Sensor Sensed Object Sensing Range
Magnetometer SUV 7 m
PIR SUV 30 m
Person 12 m
Acoustic SUV 30 m
3.2 Factors A?®ecting ExScal??™s Lifetime
The major factors a?®ecting the network lifetime of ExScal are as follows:
1. Continuous Monitoring: The region should be continuously monitored
so that intruders can be detected instantly. This may require keeping at
least one sensor continuously active, consuming significant energy.
2. Event Notification Requirement: Intrusion detection events should
be communicated to a base station quickly. In the ExScal application,
the requirement was to receive event detection notification at the nearest
base station within 2 seconds. In order to communicate event-notification
messages quickly over a multi-hop wireless sensor network, several, if not
all, sensors need to keep their radio in the receive mode either continuously
or frequently enough so that they can route an urgent event-detection
message towards the base station. This again consumes significant energy.
3. Periodic Control Messages: Two middleware services, namely routing
and time synchronization, required every XSM to transmit periodic
messages. As we will see in Section 4.6, sending periodic control messages
consumes significant energy.
269 Chapter 11 Maximizing the Lifetime of an Always-On WSN Application
Santosh Kumar, Anish Arora, and Ten H. Lai
Table 2. Current consumption of major components in the XSM platform.
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