Method for generating a code rule which cannot be intercepted in a telecommunications network, in particular a radio network

摘要

In mobile radio systems in which a selection of different encrypted identification codes is stored in each vehicle station, the code rule, i.e. the selection criterion for the code which is to be used in each case, must be protected against misuse. For this purpose, the code rule is not transmitted on the radio path but is derived from at least one of the transmission parameters which are significant only for the connection which is to be set up, said parameters being measured and evaluated separately by immediately consecutive measuring operations from both sides of the stations involved in the connection. A reciprocal propagation time measurement is preferably carried out for this purpose, the results, which must be identical, are evaluated and the code rule is derived therefrom. A unique allocation can be achieved by inserting fixed additional-propagation times in the boundary region of the code rule allocation. To increase accuracy, further significant transmission parameters can also used to form the code rule, e.g. attenuation, Doppler shift, field strength patterns and any other of the parameters which are accessible for the mathematical statistics of wave propagation (Fig. 1). IMAGE