Modification of error statistics behind equalizer to improve inter-working with different FEC codes

An apparatus comprising:

• a forward error correction (FEC) circuit configured to receive a payload symbol stream for transmission and to apply an FEC code to the payload symbol stream to generate a framed symbol stream comprising a plurality of digital symbols;
• a transmitter reorder circuit electrically connected to the FEC circuit comprising:
• an interleaver configured to rearrange one or more of the digital symbols in a non-contiguous manner,
• a scrambler configured to exchange a position of the plurality of the digital symbols output by the interleaver with a position of other symbols output by the interleaver in accordance with a link pattern in order to generate a reordered digital stream comprising an irregular permutation of exchanged digital symbols that disturbs a re-arrangement regularity introduced by the interleaver and that is useable for effective separation of burst errors at an optical receiver, and
• a permutation controller comprising a plurality of pseudo random binary sequence circuits configured to generate the link pattern and configured to regularly provide the scrambler with a different link pattern at a selected number of clock cycles for use by the scrambler to exchange
• the position of a plurality of the digital symbols with the position of the other digital symbols;
• and
• an optical transmitter circuit configured to receive the reordered digital stream and to convert the reordered digital stream into an optical signal for transmission on an optical fiber.

A method comprising:

• receiving, at an interleaver, a stream of digital symbols;
• generating a plurality of link patterns with a plurality of pseudo random binary sequence circuits;
• storing the plurality of link patterns in a memory;
• regularly selecting a different one of the plurality of link patterns from the memory at a selected number of clock cycles;
• exchanging, at a scrambler, a position of a plurality of the digital symbols output by the interleaver with a position of other symbols in the stream output by the interleaver in accordance with a most recent selected link pattern in order to generate a reordered digital stream comprising an irregular permutation of exchanged digital symbols that disturbs a re-arrangement regularity introduced by the interleaver and that is useable for effective separation of burst errors at an optical receiver;
• and
• outputting the reordered digital stream.