Research On Time Synchronization-Free Localization Algorithm Of Underwater Sensor Network

Underwater sensor networks usually compose of some autonomous and individual sensor nodes,which can sense data,forward information,and perform intelligent computations.It can be applied to many areas such as collect marine environmental data,detect marine pollution,marine resource exploration and disaster early warning.The underwater sensor network positioning technology is the most critical technology of underwater sensor network application,because if there is no node location information,many practical applications can not be implemented.At present,underwater sensor networks mainly use acoustic waves to communicate,however,due to the complexity of the underwater environment and the limitation of node life cycle,cost,memory,communication radius and so on,the underwater sensor network positioning still faces a great challenge.In particular,accurate time synchronization is more difficult for underwater environments.Therefore,some existing positioning algorithms based on accurate time synchronization between sensor nodes are not feasible for underwater sensor networks.This article focuses on the solution of time synchronization problem and studies the time synchronization-free localization algorithm of underwater sensor network,then proposes the Two-Phase Time Synchronization-Free Localization Algorithm(TP-TSFLA).In this article,we first introduce the acoustic wave communication and network architecture of underwater sensor network.According to the different characteristics of the network,the localization technology of underwater sensor network is divided into different classes.At the same time,the challenges of the underwater sensor network positioning technology are contained.Then,the Time Synchronization-Free Localization Algorithm(TSFLA)are employed to realize the distance measurement between underwater unknown sensor nodes and mobile beacons.This algorithm does not need time synchronization hypothesis and eliminates localization error because of the time synchronization hypothesis.Based on distance measurement and the coordinate of the mobile beacon,we model the localization problem to a multi-dimensional global optimization problem.Secondly,Particle Swarm Optimization(PSO)algorithm is used to solve the multi-dimensional global optimization problem.The influence of parameter setting on positioning results is studied.The relationships between particle number,number of iterations and positioning accuracy are also studied.Considering the limited energy in the underwater environment,this article further improves the PSO algorithm and uses Simulated Annealing(SA)to deal with the problem of premature convergence in the PSO algorithm so as to improve the speed of finding the optimal solution,reduce the number of iterations and save consumption of energy,thus build the SAPSO algorithm.Finally,this article takes the position estimation problem of the nodes that can not obtain the location information after using the SAPSO algorithm into account,a Circle-based Range-Free Localization Algorithm(CRFLA)is proposed to retrieve the location information of unlocated sensor nodes.Using CRFLA can improve the coverage of positioning with little energy consumption.This article also employ the coordinate adjustment mechanism and propose an Extension of Circle-based Range-Free Localization Algorithm(ECRFLA)to further improve the positioning accuracy.