Exploiting External Interference for Clock Synchronization

Abstract

Many wireless sensor network (WSN) applications require the synchronization of the network’s independent node clocks. That synchronization is a challenging problem that often requires energy-constrained devices to exchange many messages.This paper introduces the Interference-based Clock Synchronization (ICS) protocol, an approach suitable for dense WSNs located in urban environments. ICS uses external interference to synchronize the network’s nodes to either a network-local internal or global (e.g., UTC) external time. All of the network’s nodes observe interference at roughly the same time, and the node possessing the common time transmits its observed pattern to the network. The network nodes then compare and align the received and locally-observed patterns, and subsequently, they update their clocks to the common time.The protocol is evaluated using both a simulator and hardware. Using this approach, the number of transmitted messages scales linearly with the network size. In the simulator, ICS-synchronized clocks had a mean time difference of 0.3635 ms when compared with the common time. Using hardware, the difference was larger at 4.9388 ms, but much of that difference can likely be attributed to the experimental setup.