Method, system and computer program product for ranging RFID tags

• US 20130038428A1
• Filed: 04/08/2011
• Published: 02/14/2013
• Est. Priority Date: 04/09/2010
• Status: Active Grant

• Current Assignee: Teknologian tutkimuskeskus VTT Oy
• Original Assignee: Teknologian tutkimuskeskus VTT Oy
• Inventors: Viikari, Ville, Pursula, Pekka
• Granted Patent: US 9,244,162 B2
• Time in Patent Office: Days
• US Class Current: 340/10.4
• CPC Class Codes: G01S 13/756 using a signal generator for modifying the reflectivity of the reflector G01S13/758 takes precedence
• CPC Class Codes: G01S 13/84 for distance determination by phase measurement

Abstract

The invention relates to a method for ranging a radio frequency tag, comprising measuring the modulated backscattering response of the tag at a plurality of frequencies using reader and determining the dispersive properties of the tag from the amplitude of the measured backscattering response. Further, the method comprises determining a position parameter of the tag from the measured modulated backscattering response and the determined dispersive properties of the tag.

Claims

1. A method for ranging a radio frequency tag, comprising

measuring modulated backscattering response of the tag at a plurality of frequencies using a reader, and

determining at least one position parameter of the tag using the measured modulated backscattering response of the tag using Fourier transform,

wherein the method comprises

measuring said modulated backscattering response at each of said plurality of frequencies using a power which is at maximum 3 dB higher than the threshold power of the tag or more than 3 dB higher than the threshold power of the tag.

2. The method according to claim 1, wherein said position parameter is the distance between the tag and the reader.

3. The method according to claim 1, wherein the transmit power of the reader is gradually increased at said frequencies in order to find said threshold power of the tag.

4. The method according to claim 1, wherein a modulated reflection coefficient Δ

Γ

_est(ω

) of the tag is estimated based on the response measurement.

5. The method according to claim 1, wherein a difference Δ

Y_meas(ω

) between two reflection coefficient states of the tag is determined.

6. The method according to claim 1, wherein the position parameter is determined using the formula

7. The method according to claim 1, comprising determining dispersive properties of the tag based on the amplitude of said modulated backscattering response and determining the at least one position parameter using the measured modulated backscattering response of the tag and the determined dispersive properties of the tag.

8. The method according to claim 1, wherein the radio frequency tag is a passive UHF RFID tag.

9. The method according to claim 1, wherein said plurality of frequencies span a frequency range of at least 10 MHz.

10. The method according claim 1, comprising

measuring modulated backscattering responses of the tag at a plurality of frequencies using at least two reader antennas placed at a distance from each other, and

determining the location of the tag in at least two dimensions using the modulated backscattering responses.

11. The method according to claim 1, comprising ranging a plurality of tags simultaneously by distinguishing the responses of the tags.

12. A system for ranging a radio frequency tag, comprising

a reader for measuring modulated backscattering response of the tag at a plurality of frequencies, and

computing means for determining at least one position parameter of the tag using the measured modulated backscattering response of the tag using Fourier transform,

wherein

said reader is adapted to measure said modulated backscattering response at each of said plurality of frequencies using a power which is at maximum 3 dB higher than the threshold power of the tag or more than 3 dB higher than the threshold power of the tag.

13. The system according to claim 12, wherein the reader is adapted to gradually increase the power from a power level tower than the threshold power of the tag in order to find the threshold power of the tag.

14. (canceled)

15. A computer program product stored on a computer-readable data carrier for ranging a radio frequency tag, comprising

software means for reading measured modulated backscattering response data relating to the tag at a plurality of frequencies from a storage device, and

software means for determining at least one position parameter of the tag using the modulated backscattering response data using Fourier transform,

wherein computer program product further comprises

software means for controlling a radio frequency reader to measure said modulated backscattering response data at each of said plurality of frequencies using a power which is at maximum 3 dB higher than the threshold power of the tag or more than 3 dB higher than the threshold power of the tag.

16. (canceled)

17. A method for ranging a radio frequency tag, comprising

measuring a modulated backscattering response of the tag at a plurality of frequencies using reader,

determining dispersive properties of the tag from the amplitude of the measured backscattering response, and

determining a position parameter of the tag from the measured modulate backscattering response and the determined dispersive properties of the tag.

18. The method according to claim 17, comprising estimating a modulated reflection coefficient based on the measured backscattering response.

19. The method according to claim 17, wherein said position parameter is the distance of the tag from the reader or antenna of the reader.

20. The method according to claim 17, comprising

measuring modulated backscattering responses of the tag at a plurality of frequencies using at least two reader antennas placed at a distance from each other, and

determining the location of the tag in relation to the reader antennas in at least two dimensions using the modulated backscattering responses.