Research On Phase Noise Suppression With Constellations Optimization For Coherent Optical OFDM System

Coherent optical orthogonal frequency-division multiplexing(CO-OFDM)is the combination of two powerful techniques,coherent optical detection and OFDM technique.It can combat fiber chromatic dispersion and polarization-mode dispersion(PMD)with high frequency spectrum utilization.Besides,it can be compatible with the existing optical network,and in the existing infrastructure,can be expanded conveniently.Thus,CO-OFDM is one of potential technical for the next generation ultra-high speed,large capacity,long distance optical transmission systems.However,CO-OFDM is very sensitive to phase noise caused by the laser linewidth.Phase noise will cause demodulation unsatisfied.Moreover,it will bring inter-symbol interference(ISI)and inter-carrier interference(ICI).To realize phase noise suppression,several methods have been proposed.However,only suppressing CPE is not sufficient for relatively larger laser line width.Moreover,the cost of the CO-OFDM system will be increased as the laser line width become narrower.Other schemes use iterative algorithms for joint estimate the data and the phase noise vector.The common drawback of iterative algorithms is that they suffer from large latency and high implementation complexity,which is unsuitable for future real-time CO-OFDM systems.It is significant to seek a phase noise suppression method with excellent performance and low computational complexity which can increase the tolerance laser line width and reduce cost for CO-OFDM.This dissertation researches on phase noise suppression algorithm for CO-OFDM systems,focusing on the the phase noise's influence on constellation and phase noise suppression based on constellation optimization.The main research results include:1.CO-OFDM transmission system based on standard single-mode optical fiber(SSMF)is researched.According to the basic formula,an optimize OFDM frame structure for CO-OFDM system is proposed.Then,16-QAM-CO-OFDM simulation system has been built using simulation tools Optisystem and MATLAB.2.Focuses on phase noise caused by linewidth of the laser line width and its effect on OFDM.According to simulation,we compare three phase noise algorithms and analyze their advantages and disadvantages.3.In terms of the drawback of the current phase noise suppression algorithm for CO-OFDM systems,phase noise suppression algorithm based on constellation optimization is proposed.We can get the basic algorithm principle by analyzing the phase noise's effect on constellation.The simulation results show two new 16-QAM can improve the CO-OFDM tolerance towards laser line width.It also verifies the feasibility of phase noise suppression algorithm based on constellation optimization for CO-OFDM.