Method, system and computer program product for ranging RFID tags

Patent metadata

Field	Value
Publication number	US-9244162-B2
Application number	US-201113639104-A
Country	US
Kind code	B2
Filing date	Apr 8, 2011
Priority date	Apr 9, 2010
Publication date	Jan 26, 2016
Grant date	Jan 26, 2016

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.

First claim

The invention claimed is:

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 said position parameter is a distance between the tag and the reader, wherein the position parameter is determined using

max
z

⁢

{

|

∫

Δ
⁢

⁢

Y
meas

⁡

(
ω
)

ΔΓ
est

⁡

(
ω
)

⁢

ⅇ

j
⁢

2
⁢
ω

c

⁢
z

⁢

ⅆ
ω

|

}

,

wherein ΔY meas (ω) is a measured difference signal between two reflection; states of the tag corresponding to two backscattering reflection coefficients, ΔΓ est (ω) is a modulated reflection coefficient of the tag, and ω is angular frequency of the modulated backscattering response of the tag,

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 a threshold power of the tag or more than 3 dB higher than the threshold power of the tag, wherein the modulated reflection coefficient of the tag is estimated using the modulated backscattering response.

2. 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.

3. The method according to claim 1 , wherein a modulated reflection coefficient ΔΓ est (ω) of the tag is estimated based on the response measurement.

4. The method according to claim 1 , wherein a difference ΔY meas (ω) between two reflection states of the tag corresponding to two backscattering reflection coefficients is determined.

5. 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.

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

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

8. The method according to 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.

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

10. 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 position parameter is a distance between the tag and the reader, wherein the position parameter is determined using

max
z

⁢

{



∫

Δ
⁢

⁢

Y
meas

⁡

(
ω
)

ΔΓ
est

⁡

(
ω
)

⁢

ⅇ

j
⁢

2
⁢
ω

c

⁢
z

⁢

ⅆ
ω



}

,

wherein ΔY meas (ω) is a measured difference

Assignees

• Viikari Ville
• Pursula Pekka
• Teknologian Tutkimuskeskus Vtt Oy

Inventors

• Viikari Ville
• Pursula Pekka

Classifications

• G01S13/756 Primary

  using a signal generator for modifying the reflectivity of the reflector (G01S13/758 takes precedence) · CPC title

• G01S13/84

  for distance determination by phase measurement · CPC title

• G01S13/753 Primary

  using frequency selective elements, e.g. resonator · CPC title