Scrambled signal receiver
US4817143A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Nov 25, 1986 |
| Grant date | Mar 28, 1989 |
| Priority date | — |
| Expiry date | Nov 25, 2006 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N7/1675
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A system including a receiver which receives scrambled signals and subjects them to a descrambling process under the control of control words periodically conveyed to the receiver by a conditional access sub-system. A new control word is required for every 256 television frames constituting a descrambling period, which control word is transmitted during the preceding descrambling period. In order to reduce the time taken to initiate the descrambling process upon selection of a particular service or following an interruption therein, the initial control word then conveyed to the receiver is that for the 256 frame descrambling period following the existing descrambling period. The initial control word is followed by the control word for the existing descrambling period. Subsequent control words are successively conveyed to the receiver during the descrambling intervals preceding those to which such control words are respectively applicable.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.