Forward error correcting codes in synchronous fiber optic transmission systems

This paper proposes forward error correcting (FEC) codes for Synchronous Digital Hierarchy (SDH) fiber optical transmission systems. They are (18 880, 18 865) and (2370, 2358) shortened Hamming codes and are encoded at the multiplex-section layer; the check bits are embedded in auxiliary multiplex-section overhead (MSOH) bytes. The codes realize general circuit configurations regardless of the transmission speed or path-size, perfect compatibility with SDH format, suppressed processing delay accumulation, and decrease the chance of line-switching in the case of signal degradation. To ensure that the various requirements of each network-provider such as customized usage of SOH bytes and affordable circuit scale could be satisfied, a trial circuit board was constructed on the programmable hardware called PROTEUS, which enables flexible operation in terms of code-selection and check bit area. We actually confirm error-correcting capability through the first STM-64 FEC-coded-optical transmission experiment. The statistics of error occurrence in the optical transmission line are also studied. The result indicates that the proposed codes are effective in optical transmission systems if the BER is limited by optical noise and dispersion.