US 4,081,831 AGranted

High security subscription television system employing real time control of subscriber's program reception

AssigneeTwin County Trans-Video, Inc.

InventorsDanny Q. H. Tang, Bark L. Yee

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Abstract

A high security subscription television system which includes the feature of dynamic scrambling and descrambling of cable-connected television signals in response to real-time coded control signals. The system also has the ability to precisely tune the frequency converter unit at the subscriber's site, in response to real time coded control signals provided by a computer at the central transmitting station. Various methods of scrambling and descrambling are described which use manipulation of the video signals at the baseband video level, and also at the RF level. Alternate embodiments of the descramblers include a secondary source for the reference carrier signal required for proper descrambler operation. In an ultra-stable embodiment of a subscriber's control terminal, a single crystal controlled master oscillator is used to control the frequency conversion unit, to provide a clean reference carrier signal for the descrambler unit, and to tune the control signal receiver, thereby removing the need for frequent fine tuning control adjustments, and further allowing simplified system design and fabrication.

Claims9

Dependent claims

A subscription television system having means for collecting, processing and disseminating a plurality of television programs, at least some of which are in scrambled form, from a central transmitting station via cable distribution means to a plurality of individual subscribers, said system comprising;

(a) at least one video reproduction and modulation scrambling subsystem means for serving as a source of standard television program signals having sync and video components for amplitude modulating of a carrier signal, and for producing scrambled television signals characterized by the substantially complete polarity inversion of the amplitude modulation of the sync and video components of said standard television program signals, and for applying said standard television program signals or said scrambled television signals to a cable for distribution;
(b) central controlling subsystem means for:
(i) receiving program orders for individual subscribers, and for processing and storing said program orders;
(ii) generating coded control signals for controlling the scrambling sequence of said video reproduction and modulation scrambling subsystem means and for use throughout said subscription television system;
(iii) generating subscriber control signals having an address portion and a frequency determining portion for each subscriber being served to be used throughout said subscription television system;
(c) a control signal transmitting subsystem means for directing said coded control signals and said subscriber control signals to said plurality of subscribers by impressing onto said cable a signal containing said coded control and subscriber control signals modulated onto a second carrier simultaneous with and separate from said sync and video carrying amplitude modulated carrier signal;
and
(d) a plurality of subscriber control units each in receiving communication with said video subsystem means and said control signal transmitting subsystem means via said cable, and each adapted to provide standard television output signals, said subscriber control units comprising:
(i) converter means having a voltage controlled oscillator therein and connected to said cable for receiving and converting any one of a plurality of cable connected CATV channels to at least one predetermined frequency band in response to said frequency determining portion establishing a substantial part the frequency of said voltage controlled oscillator;
(ii) descrambler means connected to said receiving and converting means for descrambling said single predetermined frequency band in response to said coded control signals so as to render the resultant signal directly usable by a conventional TV receiver;
and
(iii) processor means connected to said cable for receiving and processing said coded control signals and said subscriber control signals and for applying said processed signals to, and partially controlling said descrambler means and converter means.

9 more elements

A subscriber control unit for use in a subscription television system, said control unit comprising:

(a) means for receiving and converting any one of a plurality of CATV channels, at least one of which may be in scrambled form, to at least one predetermined frequency band, said receiving and converting means having a voltage controlled oscillator controlled in part by a variable digital signal and in part by an input reference frequency for establishing said predetermined frequency band;
(b) means connected to said receiving and converting means for descrambling said one converted CATV channel in response to coded control signals so as to render the resultant descrambled channel directly usable on a conventional TV receiver, said descrambling means using in part an algebraic summation process at the radio frequency level of said predetermined frequency band to accomplish said descrambling;
(c) means for receiving and processing said coded control signals for application to and partial actuation of said descrambling means, said receiving and processing means having a local oscillator used therein;
and
(d) a fixed frequency ocsillator having a plurality of related outputs therefrom connected to said receiving and converting means and to said receiving and processing means, adapted to provide a first, and a second related frequency, each of which is harmonically related to said fixed frequency and has a predetermined phase relationship therewith, wherein:
(i) said first related frequency is applied to said receiving and converting means, to serve as said input reference frequency;
(ii) said second related frequency is applied to said receiving and processing means, for use as said local oscillator.

4 more elements

Dependencies are inferred from the claim text.