Research And Implementation Of RPL Routing Protocol Supporting Time Synchronization

Under the promotion of the Internet of things,the IPv6 Wireless Sensor Network(WSN)technology has been rapidly generalized and applied.Time synchronization as its key support technology,how to maintain the synchronization accuracy and lower the energy consumption has always been a challenge to researchers.In order to realize the time synchronization in IPv6 WSN,the synchronization accuracy,synchronization cost and the practical deployment issues need to be considered.The RPL is a routing protocol fitting in IPv6 Wireless Sensor Network with the mature theoretical support and application foundation.Therefore,this thesis studied the time synchronization method of IPv6 WSN based on RPL routing protocol.The main research work of this thesis is as follows:1.Study the pivotal techniques of the IPv6 WSN and time synchronization protocol,analyze the challenging of current time synchronization,and point out the necessity of researching the RPL routing protocol which supports time synchronization.2.For the network overhead caused by extra synchronization frames,an improved RPL routing protocol that supports time synchronization is proposed and implemented,including improving RPL control packet,designing stagger encapsulation timestamp strategy and estimating the frequency drift and phase shift of local node through one-way time synchronization algorithm.Time synchronization finished in the ad-hoc networking,ensuring the synchronization precision,overhead and security of the network to meet the requirement.3.Considering the influence of the time reference parent node to the node to be synchronized,this dissertation designed a time synchronization objective function(OF)to realize the function of selecting the optimal time reference parent node.The OF combines four constraints,including link quality,node residual energy,hops and cumulative time error,and measures the weights of each constraint through the analytic hierarchy process,which is beneficial to reduce the class cumulative synchronization error.4.Based on Contiki 3.0 operating system,this dissertation simulated the proposed method that making the RPL routing protocol supporting time synchronization,and deployed the experimental verification system using the wireless network devices which the laboratory developed independently.Finally,the proposed method is verified and analyzed in terms of the results of function tests and performance tests.Test results show that the time synchronization method of IPv6 WSN based on RPL routing protocol designed in this dissertation can reduce the energy consumption.The designed stagger encapsulation strategy can effectively reduce the channel access delay and improve the synchronization accuracy.The designed time synchronization OF enables the nodes to choose the appropriate time reference parent node,reducing the average synchronization error of the whole network.The research work in this thesis can meet the time synchronization requirements,which is of great reference value for the research direction in time synchronization of IPv6 WSN.