Reverse infrastructure location system and method

• US 20060071790A1
• Filed: 09/29/2004
• Published: 04/06/2006
• Est. Priority Date: 09/29/2004
• Status: Active Grant

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Bridgelall, Raj, Duron, Mark William
• Granted Patent: US 7,403,120 B2
• Time in Patent Office: Days
• US Class Current: 340/572.100
• CPC Class Codes: G01S 13/46 Indirect determination of position data
• CPC Class Codes: G01S 13/75 using transponders powered from received waves, e.g. using passive transponders , or using passive reflectors
• 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: G01S 2013/466 by Trilateration, i.e. two antennas or two sensors determine separately the distance to a target, whereby with the knowledge of the baseline length, i.e. the distance between the antennas or sensors, the position data of the target is determined
• CPC Class Codes: G06K 17/00 Methods or arrangements for effecting co-operative working between equipments covered by two or more of main groups G06K1/00 - G06K15/00, e.g. automatic card files incorporating conveying and reading operations

Abstract

Methods and apparatus are provided to locate a terminal within a workspace. Radio frequency identification (RFID) tags are provided in known locations, preferably in, on or adjacent the light fixtures or other workspace infrastructure. The terminal comprises an RFID tag interrogation transceiver, processor and memory. The transceiver interrogates the tags which respond with information correlatable with their unique locations. The terminal determines its locations relative to the known locations of responding tags by, for example, varying its transmit power and/or receiver sensitivity and/or by trilateration using, for example, phase or time difference of arrival measurements on the tag response signals. Once it has determined its own location it may transmit or otherwise announce its location as desired by the user. In a preferred embodiment, the natural electromagnetic radiation and/or RADAR cross section backscatter from fluorescent type fixtures, modulated with their position information, acts as the RFID infrastructure beacon.

Claims

1. A system by which an object can locate itself within an area, comprising:

multiple radio frequency identification (RFID) tags positioned at known locations within the area; and

a moveable RFID tag reader associated with the object and in signaling contact with at least some of the RFID tags, said tag reader for interrogating the at least some of the RFID tags and receiving information therefrom related to their known locations, and for using such known location information to establish its own position within the area.

2. The system of claim 1 wherein the multiple RFID tags are associated with light fixtures within the area;

3. The system of claim 2 wherein the multiple RFID tags derive energy from the light fixtures within the area.

4. The system of claim 3 wherein the multiple RFID tags derive energy from the light fixtures by optical coupling.

5. The system of claim 3 wherein the multiple RFID tags derive energy from the light fixtures by inductive coupling.

6. The system of claim 3 wherein the multiple RFID tags derive energy from the light fixtures by capacitive coupling.

7. The system of claim 2 wherein each light fixture has a ballast and the RFID tags transmit information to the reader by modulating operation of the ballast of the light fixture.

8. A method for determining the position of an object within an area having multiple RFID tags in known locations, comprising:

interrogating a tag and receiving information therefrom, wherein such information directly or indirectly identifies the tag location;

determining proximity of the object to the interrogated tag; and

repeating the interrogating and determining steps for the same or different tags to obtain a substantially unique position of the object relative to the same or different tags.

9. The method of claim 8 wherein the interrogating step comprises interrogating a tag associated with a light fixture in the area.

10. The method of claim 9 wherein the interrogating step comprises interrogating a tag deriving power from the light fixture.

11. The method of claim 8 wherein the determining step comprises determining a distance between the object and the tag and the repeating step comprises repeating the interrogating and determining steps until at least two distances are obtained.

12. The method of claim 11 further comprising using other information besides the two distances to eliminate any ambiguous positions of the object.

13. The method of claim 8 wherein the interrogating and repeating steps comprise interrogating tags in order of decreasing signal strength.

14. The method of claim 8 wherein the interrogating and repeating steps comprise interrogating tags in order of increasing signal strength.

15. The method of claim 8 wherein the determining step comprises determining a distance using phase difference of arrival of a signal from the tag.

16. The method of claim 8 wherein the determining step comprises determining a distance between the object and the tag using relative signal strength of a signal received from the tag.

17. A method for determining the position of a terminal in a workspace having beacon transmitters in known locations emitting unique IDs, comprising:

obtaining unique ID signals from one or more of the beacon transmitters;

determining locations of the one or more beacon transmitters from the unique ID signals; and

determining the terminal location based on the locations of the one or more beacon transmitters whose unique ID signals were received.

18. The method of claim 17 wherein the obtaining step comprises obtaining unique ID signals from one or more beacon transmitters associated with light fixtures.

19. The method of claim 18 wherein the obtaining step comprises obtaining unique ID signals by detecting modulation of an ionization/deionization frequency of a light emitter of the light fixture.

20. A system for determining the location of a terminal within a workspace, comprising:

multiple elements in known locations relative to the workspace, each element having a gaseous region whose RF impedance is time varying in a manner embodying information on the known location of such individual element; and

wherein the terminal comprises;

a detector wirelessly coupled to at least some of the gaseous regions, adapted to detect the time varying RF impedance containing information on the location thereof; and

a processor coupled to the detector for analyzing the time varying RF impedance detected by the detector and determining the location of the terminal relative to the workspace at least in part from the information contained in such time varying RF impedance.

21. The system of claim 20 wherein the elements comprise light fixtures.

22. The system of claim 21 wherein the gaseous region forms part of a fluorescent lamp.

23. The system of claim 21 wherein:

the time varying RF impedance is provided by ionization and de-ionization of the gaseous region, and

the system further comprises a modulator coupled to the gaseous region for impressing the location information on the time varying RF impedance thereof.

24. The system of claim 20 wherein:

each element further comprises;

a modulator adapted to impress the information concerning the location of the element on the time varying impedance of the gaseous region; and

an activator in wireless communication with the terminal for turning the modulator ON or OFF in response to an activate signal received from the terminal; and

the terminal comprises a transmitter for sending the activate signal to the activators of the at least some of the multiple elements.

25. A movable radio frequency identification (RFID) tag reader coupled to an object, for locating the object within an area equipped with a plurality of RFID tags at known positions within the area, the RFID tag reader comprising:

a transmitter for interrogating at least some of the RFID tags; and

a receiver for receiving information from the interrogated RFID tags and utilizing the information to establish the position of the tag reader within the area.