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Recent Progress in Forward Error Correction for Optical Communication Systems

Takashi MIZUOCHI

Publication
IEICE TRANSACTIONS on Communications   Vol.E88-B    No.5    pp.1934-1946
Publication Date: 2005/05/01
Online ISSN: 
DOI: 10.1093/ietcom/e88-b.5.1934
Print ISSN: 0916-8516
Type of Manuscript: Special Section INVITED PAPER (Joint Special Section on Recent Progress in Optoelectronics and Communications)
Category: 
Keyword: 
optical communications,  forward error correction,  block turbo code,  Reed-Solomon,  BCH,  concatenated code,  product code,  iterative decoding,  Shannon limit,  code rate,  

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Summary: 
The history of forward error correction in optical communications is reviewed. The various types of FEC are classified as belonging to three generations. The first generation FEC represents the first to be successful in submarine systems, when the use of RS(255, 239) became widespread as ITU-T G.975, and also as G.709 for terrestrial systems. As WDM systems matured, a quest began for a stronger second generation FEC. Several types of concatenated code were proposed for this, and were installed in commercial systems. The advent of third-generation FEC opened up new vistas for the next generation of optical communication systems. Thanks to soft decision decoding and block turbo codes, a net coding gain of 10.1 dB has been demonstrated experimentally. That brought us a number of positive impacts on existing systems. Each new generation of FEC was compared in terms of the ultimate coding gain. The Shannon limit was discussed for hard or soft decision decoding. Several functionalities employing the FEC framing were introduced, such as overall wrapping by the FEC frame enabling the asynchronous multiplexing of different clients' data. Fast polarization scrambling with FEC was effective in mitigating polarization mode dispersion, and the error monitor function proved useful for the adaptive equalization of both chromatic dispersion and PMD.