Steerable phase array antenna RFID tag locater and tracking system and methods

• US 8,742,896 B2
• Filed: 11/26/2012
• Issued: 06/03/2014
• Est. Priority Date: 09/11/2007
• Status: Active Grant

• Current Assignee: RF Controls LLC
• Original Assignee: RF Controls LLC
• Inventors: Eloy, Graham P.
• Primary Examiner(s): GIRMA, FEKADESELASS
• Application Number:
  US13/685,166
• Publication Number:
  US 20130099898A1
• Time in Patent Office: 554 Days
• Field of Search: 340/10.1, 340/12.1, 340/539.1, 340/572.1, 343/702
• US Class Current: 340/10.1
• CPC Class Codes: G01S 13/76 wherein pulse-type signals are transmitted
• CPC Class Codes: G01S 13/878 Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector G01S13/874 takes precedence
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G01S 5/12 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
• CPC Class Codes: G06K 7/01 Details
• CPC Class Codes: G06K 7/10079 the collision being resolved in the spatial domain, e.g. temporary shields for blindfolding the interrogator in specific directions
• CPC Class Codes: G08B 13/2462 Asset location systems combined with EAS inventory, tracking, logistic G06Q10/00; entrance control systems G07C9/00
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 3/36 with variable phase-shifters

Abstract

A system for and method of tracking and locating RFID tags, including where at least one steerable phase array antenna may locate the tags associated with items in three dimensions in real time, through the use of a beam steering unit and controller therewith to control the direction of a beam launched by the at least one steerable phase array antenna.

Claims

1. A method of locating and tracking an RFID tag, the steps comprising:

calibrating at least two phase array steerable antennas to optimally align the antennas with known global coordinates;

configuring an RFID reader for a working environment;

performing a two-dimensional raster scan of a visible area of the working environment with a first antenna;

calculating a minimal covering of the visible area with one or more beam areas;

defining a set of steering directions for raster scans;

using the first antenna to determine if one or more RFID tags are present in the beam areas;

estimating an expected location for at least one RFID tag in the beam area;

projecting the expected location of the RFID tag into global coordinates;

estimating the most probable conjugate pairing (“

PGPt1”

);

calculating a most likely location of the RFID tag'"'"'s projection in global coordinates relative to a second antenna (“

PGPt2”

) using an estimated random distribution of RFID tag heights and PGPt1;

calculating a projection in global coordinates inverse of PGPt2 so as to yield a most probable steering direction for the second antenna;

reading with the other antenna in the direction indicated by a plane point projection of PGPt2;

triangulating any RFID tag seen by the other antenna using PGPt1 and PGPt2;

triangulating using PGPt1 and PGPt2 if the RFID tag is not seen by the other antenna, as this location is still highly probable as a location for the RFID tag; and

repeating these steps for each beam area.

2. A method according to claim 1, further comprising:

estimating a time range over which the RFID tag was seen using data collected for the RFID tag;

fitting a model to (x,y,z,t) data produced by conjugated raster scans using Iterative Weighted Robust Least Squares Estimation;

calculating an RFID tag trajectory over the time interval t using an estimated model of the RFID tag'"'"'s motion; and

tracking the RFID tag'"'"'s direction using derivatives of the RFID tag trajectory.

3. A method of locating and tracking an RFID tag, comprising the steps of:

scanning an operating environment with a first steerable signal beam interrogation signal from a first phase array steerable antenna;

storing RFID tag response signals received by the first phase array steerable antenna in a data matrix including a direction vector of the first steerable signal beam when each response signal is received and an identification of the RFID tag providing the response signal;

scanning a subset area of an operating environment of a second steerable signal beam interrogation signal from a second phase array steerable antenna;

storing RFID tag response signals received by the second phase array steerable antenna in a data matrix including a direction vector of the second steerable signal beam when each response signal is received and an identification of the RFID tag providing the response signal;

identifying and flagging any pseudo emitter response signals that are received;

the pseudo emitter response signals being any signal within a group of response signals having a common identification that are not the response signal with the shortest time between the interrogation signal launch and reception of the response signal; and

triangulating a response signal origin location for each response signal where the identification is the same.

4. The method of claim 3, wherein the data matrix for each response signal includes a time of reception.