Carrier Phase Recovery Algorithms In Probabilistic Shaping Coherent Optical Communication System

In recent years,with the development of technologies such as the Internet of Things,big data cloud computing,and virtual reality,people have an increasing demand for network traffic,which puts forward higher requirements for the transmission rate and capacity of coherent optical communication systems.In order to improve the capacity of the communication system,constellation shaping is often used to approach the Shannon limit.Constellation shaping can be divided into probabilistic constellation shaping and geometric constellation shaping,both of which preprocess the signal at the transmitter side.Since probabilistic constellation shaping only changes the probability of the constellation points and does not change their positions,there is no need to make major changes to the system algorithm and can be combined with FEC technology to achieve flexible and adjustable rate.Therefore,it is considered to be one of the key technologies for super high-speed,large-capacity coherent optical communication systems in the future.On the other hand,coherent optical communication is affected by phase noise during transmission and the constellation points are rotated,carrier phase recovery algorithm is required at the receiver side to compensate the phase rotation.Based on the probabilistically-shaped coherent optical communication system,this paper studies the carrier phase recovery algorithm.By changing the probability distribution of the constellation points,the performance can be improved.The main research contents and innovations of this thesis are as follows:The performance of different carrier phase recovery algorithms under the Maxwell-Boltzmann(MB)distribution is compared.It is found that BPS,PCPE,and PCPE+BPS algorithms are not compatible with this distribution.Especially for the PCPE algorithm,the algorithm does not work when the shaping intensity is large.In contrast,the KL and CPANE algorithms can accurately estimate the phase noise under this distribution and obtain a higher GMI than the uniform distribution.Based on the above conclusions,we propose to use the Quasi Maxwell-Boltzmann(QMB)distribution instead of the traditional MB distribution as the probability distribution of the constellation points in the probabilistically-shaped optical communication system.We give the corresponding probabilistically-shaped signal generation scheme.The performance of the phase recovery algorithm under the two distributions is compared under the same shaping parameters,it is found that the proposed distribution can significantly improve the performance of the BPS,PCPE,and PCPE+BPS algorithms.For KL and CPANE algorithms,performance improvements can also be achieved when the shaping parameters are small.In addition,the performance of the phase recovery algorithms under different optical signal-to-noise ratios and the same information entropy is compared.The proposed distribution can achieve higher performance under low OSNRs.For 256 QAM,when the phase recovery algorithm is BPS,the maximum performance improvement is close to 2bits/symbol.Therefore,the QMB distribution has advantages over the traditional MB distribution in probabilistically-shaped coherent optical communication systems.