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A communication device for use in a non-self synchronizing scrambling (NS3) communication system and a method for using NS3 in a communication system are disclosed. A digital data stream is scrambled by modifying the digital data stream based on a pseudo-noise sequence (PNS) to produce a scrambled d

A communication device for use in a non-self synchronizing scrambling (NS3) communication system and a method for using NS3 in a communication system are disclosed. A digital data stream is scrambled by modifying the digital data stream based on a pseudo-noise sequence (PNS) to produce a scrambled digital data stream. The PNS has a timing reference that is distinct from the digital data stream. The scrambled digital data stream is capable of being descrambled by performing an inverse modification, based on the same PNS and the same timing reference. The scrambled digital data stream may be transmitted over a communication medium and descrambled at the opposing end of the communication medium. Synchronization between the scrambler and the descrambler is maintained by providing a common timing reference to the scrambler and the descrambler. The common timing reference is distinct from the data stream. The invention can be used on any communication system in which all the communication devices have a common timing reference.

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Therefore, having thus described the invention, at least the following is claimed: 1. A communication device for scrambling a digital data stream for use in a non-self-synchronizing scrambling (NS3) communication system, said system supporting a variable number of bits per symbol less than or equal

Therefore, having thus described the invention, at least the following is claimed: 1. A communication device for scrambling a digital data stream for use in a non-self-synchronizing scrambling (NS3) communication system, said system supporting a variable number of bits per symbol less than or equal to a maximum number of bits per symbol, said digital data stream comprising a series of bits and having a bit transmission rate, the communication device comprising: means for converting each N bits of the digital data stream into a symbol index to produce a stream of symbol indices; means for generating, at a rate derived from a symbol rate and different than the bit transmission rate, a pseudo-noise sequence (PNS), said PNS comprising M output bits, wherein M is at least as large as said maximum number of bits per symbol and M is independent of N; and means for modifying said stream of symbol indices based on said PNS to produce a symbol-wise scrambled digital data stream, wherein said symbol-wise scrambled digital data stream is capable of being descrambled by a second modifying means that is the inverse of said modifying means. 2. The communication device of claim 1, further comprising: means for transmitting said scrambled digital data stream. 3. The communication device of claim 1, wherein said generating means is an encryption device. 4. The communication device of claim 1, wherein said modifying means is a modulo-2 adder. 5. The communication device of claim 1, wherein said modifying means is an arithmetic adder. 6. The communication device of claim 1, wherein said rate is a whole or fractional multiple of the time interval between each symbol in said set of symbol indices. 7. A method for scrambling a digital data stream for use in a NS3 communication system, said digital data stream comprising a series of bits and having a bit transmission rate, the method comprising the steps of: generating a PNS, where said PNS is comprised of M bits, where M is greater than or equal to a maximum possible number of bits per symbol supported by the NS3 communication system; converting said digital data stream to a stream of symbol indices, said stream of symbol indices having a symbol rate; combining, at said symbol rate, said symbol indices with said PNS to produce a symbol-wise scrambled digital data stream. 8. The method of claim 7, wherein said generating step further comprises generating said PNS with an encryption algorithm. 9. The method of claim 7, where said combining step further comprises modulo-2 adding of said symbol indices and said PNS. 10. The method of claim 7, wherein said combining step further comprises arithmetic adding of said symbot indices and said PNS. 11. The method of claim 7, where said combining step combines the N least significant bits of said M bits of said PNS. 12. The method of claim 7, wherein each symbol indux is comprised of N bits, and wherein M is independent of N. 13. The method of claim 7, wherein said symbol rate is a whole or fractional multiple of the time interval between each symbol in said set of symbol indices. 14. The method of claim 7, further comprises: transmitting said scrambled digital data stream. 15. A communication system having a variable data rate and a variable number of bits per symbol, wherein the variable number of bits per symbol is less than or equal to a maximum number of bits per symbol, the system comprising: a bit-to-symbol converter configured to operate at a current number of bits-per-symbol N, to produce a stream of symbol indices from a digital bit stream; a PNS generator configured to maintain a state and to produce M output bits at a rate derived from a current symbol rate, wherein M is at least as large as the maximum number of bits per symbol; means for combining the stream of symbol indices and the N least significant output bits to produce a symbol-wise scrambled digital data stream; an encoder configured to encode the symbol-wise scrambled digital data stream; and a modulator configured to modulate the encoded symbol-wise scrambled digital data stream. 16. The system of claim 15, wherein M is independent of N. 17. The system of claim 15, wherein the state is independent of the number of bits per symbol. 18. A non-self-synchronizing scrambling (NS3) communications system, comprising: a first communications device comprising: a bit-to-symbol converter configured to oeprate at a current number of bits-per-symbol N, to produce a stream of symbol indices from a digital bit stream; a first PNS generatpr configured to maintain a first state and to produce M first PNS output bits at a rate derived from a current symbol rate, wherein M is at least as large as the maximum number of bits per symbol; first means for combining the stream of symbol indices and at least one of the first PNS output bits to produce a first symbol-wise scrambled digital data stream; and means for tramsmitting the first symbol-wise scrambled digital data stream; and a second means device comprising: means for receiving the first symbol-wise scrambled digital data stream; a second PNS generator comfigured to maintain a second state and to produce M second PNS output bits at a rate derived from a current symbol rate a second means for combining the first symbol-wise scrambled digital data stream and at least one of the second PNS output bits to produce a first symbol-wise descrambled digital data stream; and a symbol-to-bit converter configured to operate at a current number of bits-per-symbol N, to produce a bit stream for the first symbol-wise descrambled digital data stream. 19. The system of claim 18, wherein said first communication device is an Digital Subscriber Line Transceiver Unit-Central Office (DTU-C) and said second communication device is an Digital Subscriber Line Transceiver Unit-Remote (DTU-R). 20. The system of claim 18, further comprising a plurality of additional DTU-Rs, said plurality of additional DTU-Rs having the same capabilities as said second communication device. 21. The system of claim 17, wherein said first communication device further comprises a FIFO register to store previous states of said first PNS generator. 22. The system of claim 18, further comprising means for delaying said second PNS output bits, wherein said second combining means combines said delayed second PNS output bits and said symbols to produce the second symbol-wise scrambled digital data stream. 23. The system of claim 18, wherein the first PNS generator is further configured to initialize the first state using a predetermined value, and wherein the second PNS generator is further configured to initialize the second state using the predetermined value. 24. The system of claim 18, wherein the second communications device further comprises means for scrambling and transmitting a second digital data stream and wherein the first communications device further comprises means for receiving and descrambling the second scrambled digital data stream. 25. The system of claim 24, wherein the second communications device further comprises: first means for converting said second digital data stream from bits into symbols; and third means for combining said symbols and said second output bits to produce a second symbol-wise scrambled digital data stream; and wherein the first communications device further comprises: fourth means for combining the second symbol-wise scrambled digital data stream to produce a second symbol-wise descrambled digital data stream; and second means for converting said second symbol-wise descrambled digital data stream from symbols into bits. 26. The communication system of claim 18, wherein said first communications device is located at an ingress point to a communications medium and said second communications device is located at an egress point to said communications medium. 27. A method for non-self-synchronizing scrambling (NS3) in a system having a symbol rate and a symbol period equal to the inverse of the symbol rate, comprising the steps of: in a first communication device: initializing a first PNS generator state to a predetermined initial value on receipt of a final first symbol during a training phase; generating first PNS output bits each symbol period; advancing the first PNS generator state at the end of each interval in a common timing reference, where said common timing reference is a multiple of the symbol rate; in a second communication device: initializing a second PNS generator state to the predetermined initial value on receipt of a final second symbol during the training phase; generating second PNS output bits each symbol period; and advancing the second PNS generator state at the end of each interval in the common timing reference.