Bit Loading-Based Irregular LDPC Coded-Modulation for High-Speed Optical Communications

In state-of-the-art fibre-optics communication systems, the forward error correction (FEC) and high-order constellation formats are employed. It is important to approach the Shannon limit by using turbo product codes (TPC) and low-density parity-check (LDPC) codes with soft-decision decoding (SDD) algorithms. In this paper, we first study the rate-adaptive irregular LDPC coding technique in wide range of code rates enabling the flexible adjustment according to channel conditions and the simulation results show an improved SNR gain of 0.15 similar to 0.44 dB compared with regular LDPC codes under BPSK transmission. Then we propose a bit-loading rule for irregular LDPC codes combined with 16QAM and demonstrate additional 0.3 dB SNR improvements in low code rate regime, making it a viable solution for next generation high-speed optical communication systems.