Video transmission system

• US 4,682,360 A
• Filed: 12/22/1983
• Issued: 07/21/1987
• Est. Priority Date: 12/22/1983
• Status: Expired due to Fees

• Current Assignee: Frederiksen, Jeffrey E.
• Original Assignee: Frederiksen, Jeffrey E.
• Inventors: Frederiksen, Jeffrey E.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US06/564,405
• Time in Patent Office: 1,307 Days
• Field of Search: 358/120, 358/121, 358/122, 358/123, 358/124
• US Class Current: 380/212
• CPC Class Codes: H04N 7/085 the inserted signal being digital
• CPC Class Codes: H04N 7/1696 by changing or reversing the order of active picture signal portions

Abstract

A subscriber cable television system uses predominantly digital signal processing techniques and has extremely high security and an increased capacity for transmitting program and customer data to individual decoder units. For ease of data handling, two-channel audio, video, and high capacity program and customer data are multiplexed for transmission on the composite video signal. The decoder unit employs a system timing circuit which precisely synchronizes the sample times on the received composite video signal to the chrome burst, regardless of whether the video information is for a color or black-and-white program. An improved time-warp and segment scrambling method is disclosed along with means for suppressing the undesirable effects of discontinuities in the scrambled video signal. The digital audio is transmitted as scrambled most significant bits in low resolution samples and unscrambled least significant bits in a high resolution remainder sample. The system timing circuit has a horizontal sync detector accommodating variable line length such as is provided by some video recording apparatus. The clock to the horizontal counter is selectively phase-reversed in response to early or late horizontal sync so that the timing resolution is twice the clock period. An improved self-adjusting threshold detector and other means are disclosed for detecting a "20 IEEE" suppressed horizontal sync so that the full range of video modulation may be used more effectively. Circuitry is also disclosed for transmitting the customer and program information in a multi-level correlative signalling format in order to more effectively use the band width of the entire television channel.

Claims

1. A video transmission system providing secure transmission of a composite video signal over a communications channel for reception by designated customers,

the composite video signal having scrambled video information in frames having a predetermined number of lines, synchronization information indicating the starting positions of the lines and the first line in each frame, and customer data for designating individual customers permitted to receive the composite video signal and descramble the video information therein,

the video transmission system having an encoder for digitizing a composite video signal and scrambling the resulting digital video signals, and a decoder for each customer for receiving the scrambled video signal and descrambling the video signal,

multiple lines of the video signal in each frame including a max reference pulse located outside of the video portions of the lines for providing a full scale signal to establish a reference for analog-to-digital conversion of the composite video signal.

2. The video transmission system of claim 1 wherein multiple lines of the composite video signal in each frame include a ground reference signal located outside of the video portions of the lines to establish the range of the analog-to-digital conversion of the composite video signal.

3. A video transmission system providing secure transmission of a composite video signal over a communication channel for reception by designated customers,

the composite video signal having scrambled video information in frames having a predetermined number of lines, synchronization information indicating the starting positions of the lines and the first line in each frame, and customer data for designating individual customers permitted to receive the composite video signal and descramble the video information therein,

the video transmission system having an encoder for generating the composite video signal from station video and customer data, and a decoder for each customer for receiving the composite video signal and descrambling the video signal therein in response to the customer data in the composite video signal, and

said composite video signal also including a chroma burst signal and at least one bit identifying the video information as black-and-white when the video information is only black and white, means in the encoder for generating a system clock synchronized to said chroma burst signal, and means in the decoder responsive to said chroma burst signal for generating a system clock synchronized to the system clock in the encoder, and for enabling color killer circuits in response to said bit identifying the video information as black-and-white.