Conditional access scrambling techniques for terrestrial UHF television broadcasts

Describes in outline form the particular requirements and constraints which must be met by the conditional access (CA) techniques applied to an existing terrestrial UHF television broadcast network, and outline the results of BBC laboratory and over-air tests of CA television techniques. A conditional access television system combines the processes of scrambling and encryption. Scrambling is the process used to render the picture or sound, or more usually both, signals unusable without an authorised descrambler. Encryption provides a secure way of conveying descrambling control information to authorised viewers. Thus, with such a system, the signals are encoded before transmission and each viewer requires a decoder at his receiving site. The main features of the system are the scrambling techniques used for the picture and sound signals, the data transmission techniques used to carry the encrypted control signals to the receivers and the `business system´ which manages the authorisation of individual decoders and thence the mechanisms whereby the viewers pay for the services they use