On Advanced FEC and Coded Modulation for Ultra-High-Speed Optical Transmission

This tutorial paper presents an overview of advanced FEC and coded modulation (CM) for optical communications. It describes the following ultra-high-speed optical transport enabling techniques: codes on graphs (turbo-product and LDPC codes), rate-Adaptive CM, and turbo equalization. Given the high potential of LDPC codes, several binary and nonbinary LDPC decoding algorithms are described and FPGA implementation is also discussed. We then demonstrate that some recently proposed attractive LDPC codes could in fact be represented as special instances of irregular quasi cyclic (QC)-LDPC codes from pairwise balanced designs (PBDs). In addition, we describe several LDPC-coded modulation schemes, including hybrid multidimensional CM, block-interleaved CM, multilevel coding, nonbinary (NB) LDPC-CM, and multilevel NB-LDPC-CM. We also demonstrate the application of turbo equalization and rate-Adaptive coding in high-speed optical transmission to deal with fiber nonlinearities. Finally, an optimized signal constellation design approach as well as an optimized mapping rule has been discussed.