OSNR And Nonlinear Distortions Estimation Based On Link Analysis And Digital Signal Processing

With the continuous development of optical fiber communication technology and optoelectronic device technology,the capacity of long-haul large-capacity optical fiber communication systems is mainly limited by a various of impairments in the fiber links,such as the noise introduced by optical amplifiers,fiber attenuation,dispersion,and nonlinear effects,etc.In order to diagnose signal degradation caused by link impairments and recover the information carried by the signals,optical performance monitoring and impairments estimation algorithms are indispensable.With the link information,impairments will be estimated and compensated,and the power resources can be better allocated.Traditional optical performance monitoring methods often have high computational complexity and low flexibility,which need to be simplified for real-time transmission systems.The overhead of nonlinear distortion also needs to be further reduced.Based on the link parameter information and digital signal processing,this paper proposes and demonstrates a low-complexity optical signal noise ratio(OSNR)monitoring method and a cost-effective nonlinear distortion estimation algorithm for the fiber transmission system.The main research contents and innovative achievements are as follows:(1)We analyze the principle and structure of the erbium doped fiber amplifier(EDFA)in the fiber links and investigate the EDFA's noise model,furthermore,we study its influences on the OSNR.We simplify the derivation of OSNR in cascaded EDFAs fiber link by extracting link information from the network management system.The estimation range and accuracy of the proposed methods are verified through the numerical simulation and experiments with different modulation formats,transmission rates and EDFA amplification modes.Compared with the conventional methods,the proposed OSNR monitoring method has less computational complexity and is more flexible as it can be applied between any two EDFA nodes.This method is proven to be compatible to the current real-time commercial transmission system.(2)We propose and demonstrate a nonlinear distortions estimation method.Since the OSNR can be calculated by considering either the link parameters or the correlation operations of the training symbols.We can estimate the nonlinear distortions from the different nonlinearity model of these two methods.We define the ratio of nonlinear distortion power to the signal power as nonlinear penalty.This nonlinear penalty is measured under different simulation conditions,using a coherent optical orthogonal frequency division multiplexing(OFDM)system,and the results are in accordance with the expectations.As the estimation method,based on link parameters,has low computational complexity,and the training symbol used for the OSNR estimation is inherently indispensable for frame synchronization,this nonlinear distortion estimation method introduces a few complexities and no extra overhead.