| Underwater Visible Light Communication is a new underwater wireless communication method.It uses visible light as the carrier and it can transmit large-capacity data.It has many advantages,such as a high rate of transmission,a strong ability of avoiding interference and being secretive and safe.And it has a great development.And it will play a significant role in exploring and developing the marine resources in the future.But seeing that complex and varied influence of the underwater environment,the underwater visible light communication system with certain versatility,flexibility and reconfiguration needs to be broken through urgently.Based on the idea of Software Defined Radio(SDR),the concept of software defined underwater visible light communication system and its framework are proposed for the first time.The major research of this paper include:(1)The software defined underwater visible light communication system is proposed based on the idea of SDR.It needs a brief and concise introduction and analysis of the definition,the structure and characteristics of the software radio technology.And it should make a comparison and analysis towards the selection of key devices.In order to meeting the underwater wireless communication,it can be put forward with that the underwater visible light communication system can be defined by the software based on the SDR.And a bi-directional software defined underwater visible light communication system hardware link is designed with FPGA as the core.(2)It also researches the optical characteristic of the underwater visible light communication channel.It first introduces the scattering and absorption of different components in the sea.According to the optical characteristic,it sets up the attenuation model of the seawater,which can be transmitted through the visible light.Then the bi-directional software defined underwater visible light communication system hardware link as a platform,it can put forward according to the situation of the water channel,the adaptive adjustment of transmission optical pulse width and power control idea of communication.(3)The time-domain broadening characteristics of underwater visible signal are studied to provide theoretical support for the idea of adaptive pulse width adjustment.Several commonly used scattering phase functions are introduced and compared with the measured data.It also introduces the commonly used methods to study the time-domain broadening characteristics of optical signals,such as small Angle approximation method and Monte Carlo method.And the small Angle approximation method is improved by using TTHG phase function which has better fitting degree of small Angle.The pulse response of seawater channel simulated by Monte Carlo method is modeled.(4)Develop an adaptive optical power control scheme.The light source LED and light detection device APD are modeled and analyzed,and Q factor is estimated by inserting training sequence.Taking Q factor as a bridge,a specific adaptive optical power control scheme is developed to improve the dynamic communication range and stability of the system. |
