Research On Four-dimensional Modulation Technology In High Speed Optical Communication System

Now it is in an era of rapid information development of information.With the official commercialization of 5G,the Internet industry has been further developed.As the basic transmission construction in the information age,the optical communication transmission network has laid the foundation for the development of novel technologies,while the rapidly increasing traffic and bandwidth demands also pose great challenges to the communication network.Facing the demand of mass data transmission,improving the performance of optical communication transmission network is the research focus of communication researchers.Four-dimensional modulation is a four-dimensional spatial modulation mode composed of in-phase and orthogonal components on two orthogonal polarizations of an optical carrier,which increases the minimum Euclidean distance between constellation points,solves the influence between spectral efficiency and progressive power efficiency,and then effectively improves the transmission capacity of the system without increasing hardware complexity.Based on the research of the theory of four-dimensional modulation technology in high-speed optical communication system,this thesis focuses on the four-dimensional modulation optical transmission scheme using clustering algorithm for decision decoding,the four-dimensional modulation optical transmission scheme based on probabilistic shaping and channel coding for improving transmission capacity and system reliability,and the four-dimensional modulation optical transmission scheme for free space optical communication system,The main research contents are as follows:(1)A four-dimensional modulation optical transmission scheme based on clustering algorithm is proposed.The scheme adopts clustering algorithm to decode the received four-dimensional signal,which reduces the error of the signal after transmission due to the nonlinear influence.Theoretical analysis shows that clustering algorithm can reduce the influence of noise in transmission channel.The simulation results show that the BER performance of 128-SP-QAM with clustering algorithm is 0.4dB higher than that of traditional 128-SP-QAM at BER?1×10-3.The BER performance of PS-QPSK with clustering algorithm is 1dB higher than that of traditional PS-QPSK.(2)A four-dimensional PSKM-128-SP-QAM modulation scheme based on clustering algorithm and probabilistic shaping technology is proposed.In this scheme,probabilistic shaping is used to realize the non-uniform mapping of signal.This approach solves the problem that the channel capacity of uniform constellation modulation method is difficult to approach the Shannon limit,and K-means algorithm is used for signal decision.The simulation results show that shaping coding of PSKM-128-SP-QAM is better than the original four-dimensional modulation format.Compared with 128-SP-QAM,PSKM-128-SP-QAM achieves a SNR gain of 2.7dB when transmitting 50km.(3)A four-dimensional PSKM-LDPC-SP-QAM modulation scheme based on probabilistic shaping and error correction coding is proposed.In this scheme,channel coding is adopted in PSKM-128-SP-QAM system to improve the reliability of system transmission.This approach solves the problem that non-uniform constellation points are more susceptible to noise and other factors.The simulation results show that the performance of PSKM-LDPC-SP-QAM is improved by about 4.5dB in both back-to-back and 50km transmission.Therefore,the channel coding of PSKM-128-SP-QAM using LDPC code can significantly reduce the bit error rate of the system,which is suitable for high-speed long-distance optical communication transmission system.(4)Four-dimensional modulation optical transmission scheme in free space optical communication system is proposed,through the research of information transmission in free space optical communication using four-dimensional modulation format,in order to improve the spectral efficiency of the system,respectively simulation PS-QPSK and KM-128-SP-QAM modulation format in free space optical communication system information transmission.The simulation results show that the four-dimensional modulation scheme is feasible in the free space optical communication system,and the KM-128-SP-QAM,which uses clustering algorithm to make the decision,can reduce the bit error rate of the system,and is more suitable for transmitting information at high speed and long distance.