Time synchronization protocol in wireless sensor network

Introduction Wireless Sensor Networks (WSN) consist of a number of low-cost, miniature and lightweight sensor nodes that can communicate to each other over a wireless radio standard. An essential characteristic of a wireless sensor network for recording vital parameters is the time synchronization, due to the fact that all sensor nodes are physically separated from each other and every node has its own clock. Methods The system setup consists of three wireless sensor nodes based on the IEEE 802.15.4 standard with an implemented synchronisation protocol called Flooding Time Synchronization Protocol (FTSP). After synchronization the three nodes gets simultaneously an interrupt by a forth node to save their calculated global time, which can be analysed later by comparing the saved times of all nodes. Results After the implementation the gateway broadcasts its time in selectable variable intervals. If a new sensor node is con-nected to the network, the broadcast interval was reduced to synchronize the new node faster. A broadcast interval of 300 s is an optimum concerning power consumption and accuracy. The error of time is less than ± 400 ?s measured over a time of 48 hours. Conclusion Without any time synchronization the time error amounts to more than 6 ms after one hour. The implemented and eval-uated FTSP works in an optimum solution and the error is always less than 0,5 ms and in 20 % of all cases the error is even zero.