Time synchronization in IoT mesh networks

Internet of Things (IoT) devices that are wirelessly connected in mesh networks often need mutual clock time synchronization, to enable chronological ordering of sensor events, coordination of asynchronous processes across devices, or network-wide coordination of actuators. Accurate time synchronization is also critical for IoT device event logging and debugging. The widely-adopted Network Time Protocol (NTP) is less suitable for constrained mesh networks due to its high network load and sensitivity to asymmetric network delays. In this paper, Mesh Time-synchronization Protocol (MTP) is proposed for IP-based IoT wireless mesh networks and shown to outperform NTP. MTP exploits one resource-rich node on the mesh, the gateway or border router, to be the time reference or to synchronize with a (global/UTC) time reference. This reference time is efficiently disseminated throughout the mesh, using radio broadcasts. Our MTP implementation achieves a median accuracy of 0.48 ms, 1.01 ms, 1.50 ms, 2.06 ms on an event-driven embedded OS platform and 0.74 ms, 1.60 ms, 2.43 ms, 3.28 ms on a multi-threaded embedded platform respectively for mesh nodes 1, 2, 3 and 4 hops away from the gateway. Compared to NTP, the accuracy error variability over repeated measurements is an order of magnitude lower for MTP.