Method and apparatus for modeling timing relationships between clocks

Patent metadata

Field	Value
Publication number	US-9395432-B2
Application number	US-201213588710-A
Country	US
Kind code	B2
Filing date	Aug 17, 2012
Priority date	Aug 17, 2011
Publication date	Jul 19, 2016
Grant date	Jul 19, 2016

Abstract

Various methods for modeling timing relationships between clocks are provided. One example method includes identifying a link that is one of a plurality of links within a wireless locating system and receiving link data describing a reference signal event for the link. The example method may also include determining a reliability metric for the link based on the link data and comparing the reliability metric to a threshold reliability metric to determine whether the link is a reliable link. Further, the example method may include adding the link to a collection of reliable links for the wireless locating system, and generating a model describing a timing relationship between respective clocks of each of a plurality of receiver units in the wireless locating system based on link data for each of the reliable links. Related systems and apparatuses are also provided.

First claim

What is claimed is:

1. A method comprising:
identifying a link that is one of a plurality of links within a wireless locating system, the link being defined by at least a reference signal source, a first receiver unit, and a second receiver unit;
receiving link data describing reference signal events for the link, the link data for the reference signal events being defined by at least first time stamps describing times at which the first receiver unit received reference signals transmitted by the reference signal source, and second time stamps associated with the reference signal;
determining, via a processor, a reliability metric for signal transmission via the link based on the link data, wherein determining the reliability metric comprises calculating a standard deviation of the first time stamps;
comparing, via the processor, the reliability metric for the link to a threshold reliability metric to determine whether the link is a reliable link;
in an instance in which the link is determined to be a reliable link, including the link in a collection of reliable links for the wireless locating system;
generating, via the processor, a model describing a timing relationship between respective clocks of each of a plurality of receiver units in the wireless locating system based on link data for each of the reliable links; and
repeatedly applying, via the processor, the model to time-of-arrival data captured by at least some of the plurality of receiver units to correct the time-of-arrival data for unsynchronized clocks of the receiver units.

2. The method of claim 1 , wherein the link data is further defined by at least one of location coordinates for the first receiver unit, location coordinates for the second receiver unit, or location coordinates of the reference signal source.

3. The method of claim 1 , wherein at least one of the first receiver unit or the second receiver unit includes a plurality of antennas.

4. The method of claim 1 , wherein identifying the link includes identifying the link between an antenna of the first receiver unit and an antenna of a second receiver unit, the reference signal source being the antenna of the second receiver unit and the second time stamps being times when the antenna of the second receiver unit transmitted the reference signal.

5. The method of claim 1 further comprising determining a value of the threshold reliability based on a result of a holistic analysis of reliability metrics for each of the plurality of links within the wireless locating system.

6. The method of claim 1 , wherein generating a model describing a timing relationship comprises:
adjusting the timing relationship between respective clocks of each of a plurality of receiver units in the wireless locating system based on weight for each of the reliable links.

7. The method of claim 1 , wherein determining the reliability metric for signal transmission via the link includes:
adjusting the reliability metric based on a variance from a predetermined signal-time-of-arrival relationship for the link and a signal-time-of-arrival relationship based on the link data describing the reference signal events for the link.

8. The method of claim 1 , wherein calculating the standard deviation of the first time stamps comprises calculating the standard deviation relative to other ones of the first time stamps, a time-of-arrival difference predicated by a geometry or a system clock.

9. The method of claim 1 , wherein generating the model includes:
segmenting the model into a first island component and a second island component due to a topological discontinuity that occurs when no link bridges a receiver unit addressed by the first island component to a receiver unit addressed by the second island component, wherein the model includes independent timing relationships for the first island component and the second island component.

10. The method of claim 1 , wherein generating the model includes generating the model as a collection of tracking equations, wherein each tracking equation is associated with a respective receiver unit and each tracking equation describes a relationship between a selected receiver unit clock and a system time.

11. The method of claim 1 , wherein identifying the link includes identifying the link between an antenna of the first receiver unit and an antenna of a second receiver unit, the reference signal source being the antenna of the second receiver unit and the second time stamps being times when the antenna of the second receiver unit transmitted the reference signals; and
wherein determining the reliability metric includes determining that the link is one of a set of reciprocal links between the antenna of the first receiver unit and the antenna of the second receiver unit, wherein the reciprocal links use a same signal path between the antenna of the first receiver unit and the antenna of the second receiver unit in opposite directions.

12. The method of claim 11 , wherein the signal path between the antenna of the first receiver unit and the antenna of the second receiver unit is a non-line-of-sight path.

13. The method of claim 1 , wherein identifying the link includes identifying a wired link between the first receiver unit and the second receiver unit, the reference signal source being the second receiver unit and the second time stamps being times when the second receiver unit transmitted the reference signals.

14. The method of claim 13 , wherein determining the reliability metric includes determining that the wired link is one of a set of reciprocal links between the first receiver unit and the second receiver unit and wherein the reciprocal links use a same signal path between the first receiver unit and the second receiver unit in opposite directions.

15. The method of claim 1 , wherein the reference signal source of the link is a reference tag positioned at a predetermined location, the reference tag being configured to transmit a geographic identifier related to the predetermined location.

16. The method of claim 1 , wherein determining the reliability metric for signal transmission via the link includes:
identifying a second link;
determining that the second link is a reciprocal of the link, wherein determining that the second link is the reciprocal includes determining that the second link uses the same signal path, referenced in an opposite direction, as the link based on time-of-arrival information; and
adjusting the reliability metric for signal transmission via the link based on the determination that the link has a reciprocal link.

17. A non-transitory computer readable medium having program code stored thereon, that when executed causes an apparatus to:
identify a link that is one of a plurality of links within a wireless locating system, the link being defined by at least a reference signal source, a first receiver unit, and a second receiver unit;
receive link data describing reference signal events for the link, the link data for the reference signal events being defined by at least first time stamps describing times at which the first receiver unit received reference signals transmitted by the reference signal source, and second time stamps associated with the reference signal;
determine a reliability metric for signal transmission via the link based on the link data, wherein determining the reliability metric comprises calculating a standard deviation of the first time stamps;
compare the reliability metric for the link to a threshold reliability metric to determine whether the link is a reliable link;
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Assignees

• Boyd Robert W
• Zih Corp

Inventors

• Boyd Robert W

Classifications

• G01S5/06 Primary

  Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements (G01S5/12 takes precedence) · CPC title

• G01S5/021

  Calibration, monitoring or correction (G01S5/0252 takes precedence) · CPC title

• H04W24/08

  Testing, {supervising or monitoring} using real traffic · CPC title

• H04L5/0048

  Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091) · CPC title

• G01S5/10 Primary

  Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements {, e.g. omega or decca systems}(G01S5/12 takes precedence {; beacons and receivers cooperating therewith G01S1/306, G01S1/308}) · CPC title