METHOD OF DETECTING THE UNAUTHORIZED USE OF AN IDENTIFICATION ASSIGNED TO A MOBILE RADIO STATION IN A RADIO TRANSMISSION SYSTEM

摘要

The identification of a mobile radio station in a radio transmission system can be based on a subscriber's number assigned to the mobile radio station which subscriber number is registered in, for example, the telephone directory and on an identification code which is formed in accordance with a secret enciphering rule from the subscriber number. By copying the identification signal generator, for example, a magnetic card on which the subscriber's number and the identification code are stored, or by listening-in on the exchange of information via the radio transmission channel between a mobile radio station and a stationary radio station (radio exchange) an intended fraudulent user can imitate and use an external identification. So as to enable detection of this imitation additional data which change during operation of the mobile radio station are combined with fixed data, which depend on the different procedures in the system (subscriber's number and identification code of the mobile radio station, and are evaluated in the radio exchange. Such variable data can be constituted by, for example, the number of successful accesses of the mobile radio station to a radio transmission channel. There may be a fixed or a variable relationship between the number of radio messages and the number of fixed data, assigning being time-dependent in the event of a variable assigning, because of the dependence on the number of accesses of the mobile radio station onto the radio transmission channel.