Cellular telephone location system

  • US 5,327,144 A
  • Filed: 05/07/1993
  • Issued: 07/05/1994
  • Est. Priority Date: 05/07/1993
  • Status: Expired due to Term
First Claim
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1. A cellular telephone location system for determining the locations of multiple mobile cellular telephones each initiating periodic signal transmission over one of a prescribed set of reverse control channels, comprising:

  • (a) at least three cell site systems, each cell site system comprising;

    an elevated ground-based antenna;

    a baseband convertor operatively coupled to said antenna for receiving cellular telephone signals transmitted over a reverse control channel by said cellular telephones and providing baseband signals derived from the cellular telephone signals;

    a timing signal receiver for receiving a timing signal common to all cell sites; and

    a sampling subsystem operatively coupled to said timing signal receiver and said baseband convertor for sampling said baseband signal at a prescribed sampling frequency and formatting the sample signal into frames of digital data, each frame comprising a prescribed number of data bits and time stamp bits, said time stamp bits representing the time at which said cellular telephone signals were received; and

    (b) a central site system operatively coupled to said cell site systems, comprising;

    means for processing said frames of data from said cell site systems to generate a table identifying individual cellular telephone signals and the differences in times of arrival of said cellular telephone signals among said cell site systems; and

    means for determining, on the basis of said times of arrival differences, the locations of the cellular telephones responsible for said cellular telephone signals.

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