Global Synchronization in Sensornets

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Time synchronization is necessary in many distributed systems, but achieving synchronization in sensornets, which combine stringent precision requirements with severe resource constraints, is particularly challenging. This challenge has been met by the recent Reference-Broadcast Synchronization (RBS) proposal, which provides on-demand pairwise synchronization with low overhead and high precision. In this paper we introduce a model of the basic RBS synchronization paradigm. Within the context of this model we characterize the optimally precise clock synchronization algorithm and establish its global consistency. In the course of this analysis we point out unexpected connections between optimal clock synchronization, random walks, and resistive networks, and present a polynomial-time approximation scheme for the problem of calculating the effective resistance in a network based on min-cost flow. We also sketch a polynomial-time algorithm for finding a schedule of data acquisition giving the optimal trade-off between energy consumption and precision of clock synchronization. We also discuss synchronization in the presence of clock skews. In ongoing work we are adapting our synchronization algorithm for execution in a network of seismic sensors that requires global clock consistency.