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Wireless sensor networks (WSNs) have been attracting a growing attention from the
research community in recent years. A sensor node is equipped with a sensing
circuitry to measure ambient conditions such as light, heat and pressure, and a radio
for transmitting the collected data. Sensors operate on small batteries and become
non-functional when the onboard energy supply gets depleted. A sensor node also has
limited computation and memory capacity because of its miniature size. A WSN is
composed of a large number of sensor nodes that probe their surroundings and send
their data to a gateway for further processing. The gateway interfaces the network to
remote command centers. Fig. 1 shows a typical WSN architecture. Applications of
WSNs include disaster management, early detection of fires in forests, combat field
surveillance and network configuration bridged or unbridged security. In these unattended application setups energy
consumption is a major concern since a sensor node fails when it runs out of energy
and it is impractical to replace its battery in inhospitable environments. Therefore,
energy-aware design techniques both at the node and network levels are usually
pursued in order to extend the lifetime of the individual sensors.
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