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US 5,293,423 AGranted
Synchronizing method in a mobile radio system
AssigneeTelefonaktiebolaget L M Ericsson
InventorsJan E. .ANG.. S. Dahlin, Walter Ghisler, Bengt Y. Persson
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AssigneeTelefonaktiebolaget L M Ericsson
InventorsJan E. .ANG.. S. Dahlin, Walter Ghisler, Bengt Y. Persson
Estimating the term…
A synchronizing method in a mobile radio system which operates with Time Division Multiple Access (TDMA) but which lacks global time reference for all base stations and mobiles in the system. The inventive method is intended for ciphered transmission of data and speech in accordance with a given ciphering key (E2). When handing-over a call, the ciphering synchronism is lost. In accordance with the method, subsequent to hand-off (the time t.sub.2), the take-over base station (BS2) signals non-ciphered information (S1) to the mobile (MS) disclosing the number of frames (R1-R13) which shall pass until ciphering can again be commenced, calculated from a given frame (R1). Call information is transmit the following frame (R2), this information now being ciphered with the aid of a ciphering key (E1) different to the original key. This other ciphering key consists of a periodic bit sequence having a period which is equal to one frame interval.
A method for reestablishing the ciphering of information in a mobile radio system which lacks a global time reference, wherein the data messages and the signalling messages between a first base station and a mobile station are transmitted in frames having time slots and said messages are ciphered by combining said messages with a pseudorandom bit stream, wherein upon handing over the communication of the mobile from the first base station to a second base station ciphering is interrupted for a given period of time during which synchronization of the pseudorandom bit stream with said messages between the mobile and the first base station is lost due to the absence of said global time reference and frame synchronization is established between the mobile and the second base station, comprising the steps of:
A method for reestablishing encryption of information in a mobile radio system having first and second fixed stations and a mobile station comprising the steps of:
Dependencies are inferred from the claim text.