a controller to be powered up upon receiving the periodically generated signal from the timer;

a radio frequency (RF) transceiver to send an identifier associated with the RFID tag device at the predetermined time interval in response to the powering of the controller by the periodically generated signal from the timer;

a motion sensor to determine if the RFID tag device has been moved to a different position, wherein to determine if the RFID tag device has been moved comprises;

receiving a first indication of movement from the motion sensor;

receiving a time interval signal measured according to the 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 period; and

determining that the RFID tag has ceased movement according to the second indication that movement is occurring and the third indication that movement has not occurred for the predetermined time period; and

an ultrasound receiver to receive signals traveling at a second velocity compared with a first velocity of signals received by the RF transceiver that determines a location of the RFID tag device in a new position responsive to the motion sensor.

15. The RFID tag device of claim 14, further comprising:

a tag movement flag, wherein when there is an indication of movement from the motion sensor, the RFID tag movement flag is set and a time interval measurement is started by the timer.

16. The RFID tag device of claim 15, wherein when the time interval measurement is greater than a time threshold, the RFID tag movement flag is reset.

17. The RFID tag device of claim 14, wherein when the RFID tag device is stationary, the RF transceiver is to send to an interrogator an indication of stationary status of the RFID tag device.

18. The RFID tag device of claim 14, wherein the RF transceiver is to:

receive from an interrogator a first signal having a first velocity that arrives at the RFID tag device at a first time, and

receive from the interrogator a second signal having a second velocity that arrives at the RFID tag device at a second time,

wherein the controller is to determine a distance between the RFID tag device and the interrogator based upon a difference between the arrival times of the first and second signals, and

wherein the RF transceiver is to transmit to the interrogator a third signal indicative of the distance between the RFID tag device and the interrogator.

19. The RFID tag device of claim 18, wherein the first signal is a radio signal and the second signal is an ultrasound signal.