Pre-scramble encoding method and apparatus for digital communication

Abstract

A prescramble encoding mechanism divides a data word into a plurality of sequences of data bits for transmission over a fiber optic communication link. Complementary versions of control bits and odd and even parity bits are interleaved between the bit parallel data and control signals, divides a parallel data word possible series of consecutive bits of the same logical state is less than a predetermined number related to the length of the data bit sequences and to placement of the complementary control bits and even and odd parity bits. The data frame is then scrambled prior to transmission over the fiber optic link. Depending on the exact nature of the scrambling and descrambling process, a single-bit link error may produce a plurality of bit errors in the descrambled frame. To increase the likelihood that the link error will be detected by the parity checks in the descrambled frame, a frame may be resequenced to separate adjacent bits prior to scrambling and resequenced back to the original sequence after descrambling. As a consequence, a single-bit link error which causes multiple descrambled bit errors will cause widely separated bit errors so that, for the most part, each error bit will be in a separate data bit sequence which is the subject of a separate parity bit calculation. At the receive end of the link, received signals are descrambled, resequenced back to their original order and then demultiplexed to respective outputs.