Research On Damage Compensation In Optical Orthogonal Frequency Division Multiplexing System

With the rapid development of the Internet in modern society,the influx of a large number of new services has led to an increasing demand for high capacity,high speed,large bandwidth,and high reliability networks,which has promoted the invention and dissemination of various technologies in the field of communication,and the orthogonal frequency division multiplexing(OFDM)communication system has become a remedy for the problem by virtue of its excellent noise immunity,high spectrum utilization,and low-cost offline digital signal process(DSP)capability at the receiver side.OFDM communication system has been widely studied for its excellent noise immunity,high spectrum utilization and low-cost off-line digital signal processing(DSP)capability at the receiver side,which has become a remedy to solve the problem.It also accelerates the development of optical orthogonal frequency division multiplexing(Optical OFDM,O-OFDM)in the field of fiber optic communication,O-OFDM is highly regarded because it can make full use of modern advanced DSP technology at the receiver side,using low-cost solutions to improve the performance of the transmission system,therefore,O-OFDM system DSP technology is currently a major domestic and international resear-ch in the field of fiber optic communication.Therefore,DSP technology in O-OFDM systems is one of the major research hotspots at home and abroad.This thesis focuses on the research of using DSP technology to compensate system impairment in O-OFDM systems,and investigates the principles related to laser phase noise,fiber nonlinear noise and channel linear noise,and proposes a phase noise compensation scheme based on blind phase estimation,a nonlinear noise compensation scheme based on central clustering and a linear noise compensation scheme based on constant-mode blind equalization.The main research contents and innovations of this thesis are as follows:(1)Phase noise compensation scheme based on blind phase estimationIn order to solve the problem that the long duration of individual symbols in OFDM transmission makes them extremely sensitive to laser phase noise,increase the tolerance to phase noise caused by lasers and improve the transmission performance of communication systems.In this paper,we propose a phase noise compensation scheme based on blind phase estimation of constellation diagram cut.The scheme uses the constellation diagram to calculate the square of the distance from the ideal constellation point according to different radii separately after being cut,and reduces the complexity of the calculation by reducing the number of its judgments.The performance of the scheme in a 16QAM-OFDM system is investigated in simulation.The results show that the BPS algorithm complexity is further reduced on the basis of ensuring the performance is basically the same as that of the BPS algorithm.(2)Nonlinear noise compensation scheme based on central clusteringIn order to solve a variety of undesirable nonlinear effects caused by refractive index changes during the transmission of optical waves in OFDM communication systems with high speed and long distance transmission,enhance the resistance of OFDM systems to nonlinearities and improve the transmission performance of communication systems.In this paper,we propose a nonlinearity compensation scheme based on unsupervised clustering algorithm using a centroid clustering algorithm with the most central position in the cluster as the center of mass,which abandons the selection of the mean value of the sample as the center of mass and instead uses the object with the most central position in the cluster of one of the sample point data as the center of mass,weakening the interference caused by extreme data distribution.The performance of this scheme in a 16QAM-OFDM system is investigated in simulation.The results show that,compared to the commonly used K-Means algorithm,it is evident that the performance of the center-based clustering compensation algorithm consistently outperforms the traditional K-means algorithm at a small number of iterations.After the number of iterations is increased,the performance of the two algorithms is comparable,and the obvious gain in performance convergence speed of this scheme can be seen.(3)Linear noise compensation scheme based on constant-mode blind equalizationIn order to solve the dispersion damage and fiber loss and other linear damage brought by the fiber channel during the transmission of OFDM communication system,increase the tolerance to the linear damage of the channel and improve the transmission performance of the communication system.This paper proposes a channel linear damage compensation scheme based on the driven volume adaptive correction constant-mode algorithm,which optimizes the problem of slow convergence of the traditional constant-mode algorithm iterations and improves the convergence rate without additional loss in performance.The performance of the scheme in a 16QAM-OFDM system is investigated in simulation.The results show that significant gains in performance and convergence speed are obtained compared with the constant-mode equalization algorithm,and superiority in convergence rate compared with the MCMA algorithm.