Research On Carrier Phase Recovery Algorithm Of Coherent Optical Communication System

With the rapid development of various emerging technologies such as distance education,intelligent transportation,live video broadcasting,and 5G e-commerce,the requirements for signal transmission are becoming more and more strict.As one of the mainstream communication methods,optical communication is also developing towards the direction of long-distance,largecapacity and high-quality.The traditional intensity modulation/direct detection system has simple structure and single modulation mode,which cannot meet the current requirements of signal transmission rate and transmission quality.The coherent optical communication system based on digital signal processing technology and high-order modulation format can effectively improve the signal quality and increase the transmission rate,and has the advantages of good bandwidth utilization,diversified modulation methods,large communication capacity and high receiver sensitivity.However,in the current coherent optical communication system,the spontaneous emission of the receiver laser causes the phase shift of the optical signal,which leads to the signal rotation and the error judgment,which seriously reduces the quality and performance of the system transmission.Therefore,it is very important to use carrier phase estimation and recovery technology to recover carrier phase in coherent optical communication system.This thesis firstly analyzes the phase noise theoretically,conducts an indepth study on the carrier phase recovery algorithm of coherent optical communication system,proposes the 8APSK aided carrier phase recovery algorithm,designs a parallel Kalman filter phase recovery algorithm scheme based on guided frequency assistance,and also proposes a two-stage Kalman filter phase recovery algorithm based on the joint compensation of phase noise as well as amplitude noise,and conducts a simulation analysis of the research The simulation analysis is performed.The details of this thesis are as follows:(1)The 8APSK pilot aided carrier phase recovery algorithm is proposed.This algorithm uses the 8APSK modulation format signal as the pilot signal of the pilot auxiliary algorithm,which has a good carrier phase recovery effect for the probabilistic shaping signal,and solves the GMI damage problem between the blind phase search(BPS)algorithm and the PS signal.The simulation results show that when the signal-to-noise ratio is selected to be 26 and 29dB under the 7%FEC threshold,the GMI transmitted by the algorithm increases by 0.8bit/symbol and 1.3bit/symbol compared to the BPS algorithm.Moreover,compared with the QPSK pilot assisted carrier phase recovery algorithm with an amplitude selection of 15,the maximum gain of OSNR is 0.4dB.The algorithm can avoid the cycle slip problem.Also,it has a lower complexity which the complexity is reduced by 98.76%.(2)A pilot aided parallel Kalman filter phase recovery algorithm is proposed.This algorithm inserts the pilot sequence into the block head of each Kalman filter estimation block,forming a phase estimation block sequence for parallel phase estimation,improving the algorithm’s estimation speed and achieving good carrier phase recovery effect.The simulation results show that in the PS-64QAM system,compared to BPS(N=64),the GMI of the PA-KF carrier phase recovery algorithm increases by approximately 1.18bit/symbol.When the error rate is 3.8×10-3,the pilot assisted parallel Kalman filter phase recovery algorithm has an OSNR improvement of 0.12dB compared to the BPS algorithm.In addition,the proposed PA-KF phase recovery algorithm has lower complexity,reducing its complexity by approximately 68.57%.(3)The two-stage Kalman filter(Two-Stage KF)phase recovery algorithm based on the joint compensation of phase noise and amplitude noise is proposed which improves the laser linewidth tolerance and receiver sensitivity of the carrier phase recovery algorithm,and can estimate and recover the two parts of phase noise and additive Gaussian white noise that affect each other,with better recovery performance at low signal-to-noise ratio.The simulation results show that in the 64QAM system,when BER is 3.8×10-3 standard and the laser linewidth is 1 MHz,the OSNR required by this algorithm is 25.8 dB,which is 0.61 dB and 0.21 dB higher than that of linear Kalman filter and BPS algorithm.At the same time,this algorithm avoids cycle slip phenomenon and has superior phase noise tracking ability.In addition,the computational complexity of the algorithm is 56.03%lower than that of the BPS for the linear Kalman filter carrier phase recovery algorithm.