Reverse infrastructure location system and method

• US 7,403,120 B2
• Filed: 09/29/2004
• Issued: 07/22/2008
• Est. Priority Date: 09/29/2004
• Status: Expired due to Fees

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Bridgelall, Raj, Duron, Mark William
• Primary Examiner(s): Bugg; George A
• Assistant Examiner(s): Pham; Lam P
• Application Number:
  US10/954,967
• Publication Number:
  US 20060071790A1
• Time in Patent Office: 1,392 Days
• Field of Search: 340/572.1, 340/825.49, 340/539.1, 340/539.21, 340/539.23, 340/539.13, 340/988, 235/385, 235/491, 235/386, 235/492, 342/450, 342/458, 342/463, 342/357.01, 342/357.06, 342/357.02, 455/456.1, 455/456.3, 700/214, 700/225, 701/23, 701/24
• US Class Current: 340/572.1
• 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,

wherein the multiple RFID tags are associated with light fixtures within the area, and

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.

2. The system of claim 1, further comprising the ballast, wherein the ballast comprises:

a circuit adapted to provide an excitation voltage to a gas ionization lamp at a variable output frequency that includes an unmodulated excitation frequency; and

a modulator coupled to the circuit, and adapted to cause the variable output frequency to vary about the unmodulated excitation frequency so that electromagnetic energy radiated by the gas ionization lamp contains a unique identifier associated with a position of the RFID position location beacon and a portion of an RF signal reflected by the gas ionization lamp is a position modulated signal that contains the unique identifier.

3. The system of claim 2, wherein the moveable RFID tag reader is adapted to determine the position of the RFID position location beacon by decoding the position modulated signal.

4. An RFID position location beacon comprising:

an electronic ballast that includes

a circuit adapted to provide an excitation voltage to a gas ionization lamp at a variable output frequency that includes an unmodulated excitation frequency; and

a modulator coupled to the circuit, and adapted to cause the variable output frequency to vary about the unmodulated excitation frequency so that electromagnetic energy radiated by the gas ionization lamp contains a unique identifier associated with a position of the RFID position location beacon and a portion of an RF signal reflected by the gas ionization lamp is a position modulated signal that contains the unique identifier.

5. The RFID position location beacon of claim 4, wherein the circuit is adapted to provide the excitation voltage at an unmodulated excitation frequency of about 60 kHz.

6. The RFID position location beacon of claim 4, wherein the circuit is adapted to provide the excitation voltage at a variable output frequency in a range of about 30 to 130 kHz.

7. The RFID position location beacon of claim 4, wherein the circuit comprises:

a resonator adapted to provide an output signal to a lamp driver; and

the lamp driver adapted to provide the excitation voltage to the gas ionization lamp at the variable frequency, wherein the modulator is coupled to the resonator and the modulator is adapted to cause the output signal of the resonator to change in order to cause the variable excitation frequency to vary about the unmodulated excitation frequency.

8. The RFID position location beacon of claim 4, wherein the circuit comprises:

a frequency determining clock adapted to provide an output signal to a lamp driver; and

the lamp driver adapted to provide the excitation voltage to the gas ionization lamp at the variable frequency, wherein the modulator is coupled to the frequency determining clock and the modulator is adapted to cause the output signal of the frequency determining clock to change in order to cause the variable excitation frequency to vary about the unmodulated excitation frequency.

9. The RFID position location beacon of claim 4, further comprising:

an interrogation receiver coupled to the modulator, wherein the interrogation receiver is adapted to cause the modulator to become active when the interrogation receiver receives an interrogation signal.

10. The RFID position location beacon of claim 4, wherein the interrogation receiver continues to cause the modulator to be active as long as the interrogation receiver is receiving the interrogation signal.

11. The RFID position location beacon of claim 10, wherein the interrogation receiver continues to cause the modulator to be active until a time-out of a predetermined interval has occurred.

12. The RFID position location beacon of claim 4, further comprising:

the gas ionization lamp, wherein the gas ionization lamp is a fluorescent lamp.

13. The RFID position location beacon of claim 4, further comprising:

the gas ionization lamp, wherein the gas ionization lamp is a lamp selected from a group that includes a fluorescent lamp, a sodium vapor lamp, and a mercury vapor lamp.

14. A method for operating an RFID position location beacon comprising the steps of:

providing an excitation voltage to a gas ionization lamp at a variable output frequency that includes an unmodulated excitation frequency; and

causing the variable output frequency to vary about the unmodulated excitation frequency so that electromagnetic energy radiated by the gas ionization lamp contains a unique identifier associated with a position of the RFID position location beacon and a portion of an RF signal reflected by the gas ionization lamp is a position modulated signal that contains the unique identifier.

15. The method of claim 14, wherein providing the excitation voltage comprises providing the excitation voltage at a variable output frequency in a range of about 30 to 130 kHz.