| With the rapid development of the economy and society,people have more requirements on the data transmission rate,and the traditional electrical domain transmission method can no longer meet this fast-developing demand.As the backbone optical fiber communication system of the world communication network,it has developed rapidly.In order to adapt to the explosive growth of Internet services such as short video,augmented reality and virtual reality,various multiplexing technologies such as high-order modulation,pulse shaping,and polarization multiplexing have emerged.Although the use of higher-order modulation formats can improve the spectral efficiency of the system,the higher-order modulation format comes with the problem that the higher the optical signal-to-noise ratio(OSNR)requirements.In this case,multiplexing technology such as polarization multiplexing method is getting more and more attention.Therefore,it is very meaningful to study the subject about high-speed polarization coherent optical communication system.Polarization coherent optical communication systems can double the spectral efficiency of signals,but at the same time polarization-related impairments such as polarization state rotation(RSOP)and differential group delay(DGD)are introduced into polarized coherent optical communication systems.Under the polarization damage of RSOP and DGD,the signal will be damaged.At present,the commercial polarization demultiplexing method is mainly CMA/MMA algorithm.However,studies have shown that when the two effects of RSOP and PMD are combined,the CMA demultiplexing method will cause the receiver to lose lock.Therefore,in extreme scenarios,how to find a polarization demultiplexing algorithm that can be applied to the signal loss equalization requirements of high-speed optical fiber communication systems is extremely important.This paper mainly studies an adaptive Kalman filter for extreme polarization effects in optical fiber communication systems in extreme scenes.Among them,we mainly focus on the polarization-related damage in extreme scenarios.This paper introduces traditional equalization algorithms such as CMA,Extended Kalman filter algorithm,and improves the adaptive Kalman filter on this basis.The main work of this paper is as follows:(1)Based on the MATLAB software simulation of the coherent optical communication system,the influence of polarization damage on the coherent optical communication system is analyzed.(2)Analyzed the advantages and disadvantages of the equalization algorithm for PMD and RSOP in extreme scenarios,and analyzed the influence of process noise covariance matrix(Q)and measurement noise covariance matrix(R)on the performance of Kalman filter.By using a half analytic and half empirical way,we prove that,for the coefficients q and r of the covariance matrices Q and R,there is a narrow zonary region a lower boundary q<r upper boundary in which the chosen q and r are acceptable to q enable the EKF convergence and stable.At the same time,an adaptive Kalman filter equalization algorithm based on covariance matching is proposed,which can maintain good performance under inappropriate initial Q and R values.(3)We verified the performance of AEKF in different modulation formats,polarization damage and noise figure in 28GB fiber-optic communication system through simulation and experiment,and used EKF as a comparison algorithm.The numerical simulations and experiments under some severe environments of large PMD and fast RSOP,the tolerance range of AEKF for q,r is eight times larger than that of traditional EKF.In addition,the proposed AEKF scheme requires less than 1 dB OSNR-penalty when the improper initial set of q and r which locate outside the narrow zonary region optimized for the case of EKF.It is noteworthy that the BER performance of the proposed AEKF has a good performance under the four scenarios from slight to severe PMD and RSOP impairment combinations,provided that the weaker constraint r>q is satisfied. |
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