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Locating method and system

  • US 7,050,817 B2
  • Filed: 01/09/2004
  • Issued: 05/23/2006
  • Est. Priority Date: 04/24/2003
  • Status: Expired due to Fees
First Claim
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1. A method for determining a location of a digital radio transmitter comprising:

  • detecting a digitally encoded radio signal radiated from the transmitter by at least three spatially separated receivers;

    receiving, at each of the receivers, a common synchronizing pulse;

    parsing, at each of the receivers, a received radio signal into data block samples;

    time stamping, at each of the receivers, each data block sample with a time stamp offset from the common synchronizing pulse;

    detecting, at each of the receivers, potential bit transitions in the data block samples;

    generating, at each of the receivers, bit transitions from the potential bit transitions;

    recognizing, at each of the receivers, a desired pattern of bit transitions;

    determining, at each of the receivers, a respective time of acquisition for at least some of the bit transitions comprising the desired pattern;

    transmitting, from each of the receivers, an indication of the times of acquisition to a central processor;

    determining, at a central processor, time of arrival differences among receivers from differences in the respective times of acquisition for common bit transitions in a desired pattern received from each of the receivers;

    calculating, at the central processor, the location of the transmitter from the time of arrival differences,further comprising, for each receiver;

    associating a first set of times of acquisition with bit transitions comprising the binary forms “

    01” and



    10;



    comparing bit sequences among respective data strings in a repetitively transmitted data string forming at least a portion of the desired pattern to determine if a bit error exists in the data string;

    associating a second set of times of acquisition with bits in the data string having “

    good”

    calculated time stamps;

    determining an intersection of the first set and the second set of times of acquisition;

    generating a bit mask corresponding to the intersection;

    generating an absolute time of acquisition for at least one bit transition in the signal using an offset value for the common synchronizing pulse;

    generating offset times of acquisition for a remainder of bit transitions in the signal using offset values from the absolute time of acquisition; and

    generating an indication of times of acquisition comprising the bit mask, the absolute time of acquisition, and the offset times of acquisition.

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