Method and apparatus for digital transmission incorporating scrambling and forward error correction while preventing bit error spreading associated with descrambling

A multiservice transmission system for digital information transport, said multiservice transmission system including a transmitter, a transmission medium, and a receiver, said multiservice transmission system providing for forward error correction and scrambling/descrambling, said multiservice transmission system comprising:

• a scrambler, located at said transmitter, said scrambler producing a scrambled data output wherein said scrambled data output has a given number of bit transitions to maintain synchronization between said transmitter and said receiver;
• a forward error correction (FEC) encoder, located at said transmitter, said FEC encoder applying an algorithm to said scrambled data output and calculating an FEC syndrome, said transmitter transporting said scrambled data output and said FEC syndrome over said transmission medium to said receiver;
• an FEC decoder, located at said receiver, for identifying and correcting bit errors introduced to said scrambled data output during said transmission over said transmission medium;
• said FEC encoder is operable to classify each byte of said scrambled data into either a first group or a second group, said first group pertaining to said scrambled data having odd numbered bytes, said second group pertaining to said scrambled data having even numbered bytes;
• said FEC encoder is further operable to compute a first FEC number from said scrambled data of said first group;
• said FEC encoder is further operable to compute a second FEC number from said scrambled data of said second group;
• said FEC encoder byte-wise interleaves said first FEC number and said second FEC number;
• said scrambled data order remains undisturbed by operations performed by said FEC encoder;
• and
• a descrambler, located at said receiver, for descrambling said scrambled data output,
• wherein applying data to said scrambler prior to said FEC encoder at said transmitter, and applying data to said FEC decoder prior to said descrambler at said receiver, prevents bit error spreading.

A method for transmission of multiple service, multiple mode scrambled and forward error corrected data from a transmitter to a receiver, said method comprising the steps of:

• (A) dividing said transmission into a series of successive time subframes;
• (B) scrambling data to be transmitted, said scrambling producing scrambled data wherein said scrambled data has a given number of bit transitions to maintain synchronization between said transmitter and said receiver;
• (C) applying a forward error correction (FEC) algorithm to said scrambled data, said algorithm determining an FEC syndrome;
• said step of applying an FEC algorithm to said scrambled data further comprising:
• (i) classifying each byte of said scrambled data into a first group and a second group, said first group pertaining to said scrambled data having odd numbered bytes, said second group pertaining to said scrambled data having even numbered bytes;
• (ii) computing a first FEC number from said scrambled data of said first group;
• (iii) computing a second FEC number from said scrambled data of said second group;
• (iv) byte-wise interleaving said first FEC number and said second FEC number;
• (v) incorporating said first FEC number and said second FEC number within said time subframe;
• and
• (vi) incorporating said scrambled data within said time subframe, said scrambled data order remaining undisturbed by application of said FEC algorithm;
• (D) incorporating said scrambled data with said FEC syndrome within a time subframe;
• (E) transmitting said time subframe to said receiver;
• removing said FEC syndrome from said time subframe and decoding said FEC syndrome at said receiver;
• (F) identifying and correcting bit errors introduced during transmission of said scrambled data at said receiver by applying said FEC syndrome;
• and
• (G) removing said scrambled data from said time subframe and descrambling said scrambled data at said receiver, said descrambling producing descrambled data.