A new sensor platform, called an Extreme Scale Mote (XSM) [9], was
developed for ExScal. It was a refinement of Mica2 [7]. The details of this
platform with regard to its power management capabilities appear in Section
3.1. The operating system used on this platform was TinyOS. Several
middleware services such as routing, time synchronization, and localization
were custom developed for ExScal. The signal chains that were used by the
XSMs to locally process the sensor data were also custom developed. Finally,
the application software to detect and classify intruders were also developed
in-house.
To demonstrate the concept, approximately 1000 XSMs were deployed in
a 1,200 m ?— 288 m rectangular region [16] and intruders such as persons
and Sport Utility Vehicles (SUVs) were shown to be detected and classified
by the sensor network. At the end of year 2004, this was the largest wireless
sensor network in the world deployed on the ground. Figure 1 shows the XSMs
deployed for ExScal demonstration.
Fig. 1. XSMs (white dots forming a grid) deployed on the ground (a 1,200 m ?— 288
m rectangular region) for ExScal demonstration. Figure 2 zooms on a single XSM.
Each XSM ran on a pair of AA batteries. If the XSMs were left continuously
active, the ExScal network would have lasted only three days (see
Section 4.3 for details of the calculation). However, when a wireless sensor network
is deployed on the ground for real-life application (rather than to demon-
267 Chapter 11 Maximizing the Lifetime of an Always-On WSN Application
Santosh Kumar, Anish Arora, and Ten H.
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