It is known from, for example, U.S. Pat. No. 5,168,356 and U.S. Pat. No. 5,289,276, that it is advantageous to transmit compressed video signal in packets, with respective packets affording a measure of error protection/correction. The systems in the foregoing patents transmit and process a single television program, albeit with a plurality of program components, from respective transmission channels. These systems utilize inverse transport processors to extract the video signal component of respective programs for further processing to condition the video component for reproduction.
It is known, from for example, THE SATELLITE BOOK, A COMPLETE GUIDE TO SATELLITE TV THEORY AND PRACTICE, Swift Television Publications, 17 Pittsfield, Cricklade, Wilts, England, that transmitted television signal reception can be limited to particular subscribers by scrambling the signal. The limitations may be altered at the will of the broadcaster by periodically transmitting different entitlement data. The entitlement data is processed by smart cards located in respective receivers to generate decryption or descrambling keys, for use by decryption or descrambling devices in only those receivers entitled to reproduce the associated program material. In a packet video system of the aforementioned type, entitlement data may be included in specific packets which are recognizable as containing such data for easy access by smart card circuitry.
A large area broadcast system, such as a direct broadcast satellite system targeted for North America, will have very large numbers of subscribers. This number will be so large as to preclude changing the entitlement data of specific receivers on very short notice. Consider, for example, that a broadcaster is required to black out the area local to a sports stadium in the event that tickets for the sporting event are not sold out. This information may not be available until immediately before the event. The broadcaster of course will want to wait until the last possible minute before making the decision to black out the local region. The present invention provides a method and apparatus whereby entitlement data is layered to provide denial of entitlements to receive program material on short notice.