Localizing tagged assets using modulated backscatter

• US 20090212921A1
• Filed: 02/25/2008
• Published: 08/27/2009
• Est. Priority Date: 02/25/2008
• Status: Active Grant

• Current Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Original Assignee: Wirama Corporation
• Inventors: Ramchandran, Kannan, Wild, Ben J., Tkachenko, Artem, Madhow, Upamanyu
• Granted Patent: US 9,262,912 B2
• Time in Patent Office: Days
• US Class Current: 340/10.500
• CPC Class Codes: G01S 11/02 using radio waves G01S19/00 takes precedence
• 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 13/876 Combination of several spaced transponders or reflectors of known location for determining the position of a receiver G01S13/874 takes precedence
• CPC Class Codes: G08C 21/00 Systems for transmitting the position of an object with respect to a predetermined reference system, e.g. tele-autographic system

Abstract

Methods and systems for localizing an asset using the modulated backscatter from an asset tag and one or more marker tags are described. The system includes the reader, a location module and one or more marker tags. The location estimates for the asset tag are based partially on a prior knowledge of the location of each of the one or more marker tags. The location for each marker tag may be stored in a database. The location module determines a location estimate for the asset tag using the estimated parameters of the modulated backscatter signals received from one or more marker tags and from the asset tag. Using the known locations of the marker tags, a location estimate of the asset tag can be determined. The location estimate may be a relative location, an absolute location, and/or may be a zone including the marker tags. A mobile reader using the marker tags can localize asset tags throughout a large area and may, for example, take an inventory of assets throughout the large area.

Claims

1. A method comprising:

receiving modulated backscatter signals using a reader from one or more marker tags;

receiving a modulated backscatter signal using the reader from an asset tag;

estimating parameters of the modulated backscatter signals received from the one or more marker tags;

estimating a parameter of the modulated backscatter signal received from the asset tag; and

determining a location estimate for the asset tag, the location estimate based on the estimated parameters of the modulated backscatter signals received from the one or more marker tags and the estimated parameter of the modulated backscatter signal received from the asset tag.

2. The method of claim 1 wherein the estimated parameters of the modulated backscatter signals received from the one or more marker tags includes angles of arrival.

3. The method of claim 1 wherein the estimated parameter of the modulated backscatter signal received from the asset tag includes an angle of arrival.

4. The method of claim 1 wherein the estimated parameters of the modulated backscatter signals received from the one or more marker tags include ranges from the reader to the one or more marker tags.

5. The method of claim 1 wherein the estimated parameter of the modulated backscatter signal received from the asset tag includes a range from the reader to the asset tag.

6. The method of claim 5 further comprising estimating the range using a signal strength of the received modulated backscatter signal from the asset tag.

7. The method of claim 1 further comprising determining a direction of motion of the asset tag.

8. The method of claim 1 further comprising:

estimating a range from the reader to the asset tag;

retrieving locations of the one or more marker tags from a location database; and

determining the location estimate based on the estimated range from the reader to the asset tag, the locations of the one or more marker tags, the estimated parameters of the modulated backscatter signals received from the one or more marker tags, and the estimated parameter of the modulated backscatter signal received from the asset tag.

9. The method of claim 1 wherein the location estimate includes a zone.

10. The method of claim 9 further comprising scanning an electromagnetic signal across the zone using a transmit beamforming array.

11. The method of claim 10 wherein the estimated parameters of the modulated backscatter signals received from the one or more marker tags are based on using a received signal strength as a function of a scan angle of the scanned electromagnetic signal.

12. The method of claim 1 wherein the reader comprises a receive beamforming array including a plurality of antennas configured to receive the modulated backscatter signals from the one or more marker tags and the modulated backscatter signal from the asset tag.

13. The method of claim 12 wherein the estimated parameters of the modulated backscatter signals received from the one or more marker tags are received array responses.

14. The method of claim 13 wherein determining the location estimate includes using the received array responses in a clustering algorithm.

15. The method of claim 12 wherein estimating the parameters of the modulated backscatter signals received from the one or more marker tags includes estimating a received signal strength from each of the one or more marker tags.

16. The method of claim 12 wherein estimating the parameters of the modulated backscatter signals received from the one or more marker tags includes using a multiple signal classification (MUSIC) algorithm.

17. The method of claim 12 wherein estimating the parameters of the modulated backscatter signals received from the one or more marker tags includes using an estimation of signal parameters via rotational invariance (ESPRIT) algorithm.

18. The method of claim 1 further comprising using the determined location estimate and the estimated parameter of the modulated backscatter signal received from the asset tag to provide a simulated marker tag.

19. A method comprising:

estimating first parameters of modulated backscatter signals received from a plurality of marker tags when a reader is at a first position;

estimating a second parameter of a modulated backscatter signal received from an asset tag when the reader is at the first position;

moving the reader to a second position;

estimating third parameters of the modulated backscatter signals received from the plurality of marker tags when the reader is at the second position;

estimating a fourth parameter of the modulated backscatter signal received from the asset tag when the reader is at the second position; and

estimating a location of the asset tag based on the first parameters, the second parameter, the third parameters and the fourth parameter.

20. The method of claim 19 further including estimating the first position of the reader using the first parameters and the third parameters.

21. The method of claim 19 wherein the first parameters, the second parameter, the third parameters and the fourth parameter are angles of arrival.

22. The method of claim 19 wherein the first parameters, the second parameter, the third parameters and the fourth parameters are ranges.

23. The method of claim 19 wherein the reader comprises a receive beamforming array including a plurality of antennas configured to receive the modulated backscatter signals from the one or more marker tags and the modulated backscatter signal from the asset tag, and the first parameters and the second parameter are received array responses.

24. The method of claim 23 wherein estimating the location of the asset tag includes using a model for a multipath propagation environment.

25. A system comprising:

means for receiving modulated backscatter signals from one or more marker tags;

means for receiving a modulated backscatter signal from an asset tag;

means for estimating parameters of the modulated backscatter signals received from the one or more marker tags;

means for estimating a parameter of the modulated backscatter signal received from the asset tag; and

means for determining a location estimate for the asset tag, the location estimate based on the estimated parameters of the modulated backscatter signals received from the one or more marker tags and the estimated parameter of the modulated backscatter signal received from the asset tag.