DFT-Spread DMT-WDM-PON Employing LDPC-Coded Probabilistic Shaping 16 QAM

A 5 x 100-Gb/s discrete-Fourier-transform spread (DFT-spread) discrete multi-tone wavelength division multiplexing passive optical network (DMT-WDM-PON) employing low-density parity-check (LDPC) coded probabilistic shaping 16-ary quadrature amplitude modulation (PS-16 QAM) is proposed and experimentally demonstrated. We first introduce PS-16 QAM mapping scheme with 16-point constellation reshaped from 32 symbols into splitter-based DMT-WDM-PON. The DMT-WDM-PON employing PS-16 QAM can achieve superior receiver power sensitivity (RPS) and enhanced spectral efficiency (SE) compared with the unshaped one. Compatible with the forward error correction (FEC) implemented in most of the optical transponders today, an optimized bit-interleaved coded modulation iterative decoding (BICM-ID) system based on LDPC coding is proposed to encode the PS-16 QAM DMT signal without any extra shaping codes or overheads. Then the labeling optimization with the assistance of extrinsic information transfer (EXIT) chart is investigated, in which the extrinsic messages are transferred between the PS demapper and the LDPC decoder for retrieving the PS-16 QAM DMT signal. Furthermore, the experimental results show that 1.5-dB RPS improvement and 2-dB fiber nonlinear effect tolerance enhancement are respectively realized over a 20-km standard single-mode fiber (SSMF) link by using joint applications of DFT-spread scheme and PS-16 QAM mapping in proposed DMT-WDM-PON system, which can thus provide abundant system loss budget for the legacy optical distribution networks (ODNs).