Methods and Systems for Estimating Distance of a Radio Frequency Identification Tag

Patent metadata

Field	Value
Publication number	US-2016104013-A1
Application number	US-201414575575-A
Country	US
Kind code	A1
Filing date	Dec 18, 2014
Priority date	Oct 9, 2014
Publication date	Apr 14, 2016
Grant date	—

Abstract

A localization method and system, including determining at least two phases associated with at least two response signals transmitted by a radio frequency identification (RFID) tag at different frequencies in response to a plurality of interrogation signals transmitted by a reader; determining a first distance estimate of a distance between the RFID tag and the reader based on a signal strength measured from a first response signal of the at least two response signals; based upon the first distance estimate, generating a set of phase data points that follows a substantially periodic function over a range of frequencies; and determining a second distance estimate of the distance based upon the at least two phases and the periodic function.

First claim

What is claimed is:

1 . A method for determining a distance between a radio frequency identification (RFID) tag and a reader, comprising:
transmitting, by the reader, a plurality of interrogation signals to the RFID tag at a plurality of frequencies; receiving, by the reader, a plurality of response signals from the RFID tag in response to the plurality of interrogation signals; determining a first distance estimate of the distance based upon a signal strength measured from a first response signal of the plurality of response signals; based upon the first distance estimate, generating a set of phase data points that follows a substantially periodic function over a range of frequencies; and determining a second distance estimate of the distance based upon at least two of the plurality of response signals and the periodic function.

2 . The method of claim 1 , wherein the periodic function comprises a sawtooth waveform or a substantially sawtooth waveform.

3 . The method of claim 1 , wherein the generating comprises determining a period length and a first peak point of the periodic function based upon the first distance estimate.

4 . The method of claim 3 , wherein the determining the first peak point comprises comparing the first distance estimate with a predetermined data set identifying a plurality of distance values and, for each distance value, a corresponding frequency location to determine a frequency location at which the first peak point occurs.

5 . The method of claim 3 , wherein the determining the period length comprises comparing the first distance estimate with a predetermined data set identifying a plurality of distance values and, for each distance value, a corresponding period length.

6 . The method of claim 1 , wherein the at least two of the plurality of response signals include the first response signal and a second response signal of the plurality of response signals, the determining the second distance estimate including:
determining a first phase and a second phase associated with the first and second response signals, respectively; correlating the first and second phases with corresponding phase data points of the periodic function to determine a number of peaks occurring between the first and second phases; and based upon the correlating and the determined number of peaks, predicting a phase slope; wherein the second distance estimate is determined based upon the predicted phase slope.

7 . The method of claim 6 , wherein the predicting the phase slope includes altering a value of one of the first and second phases based upon the determined number of peaks, and determining a slope between the altered one of the first and second phases and the other of the first and second phases.

8 . The method of claim 7 , wherein the altering the value includes adding or subtracting a predetermined angular value to the one of the first and second phases based upon the determined number of peaks.

9 . The method of claim 8 , wherein the predetermined angular value is a product of 180 or pi radians and the determined number of peaks.

10 . A method for determining a distance between a radio frequency identification (RFID) tag and a reader, comprising:
determining a first distance estimate of the distance based upon a signal strength measured from a first response signal of a plurality of response signals received by the reader from the RFID tag in response to a plurality of interrogation signals transmitted by the reader; based upon the first distance estimate, generating a function of phase data points with respect to a range of frequencies; determining a first phase and a second phase associated with the first response signal and a second response signal of the plurality of response signals, respectively; correlating the first and second phases with a first phase data point and a second phase data point of the function, respectively; and determining a second distance estimate of the distance based upon the correlating.

11 . The method of claim 10 , wherein the function comprises a periodic wave function.

12 . The method of claim 11 , wherein the periodic wave function comprises a sawtooth wave or a substantially sawtooth wave.

13 . The method of claim 10 , wherein the determining the second distance estimate includes:
determining a number of peaks occurring between the first and second phases; altering the second phase based upon the number of peaks; determining a phase slope associated with the first phase and the altered second phase; and determining the second distance estimate based upon the phase slope.

14 . The method of claim 13 , wherein the altering the second phase includes one of adding and subtracting an angular value thereto corresponding to the number of peaks.

15 . The method of claim 14 , wherein the angular value is a product of 180° or pi radians and the determined number of peaks.

16 . A non-transitory computer readable storage medium having stored thereon instructions that when executed by a machine result in the following operations:
determining at least two phases associated with at least two response signals transmitted by a radio frequency identification (RFID) tag at different frequencies; determining a first distance estimate of a distance between the RFID tag and the reader based on a signal strength measured from a first response signal of the at least two response signals; based upon the first distance estimate, generating a set of phase data points that follows a substantially periodic function over a range of frequencies; and determining a second distance estimate of the distance based upon the at least two phases and the periodic function.

17 . The computer readable storage medium of claim 16 , wherein the periodic function comprises a sawtooth wave function or a substantially sawtooth wave function.

18 . The computer readable storage medium of claim 16 , further comprising instructions for comparing the first distance estimate with a first predetermined function and a second predetermined function to determine a period length and a first peak point of the periodic function, respectively.

19 . The computer readable storage medium of claim 16 , wherein the at least two phases include a first phase and a second phase associated with the first response signal and a second response signal of the at least two response signals, respectively, the instructions for determining the second distance estimate including instructions for:
correlating the first and second phases with corresponding phase data points of the periodic function to determine a number of peaks occurring between the first and second phases; altering one of the first and second phases based on the determined number of peaks; determining a slope between the altered one of the first and second phases and the other of the first and second phases; and determining the second distance estimate based upon the slope.

20 . The computer readable storage medium of claim 19 , wherein the altering includes one of adding and subtracting an angular value to the one of the first and second phases.

21 . The computer readable storage medium of claim 19 , wherein the at least two phases include a third phase associated with a third response signal of the at least two response signals, the instructions for determining the second distance estimate further including instructions for correlating the third phase with a corresponding phase data point of the

Assignees

• Lexmark Int Inc

Inventors

• Fessler John Thomas
• Parker Johne Michelle
• Whitney Ann Michelle
• Whitney Julie Ann Gordon

Classifications

• G06K7/10128 Primary

  the step consisting of detection of the presence of one or more record carriers in the vicinity of the interrogation device · CPC title

• G01S11/06

  using intensity measurements · CPC title

• G01B7/003

  for measuring position, not involving coordinate determination (coordinate measuring G01B7/004) · CPC title

• G01S13/84

  for distance determination by phase measurement · CPC title

• G06K19/0723

  the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs · CPC title