Research On Coding And Modulation Technology In High-speed Optical Communication Systems

For optical fiber communication system,with the rise of artificial intelligence,cloud computing and other technologies,people have higher and higher requirements on communication capacity,bandwidth and data transmission rate,and current technologies cannot meet the growing demand.The existing traditional modulation format is difficult to meet the demand,so the constellation shaping technique need further research.The application of constellation shaping technique in high-speed optical communication system can achieve better performance than the traditional modulation scheme,making the system capacity closer to Shannon limit.Compared with the traditional communication system,performance of communication system using Trellis Code Modulation(TCM)scheme has greatly improved.Orthogonal Frequency Division Multiplexing(OFDM)technology is widely used in 4G/LTE systems due to its advantages of anti-multipath interference and low complexity.However,it is not the best choice in 5G communication system because of its high peak-average power,high sensitivity to synchronization errors and high shortcomings of Out-of-Band(OOB)leakage.As an alternative to OFDM,Generalized Frequency Division Multiplexing(GFDM)solves the inherent defects of OFDM,and widely used in 5G networks.Based on the study of coding and modulation theory in high-speed optical communication systems,this paper focuses on the probabilistic shaping scheme based on Fano coding,the multi-dimensional probabilistic shaping scheme based on Fano coding,the multi-dimensional probabilistic shaping scheme based on Trellis Coded Modulation and Generalized Frequency Division Multiplexing(GFDM)scheme with geometric shaping and LDPC.Aiming to meet the requirements of greater system capacity and higher transmission rate.The main research work and innovations of the paper are as follows:1.Probabilistic shaping scheme based on Fano codingOn the basis of studying the existing probabilistic shaping scheme and Fano coding,a probabilistic shaping scheme based on Fano coding is proposed.Bit Error Rate(BER)performance of the proposed probabilistic shaping signal in the AWGN channel is studied,and compares it with the traditional M-PAM and M-QAM under the condition of equal spectral efficiency.The research results show that,compared with the 8PAM and 8QAM schemes,the proposed PS-9QAM scheme based on Fano code achieves gains of 2.3dB and 1.2dB when the BER is 10-5.2.Three-dimensional probabilistic shaping scheme based on Fano codingBased on the study of traditional probabilistic shaping technique,a three-dimensional probabilistic shaping scheme based on Fano coding is proposed.This scheme combines probabilistic shaping with multi-dimensional modulation scheme to achieve dimensional expansion,making the minimum Euclidean distance between constellation points larger,and the same power can transmit more constellation points,resulting in better performance and greater Transmission efficiency.Under the condition that the transmission power and the spectral efficiency are equal,the simulation studies and analyzes the bit error performance of the two-dimensional probabilistic shaping signals and the three-dimensional probabilistic shaping signals.The research results show that when BER=10-5,the proposed scheme can obtain 2.6dB gain compared with the two-dimensional probabilistic shaping scheme based on Fano coding.Compared with the three-dimensional 8QAM modulation scheme,a gain of 3.7dB can be obtained.3.Three-dimensional probabilistic shaping scheme based on Trellis Coded ModulationBased on the study of two-dimensional probabilistic shaping and Trellis Coded Modulation,a three-dimensional probabilistic shaping scheme based on TCM is proposed.The scheme uses Fano coding to obtain the signals to be transmitted,expands the two-dimensional constellation plane into the three-dimensional constellation space and combines with the TCM.The simulation studies the bit error rate performance of the three-dimensional probabilistic shaping signal based on TCM,and compares it with the 8QAM based on TCM in two-dimensional space,the 9QAM based on TCM in two-dimensional space and the 8QAM with TCM.The research results show that,compared with the two-dimensional 9QAM-TCM scheme,the three-dimensional 9QAM-TCM scheme improves the signal-to-noise ratio by 1.2dB when the BER is 10-4;the three-dimensional 8QAM-TCM scheme has a higher BER than the traditional one when the BER is 10-4.The two-dimensional 8QAM-TCM coding gain is reduced by 0.8dB;the two-dimensional 9QAM-TCM system has a coding gain of 0.9dB compared to the two-dimensional 8QAM-TCM.4.Generalized Frequency Division Multiplexing(GFDM)scheme based on Geometric Shaping(GS)and LDPCBased on the study of geometric shaping and low-density parity-check codes,a GFDM scheme based on geometric shaping and LDPC is proposed.This scheme simulates and studies the BER performance of the GFDM system based on GS-16QAM-LDPC,applies the constellation shaping technique to the GFDM system,and combines it with LDPC to improve the GFDM due to the non-orthogonality between subcarriers.The problem of inter-subcarrier interference(ISI)caused by inter-orthogonality is serious.The proposed scheme studies GFDM and OFDM systems,and geometrically shaped 16QAM and LDPC are adopted to improve system performance.From simulation results,the spectrum performance of OFDM and GFDM is compared and analyzed.From the PSD of them,it can be clearly seen that the sidelobes of GFDM signals decay quickly.In addition,compared with the GFDM scheme and OFDM scheme based on conventional 16QAM,the BER performance is compared and analyzed under different signal-to-noise ratios(SNR).Simulation results show that when the BER is 10-5,compared with the GFDM scheme based on the conventional 16QAM,the GFDM scheme based on the LDPC-GS-16QAM achieves a coding gain of 15.3dB.It can be concluded that the geometric shaping scheme and LDPC can better suppress the inter-subcarrier interference of the GFDM signal.