Research On Time Synchronization,Localization And Data Transmission In Underwater Wireless Sensor Networks

Time synchronization,node localization,and data gathering are three key techniques in underwater wireless sensor networks.Due to the heavy attenuation of electromagnetic,acoustical communication is the mainstream in underwater environments.With the mobility of underwater sensors and well-known acoustic characters,including long propagation delay,low bandwidth,multi-path,etc.methods that fitting for terrestrial wireless sensor network do not perform well in underwater environments.Thus,it is necessary to develop new approaches for underwater acoustical time synchronization,node localization,and data gathering.In this thesis,we analyze challenges on underwater time synchronization,node localization,and data gathering,and provide algorithms to solve these problems,respectively.Moreover,lots of numerical experiments are conducted to demonstrate the efficacy of our approaches.The contribution falls in the following aspects:1.Underwater time synchronization.By analyzing existed work on underwater time synchronization,we provide a channel-state-based acoustical time synchronization method.Based on the relationship between signal propagation delay and channel phase,the time offset can be estimated within one single message,and the clock skew can be evaluated within one round message exchange.Furthermore,this method also achieves accuracy synchronization and energy-efficient with nodes moving.2.Underwater localization.In this paper,we design an AUV localization algorithm to locate mobile AUVs.In this method,a data fusing strategy is used to accurately locate the AUV,and even with a single reference node,the AUV can also be located.For AUV swarm,a surface beacon selection algorithm is provided.Through parameter configuration,this algorithm can make tread-off between localization accurate,energy consumption and network lifetime.3.Underwater data gathering.Since the main application for underwater wireless sensor networks is underwater monitoring,how to transmit the sensing data to the surface station is a key problem.In this thesis,we consider both online data routing and offline data gathering through AUV.For online data routing,the next hop relay is chosen by solving a mix integer linear programming problem.To improve the data delivery and reduce energy consumption,an adaptive model is leveraging to dynamically choose the channel frequency and transmitting power.For AUV-aid data gathering,on the purpose of prolonging network lifetime,we utilize advantages of different wireless underwater transmission modes and the mobility of AUVs to gathering underwater sensed data.