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Time Synchronization Protocols

Time synchronization protocols can significantly increase the accuracy and stability of local clocks. In [6], a linear regression applied over multiple clock offsets measurements taken between a pair of nodes was used to achieve an accuracy of $\pm 0.04 ppm$ over short time intervals.

In general, researchers benchmark time synchronization protocols by the achieved accuracy and by how many messages these protocols transmit/receive [3]. Although these are illustriative metrics, the performance of a time synchronization protocol depends greatly on the local clock in residence. A simple ring oscillator, as can be found on the popular TI MSP430 MCU, is unsuitable due to its extreme instability with respect to both ambient temperature and supplied voltage (on the order of $\pm 10 \%$).

Intuitively, the research of low power clocks is orthogonal to the investigation of low power time synchronization protocols. Nevertheless, there is an interesting intersection, where local crystals get calibrated by the use of high precision time synchronization, and thus increase the time between resynchronization attempts through improved stability. However, in this paper we will first concentrate on the development of a low-power, high accuracy, fine granularity local clock source - leaving the interplay between local clock and synchronization protocol to future research.

Thomas Schmid 2008-11-14