Addressable subscription television system having multiple scrambling modes
US4716588A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Oct 29, 1985 |
| Grant date | Dec 29, 1987 |
| Priority date | — |
| Expiry date | Oct 29, 2005 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04N7/171
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
A multimode scrambling system for video signal transmission systems is described. The system provides for baseband video scrambling controlled by a central originating computer facility. The scrambling of each field of a video changes on a per field basis. The video signal is scrambled in several modes including vertical interval scrambling, alternate line inversion, bogus sync pulse generation, video compression and video offset techniques. A scrambling sequence is sent by a unique algorithm, sent during the vertical interval to each system decoder. The algorithm is reordered for each of a plurality of fields of the video signal and the reordering position is identified by a unique synchronization pulse transmitted during the vertical interval of the video signal. Additional security measures are provided to inhibit a subscriber from avoiding a transmitted disable command, or an attempt to invade the subscriber decoder mechanical packaging security.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.