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Electronic fence mode alert system and method

  • US RE44,526 E1
  • Filed: 09/20/2011
  • Issued: 10/08/2013
  • Est. Priority Date: 02/21/2006
  • Status: Active Grant
First Claim
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1. A remote locator that is configured to communicate with a transponder as a monitoring center for an electronic fence, the remote locator comprising:

  • a user input device;

    a time control circuit that is arranged to provide timing control signals according to an internal clock in the remote locator;

    a transmitter that is arranged to transmit a structured multi-frame transmission to the transponder when activated such that the structured multi-frame transmission has a transmit cadence and frequency that is determined by the internal clock of the remote locator, wherein the structured multi-frame transmission is coded with an identifier recognized by the transponder;

    a receiver that is arranged to capture samples when activated with an array of capture buffers;

    a circular correlator that is arranged to identify a correlation and a correlation phase in response to the captured samples from the receiver;

    anda processor that is arranged in cooperation with the time control circuit, the transmitter, the receiver and the circular correlator, wherein the processor is arranged to initialize the remote locator in a slow ping mode, wherein in the slow ping mode the processor is arranged for;

    coding a first structured multi-frame transmission with a unique identifier that is associated with the transponder;

    selectively transmitting a ping during a first time interval with the transmitter, wherein the ping comprises the first structured multi-frame transmission that is coded with the unique identifier;

    capturing samples with the array of capture buffers and the receiver over a first predetermined time interval that is sufficient to accumulate values for multiple transmissions of the a first sequence from the transponder;

    evaluating the captured samples with the circular correlator to determine if the captured samples correlate with an expected first reply transmission for the first sequence from the transponder;

    detecting a reply from the transponder when the captured samples correlate with the expected first reply transmission;

    determining a distance between the remote locator and the transponder based on a time of flight between the transmission of the ping and the receipt of the reply from the transponder;

    evaluating the distance relative to a first threshold associated with the electronic fence; and

    activating an a first alarm mechanism when the distance between the remote locator and the transponder is determined to exceed the first threshold associated with the electronic fence mode.

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