Electronic Dispersion Compensation Algorithms In High Speed Optical Communication Systems

Modern optical fiber communication technology are the direction of ultra high speed,ultra large capacity and ultra long distance.Dispersion(CD),polarization mode dispersion(PMD)and nonlinear effect are the main factors of restricting the development of optical fiber communication technology.The key to solve these problems are the coherent light detection,digital signal processing and blind equalization algorithms.In this dissertation,the basic principles of CD,PMD,coherent optical communication,blind equalization algorithms are systematically studied.The basic principle of optical fiber dispersion and polarization mode dispersion is introduced,and the influence of the two groups on the optical fiber communication system is discussed.Meanwhile,the thought method of dispersion suppression is introduced.Then,the optical domain dispersion compensation technologies and the electric domain dispersion compensation technology are introduced.The blind equalization algorithms are discussed,especially the Bussgang type blind equalization algorithms,such as Constant Modulus Algorithm(CMA),Multi-Modulus Algorithm(MMA)and Reduced Constellation Algorithm(RCA),including their advantages and disadvantages.This paper introduces the key technology of coherent communication and lays a theoretical foundation for the experimental verification of the latter.On the basis of the above,the following work has been done:(1)The ideal constellation characteristics of four kinds of 16-ary modulation schemes(e.g.,square-16 QAM,star-16 QAM,four magnitudes and four phases 16QAM(FAFP-16QAM)and 16PSK)are introduced and analyzed.Then the 112 Gbit/s polarization multiplexed coherent optical communication with classic CMA or MMA is adopted to analyze their performances when the laser linewidth,dispersion degree,noise intensity are changed.This work can be regarded as a guidance and reference to how to choose the 16-ary modulation schemes in current optical communication systems.(2)A double decision directed dispersion blind equalization method is proposed.The proposed method combines the soft decision oriented idea and variable step size decision directed.It can automatically identify the Mean Square Error threshold and achieve two ways of adaptive switching.Meanwhile,the iterative step can be adjusted adaptively,and the effect of fast convergence and smaller convergence error can be obtained.Finally,the method is effectively verified on the polarization multiplexing coherent optical communication simulation system.