Timing Synchronization in Sensor Networks
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Overview
Wireless ad-hoc sensor networks have emerged as an
interesting and important research area in the last few years. The applications
envisioned for such networks require collaborative execution of a distributed
task amongst a large set of sensor nodes. The collaborative execution is
realized by exchanging messages that are time-stamped using the local clocks on
the nodes. Therefore, time synchronization becomes an indispensable piece of
infrastructure in such distributed systems. For years, protocols such as NTP
have kept the clocks of networked systems in perfect synchrony. However, this
new class of wireless sensor networks has a large density of nodes and very
limited energy resource at every node; this leads to scalability requirements
while limiting the resources that can be used to achieve them. A new approach
to time synchronization is needed for the wireless sensor networks.
Time synchronization problem has been investigated thoroughly in Internet and LANs. Several technologies such as GPS, radio ranging etc have been used to provide global synchronization in networks. Complex protocols such as NTP [4] have been developed that have kept the Internet’s clocks ticking in phase. However, the time synchronization requirements differ drastically in the context of sensor networks. In general such networks are dense, consisting of a large number of sensor nodes. To operate in such large network densities, we need the time synchronization algorithm to be scalable with the number of nodes being deployed. Also, energy efficiency is a major concern in these networks due to the limited battery capacity of the sensor nodes. This eliminates the use of external energy-hungry equipments, such as GPS receivers. Moreover, the time synchronization requirements are much more stringent, often requiring synchronization of the order of microseconds among nodes involved in a task such as tracking a target.
We have
developed a Timing sync Protocol for Sensor Networks (TPSN) that aims at
providing network-wide time synchronization in a sensor network. We use the
classical approach of sender-receiver synchronization while developing this
protocol.