Research On Coded Modulation Methods In Optical Communication Based On Signal Shaping

With the development of Internet,Internet of things and the fifth generation of mobile technology(5G),HD live video,augmented reality(AR),virtual reality(VR),intelligent hardware devices have become an indispensable part of people's life.These network applications enrich people's lives,but also put forward higher speed,larger bandwidth,lower delay requirements for the existing optical communication network.Whether for the upgrading of existing services or the continuous emergence of new services,the backbone transmission network based on optical fiber communication technology needs to continuously improve the network speed and transmission bandwidth.In optical communication system,the main factors that restrict the performance of communication system are power utilization,spectrum efficiency,channel noise and interference.At the same time,the dispersion and nonlinear effect of communication fiber itself also have many adverse effects on the long-distance transmission performance of backbone transmission network.In Shannon's theory,channel capacity is defined as the maximum information rate that a communication channel can carry in a given bandwidth.In the decades of the development of optical communication,improving the channel capacity and even approaching the Shannon limit has been the goal of researchers.Noval probabilistic shaping coded modulation and faster than Nyquist pulse shaping are the key technologies to realize the next generation optical communication system,which can further improve the transmission capacity and transmission distance of the system,and effectively improve the performance of optical communication transmission system.They are the research hotspots in the field of optical communication recently.This thesis is based on signal shaping optical fiber communication coding and modulation method.This thesis focuses on the optical communication transmission method based on probabilistic shaping coded modulation,the optical communication transmission method based on the combination of forward error correction code and probabilistic shaping,and the optical communication transmission method based on faster than Nyquist pulse shaping.The purpose of the research is to improve the capacity of the power limited optical communication transmission system,improve the bit error rate performance and mutual information.The main contents and innovations of this thesis are as follows:(1)The theoretical basis of probabilistic shaping coded modulation and the signal distribution matching algorithm in probabilistic shaping are studied,and the optical transmission scheme of probability shaping coded modulation is proposed.In this scheme,the PS-64QAM signal is obtained by CCDM distribution matching device combined with QAM modulation at the transmitter,the nonlinearity is introduced by SSFT algorithm in the optical channel,and the received signal is processed by DSP module at the receiver.Finally,the demodulation signal is obtained by inverse distribution matching.Simulation results show that PS-64QAM signal can get shaping benefits,making the channel capacity closer to Shannon limit.(2)The method of combining FEC code with probability shaping is studied.A PS-64QAM optical transmission scheme based on BCH-LDPC concatenated code is proposed.In this scheme,LDPC code is used as inner code and BCH code as outer code.The decoder at the receiving end decodes the codewords with coding errors during internal code transmission.The simulation results show that the output of LDPC decoder can be corrected by external BCH decoder,which can greatly improve the error correction ability of the whole system.(3)The application of faster than Nyquist pulse shaping method in optical communication system is studied,and the optical communication transmission scheme based on FTN-THP is proposed.The performance simulation of four different equalization schemes is carried out.The results show that the proposed EAD scheme has higher detection performance than the traditional THP detection method,and is superior to the traditional PD detection method.