Capacity achieving nonbinary LDPC coded non-uniform shaping modulation for adaptive optical communications.

Changyu Lin,Tao Liu,Ivan B Djordjevic,Ding Zou

doi:10.1364/oe.24.018095

Abstract

A mutual information inspired nonbinary coded modulation design with non-uniform shaping is proposed. Instead of traditional power of two signal constellation sizes, we design 5-QAM, 7-QAM and 9-QAM constellations, which can be used in adaptive optical networks. The non-uniform shaping and LDPC code rate are jointly considered in the design, which results in a better performance scheme for the same SNR values. The matched nonbinary (NB) LDPC code is used for this scheme, which further improves the coding gain and the overall performance. We analyze both coding performance and system SNR performance. We show that the proposed NB LDPC-coded 9-QAM has more than 2dB gain in symbol SNR compared to traditional LDPC-coded star-8-QAM. On the other hand, the proposed NB LDPC-coded 5-QAM and 7-QAM have even better performance than LDPC-coded QPSK.

Highlights

Photonic networks have been evolving at an increased pace in the last decades thanks to convergence of technologies in both lower and upper layers’ development
The gap between Galois field (GF)(2) cases of QPSK and star 8-QAM is because the Pre-forward error correction (FEC) Byte error rate is not a good predictor for post-FEC performance [15]
Based on calculated mutual information, we propose a method to design a general constellation for optical communication, which can fill the gap of power-two constellation sizes

Summary

Introduction

Photonic networks have been evolving at an increased pace in the last decades thanks to convergence of technologies in both lower and upper layers’ development. To further improve the adaptivity and flexibility, people are looking for spaces in the subsystem level, such as flexible coded modulation schemes, which is a more efficient way to fine tune the cost and performance trade off. We propose a non-uniform nonbinary LDPC coded-modulation scheme, which is a promising solution to both flexibility and excellent performance considerations. To deal with the general M-ary constellations, such as 5-QAM and 7-QAM, we use corresponding matched nonbinary LDPC code with the same size of Galois field (GF) This scheme is providing more flexibility for the system design, and outperforms the traditional QPSK and star-8-QAM performance with even lower complexity.

Proposed generalized nonbinary coded modulation scheme

Results and discussions

Conclusions