An off-premises method and apparatus for the interdiction of unauthorized channels of a broadband cable television signal includes common circuitry for adjusting the amplitude and equalization levels of the broadband CATV signals and one or more subscriber modules for generating jamming signals of different frequencies which are used to interdict one or more unauthorized channels. Each subscriber module is associated with a subscriber and is programmable and addressable to adjust the jamming parameters of that subscriber independently of other subscribers. Each subscriber module circuit comprises a plurality of latches, each of which is associated with one of a plurality of digital to analog converters. Each of the digital to analog converters drives one or more frequency agile oscillators with its analog output to generate the jamming signals. The subscriber module is based on a sequential state machine which loads frequency control words corresponding to the jammed channels from a frequency control memory into each latch on a cyclic basis. The state machine is adapted to vary the sequence in which the voltage control words are read out of memory to modify the jamming pattern of the subscriber. In addition, according to one illustrated implementation, the loading of frequency control words to the latches in the sequence can be inhibited without changing the words in the memory. The sequential state machine will then in effect skip the deauthorized frequency control words and produce jamming signals at the previous frequencies. This provides flexibility in the system for either jamming or unjamming a specific channel to a subscriber for short periods of time. This allows a simple authorization and deauthorization technique without having to reload the frequency control memory or recalibrate a frequency control word for the specific channel selected.
An decryption system which facilitates simultaneous decryption of multiple encrypted television channel signals thus making them simultaneously available for direct tuning in television receivers. The system is characterized by the utilization of a plurality of channel signals time synchronized with respect to a common timing reference signal. Each channel signal is encrypted in accordance with a predetermined encoding rule and distributed to subscriber sites where an unencrypted block of channel signals are made simultaneously available by decrypting them synchronously with the recovered timing reference signal in accordance with the inverse of the encoding rule. An interdiction apparatus then selectively jams a plurality of television channels from within the unencrypted block of channel signals thus making it possible for a provider to programmably interdict reception of selective channels by unauthorized subscribers. The invention can be advantageously used in both over-the-air and cable subscription television distribution systems to provide subscribers with a plurality of simultaneously available decrypted television signals and selectively encrypted channels, e. g., premium channels.
The present invention concerns a method of controlling the mode of access to wanted signals, such as picture signals (IMAGE), whereby the user selects an access mode to a wanted signal remotely. A first access mode consists in supplying the user with the original wanted signal (IMAGE), and second access mode consists in transmitting to the user alternately and periodically the wanted signal and a jamming signal (MIRE, IT) into a jammed signal. This jammed signal remains intelligible so that the user can determine the content of the wanted signal and, if necessary, select the first access mode. The two access modes are billed differently. Hardware implementations of the method are described for switching grids of switching nodes in a centralized architecture, and for digital distribution networks with a more futuristic distributed type architecture.
