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Method and system for identifying an illegal terminal in a cellular radio system

  • US 6,377,791 B2
  • Filed: 10/06/1998
  • Issued: 04/23/2002
  • Est. Priority Date: 10/08/1997
  • Status: Expired due to Term
First Claim
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1. A method for identifying an entity, which is a terminal or a subscriber using a terminal, in a cellular radio system comprising terminals arranged to transmit a message of a predetermined form at least two times, so that there is a predetermined time-out between the two successive messages of said form, wherein said message of a predetermined form is a message representing a periodic location update, the method comprising the steps of;

  • associating a first message of said predetermined form, which is received from a terminal, with a code representing sold entity, regarding an entity as an identified entity If the time between the reception of the two successive messages of said form attached to the code representing the terminal is shorter than said time-out, wherein the method comprises further steps of;

    a) storing a first time indication representing a reset moment of a timer in the terminal which controls the periodic location update;

    b) storing a second time indication corresponding to reception of a message representing a periodic location update transmitted by the terminal;

    ab) between the steps a) and b), storing a third time indication, which represents the stopping of said timer in the terminal, and storing a fourth time indication, which represents restarting of sold timer in the terminal when the timer has been stopped;

    c) calculating a first difference between stored first and second time indications of the steps a) and b);

    d) comparing said first difference with said time-out; and

    cd) between the steps c) and d), subtracting a second difference between fourth and third time indications of step ab) from sold first time difference.

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