Research On Cyclic Feedback Synchronization Algorithm Based On Coherent Optical Communication System

In recent years,the development of optical communications has enjoyed a strong momentum of growing concern.As a fourth-generation optical fiber communication system,a new generation of communication technology of coherent optical communication system can realize large-capacity and long-distance communication and is always a research hotspot in the field of communication.At present,the traditional commercial optical communication system is usually a direct detection(DD)system.It uses intensity modulation(IM)technology and is longer than the amplitude information detection.However,its output is generally related to the intensity of the input signal.There is no way to compensate for linear distortion System transfer rate.However,the coherent detection technology can compensate the linear distortion in the system through linear equalization and polarization multiplexing,and is more suitable for high-order modulation format,which is more conducive to large-capacity communication.This is the basis of this paper.In coherent optical communication systems,synchronization techniques and channel equalization are one of the important aspects of the system.Signal synchronization is a prerequisite for signal transmission,the effect of synchronization will directly or indirectly affect the receiver's error rate and error performance.At present,the performance of clock recovery is often affected by intersymbol interference.The existing synchronization algorithms are only applicable to cases where the phases of adjacent symbols are reversed.Therefore,it is essential for the research of equalization in timing synchronization loops,having high research value and practical significance.Based on the research of coherent optical communication system,this dissertation focuses on the timing feedback synchronization algorithm and the clock recovery loop of the joint channel equalization and digital coherent optical receiver clock recovery module.The composition,system structure and key technologies of coherent optical communication system are introduced in detail,including clock synchronization,channel equalization and carrier synchronization.Emphasis is put on the research of timing recovery.The main research contents and innovations of this thesis are as follows:(1)An optimized clock recovery algorithm for coherent optical communication system is proposed.According to the characteristics of the clock recovery module,an optimized clock recovery algorithm for inphase and inverses of adjacent symbols is proposed based on the Gardner algorithm.The simulation analysis solves the limitation problem of the traditional algorithm and lays the foundation for the subsequent improvement of the loop performance.Especially when the roll-off factor tends to 0,the proposed algorithm shows better clock performance.(2)An adaptive interpolation feedback timing recovery loop is proposed.The feedback timing recovery loop under the clock recovery module was simulated and analyzed,and the interpolatior,timing error detector,loop filter,digital control unit(NC oscillator and fractional interval counter)in the loop were designed And based on the interpolation filter and joint adaptive equalization,an adaptive interpolation technique is proposed for coherent optical communication system.The research results show that after optimization,the intersymbol interference caused by spectrum mirroring is eliminated and the bit error rate is greatly reduced.And loop optimization,more suitable for low signal to noise ratio.(3)An adaptive interpolation signal synchronization system with joint channel equalization is proposed.Simulation analysis of the clock recovery outside the dispersion and dispersion compensation technology,carrier recovery and wavelength division multiplexing technology,combined with the optimal loop proposed in(2),the combination of loop and loop out of balance,after the establishment of research and analysis A set of more perfect timing synchronization system.