High-order QAM Constellation Design Based On Geometry And Probability Shaping

Optical fiber communication has become the core of today's communication backbone network and access network because of its advantages of low attenuation and loss,frequency bandwidth,low electromagnetic interference and high security.With the gradual commercialization of technologies such as 5G and cloud access,there is an urgent need to further greatly increase the capacity of optical fiber transmission systems to meet the needs of rapid economic and social development.All-optical orthogonal frequency division multiplexing(OFDM)and high-order orthogonal amplitude modulation(QAM—Quadrature Amplitude Modulation)can effectively improve the system's spectral efficiency(SE—Spectral Efficiency)and transmission capacity,which is an important research field of current optical communication technology.Recent research results show that,according to the characteristics of fiber channel,through appropriate constellation shaping technology,the transmission capacity of QAM fiber system can be further approached to its fragrant limit,which has very important research value and practical significance.In this paper,the effect of constellation shaping technology on all-optical orthogonal frequency division multiplexing(OFDM)system is studied on the basis of fully considering the nonlinear effect of optical fiber.First,a symmetric distributed Fourier method is used to simulate the all-optical OFDM system under nonlinear conditions,and the performance of the all-optical OFDM system before and after probabilistic shaping is subjected to different nonlinear effects and after transmission through different lengths of optical fiber.On this basis,a combination of probabilistic shaping technology and geometric shaping technology is used,and a new constellation shaping scheme is obtained using the pairwise optimization(PO-Pairwise Optimization)algorithm.The main work completed by the thesis is as follows:1.Discusses the basic mechanism of fiber nonlinear optical effects,high-order quadrature amplitude modulation(QAM)and constellation shaping technology and its important impact and role on optical communication systems.2.Establish a numerical simulation program for optical fiber nonlinear signal transmission and all-optical OFDM system based on iterative symmetrical split-step Fourier method.On this basis,the method of generating high-order probabilistic shaping QAM signals is described,and the high-order QAM signal after probabilistic shaping is applied in the system,compared with the standard QAM signal,confirms that probabilistic shaping can indeed play a role in easing the non-linear effects.3.For the all-optical OFDM system using dense orthogonal subcarriers,a 32QAM constellation design scheme based on geometric and probabilistic shaping is proposed.Simulation studies the transmission performance of the geometric and probabilistic shaping 32QAM all-optical OFDM system after being subjected to nonlinear effects.After simulation,the research results show that the designed new geometric and probabilistic shaping 32QAM constellation has a significant performance improvement compared to the traditional 32QAM and purely geometric shaping or probabilistic shaping 32QAM signals,which proves that the transmission capacity can be improved.