Research On Channel Equalization Algorithm In Coherent Optical Communication System

With the rapid emergence and rapid development of various new services such as big data,cloud computing,and artificial intelligence,the bandwidth demand for communication networks has increased dramatically.As a backbone transmission network,optical fiber communication systems must be developed in the direction of high speed,large capacity and long distance.In this process,the coherent optical communication system has gradually become a new generation of optical fiber communication technology because of its high sensitivity,good selectivity and long relay distance.However,there are various linear and nonlinear damages in the fiber.These damages will distort the transmitted signal,which will affect the demodulation and decision of the coherent reception,which seriously affects the improvement of the communication capacity of the system.Therefore,the DSP flow in coherent reception.It is of great significance and value to balance these darmages.This paper mainly studies the causes and mathematical models of optical chromatic dispersion and polarization mode dispersion,and their effects on fiber-optic communication systems.At the same time,several commonly used algorithms for chromatic dispersion compensation and polarization mode dispersion are studied.The shortcomings and shortcomings of existing algorithms are analyzed.An improved chromatic dispersion compensation algorithm and three improvements are proposed.The polarization mode equalization algorithm theoretically discusses the principle and implementation of the new algorithm,and carries out simulation verification.The research work in this paper consists of the following parts:(1)The principle of each module of the coherent optical communication system and the implementation scheme and key technologies of each DSP module in the coherent reception are studied.The causes of the chromatic dispersion and polarization mode dispersion of the fiber and its influence on the performance of the communication system are theoretically analyzed.Several existing chromatic dispersion compensation algorithms and polarization mode equalization algorithms are compared and analyzed,and the shortcomings and shortcomings of existing algorithms in different aspects are analyzed.It provides a theoretical and theoretical basis for the targeted improvement algorithm to be proposed later in this paper.(2)An improved chromatic dispersion compensation algorithm is proposed.The algorithm is based on the joint compensation algorithm of FSM and LMS.It compensates the fixed chromatic dispersion by using the FSM algorithm in the first stage,and then uses the small-tap LMS filter to perform the residual chromatic dispersion and channel noise in the second stage.Compensation,thus achieving better chromatic dispersion compensation.The simulation results show that the proposed algorithm has better performance against chromatic dispersion disturbance and better channel noise compensation.(3)Three improved polarization mode dispersion equalization algorithms are proposed.The first one is a modified constant modulus algorithm based on variable constellation matching error term.The algorithm achieves faster convergence speed and lower steady-state error than the traditional modified constant modulus algorithm.The second one is based on adaptive momentum term.Cascaded multi-mode algorithm,the algorithm inherits the advantages of cascading multi-mode algorithm for high-order QAM modulated siginals,and achieves faster convergence speed;the third is a joint equalization algorithm based on Kalman filter.Compared with the traditional algorithm,the algorithm overcomes the singularity problem and obtains faster polarization tracking speed.Through simulation analysis,the three new algorithms proposed in this paper have achieved good performance improvement in different aspects.