Impact of LLR Clipping and Quantization on NGMI in Advanced MLSE with Simple Soft Output for IM-DD Transmission with SD-FEC

We investigate the impacts of LLR clipping and quantization on NGMI in advanced MLSE with a simple soft-output scheme through a 128-Gbaud PAM4 O-band transmission experiment. We show that adequate clipping in LLR does not cause NGMI to deteriorate and the simple soft-output MLSE scheme realizes to enhance NGMI even in the case with 2-bit quantization of the LLR value.