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Abstract

A system for the synchronization of encryption and decryption in a duplex cellular radio system in which an encrypted call may be switched from one cell to another. At the instant of handoff, a rapid first resynchronization means temporarily seizes the voice channel in one direction only and transmits synchronization information in such one direction. The first resynchronization means ceases to transmit the synchronization information and releases such one direction of the voice channel as soon as an indicator of successful resynchronization is detected in the other direction. Transmission of speech traffic in such one direction is then resumed after such detection of successful resynchronization. To avoid occupying such one direction with continuous transmission of the synchronization information in the event successful resynchronization has occurred but has not been detected due to faulty transmission in the other direction, an upper limit is set on the length of time which the first rapid synchronization means may cease such one direction. After such timeout, resynchronization information may be provided by a second resynchronization means at a slower rate through a slow rate control channel bit stream which is multiplexed with the traffic data.

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First Claim