US4388643A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method of controlling scrambling and unscrambling in a pay TV system
Assignee: Nortel Networks Ltd
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Filing: 1981-04-06
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Granted: 1983-06-14
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Expires: 2001-04-06
Abstract
Abstract Scrambling of a video signal in a pay TV system is effected in dependence upon a first variable which is changed recurrently, e.g. monthly, and a second variable which changes from field to field. For each field the second variable and other data are transmitted simultaneously with the video signal together with check data produced from the transmitted data and a third variable which is changed recurrently. The first and third variables are recurrently transmitted to each authorized subscriber station, encoded in dependence upon a subscriber number stored in the subscriber station. In the subscriber station, unscrambling is effected in dependence upon the stored first variable and the transmitted second variable after the transmitted data is checked using the check data and the stored third variable. The first variable is conveniently different for different types of television programs, the type of television program being identified by the other data transmitted simultaneously with the video signal.
Inventors
- 👤 Yehuda J. Aminetzah
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 22:39
CPC Classifications
H; H04; H04N; H04N7/00; H04N7/16; H04N7/167; H04N7/1675
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
119 words
A method of controlling scrambling and unscrambling of a video signal in a pay TV system, comprising the steps of: storing a subscriber number at a subscriber station; recurrently transmitting to the subscriber station a first variable encoded in dependence upon the subscriber number; decoding the first variable at the subscriber station using the stored subscriber number, and storing the first variable before or after said decoding; scrambling the video signal in dependence upon the first variable and a second variable; transmitting the second variable to the subscriber station simultaneously with transmission of the scrambled video signal; and at the subscriber station, unscrambling the video signal in dependence upon the decoded stored first variable and the transmitted second variable.
Claim 2
Independent Claim
119 words
A method of controlling scrambling and unscrambling of a video signal in a pay TV system, comprising the steps of: storing a subscriber number at a subscriber station; recurrently transmitting to the subscriber station a first variable encoded in dependence upon the subscriber number; decoding the first variable at the subscriber station using the stored subscriber number, and storing the first variable before or after said decoding; scrambling the video signal in dependence upon the first variable and a second variable; transmitting the second variable to the subscriber station simultaneously with transmission of the scrambled video signal; and at the subscriber station, unscrambling the video signal in dependence upon the decoded stored first variable and the transmitted second variable.
Claim 3
Dependent Claim
16 words
A method as claimed in claim 1 wherein said first variable is stored after said decoding.
Claim 4
Dependent Claim
21 words
A method as claimed in claim 1 and comprising the step of producing the first variable using a random number generator.
Claim 5
Dependent Claim
28 words
A method as claimed in claim 1 and comprising the step of producing the second variable for each field of the video signal using a pseudo-random number generator.
Claim 6
Independent Claim
173 words
A method of controlling scrambling and unscrambling of a video signal in a pay TV system, comprising the steps of: storing a subscriber number at a subscriber station; scrambling the video signal in dependence upon first and second variables; recurrently transmitting to the subscriber station the first variable and a third variable each encoded in dependence upon the subscriber number; decoding the first and third variables at the subscriber station using the stored subscriber number, and storing the first and third variables before or after said decoding; producing check data from the second and third variables; transmitting the second variable and the check data to the subscriber station simultaneously with transmission of the scrambled video signal; and at the subscriber station, generating check data from the transmitted second variable and decoded stored third variable, enabling unscrambling of the video signal in dependence upon a comparison of this generated check data with the transmitted check data, and unscrambling the video signal in dependence upon the decoded stored first variable and the transmitted second variable.
Claim 7
Independent Claim
173 words
A method of controlling scrambling and unscrambling of a video signal in a pay TV system, comprising the steps of: storing a subscriber number at a subscriber station; scrambling the video signal in dependence upon first and second variables; recurrently transmitting to the subscriber station the first variable and a third variable each encoded in dependence upon the subscriber number; decoding the first and third variables at the subscriber station using the stored subscriber number, and storing the first and third variables before or after said decoding; producing check data from the second and third variables; transmitting the second variable and the check data to the subscriber station simultaneously with transmission of the scrambled video signal; and at the subscriber station, generating check data from the transmitted second variable and decoded stored third variable, enabling unscrambling of the video signal in dependence upon a comparison of this generated check data with the transmitted check data, and unscrambling the video signal in dependence upon the decoded stored first variable and the transmitted second variable.
Claim 8
Dependent Claim
18 words
A method as claimed in claim 5 wherein said first and third variables are stored after said decoding.
Claim 9
Dependent Claim
23 words
A method as claimed in claim 5 and comprising the step of producing said first and third variables using a random number generator.
Claim 10
Dependent Claim
28 words
A method as claimed in claim 5 and comprising the step of producing said second variable for each field of the video signal using a pseudo-random number generator.
Claim 11
Dependent Claim
82 words
A method as claimed in claim 8 and comprising the steps of additionally producing said second variable for each field of the video signal using a pseudo-random number generator at the subscriber station, synchronizing the production of said second variable at the subscriber station with said transmitted second variable, and unscrambling the video signal in dependence upon the decoded stored first variable and the second variable generated at the subscriber station in the event that the check data comparison indicates an error.
Claim 12
Dependent Claim
50 words
A method as claimed in claim 9 and including the steps of storing an accumulated error count at the subscriber station, incrementing said count in response to errors indicated by the check data comparison, and inhibiting unscrambling of the video signal in response to said count reaching a predetermined value.
Claim 13
Dependent Claim
115 words
A method as claimed in claim 1 or 5 and comprising the steps of: producing different said first variables for different types of television program; selectively recurrently transmitting said different first variables to the subscriber station for decoding and storage therein; scrambling the video signal in dependence upon the respective first variable, for the type of television program to which the video signal relates, and the second variable; transmitting, with said second variable, data representing the type of television program to which the scrambled video signal relates; and at the subscriber station, selecting the respective decoded stored first variable in dependence upon said data representing the type of television program for unscrambling the video signal.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1986-06-13 | 1986-12-13 | 1987-06-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-06-13 | 1990-12-13 | 1991-06-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-06-13 | 1994-12-13 | 1995-06-14 | $7700.00 | Window Closed / Lapsed |