Research On Underwater Wireless Magnetic Induction Communication Technology

With the acceleration of the marine development process,underwater wireless communication technologies have got a rapid development.However,the traditional underwater electromagnetic wave communication,underwater acoustic communication,underwater visible light communication have certain defects in the underwater environment,which cannot meet the needs of practical applications.Therefore,it is urgent to seek a new underwater wireless communication technology to meet the need of wireless data transmission in underwater environment.As a new wireless communication technology in recent years,wireless magnetic induction communication has a stable channel state in underwater environment because it transmits information through the coupling of magnetic field.In this thesis,the underwater wireless magnetic induction communication technology is researched in combination with the practical application scenarios in the underwater environment.Firstly,the transmission principle of magnetic induction signals and near-field radiation of magnetic dipoles are analyzed according to the electromagnetic field theory,and the magnetic field strength is calculated.The basic underwater wireless magnetic induction communication model is introduced.The point-to-point communication model and the magnetic induction waveguide relay communication in which the coils are in the coaxial state are analyzed,and the transmission characteristics are compared.The additional eddy current losses caused by the salinity in seawater in wireless magnetic induction communication is analyzed,and an eddy current loss model is established.Secondly,for changes of the position and direction of the transmitting and receiving antennas caused by the disturbance of water or the movement of the sensor node itself,the performance of unidirectional magnetic induction communication and omnidirectional magnetic induction communication are analyzed,and the 3D path loss is studied The results show that the unidirectional magnetic induction communication will have communication interruption during the process of position and direction change.And omnidirectional magnetic induction communication can effectively alleviate the problem of the interruption of the magnetic induction communication link caused by the change of the antenna position and direction,improving the reliability of communication.Next,in order to improve the transmission distance of underwater wireless mag-netic induction communication,an underwater cooperative wireless magnetic induction communication model is proposed by this paper,and the magnetic induction intensity distribution of the transmission antenna array is analyzed.And the path loss of the communication model is studied.The results show that the cooperative magnetic induction communication model can effectively improve the propagation distance of the magnetic induction communication system.Finally,a design scheme of underwater wireless magnetic induction communication experimental platform based on coupled coil is presented.The platform transmits information through the coupled magnetic field between the loop antennas,and uses FSK as a modulation and demodulation method.The FSK modulation and demodulation module was fabricated,and a unidirectional antenna and an omnidirectional antenna were fabricated to build an underwater wireless magnetic induction communication experimental platform.Finally,it is tested in underwater environment.The test results show that the wireless magnetic induction communication system using omnidirectional antenna can effectively alleviate the influence of the changing of antenna position and direction.