Cryptography – Key management – Having particular key generator
Patent
1989-04-28
1992-09-01
Gregory, Bernarr E.
Cryptography
Key management
Having particular key generator
380 10, 380 46, 380 47, 3701001, 370107, 375115, 375120, H04L 900, H04L 700, H04J 306
Patent
active
051446693
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to a method of communicating digital signals and a receiver for use with such method particularly, but not exclusively, applicable to the communication of digital video signals via a passive optical network.
CATV systems have, to date, used analog transmission schemes because the cost of digital equipment and the bandwidth required for transmission is high but use of digital techniques in television receiver design is increasing with a/d conversion at the input to a single digital processing integrated circuit. Digital coders are now becoming available which have the potential for low-cost implementation and which provide a picture quality that compares favorably with off-air reception. Among the benefits of digital transmission to users are guaranteed picture quality, the possibility of adding new services to receivers equipped with more advanced digital signal processing, the elimination of the requirement for a/d conversion. Until now the extensive use of digital transmission has been limited by bandwidth and cost constraints of the copper network. However new, low-cost broadcast optical networks are emerging which allow a mixture of services to be provided by time domain or wavelength domain multiplexing (TDM or WDM) on an evolutionary basis. The speed limitation of the electronic components connected to the network rather than the network itself is now the limiting factor on the digital channel capacity per wavelength. Recent papers entitled `Single mode optical networks` by Payne D. B. and Stern J. R. Proc. Globecom'85 and `Technical Options for Single Mode Local Loops` TDM or WDM by Payne D. B. and Stern J. R. Proceedings of ECOC 1986, Barcelona have discussed the merits of multiple access local networks based upon passive optical networks which use power dividers to serve a large number of customers. These include the possibility of broadband transmission on a single carrier and upgrading via wave division multiplexing (WDM). Whilst WDM would provide one solution to this problem, TDM seems more attractive because only a single transmitter is required.
The passive, multiple-access architecture has a number of operational advantages as discussed in the paper on single mode optical networks referenced above. The need for cables with large number of fibers near the head end is reduced, it is more reliable and easier to maintain than a network with active switching at splitting nodes, and it is possible to upgrade the network as wavelength multiplexing components become available. These networks are most cost sensitive in the customers' final drop and equipment as the cost of the head-end is shared by all users. An objective of the present invention is to provide a method and a receiver for use with such a method whereby customers can access a large number of digital TV channels in a way which can reduce the cost of customer equipment by eliminating the need for digital circuitry operating at the multiplex rate.
It is a further object of the present invention to provide a method of signal communication and a receiver in which a level of security can be given to some or all of the multiplexed channels by scrambling prior to transmission and in which the channel selection and descrambling is carried out automatically by the receiver.
According to one aspect of the present invention there is provided a receiver for selectively extracting one of two or more time division multiplexed channels of digital signals, which channel has been scrambled before forming the multiplexed signal using a predetermined digital sequence comprises dependent on a clock control signal; representative of the next digit in the predetermined digital sequence at the clock repetition rate; multiplexed signal sampled at the clock pulse rate; and generator sequence is phase-lockable to the sampled signal.
The scrambling and descrambling is preferably by XOR-ing with the scrambling and descrambling sequences as this tends to produce a balanced data signal. The delay lock m
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Faulkner David W.
Russ Dianne M.
British Telecommunications public limited company
Gregory Bernarr E.
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