Design And Implementation Of Multi-Source And Secure Time Synchronization Protocol In Wireless Sensor Networks

A wireless sensor network (WSN) is typically a system consisting of resource-constrained micro sensor nodes that self-organize into a multi-hop wireless network. Wireless sensor networks have wide applications such as environment monitoring, medical care, space exploration, etc. In WSNs, time synchronization protocols are with responsibility for unifying the clocks between nodes. They make the data to be processed according to the logic order which the events take place and play an important role in ensuring the real-time and effectiveness of the information in WSNs. This paper design and implementation a new time synchronization protocol aiming to the application requirements of large-scale WSNs.Constrained by several limitations, such as limited resources on sensor nodes and the interfering in wireless communication environment, design an efficient time synchronization protocols for WSNs is not easy, it is necessary to consider many factors such as precision, robustness , efficiency and so on. The increasing rigorous situation of network security makes us to consider the security of the protocol when it is designed. In this paper, we first survey the main time synchronization protocols in WSNs, then give a briefly classification and comparison to these protocols, and we introduces the evaluation parameters of protocols and influencing factors.In order to overcome the disadvantages brought by single-source and solve the problems involved in robustness and security, we designed a new time synchronization protocol named Multi-Source and Secue Time Synchronization Protocol in WSNs, which was efficiency and secure. It was implemented on the self-lappinged sensor nodes operating system named MILSOS. There's no much influence on the whole network time synchronization when some sources don't work normally by using multi-source replaced traditional single source. The current node chooses the one has a minimum distance from itself among many time souces in order to reduce accumulated errors. The security check mechanism in the protocol can effectively against of external attacks aimed at the message and internal attacks aimed at the node. It provides a great support to data acquisition and integration, technology of positioning and real-time sleep or wake up of the sensor nodes in large-scale wireless sensor networks.Simulation results showed that multi-sources can greatly speed up the convergence time of network. The actual test results on the self-lappinged sensor nodes indicated that the mechanism which was designed to select parent-node can make the current node to choose the most secure node as its parent in the condition of ensuring precision. The current node could be able to choose its parent node over again when the old one was failure, and it brought no influence to other nodes'synchronization. When there was attacks appeared on the network, the protective measures could distinguish replay messages and compromised nodes from normal ones. A new node could join the network dynamically without restarting the whole process of time synchronization. The mechanism of time-stamp in MAC layer reduced the delay for transmission greatly. In short, the protocol could cope with the corresponding problems effectively within the life cycle of the network. The precision shows that the protocol can meet the requirements of the project, and it also greatly accelerate the convergence speed of the network.