Distributed Protocols Of Clock Synchronization For Wireless Sensor Networks

Technological advances in the development of low-cost and low-power programmable sensors that are capable of data sensing,storing and processing,and communication via wireless channel have been witnessed during these years.With the technical development,the wireless sensor net-works(WSNs),closely coupled to applications,have been applied more widely in a growingly wider range of cases.Climate monitoring,target positioning and tracking,and event detection,etc.are time critical applications in which local clocks of all sensor nodes must have the same time value.However,oscillators in low-cost sensors result in different local clock tune with distinct drifting speed.Then achieving advisable clock synchronization with less burden of communica-tion and computation is an interesting and significant point attracting focus of many researches.So this thesis focuses on realizing the synchronization of all nodes' external clock time to establish a network-wide consensus time value.This thesis contributes to the research area mainly in the following aspects:1.The models of physical and virtual local clock rates have been established respectively,where clock rates of nodes can be time-varying.And based on the models,distributed protocols for the synchronization of local clock rates and that of clock time have been designed,in which a generalized method of calculating the parameters is proposed.2.Based on models of all nodesexternal clocks,a distributed protocol which can realize syn-chronization of clock time and that of time variations simultaneously is proposed.A stronger robustness against noisy measurements and clock rate drifts is gained by combining both con-troller and estimator design methods into the protocol.3.Distributed protocols in this thesis contain the design of distributed algorithms and that of com-munication schemes.In the algorithms,their inputs are ensured to be achievable while their outputs are ensured bounded to be realizable in practice.Communication schemes are specifi-cally designed to make our protocols independent on global physical time when being applied,and be able to be applied with either synchronous or asynchronous communication.All these attributes make our protocols more practical.4.This thesis establishes a stopping criterion for our distributed algorithms to make the process of synchronization stop in finite time.Meanwhile,a distributed algorithm for maintaining the clock synchronization is synthesized under the general strongly connected digraph.Then a whole power-efficient strategy containing clock synchronization achieving protocols,stopping protocols and clock synchronization maintaining protocols can be formed to conserve more energy while achieving the expected synchronization accuracy.5.The effectiveness of our protocols have been proved and analyzed theoretically,meanwhile,numerical simulations are given to illustrate the performance of these methods.