Localizing tagged assets using modulated backscatter

• US 9,262,912 B2
• Filed: 02/25/2008
• Issued: 02/16/2016
• Est. Priority Date: 02/25/2008
• Status: Active Grant

• Current Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Original Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Inventors: Wild, Ben J., Tkachenko, Artem, Ramchandran, Kannan, Madhow, Upamanyu
• Primary Examiner(s): Lim, Steven
• Assistant Examiner(s): SHERWIN, RYAN W
• Application Number:
  US12/072,423
• Publication Number:
  US 20090212921A1
• Time in Patent Office: 2,913 Days
• Field of Search: 340/10.1, 340/10.32, 340 104- 1042, 3405721-5729, 340/539.11, 340/539.13, 340/8.1, 340/5.1, 340/5.9, 340/5.92, 342/450, 342/463
• US Class Current: 1/1
• 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:

scanning, from a reader having one or more antennas, an electromagnetic signal across a zone, the zone formed between a plurality of marker tags located in an area proximate to the reader;

affixing an asset tag to an asset; and

determining a location estimate of the asset tag based on parameters of backscatter signals, the backscatter signals received by the reader from the asset tag and the plurality of marker tags;

wherein the location estimate includes a determination of whether the asset tag is positioned within the zone formed by the plurality of marker tags;

and wherein the parameters of the backscatter signals include an angle of arrival, a range from the reader to at least one of the plurality of marker tags, and a range from the reader to the asset tag;

wherein the angle of arrival of the backscatter signals is determined based on a peak received signal strength of the backscatter signals as a function of a scan angle of the scanned electromagnetic signal; and

wherein the range from the reader to the at least one of the plurality of marker tags and the range from the reader to the asset tag are determined based on comparing shapes of vectors of received powers with vectors of expected powers.

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

3. The method of claim 1 wherein the reader comprises a receive beamforming array including a plurality of antenna elements configured to receive the backscatter signals from the plurality of marker tags and from the asset tag.

4. The method of claim 3 wherein said received backscatter signals comprise a received array response corresponding to direct backscatter and another received array response corresponding to multipath reflection or scattering.

5. The method of claim 4 wherein a clustering algorithm is used on said received array responses in determining said location estimate.

6. The method of claim 4 wherein a multiple signal classification (MUSIC) algorithm is used on said received array responses in determining said location estimate.

7. The method of claim 4 wherein a rotational invariance (ESPRIT) algorithm is used on said received array responses in determining said location estimate.

8. The method of claim 1 further comprising using the location estimate of said asset tag by said reader to utilize said asset tag as a simulated marker tag.

9. A method, comprising:

(a) positioning a reader at a first stationary location;

(b) scanning, by said reader, a transmit beam through a scan angle from a transmitter beamscanning system across a zone using an array of antennas, said transmit beam comprising radio frequency (RF) signals emitted from said array of antennas, said zone formed between a plurality of marker tags located in an area proximate to the reader;

(c) affixing an asset tag to an asset;

(d) receiving, by said reader, backscatter signals from at least one marker tag and the asset tag;

(e) determining a location estimate of the asset tag based on parameters of backscatter signals, the backscatter signals received by the reader from the asset tag and the plurality of marker tags, wherein the location estimate includes a determination of whether the asset tag is positioned within the zone formed by the plurality of marker tags, and wherein the parameters of the backscatter signals include an angle of arrival, a range from the reader to at least one of the plurality of marker tags, and a range from the reader to the asset tag, wherein the angle of arrival of the backscatter signals is determined based on a peak received signal strength of the backscatter signals as a function of the scan angle, and wherein the range from the reader to the at least one of the plurality of marker tags and the range from the reader to the asset tag are determined based on comparing shapes of vectors of received powers with vectors of expected powers; and

(f) moving the reader to a second stationary position and repeating steps (b)-(e) at the second stationary position.

10. The method of claim 9 wherein the reader comprises a receive beamforming array including a plurality of antennas configured to receive the backscatter signals from at least one of the plurality of marker tags and the backscatter signals from the asset tag.

11. The method of claim 9 wherein the location estimate of the asset tag comprises a probabilistic estimate of an absolute or relative location of the asset tag.

12. A system, comprising:

a plurality of marker tags;

a reader having one or more antennas for scanning an electromagnetic signal across a zone, the zone formed between the plurality of marker tags;

an asset tag affixed to an asset; and

a location module configured to determine a location estimate of the asset tag, wherein the location estimate is based on parameters of backscatter signals received by the reader from the asset tag and the plurality of marker tags;

wherein the location estimate includes a determination of whether the asset tag is positioned within the zone formed by the plurality of marker tags;

wherein the parameters of the backscatter signals include an angle of arrival, a range from the reader to at least one of the plurality of marker tags, and a range from the reader to the asset tag;

wherein the angle of arrival of the backscatter signals is determined based on a peak received signal strength of the backscatter signals as a function of a scan angle of the scanned electromagnetic signal; and

wherein the range from the reader to the at least one of the plurality of marker tags and the range from the reader to the asset tag are determined based on comparing shapes of vectors of received powers with vectors of expected powers.

13. The system of claim 12 wherein the location estimate includes a probabilistic estimate of an absolute or relative location of the asset tag.

14. The system of claim 12 wherein the location module is further configured to determine a direction of motion of the asset tag.