Research On Time Division Duplex Underwater Blue-green Laser Communication Technology

Underwater communication technology plays an important role in the exploration of marine resources,including underwater wired optical fiber communication,underwater radio communication,underwater acoustic communication and underwater wireless optical communication.Among them,underwater wireless optical communication has the advantages of high communication rate,long transmission distance,low power consumption of optical devices,small size of communication equipment and large transmission capacity.As the carrier of wireless optical communication,the underwater penetration of blue-green light is far better than other optical bands,so underwater blue-green optical communication is the most suitable communication mode for deep-sea information transmission.Aiming at the problem of back scattering interference in two-way data transmission in underwater wireless optical channel,a design scheme of time division duplex underwater blue-green laser communication system is proposed.And we use Verilog hardware description language to complete the important module design of the system,use FPGA combined with various optical communication devices to test the system function,and carry out the research of blue-green laser transmission experiment in the actual underwater environment.The main work completed is as follows:(1)The FPGA design scheme of underwater blue-green laser communication for Ethernet service is proposed,and the digital signal processing and real-time transmission of Ethernet service are realized.The functionality of each module and the stability of the system are verified by functional simulation and board level test.(2)A design scheme of flexible time slot switching based on time division duplex is proposed,which realizes the anti backscattering interference function and the time slot allocation function of uplink and downlink services in underwater channel.Through the joint debugging test in underwater environment,the reliability of real-time video service transmission in underwater blue-green laser channel is verified.(3)A flexible modulation technology design scheme based on underwater channel characteristics is proposed,which realizes the flexible switching of different modulation rates and formats for different channels.The transmission performance of different modulation methods in underwater channel is tested and verified in an indoor pool environment,and the zero error code transmission with the highest rate of 12.5Mbps and transmission distance of 40m is realized.