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

1.7 COST METRICS

A variety of metrics and their combinations can be used to design and evaluate communication protocols for WSNs. We have discussed so far hop count and power consumption metrics. A convenient metric that can be used to avoid nodes with low remaining energy on a routing path is called reluctance (Stojmenovic and Lin, 2001b). The remaining energy g at a sensor node can be normalized in the interval (0,1). The resistance f is then f = 1/g, meaning that the reluctance becomes huge when a sensor is close to depletion.

Some applications of WSNs, where real-time or multimedia data are involved in communications, require a guarantee on QoS metrics such as delay, throughput, and bandwidth. For example, sensor networks for fire detection require short latency to transmit emergency data to the sink. QoS routing is usually performed through resource reservation in individual nodes along the route.

In the sequel, the term cost will often be used to denote one of the mentioned metrics or a newly designed metric which is often a combination of several existing metrics. One example of a combined metric is power * reluctance, which can be used in designing routing paths to balance between finding routes with a low total sum of power metrics on route and also avoiding nodes with low remaining energy. The cost metric is therefore often used to find a trade-off among these parameters.

As another example, a conditional max–min battery capacity routing is studied in Toh (2001). If there ...