Study On Performance Optimization Of NFDM System With Full Spectrum Modulation

The nonlinear damage caused by the nonlinear effect of optical fiber has become the most important factor limiting the capacity upgrade of optical fiber communication system.Nonlinear Frequency Division Multiplexing(NFDM)optical fiber communication system is regarded as an inherent property of the nonlinear fiber communication system,and the nonlinear fiber transmission scheme is designed according to the characteristics of the nonlinear fiber channel,so as to avoid the adverse effects of nonlinear fiber.The problem of nonlinear limit is solved fundamentally.Due to the low Spectral Efficiency(SE)problem of discrete spectral modulated NFDM system,continuous spectral modulated NFDM system also faced the problem of system performance degradation due to algorithm error at higher power.The combination of discrete spectrum and continuous spectrum modulation can effectively improve the spectral efficiency and data rate of the system,that is,all degrees of freedom of the nonlinear spectrum are utilized.However,in the NFDM system with full spectrum modulation,the discrete spectrum and continuous spectrum influence and interfere with each other,and the discrete eigenvalues affect the performance of the discrete spectrum and continuous spectrum at the same time.Therefore,the key to ensure the high spectral efficiency and excellent performance of full-spectrum modulated NFDM system is to determine the selection principle of discrete eigenvalues and to optimize its design.In this paper,the full-spectrum modulated NFDM system with the combined modulation of discrete spectrum and continuous spectrum is studied.In order to design a system with high spectral efficiency and excellent performance,the discrete eigenvalues of the system are optimized and analyzed under the condition that the data rate of the continuous spectrum is already high.In this paper,the influence of phase noise on the system is also analyzed,and phase noise removal methods suitable for discrete spectrum and continuous spectrum are designed.The linear minimum mean square estimate(LMMSE)equalization method is used to further improve the performance of the system.The main research work is as follows:1.The selection principle of eigenvalues in NFDM system with full spectrum modulation is determined,and multiple perspectives are analyzed from the modulation format of discrete spectrum,the real and imaginary parts of eigenvalues,the number of eigenvalues and real part spacing,etc.,to optimize the design of discrete eigenvalues.On the basis of ensuring that the continuous spectrum performance and discrete spectrum performance meet the requirements of the communication system,the full-spectrum modulated NFDM system can obtain higher spectral efficiency and data rate.For the system parameters in this paper,11 eigenvaluesλk=kπ+lj,k=｛1,2,...11} are selected.When 11 eigenvalues are added,SE increases by 6%.2.In the full-spectrum modulated NFDM system in this paper,a single polarization full-spectrum modulated NFDM system with data rate up to 113Gb/s and transmission distance of 1120 km is realized by combining multiple eigenvalues,multiple subcarriers and high-order modulation format.Considering that the actual communication system will be affected by phase noise,this paper studies the effect of phase noise on the system,and designs appropriate phase noise removal methods for continuous spectrum and discrete spectrum respectively,namely Blind Phase Search(BPS)and Phase Noise Removal(PNR)methods.In order to further improve the system performance,the correlation between the amplitude and phase perturbations at the receiver of discrete spectrum and the real and imaginary part perturbations of eigenvalue is also analyzed.Based on this correlation,the equalization method of LMMSE is used to make the Q-factor of the corresponding symbol of each eigenvalue of the discrete spectrum above the HD-FEC threshold.