Study On Skew Estimation Of Clock Synchronization With Correction For Wireless Sensor Networks

Clock synchronization is an essential component in wireless sensor networks(WSNs).It provides a global clock base for diverse demands including power management,target tracking and real-time communication in WSNs.The time synchronization in WSNs can be divided into point-to-point synchronization and multi-hop synchronization.For point-to-point synchronization,the reference node and the node to be synchronized can conduct synchronization directly.For multi-hop synchronization,the intermediate nodes are needed to establish the synchronization relationship between the reference node and the target node.However,adjustment of node's clock is not conducted at every message exchange,thusing result in deficiency of synchronization accuracy.Motivated by this end,in this thesis,two time synchronization schemes and corresponding clock skew estimation methods with immediate clock adjustment are investigated for WSNs.Utilizing statistical estimation theory,clock parameter is estimated by a set of timing message.Therefore,the synchronization error between any two nodes at every cycle could be limited to a small range,and communication overhead can also be reduced.The main work of the thesis includes:1.A summary of existing research on time synchronization in WSNs is presented,including time synchronization protocols and signal processing methods.2.Based on the one-way timing message dissemination mechanism under multihop WSNs,this thesis develops a time synchronization scheme,where node's clock is immediately readjusted upon every resynchronization before the clock parameters are estimated.Thus,the synchronization error between any two nodes at every cycle could be limited to a small range.After several message cxchanges,clock parameter can be estimated by a set of timing message.3.As for the existing synchronization schemes,the fixed delay in the propagation process was not considered,which may lead to a relatively inaccurate estimator.In order to optimize the adjustment value,this thesis analyzes and derives an estimator of clock skew considering the fixed delay in the propagation process.The thesis analyzes and derives an estimator of clock skew for linear synchronization model under the assumption that random portions of packet delays are modeled as Gaussian distributed random variables.4.The Monte Carlo simulation method is used to evaluate the proposed estimators.This thesis investigates two time synchronization schemes and corresponding clock skew estimation methods with immediate clock adjustment for multihop WSNs.The test results show that the clock skew estimators proposed in this thesis have good performance.They can reduce the communication overhead while maintaining the accuracy of clock synchronization.Therefore,the proposed time synchronization schemes have great application value in practical wireless sensor networks.