Open AccessAdaptive adjustment of reference constellation for demodulating 16QAM signal with intrinsic distortion due to imperfect modulation
Author(s) -
Takashi Inoue,
Shu Namiki
Publication year - 2013
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.21.029120
Subject(s) - quadrature amplitude modulation , demodulation , constellation diagram , computer science , constellation , optics , distortion (music) , signal (programming language) , modulation (music) , electronic engineering , physics , telecommunications , bandwidth (computing) , bit error rate , engineering , amplifier , acoustics , decoding methods , channel (broadcasting) , astronomy , programming language
We find that an adaptive equalizer and a phase-locked loop operating with decision-directed mode exhibit degraded performances when they are used in a digital coherent receiver to demodulate a 16QAM signal with intrinsically distorted constellation, and that the degradation is more significant for the dual-polarization case. We then propose a scheme to correctly demodulate such a distorted 16QAM signal, where the reference constellation and the threshold for the decision are adaptively adjusted such that they fit to the distorted ones. We experimentally confirm the improved performance of the proposed scheme over the conventional one for single-and dual-polarization 16QAM signals with distortion. We also investigate the applicable range of the proposed scheme for the degree of distortion of the signal.