Research On Crosstalk Characteristics Of Signal Transmission In Free Space Optical Network

With the continuous development of free-space optical communication technology,it is a general trend to develop from a point-to-point laser communication system to a free-space optical network system.Due to its advantages of high speed,high confidentiality,and high capacity,free-space optical communication has broad application prospects in the construction of integrated world and ground networks.However,when the optical signal is transmitted in the network,signal crosstalk occurs due to internal and external factors of the optical network node,which causes the quality of the system to decrease.Therefore,in order to improve communication quality,analyzing the causes of crosstalk and effectively reducing the impact of crosstalk on communication systems are important directions for the study of free space optical networks.This thesis studies the problem of crosstalk transmission in free space optical networks.The main contents are as follows:1)The characteristics of free space optical networks are analyzed.Taking the NELS constellation as an example,first analyze the network structure,analyze the networking mode of the network structure and the composition of nodes;then analyze the causes of crosstalk,classification and the impact of crosstalk on the wavelength in the optical network;finally,make a preliminary analysis of linear crosstalk Mathematical model analysis lays a theoretical foundation for the establishment of a linear crosstalk mathematical model in the future.2)A mathematical statistical model of crosstalk signals in nodes in the optical network is established.Firstly,the crosstalk signal is analyzed,and the statistical analysis model based on Gaussian distribution and the mathematical statistical analysis model based on zero-order Bessel function are established respectively.The performance of the two mathematical statistical analysis models under different interference sources is analyzed.3)According to the system performance,a variable step size CMA-LMS equalization algorithm is proposed.First,it briefly introduces the least mean square error algorithm(LMS)and constant modulus algorithm(CMA)in adaptive equalization;second,this thesis proposes a variable step size CMA-LMS adaptive equalization algorithm to equalize optical signals and crosstalk signals,and Theoretical derivation of the algorithm.The experimental results show that the proposed algorithm can effectively improve the system performance.4)Analyze the crosstalk signal between nodes in the optical network and propose an improved genetic algorithm.When the network load is 140 Erlang,the blocking rate of the improved genetic algorithm is 33% lower than that of the unimproved algorithm.At the same time,when the network load is constant,as the number of wavelengths increases,the number of wavelengths affected by crosstalk will decrease;experiment The results show that the improved genetic algorithm can effectively select the wavelength combination that is least affected by crosstalk and improve the network quality.The research results of this thesis can provide a theoretical reference for the design and feasibility of the space all-optical network in the future.