The Research On Improvement Of Photoelectric Reception By Underwater Spatial Diversity

At present,the exploration of underwater turbulent channel has become a research hotspot in recent years.There are many resources in deep water,such as natural gas,combustible ice and mineral resources,which require research and improvement of underwater detection technology.The research of underwater channel is the premise of light detection and communication.There are basically four kinds of underwater communication:underwater sound,radio frequency,fiber optic cable and wireless light.At present,underwater acoustic communication and optical cable communication are widely used.The former has poor collimation and confidentiality,while the latter has a long transmission distance,but high maintenance and relay costs.However,the transmission rate of RF communication is relatively low,so a communication device with small volume,high speed and good collimation is needed.Therefore,underwater FSO communication has become the research topic of many researchers.However,for wireless light,its underwater optical characteristics are complex,which will affect the transmission of wireless light.Underwater absorption and scattering lead to serious attenuation of light.In addition,there are also turbulence problems in the underwater channel:the random change of medium refractive index caused by temperature difference and salinity difference will lead to problems such as light intensity flicker and drift,which seriously affect the light intensity received underwater and the stability of the link.Aiming at the turbulence problem in underwater channel,the paper conducts simulation research on spatial diversity receiving technology.The relationship between Single Input Single Output（SISO）and spatial diversity receiver systems and turbulence parameters such as mean square temperature dissipation rate,relative intensity of thermo-salt equilibrium and light intensity scintillation is compared.It is found that the spatial diversity receiver system can effectively improve the intensity flicker of the system in turbulent channel.The relationship between the distance between the receiver and the intensity flicker is analyzed.It is found that the intensity flicker coefficient decreases with the increase of the receiver distance.It is concluded that the spatial diversity receiver system has a good effect on the suppression of light intensity scintillation.Then,field experiments are carried out according to the simulation,and the bit error rate of traditional singleton transmitting and singleton receiving is compared with that of spatial diversity receiving.It is found that the bit error rate of SISO system is 10^-6,while that of diversity receiving system is up to10^-7.5,which verifies that diversity receiving system can effectively reduce the bit error rate.Secondly,in view of the underwater light intensity scintillation and drift problems,the article will be a classic spot detection algorithm using them,and according to the correlation distance,spatial diversity receiving system adopted based on spatial diversity reception related distance of the mass center method,analyzes the characteristics of the advantages of the algorithm,and compared with the traditional spot detection algorithm:mass art,Hough transform and circle fitting method were compared.Then,the system construction and BER experiment of the three algorithms are carried out.It is found that the BER of the improved algorithm in the underwater turbulent channel is changed from about 10^-7to 10^-8.836compared with the traditional center of mass method and circle fitting method,and the conclusion is drawn:The improved algorithm makes the receiving link more stable under weak turbulence,and the fluctuation rate of light intensity receiving is smaller,which reflects the accuracy of the improved algorithm for the center coordinate of light spot,which has a certain improvement effect on the link stability of underwater optical communication system.Finally,the field simulation of turbulence,overall hardware design,software debugging and cascade of each system are carried out.