Design Of Underwater Omnidirectional Optical Communication System Based On LED

With the development of marine resources all over the world,more and more underwater activities are being carried out,which makes higher demands on the underwater wireless communication technology.At present,underwater wireless communication mainly realizes the transmission of information through sound waves,light and radio frequency.Underwater RF communication has skin effect,which leads to large attenuation of signal energy,short communication distance and poor transmission quality.But the underwater wireless optical communication uses the visible light in the blue and green band,its underwater absorption loss is small,the light carrier capacity is big,is similar to underwater acoustic wave communication,underwater optical communications communication has the low communication delay and the transmission rate is high.Although compared with traditional underwater communication technology,underwater wireless optical communication has many advantages,the current research still faces many challenges.For example,underwater optical communications equipment is difficult to align at both ends of transmitters and receivers because of the limited range of light sources and the small angle of view at which the beams are emitted.However,mechanical positioning equipment is expensive and difficult to be widely used in practical engineering.Aiming at the above problems of underwater wireless optical communication technology,a multi-plane array structure based on LED for underwater multiangle optical transmission and multiangular optical reception is proposed,and an integrated system of all-round underwater optical transceiver is designed and realized.The system can realize multi-angle omni-directional optical communication without using mechanical alignment equipment.The main tasks of this document are as follows:(1)The intrinsic optical properties of light in the underwater optical communication channel are studied.Taking three different typical sea areas in South China Sea as examples,the absorption and scattering characteristics of seawater are analyzed,and the model of subaqueous optical transmission attenuation is established,which provides the theoretical basis for the selection of the optical belts of system luminous sources and calculation of effective distance of ocean light transmission.(2)The principle and link model of light-emitting diode(LED)in underwater optical communication system are studied.The optical attenuation coefficient and selected led parameters in the South China Sea are used to model and analyze the communication system links,and the distribution of optical power of the omni-directional optical transmission system with different structures is compared.A photocommunication prototype with a polyhedron array structure is designed,and the LED power model is established,which realizes the effect of multi-angle emission and wide coverage of the optical transmitter.(3)This paper studies the underwater intensity modulation/direct detection technology and simulates the performance of several common modulations in IM/DD communication system.Through the comparison of simulation experiment,dual pulse position modulation is selected to design the optical communication system.(4)Based on the hardware design of a prototype communication system with a polyhedron array structure,an underwater omni-directional optical communication transceiver system is developed and implemented using the FPGA platform.At the same time,the communication performance of the system is tested.The test results show that the communication system can keep communication link connection in the range of 0?360degree,and the system bit error rate is less than10^-5.