Research On Signal Shaping Method In High Speed Optical Fiber Communications

With the progress of technology,in the development of 5G,cloud services and other cutting-edge technologies,the growing Internet traffic has been driving the development of communication technology,while the demand for communication capacity is increasing.As the technology for power-efficient and spectrum-efficient communication,the combination of digital signal processing and coherent detection is widely used in advanced optical transmission systems,and advanced modulation formats such as QAM modulation have been widely used to improve spectral efficiency.However,in the high speed optical communication system,there is still a gap between the system capacity of QAM modulation format with traditional uniform signal transmission and the Shannon capacity limit.According to Shannon theory that in the AWGN channel,when the probabilistic of signal points in the constellation is Gaussian distribution,the transmission capacity of the system can approach the Shannon limit,the constellation shaping technology is developed.The constellation shaping technology mainly includes the probabilistic shaping technology to change the probabilistic distribution of signals and the geometric shaping technology to adjust and optimize the constellation structure,which has great research significance to improve the transmission capacity of the system and improve the anti-interference performance of the systemThe principles of probabilistic and geometric shaping are studied in this thesis.The probabilistic shaping and geometric shaping signal generation scheme based on Huffman coding,the novel QAM signal generation scheme based on probabilistic shaping mixed geometric shaping and the constellation geometric probabilistic shaping dense subcarrier signal generation scheme are mainly researched.The research works and achievements of this thesis are as follows:(1)Probabilistic shaping technique using Huffman coding is studied.A method is proposed to generate signals,based on probabilistic shaping combined with geometric shaping with Huffman coding technology.Huffman coding is used to obtain the 11 QAM code words,and combine block interleaver to generate the non-uniform 11 QAM signals by interleaver coding modulation and the constellations structure is optimized and improved.The simulation results show that the BER performance of the proposed scheme is better than that of the traditional non-uniform 9QAM and non-uniform 8QAM signals generation schemes.Experimental results show that the BER performance of the proposed scheme is 2.9dB and 1.2dB higher than that of the traditional non-uniform 8QAM respectively,which verifies that the proposed scheme has obvious performance advantages.(2)The probabilistic shaping technique with distributed matcher is studied,and a novel QAM signal generation scheme based on probabilistic geometric hybrid shaping is proposed.In this scheme,according to the characteristics of geometric probabilistic mixed shaping technology,an optimizing scheme which can optimize constellation is designed.It can improve the structure performance of the constellation after probabilistic shaping.The signals are mapped to the geometric shaped constellation after probabilistic shaping of the distribution matching for transmission.The constellation of proposed scheme has a larger minimum Euclidean distance than that of the traditional scheme.The simulation results show that the proposed probabilistic geometry hybrid shaping 16QAM signal generation scheme has better BER performance than the traditional rectangular PS-16QAM scheme.The larger the degree of shaping,the greater the performance gain.In addition,the proposed scheme has a higher Generalized Mutual Information(GMI)value,which can reduce the gap between system capacity and Shannon limit.(3)Probabilistic shaping combined with orthogonal frequency division multiplexing technology is studied,and a compact subcarrier generation scheme based on constellation geometric probabilistic hybrid shaping is proposed.In this scheme,the OFDM technology is used to generate multiple subcarriers.Before sending signals,a rectangular filter is used to process the subbands,and a similar filter is used to process the signals received.The geometric probabilistic hybrid shaping technique is used to optimize signals.Simulation results show that when the signal entropy is 3.5252bits/symbol,the proposed F-OFDM 16QAM subcarrier generation scheme based on geometric probabilistic hybrid shaping has a 3.2dB BER performance gain compared with the conventional rectangular PS-16QAM multi-carrier generation scheme for OFDM,and a 5.3dB BER performance gain compared with the conventional rectangular uniform 16QAM multi-carrier generation scheme for OFDM.At the same time,the GMI value of the proposed scheme is higher than that of traditional scheme.The proposed scheme can make better performance of capacity in the transmission system.Because of its low out of band power leakage,it has obvious advantages in multi-subband transmission of multi-service scenes.