Research Of Multi-OAM Optical Communication System On Atmospheric Trubulence Channels

With the acceleration of social informationization process,people have put forward higher requirements on the transmission capacity and reliability of the communication system.Compared with the existing optical communication technologies,the dimension resources such as spectrum,amplitude and phase of light have been obtained of the full research and development,the capacity of the existing optical communication system is close to Shannon's limit.With the discovery of Orbital Angular Momentum(OAM),it provides a completely new dimension and is compatible with the original polarization dimension.Many scholars think this is an opportunity to break the limit of traditional optical communications.Therefore,OAM and Multiple Input Multiple Output(MIMO)communication technology have attracted the attention of many scholars at home and abroad for the transmission of the air channel in free space.It is noteworthy that the effective scheme is to combine OAM with the two key technologies of multiplexing and diversity in MIMO and to consider simultaneously the turbulence effects in the atmosphere and how the OAM spiral phase is distorted.In this dissertation,we study on OAM Free Space Optical Communication(FSO),and focus on the combination of OAM with multiplexing and diversity in MIMO,as well as the study of compensated OAM over atmospheric turbulence channel equalization algorithm,OAM-based MIMO communication system is set up on the MATLAB simulation platform,and the results are analyzed.The main work and results are divided into the following sections.1.The characteristics of atmospheric channel are analyzed,the essence of turbulence is introduced,the effect of turbulence effect on the principle of vortex beam and the phase distortion caused by vortex beam are introduced.Based on the modified von Karman turbulence spectrum model and the Monte Carlo phase-angle method,a simulation model of atmospheric turbulence channel is established by using MATLAB software,which lays the foundation for the following work.2.OAM multiplexing and polarization multiplexing are studied theoretically,and a scheme of OAM polarization multiplexing system is designed.By means of numerical simulation,the communication performance of OAM based polarization multiplexing system is analyzed by bit error rate and channel capacity.3.A theoretical study of MIMO equalization algorithm is proposed,and a variable step size constant modulus algorithm is proposed for OAM-based MIMO communication system.The algorithm adaptively adjusts the iteration step size through root-mean-square error,so as to dynamically compensate channel crosstalk.The simulation results show that the variable-step constant modulus algorithm can effectively compensate the channel crosstalk and has faster convergence rate and less convergence error than the original constant modulus algorithm.