Scrambled television signals

Details Scrambled television signals Scrambled television signals

H - Electricity

04

N

350/30

H04N 7/167 (2006.01)

Patent

CA 1232962

PHQ 83 015 13 ABSTRACT: A television receiver for receiving scrambled television signals has an arrangement which provides scrambled vision components (V) and packet arranged sound/data components (D) some of which are also scrambled. The components (D) are applied to a packet demultiplexer where the packets are assembled from the data in several lines in the signal to provide a first output (P) the respective packets carrying sound/data information and at a second output (E) encrypted control data which is applied to a sub-system to produce a vision scrambling control word (VS) for each line of the vision components. The sub- system during each line produces further bits which are applied to a descrambling control word generator which assembles these further bits from three lines to form a packet scrambling control word. This control word and the packets associated with it are added in an adder and applied to a main packet buffer store from which each packet is read out by a packet selector and the packet is applied to a packet descrambler whilst the packet scrambl- ing control word is selected by a register and used to control the generation of a binary sequence by a pseudo random binary sequence generator which sequence is added to the packet in the descrambler, modulo-two, to achieve descrambling. A packet identifier examines the packet address to ensure the packet requires descrambling and inhibits the generator should descrambling not be required. With such a receiver the control data (E) can be used for controlling descrambling of both the vision and the sound/ data components.

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