Method and apparatus for locating items

• US 5,528,232 A
• Filed: 05/20/1994
• Issued: 06/18/1996
• Est. Priority Date: 06/15/1990
• Status: Expired due to Term

• Current Assignee: OL Security LLC (Intellectual Ventures LLC)
• Original Assignee: Savi Technology Incorporated
• Inventors: Mihovilovic, Domingo A., Keleshian, Philip J., Verma, Vikram, Reis, Robert S.
• Primary Examiner(s): ZIMMERMAN, BRIAN A
• Application Number:
  US08/247,182
• Time in Patent Office: 760 Days
• Field of Search: 340/825.54, 340/825.49, 367/118, 367/127, 367/128, 33/713, 33/714
• US Class Current: 340/8.1
• CPC Class Codes: G01S 13/74 Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
• CPC Class Codes: G01S 13/751 wherein the responder or reflector radiates a coded signal
• CPC Class Codes: G01S 13/765 with exchange of information between interrogator and responder
• 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 13/825 with exchange of information between interrogator and responder
• 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 7/10059 transponder driven
• CPC Class Codes: G06K 7/10346 the antenna being of the far field type, e.g. HF types or dipoles

Abstract

A communication system that communicates for locating one or more tags in a time and energy efficient manner. The tags are positioned in a communication region and are located by a locator. The tags are located through organized transmission and reception of signals between the tags and the locator. The locator locates and gives directions to tags from the locator using a radio link and a multi-channel ultrasonic acoustic link. The combination of linkages provides the means to determine the unobstructed bearing and distance between the locator and the tag and resolves multipath reflections.

Claims

1. A communication system including distance measuring apparatus to determine the distance from a first location to one or more of a plurality of second locations in a communication region comprising:

a locator at said first location including;

locator acoustic means including locator acoustic transmitter means for transmitting a first acoustic frequency signal commencing at a first time;

locator memory for storing locator sequencing code including a broadcast command and a directed command;

locator processor means connected for accessing said locator memory and for processing said locator sequencing code to sequence said broadcast command and said directed command;

locator radio transceiver means connected to said locator processor means for sending and receiving communications in said communication region over a common radio frequency communication channel including sending said broadcast command and said directed command and including sending a locator radio frequency signal to identify said first time;

a plurality of tags, each of said tags at one of said second locations and each including,

a tag memory for storing information including tag sequencing code;

a tag transceiver for sending and receiving radio frequency communications to and from said locator radio transceiver means over said common communication channel, for receiving said locator radio frequency signal and for indicating a tag representation of said first time when said locator radio frequency signal is received, and for sending a radio frequency tag signal to said locator radio transceiver means;

tag acoustic means including tag acoustic receiver means for receiving said first acoustic frequency signal at a second time, wherein the second time is delayed after the first time the duration of the transmission time of said acoustic frequency signal from said first location to said second location;

a tag processor, connected to said tag transceiver to receive said broadcast command and said directed command, said tag processor including

means for processing said tag sequencing code to send a response to said locator through said tag transceiver,

difference determining means for determining the time difference between said tag representation of said first time and said second time to provide a time difference measurement, and

means for processing said tag sequencing code to cause said tag transceiver to send said time difference measurement to said locator as said radio frequency tag signal in response to receipt of said directed command whereby the distance between the first location and the second location is determined as a function of said time difference measurement.

2. The communication system of claim 1 wherein each of said tags includes a controllable power means for providing power to said tag transceiver in a low-power state for a sleep mode and in a normal-power state for an awake mode where said tag processor controls said power means to select said low-power state or said normal-power state.

3. The distance measuring apparatus of claim 1 wherein,

said acoustic frequency signal has a propagation velocity, and

said processor means includes means for multiplying said time difference measurement by said propagation velocity to determine the distance to said second location from said first location.

4. The distance measuring apparatus of claim 1 wherein

said locator radio transmitter means includes means for modulating said locator radio frequency signal to mark said locator radio frequency signal with said first time;

tag radio receiver means in said tag radio means includes means to detect the modulation of said radio frequency signal to form said tag representation of said first time when said modulation is detected to enable said time difference measurement to be precisely determined.

5. The distance measuring apparatus of claim 1 wherein

said locator acoustic transmitter means includes means for modulating said acoustic frequency signal to mark said acoustic frequency signal;

said tag acoustic receiver means in said tag acoustic means includes means to detect the modulation of said acoustic frequency signal to form a tag representation of said second time when said modulation is detected to enable said time difference measurement to be precisely determined.

6. The distance measuring apparatus of claim 1 wherein said locator radio frequency signal has an origination time offset from said first time by a time origination factor whereby the distance between said first location and said second location is determined as a function of said time difference measurement less said time origination factor.

7. The distance measuring apparatus of claim 1 wherein said locator radio means is responsive to trigger means at another location remote from said first location to trigger transmitting said acoustic frequency signal.

8. The distance measuring apparatus of claim 1 wherein,

said locator acoustic means includes second locator acoustic transmitter means, at said first location, spatially offset from said first locator acoustic transmitter means for transmitting a second acoustic frequency signal commencing at a time-offset from said first time,

said tag acoustic means receiving said second acoustic frequency signal at a time-offset from said second time,

said processor means determining said time-offset to determine the direction of said second location from said first location.

9. The communication system of claim 1 wherein,

said broadcast command requests tag identifiers from all of said tags;

for each tag, said tag processor sends a tag identifier with said response upon receipt of said broadcast command;

for each tag for which said locator receives a tag identifier, said locator processor sends said directed command to acknowledge that said tag identifier has been received.

10. The communication system of claim 9 wherein,

said broadcast command requests all tags but one specific tag to go to said sleep mode;

for each tag except said one specific tag, said tag processor upon receipt of said broadcast command causes said tag to go to said sleep mode;

for said specific tag, said locator processor means sends said directed command to command an action by said specific tag;

said tag processor for said specific tag upon receipt of said directed command sends said response including the tag identifier to said locator.

11. The communication system of claim 9 wherein said locator includes wake-up means for sending a wake-up signal to said tags and wherein each of said tags includes wake-up detection means connected to said tag transceiver and responsive to said wake-up signal from said locator for switching to said normal-power state.

12. The communication system of claim 9 wherein said tag transceiver in each of said tags includes,

a radio frequency transmitter;

a radio frequency receiver;

an antenna connected to said transmitter and receiver.

13. The communication system of claim 9 wherein each of said tags has a unique tag identifier and said locator collects the tag identifiers from tags in the communication region using communications between said locators and said tags during a plurality of collection periods, said locator having in said locator code;

synchronizing code for sending synchronizing signal to said tags to initiate each of said collection periods;

bandwidth code for controlling the bandwidth of said collection periods;

each said tag having means for inhibiting sending a tag identifier after receipt of one of said acknowledge signals.

14. The communication system of claim 9 wherein each of said tags has a unique tag identifier and said locator collects the tag identifiers from tags in the communication region using communications between said locators and said tags during a plurality of collection periods, said locator having in said locator sequencing code;

synchronizing code for sending synchronizing signals to said tags to initiate each of said collection periods;

bandwidth code for controlling the bandwidth of said collection periods;

each said tag having means for inhibiting sending a tag identifier after receipt of one of said acknowledge signal and for sending said tag identifier only once for each of said collection periods.

15. The distance measuring apparatus of claim 1 wherein said distance is measured between said first location and each second location of a subset of a plurality of second locations, each second location of said subset having a processor for separately determining a respective time difference measurement and each second location having tag radio transmitter means as part of said tag radio means for separately communicating said respective time difference measurement back to said first location in response to being interrogated.

16. The distance measuring apparatus of claim 15 wherein each processor includes means for separately controlling the communicating of said time difference measurement back to the first location after a time delay time predetermined for each of said plurality of second locations of a subset.

17. The distance measuring apparatus of claim 1 wherein,

said locator acoustic means includes second locator acoustic transmitter means, at said first location, spatially offset from said first locator acoustic transmitter means for transmitting a second acoustic frequency signal commencing at a time-offset from said first time,

said tag acoustic means receiving said second acoustic frequency signal at a time-offset from said second time,

said processor means determining said time-offset from said second time to determine the direction of said second location from said first location.

18. The distance measuring apparatus of claim 1 wherein a travel-path from said first location to said second location is determined by said processor means determining said distance a plurality of times to form a plurality of distances and averaging said plurality of distances.