Forward error correcting codes in fiber-optic synchronous code-division multiple access networks

Abstract

In optical code-division multiple access (OCDMA) networks, the performance is limited by optical multiple access interference (OMAI), amplified spontaneous emission (ASE) noise and receiver noise. To reduce OMAI and noise effects, use of forward error correcting (FEC) (18880, 18865) and (2370, 2358) Hamming codes are explored for STM-1 (155 Mbps) bit stream. The encoding is carried out at the multiplex-section layer. The check bits are embedded in the unused bytes of multiplex section overhead (MSOH). The expression for probability of error is derived taking into consideration OMAI, various sources of noise and effect of group velocity dispersion (GVD). It is observed that for a BER of 10 −9, use of FEC gives a coding gain of 1.4–2.1 dB depending upon the type of coding scheme used. It is also seen that there is a sensitivity improvement of about 3 dB if the source is suitably pre-chirped.