RFID Tag Movement Determination

• US 20100156651A1
• Filed: 12/19/2008
• Published: 06/24/2010
• Est. Priority Date: 12/19/2008
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Broer, Dirk A
• Granted Patent: US 8,537,014 B2
• Time in Patent Office: Days
• US Class Current: 340/670
• CPC Class Codes: G01S 13/74 Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
• 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: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10079 the collision being resolved in the spatial domain, e.g. temporary shields for blindfolding the interrogator in specific directions

Abstract

A system, techniques, and apparatus for determining RFID tag movement are disclosed. The system includes an RFID reader that is configured to detect an RFID tag'"'"'s motion by comparing backscattered signals received from the tag. The system can also generate and filter alerts according to pre-defined business rules based on the detection.

Claims

1. A method of detecting movement of a RFID tag comprising:

transmitting a plurality of RF signals from at least one RFID reader to the RFID tag;

receiving at least two modulated backscattered signals from the tag in response to the transmission of signals;

comparing the at least two backscattered signals to one another; and

detecting movement of the RFID tag based on the comparison.

2. The method of claim 1, further comprising singulating the RFID tag prior to comparing the at least two modulated backscattered signals.

3. The method of claim 2, wherein comparing the at least two back scattered signals comprises:

calculating at least one of a return signal strength indicator (RSSI) and return signal phase angle for each of the backscattered signals;

comparing the at least one RSSI and phase angle of each backscattered signal to one another; and

detecting movement of the RFID tag if the at least one RSSI and phase angle calculated for each backscattered signal differ from one another.

4. The method of claim 3, wherein calculating the phase angle comprises calculating an in-phase (I) and quadrature (Q) signal for each backscattered signals.

5. The method of claim 3, further comprising:

receiving the at least two modulated backscattered signals on an antenna of the at least one REID reader; and

calculating a velocity of the tag relative to the antenna.

6. The method of claim 5, further comprising smoothing the at least two modulated backscattered signals.

7. The method of claim 5, further comprising:

generating an alert based on detecting movement of the tag; and

processing the alert using a business rule.

8. The method of claim 7, comprising filtering the alert by interrogating a field of the tag in response to detecting movement of the tag.

9. The method of claim 1, comprising triangulating a velocity of the tag using a plurality of RFID readers.

10. An RFID reader including at least one antenna, the RFID reader including a processor and memory including memory storing instructions that, in response to a request, cause the processor to:

transmit a plurality of RF signals to an RFID tag through the at least one antenna, compare at least two backscattered signals from the tag to one another in response to transmission of signals through the antenna, and detect movement of the RFID tag based on the comparison.

11. The RFID reader of claim 10, wherein the memory stores instructions that, in response to receiving the request, cause the processor to singulate the RFID tag prior to comparing the at least two backscattered signals.

12. The RFID reader of claim 10, wherein the memory stores instructions that, in response to receiving the request, cause the processor to:

calculate at least one of a return signal strength indicator (RSSI) and return signal phase angle for each of the backscattered signals;

compare the at least one RSSI and phase angle of each backscattered signal to one another; and

detect movement of the RFID tag if the at least one RSSI and phase angle calculated for each backscattered signal differ from one another.

13. The RFID reader of claim 12, wherein the memory stores instructions that, in response to receiving the request, cause the processor to calculate an in-phase (I) and quadrature (Q) signal for each backscattered signals.

14. The REID reader of claim 12, wherein the memory stores instructions that, in response to receiving the request, cause the processor to calculate a velocity of the tag relative to the antenna in response to receiving the at least two modulated backscattered signals on an antenna of the at least one RFID reader.

15. The RFID reader of claim 14, wherein the memory stores instructions that, in response to receiving the request, cause the processor to smooth the at least two modulated backscattered signals.

16. The RFID reader of claim 14, wherein the memory stores instructions that, in response to receiving the request, cause the processor to:

generate an alert based on detecting movement of the tag; and

process the alert using a business rule.

17. The RFID reader of claim 16, wherein the memory stores instructions that, in response to receiving the request, cause the processor to filter the alert by comparing the velocity to a pre-determined value.

18. The RFID reader of claim 10, wherein the memory stores instructions that, in response to receiving the request, cause the processor to triangulate a velocity of the tag using a plurality of RFID readers.

19. An RFID system comprising:

a plurality of RFID tags;

at least one RFID reader for communicating with the plurality of RFID tags, the at least one RFID reader configured to transmit a plurality of RF signals to one of the plurality of RFID tags, compare at least two backscattered signals received from the one of the plurality of tags to one another, and detect movement of the one of the plurality of tags based on the comparison.

20. The RFID system of claim 19, wherein the RFID reader calculates at least one of a return signal strength indicator (RSSI) and return signal phase angle for each of the backscattered signals, compares the at least one RSSI and phase angle of each backscattered signal to one another, and detects movement of the one of the plurality of RFID tags if the at least one RSSI and phase angle calculated for each backscattered signal differ from one another.