Research On Orbital Angular Momentum Shift Keying Communication Systems Based On Convolutional Neural Network

Orbital angular momentum shift keying(OAM-SK)is an optical communication method based on vortex beams that carry orbital angular momentum.it uses one-to-one correspondence between different OAM modes of vortex beams and digital signals to modulate information.Convolutional neural network(CNN)is very suitable for processing image data,and CNN has high recognition accuracy for images.Therefore,OAM-SK based on CNN is a subject of great research value.In this dissertation,the background,significance,and status of this topic are first introduced.Then the basic theory of vortex beam and CNN is introduced,a detection method of vortex beam using CNN is designed,and based on this detection method,a coherent demodulation OAM-SK system based on CNN is proposed.Finally,a comprehensive analysis is made on the OAM-SK system based on CNN.The main research contents and contributions of this dissertation are as follows.(1)A new method of detecting vortex beams is proposed.Use a camera to record the intensity map of the vortex beam or the interference pattern obtained by mixing the vortex beam with another beam,and then use a CNN-based image identifier to detect the topological charge of the vortex beam.The theoretical analysis and numerical simulation were used to analyze this detection method.(2)A coherently demodulated OAM-SK system using a CNN-based image identifier as demodulator is investigated.The OAM-SK system is analyzed in detail in terms of demodulation accuracy,system signal-to-noise ratio and image contrast.And compared with incoherently demodulated OAM-SK system using a CNN-based image identifier as demodulator,it is concluded that under the same conditions,coherently demodulated OAM-SK system has higher demodulation accuracy and system signalto-noise ratio,and is superior to the incoherently demodulated OAM-SK system.(3)The OAM-SK systems based on CNN with different OAM modes at the transmitter side and demodulation methods at the receiver side are studied.The demodulation accuracy of each system is compared,and the analyses are performed between incoherently and coherently demodulated systems,among incoherently demodulated systems,and among coherently demodulated systems.