Radio geo-location system with advanced first received wavefront arrival determination

• US 6,121,926 A
• Filed: 11/19/1999
• Issued: 09/19/2000
• Est. Priority Date: 01/21/1997
• Status: Expired due to Term

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Wherenet Corporation (Zebra Technologies Corporation)
• Inventors: Belcher, Donald K., Boyd, Robert W., Wohl, Michael A.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US09/442,710
• Time in Patent Office: 305 Days
• Field of Search: 342/450, 342/463, 342/465, 375/200
• US Class Current: 342/450
• CPC Class Codes: G01S 1/0428 Signal details
• CPC Class Codes: G01S 13/767 Responders; Transponders teaching or practice apparatus for gun-aiming or gun-laying using reflecting targets or active targets F41G3/26
• CPC Class Codes: G01S 13/82 wherein continuous-type signals are transmitted
• CPC Class Codes: G01S 13/825 with exchange of information between interrogator and responder
• 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 5/02 using radio waves using satellite radio beacon systems for determining position G01S19/00
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• 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

Abstract

An asset management radio location system uses time-of-arrival differentiation for random and repetitive spread spectrum, short duration pulse `blinks` from object-attached tags, to provide a practical, continuous identification of the location of each and every object within an environment of interest, irrespective whether the object is stationary or moving. Correlation-based RF processors determine which signals received spatially diverse antennas coupled to tag transmission readers are first-to-arrive signals as transmitted from any blinking tag. An object location processor carries out time-of-arrival differentiation of first-to-arrive transmissions from any blinking tag to determine where the respective object is located within the environment.

Claims

1. A method for locating an object comprising the steps of:

(a) transmitting from said object a signal containing information representative of the identification thereof;

(b) at each of a plurality of spaced apart monitoring locations, receiving said signal at a plurality of mutually diverse antennas;

(c) processing signals received by said plurality of mutually diverse antennas at said plurality of spaced apart monitoring locations, to determine which received signals are first-to-arrive signals; and

(d) conducting time-of-arrival differentiation processing of said first-to-arrive signals to locate said object.

2. A method according to claim 1, wherein step (a) comprises transmitting said signal in a random and repetitive manner that does not depend upon whether said object is in motion or is stationary.

3. A method according to claim 1, wherein step (d) comprises conducting said time-of-arrival differentiation of earliest-in-time ones of said first-to-arrive signals determined in step (c).

4. A method according to claim 1, wherein step (c) comprises performing matched filter correlation of said signals received by said plurality of mutually diverse antennas at said plurality of spaced apart monitoring locations, to determine which received signals are first-to-arrive signals.

5. A method according to claim 1, wherein said signals transmitted in step (a) comprise spread spectrum RF signals, and wherein step (c) comprises correlating a received spread spectrum RF signal with successive time offset versions of a reference spreading code corresponding to that of said spread spectrum RF signals.

6. A method according to claim 1, wherein said mutually diverse antennas comprise spatially diverse antennas that are spaced apart from one another by a distance sufficient to effectively statistically minimize destructive multipath interference at said antennas simultaneously, and wherein said antennas are spaced close enough to one another so as to not significantly affect determination of the location of said object.

7. A method according to claim 1, wherein said mutually diverse antennas comprise circularly polarized antennas.

8. A method according to claim 1, wherein

step (c) further comprises coupling a plurality of auxiliary `phased array` signal processing paths to said mutually diverse antennas, summing energy received from said antennas in a prescribed phase relationship to produce a respective energy sum, and processing said respective energy sum to derive a further first-to-arrive signal, and

step (d) further comprises conducting said time-of-arrival differentiation to include said further earliest-in-time signal.

9. A system for locating an object comprising:

coupling, with said object, a tag transmitter which is operative to transmit a signal containing information representative of said object;

a plurality of spaced apart tag transmission monitoring locations, each having a plurality of mutually diverse antennas coupled to tag transmission readers which are operative to detect said signal transmitted by said tag transmitter;

reader output processors which are operative to process signals detected by said tag transmission readers to determine which signals received by said tag transmission readers are first-to-arrive signals; and

an object location processor coupled to said reader output processors, and operative to conduct time-of-arrival differentiation of said first-to-arrive signals as detected by said tag transmission readers, so to locate said object.

10. A system according to claim 9, wherein said tag transmitter is operative to transmit said signal in a random and repetitive manner that does not depend upon whether said object is in motion or is stationary.

11. A system according to claim 9, wherein said object location processor is operative to conduct said time-of-arrival differentiation of earliest-in-time ones of first-to-arrive signals detected by said tag transmission readers.

12. A system according to claim 9, wherein a respective reader processor comprises a matched filter correlator.

13. A system according to claim 12 wherein said signals comprise spread spectrum RF signals, and wherein a respective matched filter correlator contains a plurality of matched filter banks containing parallel correlators, which are operative to correlate a received spread spectrum RF signal with successive time offset versions of a reference spreading code corresponding to that of said spread spectrum RF signals.

14. A system according to claim 9, wherein said mutually diverse antennas comprise spatially diverse antennas, that are spaced apart from one another by a distance sufficient to effectively statistically minimize destructive multipath interference at said antennas simultaneously, but are spaced close enough to one another as to not significantly affect determination of the location of said object by said object location processor.

15. A system according to claim 9, wherein said mutually diverse antennas comprise circularly polarized antennas.

16. A system according to claim 9, further including a plurality of auxiliary `phased array` signal processing paths coupled to said mutually diverse antennas to which said tag transmission readers are coupled, and wherein each auxiliary phased array path is configured to sum energy received from said antennas in a prescribed phase relationship, and to couple a respective energy sum to an associated tag transmission reader, and wherein a further reader output processor is coupled to said associated tag transmission readers, and is operative to process the energy sum supplied to said associated tag transmission readers and to generate a further first-to-arrive signal, and wherein said object location processor is operative to carry out time-of-arrival differentiation of earliest-in-time ones of signals provided by said tag transmission readers.