Research On Phase Noise And IQ Mismatch Compensation Algorithm In Polarization Division Multiplexing Coherent Optical OFDM Systems

In this paper,the IQ imbalance and phase imbalance in PDM CO-OFDM system are studied,and the estimation and compensation algorithms are analyzed and designed from theory and simulation respectively.Firstly,this paper expounds the system model of PDM CO-OFDM and describe each module.And then the mathematical model of the existence of IQ imbalance and the existence of IQ imbalance under phase noise is deduced.Next,the principle and disadvantage of the existing compensation pilot structure and compensation algorithm are analyzed.On this basis,a new pilot structure is proposed to estimate and compensate the channel,IQ imbalance and phase noise.The simulation platform is established with MATLAB and Optisystem 7.0,then the accuracy and compensation performance of the theory are verified by simulation.The main work of this paper is as follows:(1)Two new training sequence structures are proposed to solve the imbalance of IQ of the transmitter,which can realize channel and IQ imbalance estimation.In references,the mathematical model of the IQ imbalance is presented,which uses the training sequence structure to estimate the imbalance factor and the channel together.But since the design of the training sequence structure belongs to the half-load structure,the estimation error of the subcarrier affects the compensation of the whole symbol,which reduces the system performance.In this paper,the new training sequence structures are presented.One of the new training sequence structures can achieve independent estimation of channel and IQ imbalance,and both of these structures can achieve better compensation,and reduce the computational complexity.(2)This paper presents an estimation and compensation algorithm for the IQ imbalance in the transmitter under the influence of phase noise.The current existing compensation algorithm does not consider the channel,IQ imbalance and phase noise simultaneously.In this paper,the OBE algorithm and the compensation method based on the DA algorithm for the phase noise are combined with the pilot structure proposed to realize the compensation of the PDM CO-OFDM system.And then based on mentioned above,the paper studies the influence of the phase noise estimation dimension on performance of system and overhead.The results of simulation show that the increase of dimensions will reduce the performance of the system(3)A new pilot structure is proposed to solve the IQ imbalance of transmitter under the influence of phase noise.This structure can realize the joint estimation of channel,IQ imbalance and phase noise.The existing phase noise algorithm is not applied to PDM CO-OFDM systems with IQ imbalance.The pilot structure proposed in this paper consists of two parts: block pilot and comb pilot,which are used to realize the channel imbalance factor estimation and phase noise estimation respectively.The simulation results show that the proposed structure can better compensate the system and achieve better performance.