Research On Phase Compensation And Channel Model Of Modulating Retroreflector Free-space Optical Communication

The modulating retro-reflector(MRR)free-space optical(FSO)system is an asymmetric FSO system based on retroreflectors,which can not only avoid the problem of tight spectrum resources,low transmission rate and insufficient security of the traditional radio frequency communication system,but also overcome the disadvantages of large power consumption and large size of the traditional FSO system terminal.However,the double-pass propagation through the atmospheric turbulence of the MRR FSO system leads to much more optical distortions such as beam drift and light intensity flicker,thereby reducing the stability and reliability of the system.Therefore,in order to further improve the performance of the MRR FSO system,the main research of this thesis focuses on the phase compensation of the micro corner-cube reflector array(MCCRA)for the double-pass propagation through the atmospheric turbulence and the corresponding channel characteristics.The details are as follows:Firstly,this thesis explains the research background and significance of MRR FSO system,as well as the current research status of MRR FSO phase compensation technology and channel model.For the double-pass atmospheric channel of the MRR FSO system,the principles of atmospheric turbulence,the Kolmogorov turbulence theory and the Rytov approximation theory are briefly introduced.Then it specifically introduces the MRR FSO system structure based on MCCRA,and describes the physical model and reflection characteristics of MCCRA in detail.In order to better study the subject content,numerical calculation method is adopted to simulate the MRR FSO system,and the propagation process of the laser beam in the atmospheric turbulence is simulated by the splitstep beam propagation method.Secondly,for the MRR FSO system based on MCCRA,theoretical derivation proves that MCCRA can effectively compensate the disturbance phase caused by double-pass atmospheric turbulence,and the performance indicators of the MRR FSO system based on MCCRA and CCR are compared through the numerical simulation.The MRR FSO system based on MCCRA has a smaller scintillation index(SI)and a higher Strehl ratio(SR),and larger MCCRA reflective aperture and smaller unit size can improve the phase compensation effect of double-pass atmospheric turbulence.MCCRA can also play a fairly effective compensation role in the case of oblique incidence of the beam,processing errors,and increased transmission distance.In addition,relevant experimental tests were carried out indoors and outdoors,and the results obtained verified the correctness and feasibility of the theoretical and simulation conclusions.Finally,this thesis analyzes the channel model of the MRR FSO system based on MCCRA,and numerically fits the simulation data of the double-pass channel and the forward and backward separated channels.Compared with the Gamma-Gamma distribution model,the Lognormal distribution can better describe the channel model under weak to strong turbulence conditions,which also confirms the effective compensation effect of MCCRA on atmospheric turbulence.On the other hand,as the reflection aperture of MCCRA increases,the enhanced backscatter(EBS)effect becomes more obvious,and the EBS enhancement factor increases with the increase of turbulence intensity.It can be seen that MCCRA can still achieve effective phase compensation even under strong turbulence conditions.