Distributed Kalman filter for precise and robust clock synchronization in wireless networks

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Abstract
A novel concept for robust and precise clock synchronization in wireless networks is introduced. The concept is based on a Kalman filter that is parallelly distributed on all network nodes. Each node uses the state estimates of other nodes to determine a local estimate of the global clock. A voting algorithm that evaluates the state estimates of several nodes is used to adjust the virtual global clock master. By avoiding any physical central clock master the distributed global clock is extremely tolerant of single nodes malfunction and no single points of failure exist in the network and protocol. In experiments with an IEEE 802.15.4 (ZigBee-PHY) network it was shown that even with a packet loss of 75% the achieved clock synchronization was always better than 4 mus. Another advantage of the realized protocol is that it requires only very low basic data traffic. Thus, the concept is ideally suited for time-synchronized sensor networks, ad hoc networks, or wireless time-triggered real-time systems.