Underwater OFDM Wireless Visible Light Communication System Based On FPGA

With the development of society,resources on land will become insufficient to meet the growing demands of mankind,and more and more countries will focus their attention on the ocean.The ocean not only contains abundant aquatic resources,but also lurks incalculable other resources such as energy resources,which makes the competition of plundering marine resource among countries become more and more fierce.Science and technology play an important role in this competition.More and more countries have deployed observation networks on the seabed for real-time monitoring and intelligent exploration.In those underwater observation networks,a large amount of data need to be transmitted and stored.Compared with underwater acoustic or radio communication,underwater wireless visible light communication can support much higher transmission data rate.In this thesis,the existing underwater communication technologies are reviewed,and the principle of orthogonal frequency division multiplexing(OFDM)is explained in details.In the off-line processing-based underwater OFDM wireless visible light communication system,an arbitrary waveform generator and a mixed signal oscilloscope were used in the transmitter and receiver,respectively.Using Matlab,the code for signal generation at the transmitter and signal demodulation at the receiver were achieved,based on which we verified the feasibility of an underwater OFDM wireless visible light communication system.Then,we developed the entire communication system based on QUARTUS ? 11.0,which is a generic software development platform for field programmable gate array(FPGA).The main modules included system working clock module,transmitter control signal module,long and short training symbol generation module,parallel-to-serial conversion module,quadrature amplitude modulation(QAM)module,inverse fast fourier transform module,windowing and cyclic prefix module,frame detection module,timing synchronization module,fast fourier transform module,channel estimation and equalization module,QAM demodulation module and four-bit to eight-bit conversion module.We simulated the entire communication system by using ModelSim-Altera and set up an underwater OFDM wireless visible light communication test platform based on FPGA.By comparing the experimental results and simulation results,we verified that the developed system can successfully realize underwater data transmission.The transmission rate of the entire communication system could reach 80 Mbps measured in the 2-meters water tank with 1.2 g Mg(OH)2 mixed to emulate the turbid water,and the BER was 2.24×103.