VERWENDUNG VON DUPLEX-VERSCHLÜSSELUNGSALGORITHMEN FÜR SATELLITSKANÄLE MIT VERZÖRGUNG

摘要

An apparatus and method for ciphering traffic exchanged in both directions between a satellite/cellular telephone and a ground station network using an orbitial satellite. A buffer memory is provided at either the mobile telephone station or the ground network station or both. The buffer memory is used to store the deciphering bits output from a duplex ciphering algorithm at the time the ciphering bits are generated. The stored ciphering bits are used to decipher a later-to-be-received traffic information block. The delay in using stored deciphering bits is determined for each call at call set-up to the nearest integer number of block periods by measuring the loop propagation delay from the ground station to the mobile telephone station during an exchange of signals at call set-up.