System and method for positioning active RFID tag

• US 8,339,243 B2
• Filed: 12/31/2008
• Issued: 12/25/2012
• Est. Priority Date: 12/31/2008
• Status: Active Grant

• Current Assignee: Mitac Technology Corporation (MiTAC Holdings Corp.)
• Original Assignee: Mitac Technology Corporation (MiTAC Holdings Corp.)
• Inventors: Shiau, Jun-Ting, Hsu, Jen-Hao, Yu, Chia-Chin
• Primary Examiner(s): Wu, Daniel
• Assistant Examiner(s): Terrell, Emily C
• Application Number:
  US12/347,833
• Publication Number:
  US 20100164723A1
• Time in Patent Office: 1,455 Days
• Field of Search: 340/10.1, 340/10.2, 340/10.4, 340/10, 340/572.1, 340/572
• US Class Current: 340/10.1
• 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 positioning system and method are provided to use multiple RFID readers to position a target object with an active RFID tag equipped thereon. The system and method defines a geometric center of the locations of the RFID readers as a first coordinate. When the RFID readers continuously receive RF signals of the active RFID tag, a corresponding signal intensity of each of the RF signals is calculated and compared to obtain an approaching vector corresponding to the location of the RFID reader with the greatest signal intensity of the RF signal. A positioned location of the target object is then approached from the first coordinate to a second coordinate according to the approaching vector. The first coordinate and the positioned location of the target object will be reset as the second coordinate. The reset first coordinate is output as the latest positioned location of the target object.

Claims

1. A system adapted to determine the position of a stationary target object equipped with an active RFID (Radio Frequency Identification) tag by using a plurality of RFID readers, wherein the system uses iteration to determine the position with greater accuracy than triangulation, the system comprising:

a receiving module receiving a RF (Radio Frequency) signal of the active RFID tag received from each of the RFID readers respectively, and calculating a corresponding signal intensity of each of the RF signals;

a setting module defining the first estimated location of the target object as a middle point between the RFID readers and then moving the estimated location according to an estimated location vector when the location of the RFID reader with the greatest signal intensity is determined;

a comparison module comparing the corresponding signal intensities of the RF signals to calculate the estimated location vector corresponding to the location of the RFID reader with the greatest signal intensity of the RF signal, wherein the estimated location vector is collinear with the line that connects the estimated location and the RFID reader with the greatest signal intensity of the RF signal; and

an output module outputting the estimated location of the target object;

wherein the setting module, the comparison module and the output module operate to output the latest estimated location of the target object as long as the receiving module receives the RF signals.

2. The system as claimed in claim 1, wherein the RFID reader further calculates the signal intensity of each of the received RF signals.

3. The system as claimed in claim 1, wherein the comparison module further calculates the signal intensity of each of the received RF signals.

4. The system as claimed in claim 1 further comprising a positioning duration threshold, wherein the system is operative when the accumulated time for the positioning operations reaches the positioning duration threshold, the estimated location last output by the output module will be used as the location of the target object.

5. The system as claimed in claim 1 further comprising a positioning times threshold, wherein when the positioning times threshold is reached, the estimated location last output by the output module will be used as the location of the target object.

6. The system as claimed in claim 1 further comprising a reset times threshold, wherein when comparing through the comparison module, if the ranking of the signal intensities of the RF signals received by the RFID readers remains the same for the reset times threshold, then the estimated location last output by the output module will be used as the location of the target object.

7. The system as claimed in claim 1, wherein the setting module sets estimated location (n plus one) as a midpoint between estimated location (n) and the RFID reader with the greatest signal intensity.

8. The system as claimed in claim 1, wherein the setting module sets the estimated location (n plus one) by approaching a unit length from estimated location (n) towards the RFID reader with the greatest signal intensity.

9. A method adapted to use a plurality of RFID (Radio Frequency Identification) readers to determine the position of a stationary target object equipped with an active RFID (Radio Frequency Identification) tag, wherein the system uses iteration to determine the position with greater accuracy than triangulation, the method comprising the steps of:

defining the first estimated location of the target object as a middle point between the RFID readers;

repeating the following steps as long as the RFID readers continuously receive RF (Radio Frequency) signals of the active RFID tag;

receiving the RF signals of the active RFID tag through the RFID readers to calculate a corresponding signal intensity of each of the RF signals;

comparing corresponding signal intensity of each of the RF signals;

calculating an estimated location vector corresponding to the location of the RFID reader with the greatest signal intensity of the RF signal, wherein the estimated location vector is collinear with the line that connects the estimated location and the RFID reader with the greatest signal intensity of the RF signal;

moving the estimated location according to the estimated location vector;

outputting the latest estimated location of the target object.

10. The method as claimed in claim 9, wherein the RFID reader further calculates the signal intensity of each of the received RF signals.

11. The method as claimed in claim 9 further comprising the step of calculating the signal intensity of each of the received RF signals.

12. The method as claimed in claim 9, wherein the repeated steps are terminated by a default positioning duration threshold.

13. The method as claimed in claim 9, wherein the repeated steps are terminated by a default positioning times threshold.

14. The method as claimed in claim 9 further comprising the steps of:

terminating the repeated steps if the ranking of the signal intensities of the RF signals received by the RFID readers remains the same for a reset times threshold; and

outputting the latest estimated location as the location of the target object.

15. The method as claimed in claim 9, wherein estimated location (n plus one) is defined as a midpoint between estimated location (n) and the RFID reader with the greatest signal intensity of the RF signal.

16. The method as claimed in claim 9, wherein estimated location (n plus one) is determined by approaching a unit length from the location of estimated location (n) towards the RFID reader with the greatest signal intensity.

17. A system to use a plurality of RFID (Radio Frequency Identification) readers to position a target object with an active RFID tag equipped thereon, the positioning system comprising:

a receiving module receiving a RF (Radio Frequency) signal of the active RFID tag received from each of the RFID readers respectively;

a selection module selecting pairs of the RFID readers at random until all possible combinations have been selected thus providing a plurality of comparison pairs;

a comparison module comparing the RF signals of the RFID readers within the comparison pairs, and determining the RFID reader with the greater signal intensity within each of the comparison pairs;

a positioning module positioning an effective range of each of the RFID reader with the greater signal intensity within each of the comparison pairs to calculate an overlapped range of the effective ranges; and

an output module outputting the overlapped range as the estimated location of the target object, wherein, for each comparison pair, a first line connects the two RFID readers in the comparison pair and a second line bisects the first line to define two half areas wherein the effective range of a comparison pair is the half area that contains the RFID reader with the greater signal intensity within the comparison pair.

18. The system as claimed in claim 17, wherein the RFID reader further calculates the signal intensity of each of the received RF signals.

19. The system as claimed in claim 17, wherein the comparison module further calculates the signal intensity of each of the received RF signals.

20. The system as claimed in claim 17, wherein the effective range indicates a half area that is divided by a middle line of the two RFID readers within the comparison pair and corresponding to the RFID reader with the greater signal intensity within the same comparison pair.