Research On Phase Damage Mechanism And Compensation Of High Speed Coherent Optical Communication System

Filter bank Multicarrier/offset quadrature amplitude modulation?FBMC/OQAM?is a kind of multicarrier modulation technology which is based on good time-frequency symmetry filter,it is with high spectrum efficiency,small inter-symbol interference and inter-carrier interference.However,the orthogonality between adjacent subcarriers only occurs in the real-valued domain,so this system has inherent imaginary interference?IMI?.IMI connected with phase noise and frequency offset would generate new crosstalk,which makes the original algorithms which are adapted to orthogonal frequency division multiplexing?OFDM?difficult to apply,so exploring new methods to solve IMI,realize phase noise and frequency offset compensation is the main problem of FBMC/OQAM system.This thesis discusses the reasons for the emergence of IMI in FBMC,analyzes the basic principles of phase noise and frequency offset in detail,and builds the CO-FBMC/OQAM system for simulation verification of new algorithms.In this thesis the phase noise estimation algorithm based on Kalman filter is studied.Kalman filter can fit the phase noise.Based on the analysis of the disadvantages of the phase noise estimation algorithm by the blind Kalman filter,a pilot-based Kalman filter algorithm is proposed.By designing the pilot,the pilot is not affected by the IMI,thereby ensuring the accuracy of the phase noise recorded by the pilot symbol.The results show that under the same OSNR,the normalized linewidth that P-EKF can compensate is1.344?10^-2,while the B-EKF and M-BPS are4.48?10^-3 and 2.24?10 ^3-,respectively.At the same time,the tolerance to residual frequency offset is?3500kHz,?1500kHz,?300kHz,respectively.The proposed algorithm effectively improves the performance of the system.Joint phase noise and frequency offset estimation methods based on pseudo pilots are studied in this thesis.Aiming at the problem that the existing SC algorithm is too much affected by Gaussian noise,a new frequency offset estimation method is explored.The pilot is used to estimate the frequency offset in the frequency domain,so that the method is not affected by Gaussian noise.And as the pseudo-pilot is used,so the processing of phase noise reduces computational complexity and improves spectral efficiency.The results show that when the normalized linewidth is1.28?10^-3,the OSNR needed is 17dB,and the tolerance of carrier offset is 10GHz while the transmitting speed is set to 20GHz.The proposed algorithm can be applied to the laser with low cost and large linewidth and can promote the cost reduction of coherent systems.The research results of this paper have important practical significance and theoretical value for the development of the next generation high-speed large-capacity long-distance optical fiber communication system.