Addressable subscription television system having multiple scrambling modes

• US 4,716,588 A
• Filed: 10/29/1985
• Issued: 12/29/1987
• Est. Priority Date: 10/29/1985
• Status: Expired due to Term

• Current Assignee: Payview Limited
• Original Assignee: Payview Limited
• Inventors: Thompson, John R., Masson, Ronald K., Trivelpiece, Craig E., Hunting, Curtis J.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US06/792,704
• Time in Patent Office: 791 Days
• Field of Search: 358/117, 358/120, 358/122, 358/124, 380/15, 380/17, 380/20, 380/11, 178/37
• US Class Current: 380/224
• CPC Class Codes: H04N 7/1675 Providing digital key or authorisation information for generation or regeneration of the scrambling sequence pseudo-random number generators in general G06F7/58
• CPC Class Codes: H04N 7/1693 by displacing synchronisation signals relative to active picture signals or vice versa
• CPC Class Codes: H04N 7/171 Systems operating in the amplitude domain of the television signal

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.

Claims

1. A method for scrambling a video signal, said video signal including a plurality of sequential fields, each field having a plurality of active line portions preceded by a horizontal synchronization period comprising:

removing horizontal synchronization pulses from said synchronization period;

compressing the amplitude of said active line portions;

adding a pseudo synchronization pulse having an amplitude greater than said removed synchronization pulse to said synchronization period from which said horizontal synchronization pulses were removed, said pseudo synchronization pulse leading edge occurring at a time different than that of said removed synchronization pulse;

changing the position of said pseudo synchronization pulses leading edge in subsequent fields; and

;

adding an offset voltage to said video signal during the active line period of said video signal.

2. The method of scrambling of claim 1 wherein said offset voltage is of a magnitude to place said active video line portions substantially below a black level, whereby said active video is normally not displayable on a normal television receiver.

3. The method of scrambling of claim 1 wherein said pseudo synchronization pulse has a magnitude of 140 IRE units.

4. A video signal scrambling system comprising:

means for supplying a video signal for scrambling, said video signal comprising a plurality of fields of a plurality of signals each representing a horizontal line of information;

said plurality of signals including a horizontal synchronization pulse identifying a beginning of a line, said field including a vertical synchronization portion for separating subsequent fields;

means for removing said horizontal synchronization pulses in a plurality of said fields; and

means for inserting in place of each removed horizontal synchronization pulse a bogus sync pulse having a leading edge which is earlier in time than said removed horizontal synchronization pulses for one of said fields, and inserting bogus sync pulses during a second field in place of each removed horizontal synchronization pulse having a leading edge which occurs subsequent to said bogus synchronization pulses of said one field and which occur prior to said removed synchronization pulses.

5. The video signal scrambling system of claim 4 further comprising means for compressing the amplitude of said video signal during that portion of the video signal which occurs between horizontal synchronization pulses.

6. The video signal scrambling system of claim 5 further comprising means for applying an offset voltage to said video signal during a portion of said video signal which occurs between vertical intervals and which occurs between horizontal synchronization pulses whereby the brightness level represented by said video signal is maintained below a predetermined brightness level.

7. The video signal scrambling system of claim 6 wherein said offset voltage is at a magnitude for offsetting said video signal portion to a position representing a substantially black picture level whereby an opaque picture is produced.

8. The video signal scrambling system of claim 4 wherein said bogus sync pulses have a magnitude greater than said removed sync pulses.

9. In a system for scrambling a video signal, an apparatus for transmitting a signal identifying one of a plurality of scrambled sequences comprising:

means for generating during a vertical blanking interval of said video signal at least three unique horizontal synchronization pulses having a pulse width different from the pulse width of a plurality of remaining horizontal synchronization pulses, said unique pulses identifying specific lines of each field of said video signal; and

means for inserting two of said generated synchronization pulses at the beginning of two lines of said video signal vertical interval, said two lines being the same for every transmitted field, and inserting a third of said unique pulses at a line the number of which identifies a scrambling sequence.

10. The scrambling system of claim 9 wherein said two unique synchronization pulses are inserted at the beginning of lines 1 and 10 of each vertical interval.

11. The scrambling system of claim 10 wherein said third unique pulse is located at the beginning of any of lines 11-17.

12. In a system for scrambling and descrambling a video signal, in accordance with one of a plurality of scrambling algorithms, means for transmitting to a receiving station the identity of a scrambling sequence comprising:

means for inserting during the vertical interval of a field of said video signal a first group of horizontal synchronization pulses having a width greater than the remaining synchronization pulses at predetermined line numbers;

means for inserting a second group of synchronization pulses of a pulse width less than the width of said synchronization pulses of a predetermined number of lines between said predetermined lines, said predetermined line numbers identifying one of said scrambling sequences; and

means for transmitting said video signal to said receiving station.

13. In a system for scrambling and descrambling video signals, wherein a plurality of video lines are inverted in accordance with one of a series of scrambling sequences, a method for sending and receiving a decoding signal, comprising:

inserting during each field of said video signal at a plurality of predetermined line numbers horizontal synchronization pulses which are greater in width than the remaining synchronization pulses in said video signal;

the position of said pulses identifying one of a series of said scrambling sequences;

inserting for a plurality of lines between said horizontal synchronization pulses a number of synchronization pulses of a different width;

transmitting to a receiving station said video signal;

detecting the width of each of said horizontal synchronization pulses received at said receiving station whereby said predetermined line numbers are identified;

storing in a predetermined order at said receiving station each of said scrambling sequences;

identifying one of said stored scrambling sequences by said predetermined line numbers; and

inverting lines of said video signal in accordance with said identified scrambling sequence.

14. A system for scrambling a video signal with a different scrambling sequence for each field of said video signal comprising:

means for transmitting a scrambling algorithm signal during the vertical interval of said video signal, said scrambling algorithm identifying one plurality of scrambling sequences from another plurality of scrambling sequences;

means for inverting each of a plurality of video lines in accordance with one of a plurality of scrambling sequences;

means for transmitting during a vertical interval of said video signal a unique pulse having a position in said vertical field which identifies said one of a plurality of scrambling sequences;

means for receiving said transmitted video signal including;

means for decoding said scrambling algorithm and identifying said plurality of scrambling sequences;

means for detecting the position of said unique pulse from a received video signal whereby one of said plurality of scrambling sequences is identified; and

means for reinverting said video signal in accordance with said identified scrambling sequence whereby a descrambled video signal is produced.

15. A system for scrambling a video signal which includes a plurality of fields of line information, each field separated by a vertical interval, comprising:

means for transmitting during said vertical interval data identifying a scrambling algorithm, said scrambling algorithm specifying a plurality of scrambling sequences for a plurality of fields of said video signal;

means for inserting a unique pulse of a specified duration at a location in said vertical interval which identifies one of said scrambling sequences;

means for decoding said scrambling algorithm data and generating the identity of each of said plurality of scrambling sequences from said algorithm;

means for detecting the position of said unique pulse in said vertical interval whereby one of said scrambling sequences are identified; and

means for descrambling each of said video signal fields in accordance with an identified sequence, said sequence changing in subsequent fields in accordance with the position of said unique pulse in each newly received vertical interval.

16. The system of claim 15 wherein said scrambling sequences identify lines of said video signal which are inverted.

17. The system of claim 16 wherein each scrambling sequence comprises a plurality of alternate inverted lines of said video signal, the beginning line of each sequence changing for different fields of said video signal.

18. A system for descrambling a video signal including false synchronization pulses which are inserted in the video signal, an offset added to said video signal whereby active portions of said video signal are biased to below a black level, said video signal including during a specified line of said video signal, a reference black level and a white level, comprising:

means for sampling said video signal reference black level and white level whereby first and second video signal reference levels are produced;

buffer amplifier means for receiving said video signal and clamping said video signal at a level proportional to said black level whereby said video signal offset is removed;

means for detecting the pedestal edge of each horizontal blanking interval, and generating a sync pulse synchronized with said detected pedestal edge having a leading and falling edge of a normal descrambled video signal sync pulse; and

means for inserting said synchronization pulse into said video signal in place of said false synchronization pulses whereby said video signal synchronization is restored.

19. The system of claim 18 further comprising means for inverting alternate lines of a video signal produced by said buffer amplifier.

20. The apparatus of claim 18 wherein said horizontal synchronization pulses have an amplitude level which is scaled from the level of said white signal and black level signal reference samples.

21. In a system for scrambling a video signal, wherein each subscriber of the system includes a decoder which can be disabled by transmitting a disable command, a method to prevent said subscriber from avoiding a disable command by disconnecting said decoder comprising:

sending a timing command as digital data in said video signal at a periodic interval to said subscriber decoder;

resetting a timer when each of said timing commands at said decoder have been received;

disabling said decoder from decoding a received scrambled signal when said timer indicates that a reset has not been received within a predetermined time interval.

22. The system of claim 21 further comprising:

sensing the mechanical integrity of a package containing said decoder; and

disabling said decoder when said integrity has been broken.