Estimation And Compensation Of Carrier Phase Noise In Coherent Optical Communication Systems

As an important link connecting the whole world in the information age,is facing the challenge that both optical transmission backbone networks and datacenters with short-range interconnection are facing the transmission capacity tending to the limit in the face of the huge demand for information transmission.The development of coherent optical communication transmission systems through devices,transmission technology and algorithms has greatly contributed to the capacity enhancement of fiber optic transmission systems.Coherent optical communication technology using a combination of higher-order modulation code patterns,coherent detection,and digital signal processing has greatly improved the communication transmission spectrum utilization,however,along with the increase in the number of higher-order modulation orders,the Euclidean distance between the receiving constellation points decreases,leading to a significant reduction in the tolerance of laser phase noise,resulting in constellation rotation at the receiving end and triggering phase mismatch.Therefore,it is of great significance for the development of optical communication transmission systems by improving the carrier phase estimation algorithm in coherent optical communication systems.This paper encapsulates the various system impairments in coherent optical communication systems,focusing on the analysis of various carrier phase noise recovery algorithms and the improvement of some of them,the main work of this paper is as follows.1.To address the problem of high hardware complexity of the Blind Phase Search(BPS)algorithm,a two-stage BPS carrier phase estimation algorithm based on Cubic Spline Interpolation(CSI)is proposed,which effectively reduces the number of test phases and the computational complexity of the algorithm implementation.The 16-QAM single-carrier coherent optical transmission system is built using Optisystem software,and the CSI algorithm is used in the MATLAB module to estimate and compensate for the phase noise in the simulation,and the recovery performance of the CSI algorithm is verified.The results of the simulation experiments verify the feasibility of the CSI algorithm for phase noise compensation in the system.The algorithm is not only effective in recovering the carrier phase,but has also been verified by the system to reduce the computational complexity(multiplier/adders)by 1.61/1.73(16-QAM)compared to the BPS algorithm.2.The recursive CSI algorithm is proposed,using the idea of symbolic recursion to change the long filter structure in the CSI algorithm,effectively removing the effect of additive noise,and solving the problem caused by the CSI algorithm using long window filtering to obtain close to the theoretical channel mutual information.The PS-16 QAM coherent optical communication transmission system is built using the(Probabilistic Amplitude Shaping,PAS)shaping scheme,and the carrier phase recovery algorithm in the probabilistic shaping coherent optical communication system is analysed.The performance shortcomings of the CSI algorithm in the system transmission were pointed out,and thus the recursive CSI algorithm was proposed to achieve better carrier phase recovery performance by optimizing the forgetting factor of the recursive CSI algorithm.The results show that the recursive CSI algorithm can effectively reduce the carrier phase noise estimation error in probabilistic shaping coherent optical communication systems,reduce the computational complexity of the implementation of the algorithm more effectively under the condition of achieving the same channel mutual information,and achieve the Optical Signal-to-Noise Ratio(OSNR)gain to a certain extent.The results show that the recursive CSI algorithm can replace the CSI algorithm to achieve better performance in probabilistic shaping coherent optical communication systems and is a feasible algorithm for carrier phase noise compensation.