Methods for Noise Validated Phase Ranging RFID Location

• US 20110090061A1
• Filed: 11/24/2009
• Published: 04/21/2011
• Est. Priority Date: 10/16/2009
• Status: Active Grant

• Current Assignee: RF Controls LLC
• Original Assignee: RF Controls LLC
• Inventors: Bloy, Graham P., Hofer, Russell
• Granted Patent: US 8,159,367 B2
• Time in Patent Office: Days
• US Class Current: 340/10.3
• CPC Class Codes: G01S 13/825 with exchange of information between interrogator and responder
• CPC Class Codes: G01S 13/84 for distance determination by phase measurement
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems

Abstract

A method and apparatus for validating a distance output of a phase ranging RFID location system, based upon the phase readings included in data sets obtained from monitoring reply signals corresponding to interrogation signals at multiple frequencies and a common interrogation signal beam direction; by comparison of measured phase and frequency data sets with theoretical phases calculated with respect to the same frequencies over a range of positions corresponding to a beam extent of the interrogation signal. The distance output validated by comparison with theoretical threshold data processed to generate an extreme values distribution from which a cumulative distribution function is extracted and against which a confidence level is applied.

Claims

1. A method for phase ranging in an RFID location system, comprising the steps of:

receiving a reply signal from an RFID tag when an interrogation signal beam at a frequency is pointed in a direction;

generating a data set corresponding to the reply signal including a measured phase of the reply signal and the frequency;

alternating the frequency between a plurality of frequencies and generating further data sets for each of a plurality of reply signals corresponding to the plurality of frequencies;

generating a theoretical phase with respect to each of the frequencies at each of a plurality of distances along the beam;

comparing a slope of a line through the theoretical phases at each of the frequencies at each of the plurality of distances with a slope of a line through the phase at each of the frequencies at each distance;

designating the distance at which the slope of the line through the theoretical phase with respect to each of the frequencies is closest to the slope of the line through the phase with respect to each of the frequencies as an output distance;

generating an R_rawData indication of fit;

replacing the measured phase data in the data set with a range of phases and processing in multiple iterations as generated to obtain R_rawData, to generate a corresponding array of R_randomData;

processing the array of R_randomData in an extreme values distribution to obtain a cumulative distribution function;

applying a confidence level to the cumulative distribution function to generate a Threshold_R_rawData; and

accepting the output distance if the R_rawData is greater than the Threshold_R_rawData.

2. The method of claim 1;

wherein R_rawData=1−

SSE/SST;

where a SSE calculation generates an SSE as a sum of square error obtained by subtracting each of the theoretical phase from the measured phase corresponding to each frequency of the data set to obtain a measured data;

squaring the measured data and summing each of the measured data; and

a SST calculation generates an SST as a sum of square total calculated with respect to a theoretical line of slope zero obtained by subtracting each of the theoretical phase, derived at distance zero, from the measured phase corresponding to each frequency of the data set to obtain a slope zero measured data;

squaring the slope zero measured data and summing.

3. The method of claim 1, wherein the range of phases that replace the measured phase data extend between 0 and 360.

4. The method of claim 1, wherein the confidence level is at least 99%.

5. The method of claim 1, wherein the cumulative distribution function is a histogram of the array of R_randomData and the confidence level is a position along a data axis where the desired percentage of the array of R_randomData is to the right of the position.

6. The method of claim 1, wherein the SSE calculation and the SST calculation is performed in parallel with the comparison of the slopes of the lines through the theoretical phases at each of the frequencies at each of the plurality of distances with the slopes of the lines through the phase at each of the frequencies at each distance.

7. The method of claim 1, wherein the theoretical phase is generated by the equation:

theoretical phase=((phase at min Freq−

Freq)*distance*360)/(c*2),

wherein phase at min Freq is the phase corresponding to a minimum frequency of the data sets;

Freq is the frequency corresponding to the frequency for which the theoretical phase is being calculated;

distance is a distance for which the theoretical phase is being calculated and c is the speed of light.

8. The method of claim 1, further including the step of converting the output distance with respect to the direction into a three dimensional co-ordinate location of the RFID tag.

9. The method of claim 8, further including the step of comparing the three dimensional co-ordinate location of the RFID tag with an alternative three dimensional co-ordinate location corresponding to the RFID tag generated by an alternative data set from an alternative interrogation signal beam.

10. A method for phase ranging in an RFID location system, comprising the steps of:

generating multiple measured phase and frequency data sets for each of a plurality of reply signals corresponding to the plurality of frequencies;

generating a theoretical phase with respect to each of the frequencies at each of a plurality of distances along the beam;

comparing a slope of a line through the theoretical phases at each of the frequencies at each of the plurality of distances with a slope of a line through the phase at each of the frequencies at each distance;

designating the distance at which the slope of the line through the theoretical phase with respect to each of the frequencies is closest to the slope of the line through the phase with respect to each of the frequencies as an output distance;

generating an R_rawData=1−

SSE/SST;

where a SSE calculation generates an SSE as a sum of square error obtained by subtracting each of the theoretical phase from the measured phase corresponding to each frequency of the data set to obtain a measured data;

squaring the measured data and summing each of the measured data; and

a SST calculation generates an SST as a sum of square total calculated with respect to a theoretical line of slope zero obtained by subtracting each of the theoretical phase, derived at distance zero, from the measured phase corresponding to each frequency of the data set to obtain a slope zero measured data;

squaring the slope zero measured data and summing;

generating a R_randomData=1−

SSE/SST;

where a SSE calculation generates an SSE as a sum of square error obtained by subtracting each of the theoretical phase from a range of phases corresponding to each frequency of the data set to obtain a theoretical data;

squaring the theoretical data and summing each of the theoretical data; and

a SST calculation generates an SST as a sum of square total calculated with respect to a theoretical line of slope zero obtained by subtracting each of the theoretical phase, derived at distance zero, from the range of phases corresponding to each frequency of the data set to obtain a slope zero theoretical data;

squaring the slope zero theoretical data and summing;

processing R_randomData in multiple iterations to generate a corresponding array of R_randomData;

processing the array of R_randomData in an extreme values distribution to obtain a cumulative distribution function;

applying a confidence level to the cumulative distribution function to generate a Threshold_R_rawData; and

accepting the output distance if the R_rawData is greater than the Threshold_R_rawData.

11. The method of claim 10, wherein the range of phases that replace the measured phase data extend between 0 and 360.

12. The method of claim 10, wherein the confidence level is at least 99%.

13. The method of claim 10, wherein the cumulative distribution function is a histogram of the R_randomData array and the confidence level is a position along a data axis of the histogram where the desired percentage of the R_randomData is to the right of the position.

14. The method of claim 10, wherein the SSE calculation and the SST calculation is performed in parallel with the comparison of the slopes of the lines through the theoretical phases at each of the frequencies at each of the plurality of distances with the slopes of the lines through the phase at each of the frequencies at each distance.

15. The method of claim 10, wherein the theoretical phase is generated by the equation:

theoretical phase=((phase at min Freq−

Freq)*distance*360)/(c*2),

wherein phase at min Freq is the phase corresponding to a minimum frequency of the data sets;

Freq is the frequency corresponding to the frequency for which the theoretical phase is being calculated;

distance is a distance for which the theoretical phase is being calculated and c is the speed of light.

16. The method of claim 10, further including the step of converting the output distance with respect to the direction into a three dimensional co-ordinate location of the RFID tag.

17. The method of claim 16, further including the step of comparing the three dimensional co-ordinate location of the RFID tag with an alternative three dimensional co-ordinate location corresponding to the RFID tag generated by an alternative data set from an alternative interrogation signal beam.

18. A method for validating a phase ranging RFID location system output, comprising the steps of:

generating an R_rawData indication of fit;

replacing a measured phase data in a data set of measured reply signals with a range of theoretical phases and processing, according to a process of the phase ranging RFID location system which generated the phase ranging RFID location system output, to obtain R_rawData in multiple iterations, to generate a corresponding array of R_randomData;

processing the array of R_randomData in an extreme values distribution to obtain a cumulative distribution function;

applying a confidence level to the cumulative distribution function to generate a Threshold_R_rawData; and

accepting the output distance if the R_rawData is greater than the Threshold_R_rawData.

19. The method of claim 18, wherein R_rawData=1−

SSE/SST;

where a SSE calculation generates an SSE as a sum of square error obtained by subtracting each of the theoretical phase from the measured phase corresponding to each frequency of the data set to obtain a measured data;

squaring the measured data and summing each of the measured data; and

a SST calculation generates an SST as a sum of square total calculated with respect to a theoretical line of slope zero obtained by subtracting each of the theoretical phase, derived at distance zero, from the measured phase corresponding to each frequency of the data set to obtain a slope zero measured data;

squaring the slope zero measured data and summing.

20. The method of claim 18, wherein the cumulative distribution function is a histogram of the R_randomData and the confidence level is a position along a data axis where the desired percentage of the R_randomData is to the right of the position.