A Study On Channel Characteristics For Underwater Wireless Optical Communication

With the increasing exploration of ocean underwater robots,various kinds of sensors and other equipments are widely used in marine research and exploitation,which requires reliable underwater communication technologies.Underwater wireless optical communication has the advantages in bandwidth,security,power consumption and size over traditional underwater acoustic c electromagnetic communications,and has become a promising technology.The optical signal will be absorbed and scattered by sea water,which causes attenuation of the energy and distortion of the signal waveform.Communication distance and bandwidth will be affected.The purpose of this thesis is to study the relationship between channel characteristics and diverse parameters so as to provide theoretical guidance for optimizing an underwater wireless optical communication system.Based on the optical properties of seawater,the Monte Carlo method is used to simulate the propagation path of light in seawater,and the simulation of underwater optical channel is carried out.Three types of water,namely clean seawater,coastal seawater and harbor seawater,are simulated.Two kinds of common light sources,laser and light-emitting diode,are modeled with a variety of communication distances and optical receiver parameters set in the simulation.The characteristics of the underwater optical channel,the pulse broadening and the frequency domain characteristics are analyzed.The influence of diverse parameters on the channel is studied,and guidelines on designing an underwater wireless optical communication system are given.While blue-green light is believed to be more suitable for underwater communication,we propose that red light can also be adopted in underwater communication.The channel of red light is calculated by Monte Carlo method and compared with that of blue-green light.We find that red light has larger bandwidth in turbid seawater and better performance in certain environments.Convectional Monte Carlo method is normally very time-consuming,for which we propose a novel method to speed up the simulation.This method is obtained by analyzing the actual characteristics of underwater optical channels and verified by both simulation calculation and experiment.This method can significantly shorten the time required by the simulation.