The Forward Error Correction Technology Research Of High-speed Optical Communications

At present, the major limiting factor of the high-speed optical communicationsystems is the optical signal to noise ratio (OSNR). The requirement of100Gbit/scommunication systems for OSNR is4dB higher than the present40Gbit/scommunication systems. Among the available technologies to further improve theOSNR deficit, Forward Error Correction (FEC) solutions to obtain the net codinggain is the most effective way. Now, the traditional FEC scheme can’t meet the needs ofthe system, we need to structure more effective Super-FEC scheme.In the FEC code, BCH code is simple in structure and relative device is mature. Inresent years, researchers pay more attention to LDPC code, which has good errorcorrect performance approaching the Shannon limit.This paper uses Super-FEC schemes recommened by ITU-T G975.1as a guide,analyzes and researches the performance of FEC technology. According to the need ofhigh-speed optical communication systems for FEC technology, we simulate andanalyze the properties of different BCH codes. Moreover, for the LDPC code, we havedetailed analysis of the performance of both hard-decision and soft-decision of thedemodulation. In addition, the influence of the system performance due to differentiterations of decoding algorithm, different decoding algorithm and different code rate isalso analyzed comprehensively. The results show that the perpormance of thesoft-decision is1.9dB to2.2dB better than the hard decision. Also,20iterations ofdecoding algorithm can achieve a relative balance of properties and costs. The BPalgorithm is0.3dB better than the min-sum decoding algorithm. The lower the code rateis, the better the performance is, while the redundancy is higher. Furthermore, thetermination condition whicn can shorten the simulation time is designed and its impacton performance is discussed.In order to obtain better performance, this paper proposes a concatenatedSuper-FEC scheme based on the long irregular LDPC code. The Super-FEC schemeuses concatenated codes, different system of BCH code is used as the outer code, LDPCcode is used as the inner code. For different systems, we have desiged four schemes: BCH(63,51)+LDPC(64800,32400),RS(255,239)+LDPC(64800,43200),RS(1023,1007)+LDPC(64800,51840) and BCH(511,493)+LDPC(64800,57600), and the loss of code rate in thelength match of four schemes is small. Through simulation analysis, additional rateoverhead of BCH(511,493)+LDPC(64800,57600) scheme is smallest in the fourSuper-FEC schemes, and its NCG is7.46dB...