ABSTRACT
Recent technological advances have led to the emergence of pervasive networks of small, low-power devices that integrate sensors and actuators with limited on-board processing and wireless communication capabilities. These sensor networks have opened new vistas for many potential applications, such as civilian surveillance, environment monitoring, biological detection, and situational awareness in the battlefield.2,6,11,14
Because most low-power devices have limited battery life and replacing batteries on tens of thousands of these devices is infeasible, it is well accepted that a sensor network should be deployed with high density (up to 20 nodes/m3)16 to prolong the network lifetime. In such a high-density network with energyconstrained sensors, if all the sensor nodes operate in the active mode, sensor data collected is likely to be highly correlated and redundant; and moreover, excessive packet collision may occur as a result of sensors attempting to send packets simultaneously in the presence of certain triggering events. All these amount to energy waste. It is thus neither necessary nor desirable to have all nodes simultaneously operate in the active mode.
