Research On Signal Damage Equalization Algorithm In Multi-Core And Few-Mode Optical Transmission System

Since the 20th century,with the widespread popularity of the Internet of Things,the Internet,high-definition video,cloud storage,and computing,people have put forward higher requirements for network bandwidth.However,the transmission capacity of traditional single-core single-mode optical fiber communication systems has approached Shannon’s limit.The space-division multiplexing optical fiber communication system realizes the parallel transmission of the channel by using the expansion of the fiber core and the mode,and then realizes the expansion of dozens of times of capacity,which has become a key technology to break through the capacity limitation.However,due to damages such as mode and inter-core crosstalk in the optical space division multiplexing transmission system,these damages will degrade the channel transmission performance,increase the difficulty of digital signal processing at the receiving end,and affect its equalization effect.Therefore,it is of great significance to study the signal damage equalization algorithm of multi-core few-mode optical fiber communication system in this thesis to improve the transmission performance of the system.First of all,this thesis theoretically analyzes the channel impairment in the multi-core few-mode optical communication system,and establishes a space-division multiplexing channel transmission model based on sevencore six-mode optical fiber.Secondly,aiming at the insufficient performance of the equalization algorithm,the MIMO equalization algorithm at the receiving end is studied,and the least mean square algorithm in the frequency domain with variable step size is proposed to optimize the equalization effect.Finally,aiming at the problem of high complexity in the MIMO equalization process,a frequency domain equalization method of frequency band selection is proposed to reduce the complexity.This research is mainly composed of the following three parts:(1)The mechanism of channel damage has been studied,such as mode coupling,inter-core crosstalk,inter-mode dispersion,differential mode delay,etc.,and the channel model of the seven-core six-mode optical fiber communication system has been established by combining the coupled mode theory with the matrix transmission theory.A transmission system with a transmission rate of 20GBaud,a transmission distance of 100km,and a transmission signal modulation format of 16QAM is established and verified by simulation.The research results show that when the signal-to-noise ratio is 22dB,the bit error rate reaches 3.8×10-3,which meets the hard-decision forward error correction threshold.(2)A variable step size frequency domain minimum mean square MIMO equalization algorithm is proposed,which transforms the signal into the frequency domain,and compensates the average power difference between different blocks in the frequency domain by changing the iteration step size.The results show that the algorithm can improve the convergence speed and reduce the convergence error.Compared with the traditional time-domain least mean square algorithm,the rate of convergence becomes faster Compared with the traditional frequency-domain least mean square algorithm,it has improved by nearly 2dB.(3)A frequency domain equalization algorithm based on frequency band selection is proposed,which uses the prior knowledge of the signal bandwidth to selectively perform operations on only the in-band components of the signal,reducing redundant calculations for invalid bandwidths,and reducing the number of complex multiplications.Reduce the computational complexity and verify it in the seven-core six-mode optical transmission simulation platform.The results show that in the seven-core six-mode optical communication system,the equalization method can reduce 45%of the equilibrium complexity.