Conditional Access Mechanisms in the DAB System
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The conditional access in the DAB system is a set of procedures responsible for controlling access of authorized categories of recipients to the specific DAB data and services. An access lock is implemented by a controlled distortion of the useful signal in a process called scrambling. Scrambling involves adding the bits of the specified information program with a string of bits from a pseudo-random generator. Reading such a signal in the receiver requires summation with identical re-synchronized pseudo-random sequence. For this purpose, it is necessary to know the activation code of a pseudo-random generator. Code is made available after verifying an authorization to receive scrambled information. Conditional access of the DAB system includes mechanisms allowing to distribute entitlements to specified (purchased) content and services.