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Determining clock-drift using signals of opportunity

  • US 9,681,408 B2
  • Filed: 04/29/2015
  • Issued: 06/13/2017
  • Est. Priority Date: 04/30/2014
  • Status: Active Grant
First Claim
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1. A method, for a movable device having a local clock, of determining a drift between the local clock and a reference clock that is used by one or more reference devices, by observing one or more signals transmitted by the respective one or more reference devices, the method comprising:

  • when the movable device is at a calibration location, receiving at the movable device, at a first time, a first portion of the signal transmitted by one of the reference devices;

    moving the movable device to an operating location; and

    when the movable device is at the operating location, receiving at the movable device, at a second time, a second portion of the signal transmitted by one of the reference devices, the first portion and the second portion having been transmitted with a time-interval between them, according to the reference clock;

    the method further comprising;

    determining the time-interval;

    obtaining a model of the one or more signals, describing for each signal at least one of;

    a direction of propagation of that signal, andthe location of the respective reference device;

    determining local time information comprising;

    the first time and the second time, or a time difference between them, according to the local clock;

    defining position variables comprising;

    the calibration location and the operating location, ora displacement vector between them;

    constructing a set of one or more equations, which relates the position variables, the model, the local time information, the time-interval, and the drift;

    solving the set of one or more equations, to determine the drift; and

    correcting the clock of the movable device based on the determined drift.

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