The Research And Performance Analysis Of Consensus-based Time Synchronization Algorithms With Random Time Delay

Recently,wireless senor networks(WSNs)have drawn great interest and have obtained exciting advances in many fields including environment monitoring,industrial quality control,military operation,home automation and so forth due to the development of inexpensive,miniature,self-configuring and powerful sensor terminals in micro-electro-mechanical systems(MEMS)technology.WSNs are comprised of a collection of nodes with sensing,memory and computational capabilities that are deployed within an environment and can communicate with their neighbors to execute mission cooperatively.Most of the applications based on WSNs demand all of the nodes to operate on a common notion of time.The requirement for precision time synchronization has become more and more critical in WSNs as it makes no sense to integrate and interpret information sensed at different nodes without accurate time information.Traditional time synchronization protocols suffer from large overhead in building and maintaining specific structures and show poor robustness and scalability to the topology changes and failures of nodes.Inspired by great advances in convergence analysis tools for consensus problem,design and convergence analysis of consensus-based distributed time synchronization(CBTS)protocols have begun to emerge.This dissertation specially investigates the problem of structural modeling and convergence analysis of consensus-based distributed time synchronization algorithms under the general directed communication topology with random communication delays,and attempts to discover the impacts of the topological structure and round delay on the performance of time synchronization steady state error.The main analysis tools utilized in this dissertation include algebraic graph,matrix theory and consensus theory.The main work of the dissertation is summarized as follows:1.The divergence conditions of a consensus-based time synchronization algorithm have been studied over a network with random communication delays.A unified structural model of CBTS algorithms is presented firstly.Then different CBTS algorithms such as ATS,WMTS and LSTS,are fitted into the same structural model with just different algorithm parameters respectively.Divergence conditions and meansquare divergence conditions of CBTS algorithms have been discovered by studying the asymptotic property of the relative drift estimation error.It clearly point out that the ATS algorithm is divergent almost surely,the WMTS algorithm is mean-square divergent,but the LSTS overcomes all of these divergence conditions.2.The relationship is analyzed between the steady state error and the topological structure for a least square estimation bases time synchronization(LSTS)algorithm in wireless sensor networks.Given the presence of random bounded communication delays between nodes,the performance of the steady state error is considered under the basic,complex and determined/random switching topology.The definition of an error indicator is proposed to describe the impact on the statistical property of the global synchronization error.The error indicators are computed among several network architectures with the existence of root node and paths(or cycles).It is discovered that the more paths or cycles between nodes(except root node)exist,the larger the global synchronization error appears which is against our intuition.3.In order to tackle the problem of random communication delays in time synchronization process,the relationship is discussed between the steady state error and the probability distribution of delay for LSTS algorithm in wireless sensor networks.It is shown that the error of clock drift compensation mainly depends on the variance of random communication delays rather than expectation,while the global synchronization error depends on the expectation of communication delays.Considering the characteristic of round delay in pairwise synchronization of sensor nodes,clock offset compensation is added with round delay.The introduction of round delay and decaying factor in consensus based algorithm can decrease both the expectation and the variance of time synchronization error.