Research On Positioning Technology Of Underwater Optical Wireless Sensor Network

Due to the unrestrained exploitation of terrestrial resources by early humans,the available resources are becoming less and less.For this reason,people gradually shifted the direction of resource exploitation to the ocean.As an extension of wireless sensor network on land,underwater wireless sensor network has become a conventional technical means to realize the exploration of marine resources,carry out marine military activities and prevent marine natural disasters.In the underwater environment,considering that the performance of radio frequency wave is seriously weakened and the acoustic wave has the problems of low transmission speed and long transmission delay,this thesis takes advantage of the window effect of some spectra in the sea water,uses the blue-green light which can carry out high-speed transmission in the underwater as the communication signal,and combines with the underwater wireless sensor network to realize the communication of network nodes location.Therefore,this thesis mainly studies the node positioning technology of underwater optical wireless sensor network.The specific research work and innovations are as follows:1.Aiming at the problems of short transmission distance,low network connectivity and positioning accuracy caused by absorption and scattering effect of optical signal in underwater transmission,this thesis proposes a network connectivity scheme which is extended from underwater two-dimensional space to three-dimensional space,and on the basis of this scheme,proposes to use the Received Signal Strength(RSS)modified Distance Vector-Hop(DV-Hop)distributed localization algorithm.Firstly,the actual transmission distance between nodes is estimated by the RSS algorithm,and then the number of hops is calculated by the ratio of the distance to the communication radius of nodes.Then,for the nodes that need relay to reach,the total distance between nodes is calculated by the RSS algorithm,and the difference between the nodes and the standard euclidean distance is introduced to introduce the error factor of the average Hop distance,so as to further correct the traditional DV-Hop average hop distance.Finally,the distance between the unknown node and the reference node is weighted by the network node connectivity.Simulation results show that the proposed scheme has better positioning accuracy compared with the existing schemes.2.In view of the problem that the power of the receiving signal fading due to the influence of the turbulence effect on the underwater transmission of optical signal,the positioning accuracy of receiver node is unstable.This thesis proposes a positioning strategy based on the MIMO-OFDM system model.Firstly,the system model is used to suppress the turbulence effect,and the power analytical formula of the receiver is derived in this environment.Secondly,a three-dimensional positioning scheme based on the mixture of RSS and Angle of Arrival(AOA)is presented in the system model,and the mathematical analysis of the positioning scheme is linearized by using the Taylor series approximation theory,and the semi-definite relaxation technique is used to transform it into a semi-definite programming problem.Finally,the convex optimization theory is used to solve the problem effectively,and the CRLB is deduced for comparison.The simulation results show that the proposed algorithm is closer to CRLB than the existing algorithms,and effectively improves the node positioning accuracy.