Uncertainty Aware Hybrid Clock Synchronisation in Wireless Sensor Networks

Wireless Sensor Networks, aiming to monitor the real world’s phenomena reliably, need to combine and postprocess the detected individual events. This is not possible without reliable information of the context of the individual event. One such information of very high importance is time. It enables ordering of events as well as deduction of further data like rates and durations. An unreliable time base influences not only the ordering of events, but also the deduced values, which in consequence are unreliable as well. Therefore the synchronization of the clocks of the individual nodes is of high importance to the reliability of the system. On the other hand tight and reliable synchronization typically induces a large message overhead, which is often not tolerable in WSN scenarios. This paper proposes a new hybrid synchronization mechanism enabling tight synchronization in single hop environments and looser synchronization in multi hop environments. The lack of a guaranteed synchronization precision is mitigated by an explicit synchronization uncertainty, which is passed to the application. This enables the application to react to changes in the current synchronization precision. Keywords—Wireless Sensor Networks, Time Synchronization, Uncertainty