Design Of Underwater Full-duplex Wireless Optical Communication System Based On LED

Presently,with the promotion of the national policy of building a"strong ocean country",more and more professionals and researchers are involved in the investigation and exploration of the ocean industry.The development of advanced marine business,data transmission and information sharing between underwater devices are inseparable from underwater communication technology.The underwater wireless optical communication has the benefits of high reliability,high bandwidth,high confidentiality as well as low cost,low power consumption,and has been widely used in the fields of submarine communication,underwater sensing device,ocean exploration,frogman operation,etc.in recent years.This research paper mainly concerns the communication requirements of underwater unmanned submarine vehicles during the process of docking and recovery,and designs a miniaturized,low-power underwater two-way wireless optical communication system under the premise of ensuring a certain light intensity for guidance.The system uses FPGA as the core to complete the modulation and demodulation of communication data,coding and decoding processing,combined with peripheral hardware circuit design to realize the bi-directional transmission of underwater data.The following aspects are included in the main research work of this issue:（1）Analyze the impact of light transmission underwater from sea-water optical characteristics,seawater absorption and scattering characteristics lead to the attenuation of optical power and the generation of multipath effect,establish the channel model of underwater visible direct vision link on this basis,analyze the power loss of light at different distances underwater,simulate the transmission of photons underwater using Monte Carlo imitation model,analyze the impulse response of the channel and The pulse width expansion problem caused by multipath effect is analyzed.The performance of the UWOC system is analyzed from a system perspective by establishing a model for underwater two-way wireless optical communication and estimating the emitted power of the light source.（2）Comparing the performance of several commonly used modulation and demodulation methods in optical communication system,combined with the requirements of this paper’s design,the MOOK modulation and demodulation system is proposed,which solves the equalization disorder problem in OOK modulation by adding 8B/10B coding and increases the anti-multipath capability by adding protection time slot,focusing on the FPGA implementation process.By comparing several common coding and decoding methods and combining with the underwater communication environment,RS compiled code is selected to realize channel error correction.（3）Study the overall hardware architecture of the system,focus on the analytical processes of light source and detector selection,detailed discussion of the circuit design and implementation of the circuit system of LED array module,light source driver module,FPGA master control module,PMT detection module,signal conditioning module,power supply module,network communication module and other parts.（4）The hardware and software interconnection of the system is carried out to verify the essential capabilities of the device,and the outcome shows that the optical communication system designed in this topic can achieve half-duplex communication at a communication rate of 10 Mbps;the underwater experimental platform is built to test the BER of the system under the situation of different transmission rates and communication distances,and the experimental results showed that the system can achieve data communication with a transmission rate of 100kbps at a distance of 50m underwater,and the BER is lower than 10^-6.