Design And Implementation Of Underwater Visible Light Communication System Based On OFDM

With the increasing importance of maritime rights and interests in the world,and the increasing number of marine and economic interests related to the ocean,underwater wireless communication is becoming one of the core technologies competing in the world.At the same time,the key technologies such as semiconductor light source devices,t he continuous development and maturation of visible light communication(VLC),as well as the advantages of sea water on blue and green light with “transmission window” and other advantages,making the research and application underwater visible light communication(UVLC)will provide a new technical means for high-speed data exchange of underwater.Due to the complexity of the underwater optical channel,there are many factors that affect the transmission of the optical signal,and there is not an effective universal theoretical model to describe the interference.In this paper,the UVLC channel model and high-speed transmission technology are studied,and finally the UVLC transmission test system is designed and implemented based on light emitting diodes(LEDs).The main research contents are as follows:1.According to the limitation of the existing underwater optical channel model,Monte Carlo method is used to simulate the photon transmission in the water,and the optical channel model is established under the condition of water quality.According to the characteristics of underwater optical channel,this paper makes some improvement on the traditional Monte Carlo process,and finally uses the double gamma function(DGF)to fit the simulation results of Monte Carlo,and obtains the fitting channel model.By comparing the actual results of the underwater optical signal,the channel model is more adaptive than the simple Beer's law in complex water.2.In view of the traditional single carrier modulation in underwater optical communication problems,the orthogonal frequency division multiplexing(OFDM)technology is applied to the study of UVLC.Aiming at the traditional single carrier OOK signal,the optical signal transmission by using OFDM technology,can effectively combat underwater high speed communication of seawater caused by scattering of inter symbol interference(ISI),and reduce the receiver BER;The underwater optical OFDM technology using single photon avalanche diodes(SPAD)detection receiver is designed in a long distance attenuation environment,design scheme is put forward by the validation,and greatly enhances the transmission performance of the system.3.According to the main application scenarios of UVLC,this paper designs and implements two kinds of high-speed UVLC off-line processing system.The first one is the design and implementation of UVLC test and verification system,which is based on the application requirements of two-way UVLC.The second is for high-speed UVLC applications,using the balanced circuit design of transceiver front-end based on underwater optical OFDM signal transmission method,set up UVLC off-line processing system based on OFDM,the test results show that the off-line rates can reach 1Gbps.