Research Of Time-synchronization And Localization In Underwater Wirelss Sensor Networks

Consisting of a large number of small sensor nodes with sensing,computing,and communication capabilities,Wireless sensor networks(WSN) is declared as one of the most important technologies for the 21st century.With the recently increasing interests in ocean,including environmental,economical and military purposes,underwater wireless sensor networks(UWSN) received tremendous attention from both academia and industry because of its promise of a wide range of potential applications in both civil and military areas.Time synchronization and node localization are two critical services needed by WSN. In UWSN,there are two main differences from land based WSN:the huge delay caused by acoustic communication signal propagation;the three dimensional deployment.Due to these limitations,most existing WSN synchronization and node localization algorithms/protocols can not be applied to UWSN directly.This paper tries to introduce the state of art of synchronization and node localization research in wireless sensor networks,together with their challenges in UWSN.Then we respectively propose new algorithms for synchronization and node localization,which is especially applied to UWSN.Based on extensive simulations,the effectiveness and performance of these algorithms are verified.The contributions of this thesis include:(1) We analyze time synchronization under high latency acoustic communication context.Based on through mathematical deduction of TSHL(Time Synchronization for High Latency networks),we propose to increase the beacons intervals without sacrifice synchronization performance.Further,we propose a light weight high latency network synchronization algorithms which need only three messages exchange.This algorithm not only adapt to high latency propagation delay but also reduce computation costs,which is especially suitable to resource-constrained UWSN.The simulations verified its effectiveness.(2) Due to technical limitations,mostly the anchor nodes can only be deployed at the ocean surface.This is a challenge to multi hop underwater localization.Exploiting the feature that depth information is easy accessed in underwater environment,we improved Dv-Hop and Dv-Distance algorithms to contain depth constraints to remedy for the anisotropy caused by surfaced anchors.Further,we proposed a three dimensional iterated underwater localization algorithms.(3) We developed a mixed localization algorithms for sparse UWSN.Directional vector hydrophone is an assumed component of nodes.Multiple TOA/AOA measurements are introduced to constraints of node localization,and we proposed a multi-hop underwater mixed UWSN localization algorithm.Through extensive simulations,the algorithm is proved to be effective under low connectivity networks.The entire works of this dissertation are exploring forefront in synchronization and localization algorithms in underwater sensor networks.Proposals and results are expected to optimize the design of network protocols and improve the network performance.