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Rate-Configurable SC-LDGM Codes Concatenated with Zipper Codes for Optical Communication

In this paper, we propose a new rate-configurable concatenated forward error-correction (FEC) scheme for optical communication. The inner code is a systematic convolutional low-density generator matrix (SC-LDGM) code, and the outer code is a zipper code. Multilevel coding (MLC) with high-order modulation is employed, where all bits are protected by the outer coder but only one bit-level is protected by the inner code. The presented scheme can operate at various transmission rates, channel qualities and modulation orders thanks to the flexible construction of the inner SC-LDGM code. Genie-aided (GA) bounds are derived, which can be utilized to predict the performance and is helpful to the code design. The simulation results show that, for low overhead (OH), the required SNR for target bit error rate (BER) is around 1.1 dB gap to the constrained Shannon limits, while for high OH, the performance is mainly governed by the GA bound.