Wireless time reference system and method

• US 8,742,986 B2
• Filed: 10/10/2011
• Issued: 06/03/2014
• Est. Priority Date: 12/23/2005
• Status: Active Grant

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: ZIH Corp. (Zebra Technologies Corporation)
• Inventors: Chen, Keming, Turner, Belinda, Ameti, Altan, Fontana, Robert J, Richley, Edward A
• Primary Examiner(s): LIU, HARRY K
• Application Number:
  US13/270,061
• Publication Number:
  US 20120086607A1
• Time in Patent Office: 967 Days
• Field of Search: 342386-387, 342/31, 342/451, 342463-465
• US Class Current: 342/387
• CPC Class Codes: G01S 5/0009 Transmission of position information to remote stations involving assistance data G01S5/0236
• CPC Class Codes: G01S 5/021 Calibration, monitoring or correction G01S5/0252 takes precedence
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location

Abstract

Various methods and apparatuses that utilize a wireless time reference system are provided herein. One example method involves calibrating independent, spatially-located clocks of a geoposition system in order to geolocate an object having an associated object tag. The example method may include transmitting an RF pulse pair, receiving the pulse pair at multiple locations, utilizing respective frequencies of first and second spatially-located clocks to produce count values to effect measurement of an interarrival interval at each of multiple locations, determining a ratio of count values relative to said first and second spatially-located clocks, and utilizing said ratio to calibrate time indications of said clocks. Other related methods and apparatus are also provided.

Claims

1. A method calibrating independent, spatially-located clocks of a geoposition system in order to geolocate an object having an associated object tag, said method comprising:

utilizing respective frequencies of first and second spatially-located clocks to produce count values to effect measurement of an interarrival interval defined for an RF pulse pair received at each of a first receiver location and a second receiver location,

determining, by a processor, a ratio of count values relative to the first and second spatially-located clocks, and

calibrating time indications of said clocks based on the ration of count values.

2. The method of claim 1, further comprising utilizing a ratio of an initial pulse pair to maintain synchronization of said clocks during subsequent pulse pair transmissions.

3. The method of claim 2, further comprising wirelessly transmitting said count values to a central processing hub that determines object position according to said ratio.

4. An object location system, said system comprising:

a reference transmitter to transmit at least two UWB pulses comprising short bursts of RF energy,

multiple monitoring stations positionable at known locations, each including a UWB receiver and a local clock that responds to receipt of said UWB pulses to determine a clock count based on an interarrival interval,

each said monitoring station further including transmitter to transmit a digital representation of said clock count to a central processing hub, and

said central processing hub including a processor to compute a ratio of count values relative to first and second ones of said multiple monitoring stations and to utilize said ratio to align indications of timing references of said monitoring stations in order to determine the position of said object.

5. The object location system of claim 4, wherein said processor computes a second count value ratio between first and third ones of said monitoring stations and utilizes said first and second count values to align respective local clocks to determine the position of said object.

6. The object location system of claim 5, wherein said processor utilizes a clock count value of one of the monitoring stations as a common reference in order to compute ratios with respect to clock count values of other monitoring stations, and said processor determines object location by aligning local clocks of other monitoring stations with said first monitoring station.

7. The object location system of claim 4, wherein said reference transmitter transmit multiple pulse pair groups, and said processor corrects indications of clock drifts among said monitoring stations in order to maintain synchronization of local clocks whereby to determine the location of object based upon subsequent object tag transmissions.

8. The object location system of claim 7, wherein said processor corrects local clocks relative to higher order anomalies.

9. The object location system of claim 4, wherein said digital representation further includes a station identifier to identify respective ones of said monitoring stations.

10. The object location system of claim 4, wherein said processing hub is co-located with one of said monitoring stations.

11. The object location system of claim 4, wherein the monitoring stations and processing hub are remotely located, and said monitoring stations transmit said clock count to said central processing hub via an over-the-air RF transmission.

12. The object location system of claim 4, further including a free-running cyclic ring counter that is indexed by said local clock of each said monitoring station in order to measure respective clock count values during said interarrival interval of said UWB pulses.