Extensible object location system and method using multiple references

• US 9,360,547 B2
• Filed: 03/30/2012
• Issued: 06/07/2016
• Est. Priority Date: 05/10/2005
• Status: Active Grant

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: ZIH Corp. (Zebra Technologies Corporation)
• Inventors: Ameti, Aitan, Chen, Keming, Fontana, Robert J., Richley, Edward A., Turner, Belinda
• Primary Examiner(s): Issing, Gregory C
• Assistant Examiner(s): Mull, Fred H
• Application Number:
  US13/436,029
• Publication Number:
  US 20120188129A1
• Time in Patent Office: 1,530 Days
• Field of Search: 342/387, 342/463, 342/465, 375355-356
• US Class Current: 1/1
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/02213 Receivers arranged in a network for determining the position of a transmitter
• 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: 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

Abstract

An ultra wideband (UWB) or short-pulse RF system is disclosed that can be used to precisely locate or track objects (such as personnel, equipment, assets, etc.) in real-time in an arbitrarily large, physically connected or disconnected, multipath and/or noisy environment. A system implementation includes multiple zones or groups of receivers that receives RF signals transmitted by one or more timing reference tags and one or more objects having associated object tags. Each zone or group may share a common receiver. By combining a multiple reference tag system with a virtual group of receivers, i.e., a zoning technique or system, a cost-effective system can be provided that offers scalability and flexibility to monitor a significantly expanded coverage area.

Claims

1. A location system comprising:

an object tag associated with an object and configured to transmit a radio frequency signal within a monitored region;

a plurality of reference tags each associated with a respective zone of a plurality of zones within the monitored region, each reference tag configured to transmit a reference signal and wherein each reference tag is positioned at a known reference location within the monitored region;

a plurality of receivers positioned in or around the monitored area at known receiver locations, wherein the plurality of receivers are configured to receive the object tag radio frequency signal and the reference signal, wherein each receiver comprises a free running digital counter configured to detect an object time of arrival of the object tag radio frequency signal and a reference time of arrival of the reference signal; and

a processing hub comprising a common source clock, disposed in wired communication with the free running digital counters through daisy chained cables, wherein the common source clock is configured to synchronize the free running digital counters in frequency and lock the free running digital counters in a relative phase relationship, wherein the processing hub is configured to receive the object time of arrival data of the object tag radio frequency signal and the reference tag signal and determine an object location based on the object time of arrival and phase offsets associated with the respective receivers of the plurality of receivers, wherein the phase offsets are determined based on the reference time of arrival at the respective receivers, the known receiver locations, and the known reference location, wherein the processing hub is further configured to define the respective zones among the plurality of zones, prior to determining the object location, wherein the respective zones comprise a group of receivers and the respective reference tag, wherein at least one receiver of the group of receivers is common to at least two of the plurality of zones, wherein the determination of the object location is within one of the respective zones.

2. The location system of claim 1, wherein the defining a respective zone is based on a transmission range of the reference tag.

3. The location system of claim 1, wherein the detecting an object time of arrival of the object tag radio frequency signal and a reference time of arrival of the reference signal comprises latching or recording count values of the free running digital counter.

4. The location system of claim 1, wherein the determining the object location comprises a gradient search to minimize an error function.

5. The location system of claim 1, wherein the phase offsets are determined prior to the determining the object location.

6. The location system of claim 1, wherein the object tag comprises an ultra-wide band transmitter, wherein the radio frequency signal is ultra-wide band.

7. The location system of claim 1, wherein the radio frequency signal or the reference signal comprises a tag identification.

8. A method comprising:

transmitting a radio frequency signal, from an object tag associated with an object, within a monitored region;

transmitting a reference signal, from one of a plurality of reference tags, wherein each of the plurality of references tag is associated with a zone within the monitored region and is positioned at a known reference location within the monitored region;

receiving the object tag radio frequency signal and the reference signal, at a plurality of receivers positioned in or around the monitored area at known receiver locations, wherein each receiver comprises a free running digital counter configured to detect an object time of arrival of the object tag radio frequency signal and a reference time of arrival of the reference signal;

synchronizing, by a common clock source of a processing hub, the free running digital counters in frequency and locking the free running digital counters in a relative phase relationship, wherein the common clock source is disposed in wired communication with the free running digital counters through daisy chained cables;

receiving, by the processing hub, the object time of arrival data of the object tag radio frequency signal and the reference tag signal;

determining an object location based on the object time of arrival and phase offsets associated with the respective receivers of the plurality of receivers, wherein the phase offsets are determined based on the reference time of arrival at the respective receivers, the known receiver locations, and the known reference location; and

defining respective zones among the plurality of zones, prior to determining the object location, wherein the respective zones comprise a group of receivers and a respective reference tag, wherein at least one receiver of the group or receivers is common to at least two of the plurality of zones, wherein the determination of the object location is within one of the respective zones.

9. The method of claim 8, wherein the defining a respective zone is based on a transmission range of the reference tag.

10. The method of claim 8, wherein the detecting an object time of arrival of the object tag radio frequency signal and a reference time of arrival of the reference signal comprises latching or recording count values of the free running digital counter.

11. The method of claim 8, wherein the determining the object location comprises a gradient search to minimize an effort function.

12. The method of claim 8, wherein the phase offsets are determined prior to the determining the object location.

13. The method of claim 8, wherein the object tag comprises a ultra-wide band transmitter, wherein the radio frequency signal is ultra-wide band.

14. The method of claim 8, wherein the radio frequency signal or the reference signal comprises at least a tag identification.