  We consider energy-efficient time synchronization in a wireless sensor
network where a head node (i.e., a gateway between wired and wireless networks
and a center of data fusion) is equipped with a powerful processor and supplied
power from outlet, and sensor nodes (i.e., nodes measuring data and connected
only through wireless channels) are limited in processing and battery-powered.
It is this asymmetry that our study focuses on; unlike most existing schemes to
save the power of all network nodes, we concentrate on battery-powered sensor
nodes in minimizing energy consumption for time synchronization. We present a
time synchronization scheme based on asynchronous source clock frequency
recovery and reverse two-way message exchanges combined with measurement data
report messages, where we minimize the number of message transmissions from
sensor nodes, and carry out the performance analysis of the estimation of both
measurement time and clock frequency with lower bounds for the latter.
Simulation results verify that the proposed scheme outperforms the schemes
based on conventional two-way message exchanges with and without clock
frequency recovery in terms of the accuracy of measurement time estimation and
the number of message transmissions and receptions at sensor nodes as an
indirect measure of energy efficiency.

Networking and Internet Architecture;Applications