Research On Probability Amplitude Shaping Technology In QAM Modulation Format

With the advent of the era of the Internet of Everything,the communication transmission rate and the data flow in the network continue to increase.Optical fiber communication network is an indispensable bearing platform in the process of information transmission and exchange.Continuously improving its system capacity is the eternal goal of optical communication development.The high-order modulation format optical signal makes each symbol carry more bit information,thereby improving the spectral efficiency and transmission capacity,and is the main modulation method used in the current high-speed and large-capacity coherent optical communication system.Since the probability of occurrence of each symbol in the standard M-QAM modulation format optical signal is the same,the system capacity is difficult to approach the Shannon limit.In the additive white Gaussian noise channel,the gap between the transmission capacity of the standard M-QAM signal and the Shannon capacity is about 1.53dB.As a typical high-order modulation format optimization technology,constellation probability shaping technology improves the amount of mutual information and generalized mutual information by optimizing the probability distribution of each constellation point of the signal.It can improve the transmission capacity of the same order M-QAM signal under the condition of limited average transmission power,and further narrow the gap with Shannon limit capacity.It has important research significance and application value.Focusing on the constellation probability shaping technology,this paper deeply studies the probability amplitude shaping system and distribution matcher.The main work and research contents of this paper are as follows:1.The theory and implementation of the probabilistic amplitude shaping system are studied.Based on the constant composition distribution matcher and LDPC coding,a probability amplitude shaping system is built,which realizes the probability shaping of 16QAM,64QAM and 256QAM signals.The generalized mutual information of shaped signals under different optical signal-to-noise ratios is analyzed,the correctness of the simulation system is verified by the maximum shaping gain.PS-64QAM and PS-256QAM signals with different spectral efficiencies are designed,their back-to-back and optical fiber transmission bit error rates under different optical signal-to-noise ratios are simulated,and the improvement of probability shaping signal on system bit error performance and transmission distance is analyzed.Four kinds of PS-16QAM and PS-64QAM signals with the same net bit rate and different shaping degree and LDPC coding rate are designed respectively.Their generalized mutual information and bit error rate before and after LDPC decoding under different optical signal-to-noise ratio are simulated.The advantages of probability shaping signal compared with uniformly distributed signal under the condition of the same net bit rate are analyzed.2.The implementation principle and rate loss of constant composition distribution matcher are studied.The realization process,arithmetic coding principle and rate loss problem of the constant composition distribution matcher are analyzed.Aiming at the problem of rate loss,using the idea of pairwise optimization,a parallel distributed matcher structure based on CCDM is proposed,the rate loss of the structure under different short block lengths is calculated,and the feasibility of the scheme and its advantages compared with CCDM are explained from both theoretical calculation and system simulation.