Radio location system for precisely tracking objects by RF transceiver tags which randomly and repetitively emit wideband identification signals

• US 5,920,287 A
• Filed: 01/21/1997
• Issued: 07/06/1999
• Est. Priority Date: 01/21/1997
• Status: Expired due to Term

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Widata Corporation (Zebra Technologies Corporation)
• Inventors: Belcher, Donald K., Wisherd, David S., Eisenberg, John A.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US08/786,232
• Time in Patent Office: 896 Days
• Field of Search: 342/450, 342/463, 342/465, 375/207, 375/200
• US Class Current: 342/450
• 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 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308
• 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 by tag transmission readers are first-to-arrive signals as transmitted from any blinking tag, and an object location processor carries out time-of-arrival differentiation of these first-to-arrive transmissions from any blinking tag to determine where the respective object is located within the environment. A low power interrogation wand may be employed to refine the location of an object by a user programmed transmission-response exchange between the wand and the tag associated with the object of interest.

Claims

1. A system for identifying locations of objects within a monitored environment, using time-of-arrival differentiation for transmissions from tags disposed with said objects, as detected at a plurality of spaced apart tag transmission readers for said monitored environment comprising:

for each of said objects, a respective tag disposed therewith containing a tag transmitter which is operative to randomly and repetitively transmit, irrespective of motion of said each object and in a random and repetitive manner that does not depend upon whether said each object is in motion or is stationary, a pseudo random spread spectrum RF signal encoded with information representative of the identification of said each object, and wherein said tag transmission readers are operative to detect pseudo random spread spectrum RF signals transmitted by said each object;

reader output processors coupled to said plurality of tag transmission readers, each reader output processor comprising a correlation-based RF signal processor that is operative to correlate pseudo random spread spectrum RF signals detected by its associated tag transmission reader with spread spectrum reference signal patterns, and thereby determine which pseudo random RF spread spectrum signals received by said plurality of tag transmission readers are first-to-arrive pseudo random spread spectrum RF signals as transmitted from said respective tag, and wherein said correlation-based RF signal processor comprises a matched filter correlator, having a plurality of matched filter banks containing parallel correlators, which are operative to correlate a received pseudo random spread spectrum RF signal with successive time offset versions of a reference pseudo random spreading code corresponding to that of said pseudo random spread spectrum RF signals transmitted by said respective tag; and

an object location processor which is coupled to said reader output processors and is operative to carry out time-of-arrival differentiation of said first-to-arrive transmissions from said respective tag, as detected by said plurality of tag transmission readers, so to locate said respective tag and its associated object within said environment.

2. A system according to claim 1, wherein said respective tag includes memory which stores a multibit word representative of the identification of said object and additional parameter data provided to said memory, and wherein said tag transmitter is operative to randomly and repetitively transmit said pseudo random spread spectrum RF signal encoded with said information representative of the identification of said object and said additional parameter data.

3. A system according to claim 1, wherein said tag transmitter comprises a pseudo random spreading sequence generator, which randomly and repetitively generates a pseudo random spreading sequence modulating an RF carrier for transmission by said tag, and a pseudo random pulse generator, which is operative to cause said pseudo random spreading sequence generator to randomly and repetitively generate said pseudo random spreading sequence modulating said RF carrier for transmission by said tag.

4. A system according to claim 1, wherein said respective tag contains a tag transceiver, that includes said tag transmitter and a tag receiver, and a timing circuit which is operative to periodically enable said tag receiver.

5. A system according to claim 4, wherein said respective tag further includes memory, which is arranged to store a multibit word representative of the identification of said object and information received by said tag receiver.

6. A system according to claim 5, wherein said tag transmitter includes a pseudo random spreading sequence generator, which randomly and repetitively generates a pseudo random spreading sequence modulating an RF carrier for transmission by said tag with information stored in said memory, and wherein said tag transmitter is operative to transmit said spread spectrum signal encoded with information stored in said memory, in response to said tag receiver detecting a signal identifying said respective tag.

7. A system according to claim 4, further including an interrogator unit containing a relatively low power transmitter that is selectively operative to transmit a query signal to said tag receiver, said query signal causing said respective tag to transmit said signal encoded with information representative of the identification of said each object, as received by said tag receiver.

8. A system according to claim 7, wherein said interrogator unit is operative to repetitively transmit a query code sequence, which uniquely identifies said respective tag, over a duration sufficient to include periodic enabling of said tag receiver by said timing circuit.

9. A system according to claim 8, wherein said interrogator unit includes a receiver that is operative to receive a response signal encoded with information representative of the identification of said each object.

10. A system according to claim 9, wherein said interrogator unit is operative to determine the proximity of said object relative to said interrogator unit in accordance with signal strength of said response signal.

11. A system according to claim 1, wherein a respective tag transmission reader is configured to provide DC power for circuitry of said reader in accordance with energy contained in a detected signal transmitted by said respective tag.

12. A system according to claim 1, wherein said correlation-based RF signal processor comprises a digital signal processor, which processes signals supplied to said matched filter correlator and said first-to-arrive signals to identify the time of arrival of said first-to-arrive signals at a respective reader, and the amount of energy in the signal produced said reader'"'"'s input for application to said object-location processor.

13. A system according to claim 12, wherein said object-location processor is operative to locate each object in accordance with a geometry algorithm that relies upon time-of-arrival inputs from at least three spatially separated tag transmission readers to compute the location of said object.

14. A system according to claim 9, wherein said respective tag further includes memory, which stores a multibit word representative of the identification of said object and auxiliary information, and wherein said object-location processor is operative to couple, to an asset management data base, data that has been read out of said memory of said respective tag and included in said signal transmitted by said tag.

15. A system according to claim 1, wherein said tag includes memory which stores a multibit word representative of the identification of said object and elevation data associated with said object, and wherein said tag transmitter is operative to transmit a spread spectrum signal encoded with information representative of the identification of said each object and said elevation data.

16. A system according to claim 15, wherein said elevation data is representative of a change in elevation of said object.

17. A system according to claim 15, wherein a tag transmission reader is operative to monitor transmission of said object and elevation data transmitted by said tag transmitter so as to enable said object location processor to determine a change in elevation of said object.

18. A method for locating objects within a monitored environment, using time-of-arrival differentiation for transmissions from tags associated with said objects, as detected at a plurality of spaced apart tag transmission readers for said monitored environment, comprising the steps of:

(a) irrespective of motion of an object, causing its associated tag to randomly and repetitively transmit in a random and repetitive manner that does not depend upon whether said object is in motion or is stationary, a pseudo random spread spectrum signal encoded with information representative of the identification of said object;

(b) processing, by correlation-based RF signal processors, signals detected at said plurality of spatially separated tag transmission readers, each of which is operative to detect pseudo spread spectrum RF signals transmitted by said tags of said objects, to determine which signals received by said plurality of tag transmission readers are first-to-arrive signals as transmitted from said associated tag, each correlation-based RF signal processor being operative to correlate pseudo random spread spectrum RF signals detected by its associated tag transmission reader with spread spectrum reference signal patterns, and thereby determine which pseudo random RF spread spectrum signals received by said plurality of tag transmission readers are first-to-arrive pseudo random spread spectrum RF signals as transmitted from said associated tag, and wherein said correlation-based RF signal processor comprises a matched filter correlator, having a plurality of matched filter banks containing parallel correlators, which are operative to correlate a received pseudo random spread spectrum RF signal with successive time offset versions of a reference pseudo random spreading code corresponding to that of said pseudo random spread spectrum RF signals transmitted by said associated tag; and

(c) conducting time-of-arrival differentiation of said first-to-arrive signals to locate said associated tag and thereby said object within said environment.

19. A method according to claim 18, wherein said associated tag includes memory which stores a multibit word representative of the identification of said object and additional parameter data, and wherein step (a) comprises randomly and repetitively transmitting a spread spectrum signal encoded with said information representative of the identification of said object and said additional parameter data.

20. A method according to claim 18, wherein step (a) comprises randomly and repetitively transmitting RF carrier modulated with a pseudo random spreading sequence that is generated in a random manner in accordance with a relatively slow pseudo random pulse sequence.

21. A method according to claim 18, further including the step of (c) providing a tag receiver and periodically enabling said tag receiver to be capable of receiving query signals to said tag.

22. A method according to claim 21, further including the step of (d) providing memory with said tag and storing in said memory a multibit word representative of the identification of said object and information received by said tag receiver, and wherein step (a) comprises randomly and repetitively modulating an RF carrier with a pseudo random spreading sequence with information stored in said memory, in response to said tag receiver receiving a signal identifying said respective tag.

23. A method according to claim 22, further including the step of (d) providing a portable transceiver unit and transmitting therefrom a query signal to said tag receiver, and causing said tag to transmit said signal encoded with information stored in said memory.

24. A method according to claim 23, wherein step (d) comprises causing said portable transceiver unit to repetitively transmit a query code sequence, which uniquely identifies said respective tag, over a duration sufficient to include said periodically enabling of said tag receiver.

25. A method according to claim 24, wherein step (d) further includes receiving, at said interrogator unit, a response signal transmitted by said tag and encoded with information representative of the identification of said object.

26. A method according to claim 23, wherein step (d) further includes determining the proximity of said object relative to said interrogator unit in accordance with signal strength of said response signal.

27. A method according to claim 18, wherein step (c) comprises conducting time-of-arrival differentiation of said first-to-arrive signals in accordance with a geometry algorithm that relies upon time-of-arrival inputs from at least three spatially separated tag transmission readers to compute the location of said object.

28. A method according to claim 18, wherein said tag further includes memory, which stores a multibit word representative of the identification of said object and auxiliary information, and wherein step (c) further comprises coupling to an asset management data base data that has been read out of said memory of said respective tag and imparted to said signal encoded with information representative of the identification of said object and transmitted by said tag in step (a).

29. A method for locating objects within a monitored environment, using time-of-arrival differentiation for transmissions from tags associated with said objects, as detected at a plurality of spaced apart tag transmission readers for said monitored environment, comprising the steps of:

(a) causing an object'"'"'s associated tag to transmit, in a random and repetitive manner that does not depend upon whether or said object is in motion or is stationary a pseudo random spread spectrum RF signal encoded with information representative of the identification of said object, and wherein said tag transmission readers are operative to detect pseudo random spread spectrum RF signals transmitted by said object;

(b) processing signals detected at said plurality of spatially separated tag transmission readers, in reader output processors coupled to said plurality of tag transmission readers, each reader output processor comprising a correlation-based RF signal processor that is operative to correlate pseudo random spread spectrum RF signals detected by its associated tag transmission reader with spread spectrum reference signal patterns, and thereby determine which pseudo random RF spread spectrum signals received by said plurality of tag transmission readers are first-to-arrive pseudo random spread spectrum RF signals as transmitted from said respective tag, and wherein said correlation-based RF signal processor comprises a matched filter correlator, having a plurality of matched filter banks containing parallel correlators, which are operative to correlate a received pseudo random spread spectrum RF signal with successive time offset versions of a reference pseudo random spreading code corresponding to that of said pseudo random spread spectrum RF signals transmitted by said respective tag, and thereby determine which signals received by said plurality of tag transmission readers are first-to-arrive signals as transmitted from said associated tag;

(c) conducting time-of-arrival differentiation of said first-to-arrive signals to determine the approximate location of said associated tag and thereby said object;

(d) transmitting a query signal from a portable transceiver unit to said tag receiver, and causing said tag to transmit a response signal; and

(e) detecting said response signal at said portable transceiver and processing said response signal to locate said associated tag and thereby said object.

30. A method according to claim 29, wherein step (d) comprises locating said object in accordance with the signal strength of said response signal.

31. A method for identifying locations of objects within a monitored environment, using time-of-arrival differentiation for transmissions from tags disposed with said objects, as detected at a plurality of spaced apart tag transmission readers for said monitored environment comprising the steps of:

(a) at each of said objects, randomly and repetitively transmitting, in a random and repetitive manner that does not depend upon whether said each object is in motion or is stationary a pseudo random spread spectrum RF signal encoded with information representative of the identification of said each object, and wherein said tag transmission readers are operative to detect pseudo random spread spectrum RF signals transmitted by said object;

(b) correlating spread spectrum signals detected by associated tag transmission readers with spread spectrum reference signal patterns, by means of a matched filter correlator, having a plurality of matched filter banks containing parallel correlators, which are operative to correlate a received pseudo random spread spectrum RF signal with successive time offset versions of a reference pseudo random spreading code corresponding to that of said pseudo random spread spectrum RF signals transmitted by said respective tag, and thereby determining which spread spectrum signals received by said plurality of tag transmission readers are first-to-arrive spread spectrum signals as transmitted from said respective tag; and

(c) conducting time-of-arrival differentiation of said first-to-arrive transmissions from said respective tag, as detected by said plurality of associated tag transmission readers, so to locate said respective tag and its associated object within said environment.

32. A method according to claim 31, wherein said tag includes memory which stores a multibit word representative of the identification of said object and elevation data associated with said object, and wherein step (a) comprises transmitting a spread spectrum signal encoded with information representative of the identification of said each object and said elevation data.

33. A method according to claim 32, wherein said elevation data is representative of a change in elevation of said object.

34. A method according to claim 33, wherein a tag transmission reader is operative to monitor transmission of said object and elevation data transmitted by said tag transmitter so as to enable a change in elevation of said object to be determined in step (c).