Research On Fault-tolerant Of Time Synchronization Protocol For Wireless Sensor Networks

Time synchronization technology is an important part of wireless sensor networks(WSNs). Many applications of WSNs are built on the basis of an accurate synchronized timing. However, the reliability of message transmission among nodes becomes very low since they are usually deployed in harsh environment. Therefore, the fault tolerance is the emphasis in the research work of time synchronization protocols.By analyzing several typical time synchronization protocols, we find that these protocols are all putting the emphasis on meeting the requirements of accuracy, power consumption or scalability, and giving rare consideration to fault tolerance. Here we choose to analyze flooding time synchronization protocol (FTSP) and improve its fault tolerant ability, since it is the most comprehensive typical synchronization protocol so far. This article mainly proposed three improvement measures:(1) Bring in residual analysis to find the abnormal information that received by nodes and give it an error judgment. This measure can help to make up the limitation of the error message exclusion mechanism of FTSP and handle the messages correctly.(2) Revise the clock drift rate that estimated with linear regression. This approach can help to further reduce the influence of abnormal messages to those estimated clock drift rates.(3) Choose the slop with minimum variance during the linear regression to be the clock drift rate. This measure can help to reduce the variance of estimated clock drift rate in the multi-hop network. Meanwhile, the estimated clock drift rate of a node could get less influence with this method when the information in regression table cannot be updated because of communication failure.Finally, this article put forward fault-tolerant flooding time synchronization protocol (FTFTSP), which combines the three improvement measures mentioned above. FTSP and FTFTSP are tested under the same conditions in MATLAB. The simulation results show that compared to FTSP, FTFTSP not only has better fault tolerance, but also implements higher synchronous accuracy and greater stability.