Abstract: Watermark data consisting of known two-dimensional codeword patterns are added to a first portion of each video frame by modifying parameters defining the first portion. Limited randomization of the spatial position of the codeword pattern is also provided. During a decoding process, a predictor continuously estimates the current value of the modified parameters. In one embodiment of the present invention, the predictor employs video samples taken from unmodified areas of the frame to provide the estimates. The estimated parameter values are subtracted from the actual parameter values to provide an error signal. Multiple correlators attempt to detect the presence of the codeword pattern in the error signal within a range of spatial locations surrounding a nominal position of the codeword pattern. The use of multiple correlators provides immunity to feasible attacks aimed at damaging or obscuring the watermark.

Abstract: A subscription television system for distributing program material protected by copyright to subscribers comprises a transmitter including a data insertion circuit for inserting a control bit in a transmitted signal comprising other control data and the protected program material. A receiver of the system includes a memory for storing a pre-assigned subscriber identification. Upon receipt and identification of the control bit at the receiver, the receiver inserts the subscriber identification into the program material so that any unauthorized copy made of the program material may be found to include the subscriber identification.

Abstract: A subscription television system in which individual decoders are enabled to receive individually addressed messages is disclosed. The composite signal, including video and teletext, also comprises addressed packets which are detected by decoders and which indicate that a message addressed to a particular subscriber is forthcoming, and system control data. In a preferred embodiment, both addressed packets and teletext are encrypted. The addressed packet is decrypted using a decoder-specific code and a transmitted code, while the teletext message is decrypted using a decryption key contained in the system control data. The teletext message cannot be received until the addressed packet has been decrypted. Therefore, redundant levels of security are provided to the system. Messages for display to the user can be selected in response to user initiated commands, in response to decoder initiation, or in response to the transmitter.

Abstract: A communication system enabling transmission of individual subscriber teletext messages, audio and video to individual subscribers and permitting group communications of audio, video, teletext and data information from a single central subscriber location, such as a corporate head office to a plurality of satellite offices, such as field or sales offices of the corporation, is disclosed. A composite signal including the information to be transmitted as well as system wide, individual decoder and group decoder control signals is transmitted. The system-wide control signals include data germane to operation of each of the decoders of this system, including key information needed to decode the composite signal. The system-wide control data is transmitted at a first relatively high frequency. The group decoder information includes information permitting individual groups of decoders to receive information portion of the composite signal being transmitted at a given time.

Abstract: A subscription television system in which individual decoders are enabled to receive individually addressed messages is disclosed. The composite signal, including video and teletext, also comprises addressed packets, which are detected by decoders and which indicate that a message addressed to a particular subscriber is forthcoming, and system control data. The decoder detects an addressed packet addressed to itself, whereby it is enabled to select the appropriate teletext message and to display the same. In a preferred embodiment, both address packets and teletext are encrypted. The addressed packet is decrypted using a decoder-specific code and a system key transmitted as part of the system control data, while the teletext packet is decrypted using the system key, but cannot be received until the addressed packet has been decrypted. Therefore, redundant levels of security are provided to the system.

Abstract: A secure communications system requires special arrangements for the establishment and maintenance of framing and synchronization. A framing word is transmitted at a fixed frequency, and a key necessary to unscramble the transmission is transmitted in a fixed position in relation to the framing word. Synchronization information (reference clock bursts) is scrambled with the intelligence and may only be recovered once the key is available. When framing is being maintained, the receiver's phase-locked loop opens only during the short reference clock bursts in the incoming signal, and the framing signal generator is able to predict the occurrence of successive framing signals without reference to the incoming signal. When framing is lost, the receiver enters a "soft lock" condition in which its phase-locked loop is opened to receive the entire incoming signal and in which the framing signal generator refers solely to the incoming signal to generate framing signals.