Research On Linear Impairments Equalization Based On Kalman Filter In High-Speed Optical Fiber Communication Systems

The rapid development of services such as the Internet,cloud computing and virtual reality has led to a sharp increase in the demand for data traffic.The optical fiber communication system with large capacity and high transmission rate has become the mainstream of the current development.In order to improve the channel capacity and transmission rate,the high-order modulation format,as well as the probabilistic shaping(PS)technology proposed in recent years,polarization division multiplexing(PDM)technology,coherent detection technology and powerful digital signal processing(DSP)technology are widely used in optical fiber communication systems.It greatly promotes the development of the high speed coherent optical fiber communication systems.When optical signals are propagated along optical fiber links,they suffer from various impairments,including chromatic dispersion(CD),polarization mode dispersion(PMD),rotation of State of polarization(RSOP),and polarization dependent loss(PDL),carrier frequency offset(CFO)and carrier phase noise(CPN),etc.,which lead to signal distortion and system performance degradation.The impairments mentioned above can be equalized in the DSP module of the receiver.However,with the increase of transmission rate and the increase of modulation format of coherent optical communication system,the interation of various impairments have enhanced.The architecture of each impairment equalization module in the receiver is not unified,and the equalization effect cannot be fully exerted,especially in extreme polarization scenarios.In a thunderstorm day(the overhead optical cable is struck by lightning or the train passes by causing huge vibrations),the performance of the polarization demultiplexing(PolDemux)algorithm drops sharply or even fails directly,causing the communication interruption.In addition,in order to further improve the transmission performance of the optical fiber communication system,PS technology is introduced into the optical fiber communication system to increase the channel capacity and make it close to the Shannon limit.Therefore,the research on the DSP algorithm with excellent performance of the integrated architecture,the PolDemux algorithm with high stability and low complexity,and the impairment equalization algorithm suitable for PS signal is of great significance.This thesis focuses on the topic of linear impairments equalization in the high speed PDM coherent optical fiber communication systems,and conducts in-depth research and analysis on the linear impairments equalization technology of high-order modulation format signals and PS modulation format signals.Explore an integrated joint equalization scheme for linear impairments based on the Kalman filter architecture to provide a high-performance algorithm foundation for ultra-100G systems.And in order to improve the robustness of the PolDemux algorithm and reduce the complexity of the algorithm,a PolDemux algorithm based on the pilot-aided frequency domain Kalman filter is proposed.In addition,a carrier phase noise equalization algorithm suitable for PS modulation format signals is studied.The main research work is as follows:(1)Research on linear impairments equalization scheme based on a unified architecture Kalman filterA linear impairments equalization scheme using a unified architecture algorithm in terms of Kalman Filter was proposed.The Kalman integration algorithm includes two stages.In the first stage,the time-frequency domain sliding window Kalman filter architecture is used to compensate residual chromatic dispersion(rCD)and PMD in the frequency domain,and RSOP in the time domain.The second stage uses the time domain Kalman filter architecture to compensate for CFO and CPN at the same time.Compared with the classic CMA-IMP-BPS the CFO and CPN are small,the two schemes show basically the same performance(the bit error rate is in the same order of magnitude).When the normalized linewidth is greater than 4×10-4(for the 28GBaud system,the corresponding linewidth is 11.2 MHz),the Kalman filter scheme shows better carrier recovery performance.(2)Research on PolDemux scheme based on pilot-aided frequency domain Kalman filterA PolDemux scheme based on pilot-aided frequency domain Kalman filter was proposed.Use the known pilot symbol information to construct the measurement of the Kalman filter algorithm,and perform iterative update to obtain the state vector.The proposed pilot-aided frequency domain Kalman filter algorithm shows good performance for the equalization of ultra-fast RSOP and large PMD,and reduces the OSNR penalty.In addition,the proposed pilot-aided Kalman scheme has lower computational complexity and is more robust.(3)Research on CPN equalization scheme of probabilistic shaping QAM modulation formatA Kalman filter based CPN equalization scheme suitable for probabilistic QAM modulation format was proposed.For PS 16-QAM and PS 64-QAM signals,at the optimum shaping factor,the performance of the proposed Kalman filter scheme does not decrease,and at other shaping factors,the Kalman scheme shows the same performance as BPS.The proposed Kalman filter scheme overcomes the limitations of the BPS in the probabilistic shaping system and has a good performance in the carrier phase noise equalization of PS QAM signal.