Wireless Sensor and Actuator Networks: Algorithms and Protocols for Scalable Coordination and Data Communication

3.7 PHYSICAL LAYER-BASED SENSING, PROTOCOLS, AND CASE STUDIES

Most of existing works on sensor area coverage employ the UDG model. The sensing area of a node is a disk with SR centered at the node itself. A point in the monitoring region is covered by a sensor if and only if, the point is inside the coverage disk of the sensor. However, as discussed in previous chapters, the UDG model is not realistic since variations of received signal strengths are not considered. Nondeterministic radio fluctuations cannot be ignored in sensor area coverage, and the monitoring ability of sensors is probabilistic.

Gallais et al. (2006) studied k-layer coverage in WSNs with realistic physical layers. The probability of detecting an event depends on the distance of sensor from it. The approximated function that is introduced in Kuruvila et al. (2004)is applied:

where x is the distance between the point and the sensor, and α is the signal decline factor which depends on the environment (Eq. 3.1). The SR is selected so that the probability for a sensor to correctly sense a target, which is located at distance SR from the sensor is 0.5. The sensing function is drawn in Figure 3.8 where SR = 1 and α = 2. It resembles the lognormal shadowing model used to model communication between nodes.

The proposed sensor area k-layer coverage protocol (Gallais et al., 2006) works as follows. Suppose sensors are time ...