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

6.3 ENERGY EFFICIENCY BY SINK MOBILITY

This section briefly discusses how to achieve energy efficiency by exploiting sink mobility. Sink mobility may be classified as uncontrollable or controllable, in general. The former is obtained by attaching a sink node on a certain mobile entity such as an animal or a shuttle bus, which already exists in the deployment environment and is out of control of the network. The latter is achieved by intentionally adding a mobile entity for example, a mobile robot or an unmanned aerial vehicle, into the network to carry the sink node. In this case, the mobile entity is an integral part of the network itself and thus can be fully controlled.

6.3.1 Delay-Tolerant Scenarios

In a delay-tolerant WSN, for applications such as habitat monitoring and water quality monitoring, energy usage optimization embraces a lot of options. To maximize energy savings for sensors, direct contact data collection is the best option. That is, sinks visit (possibly at slow speed) all data sources and obtain data directly from them (Shah et al., 2003; Gu et al., 2005; Nesamony et al., 2007; Sugihara and Gupta, 2008). This method completely eliminates the message relay overhead of sensors, and thus optimizes their energy savings. However, it has a large data collection latency for slow moving sinks. To reduce time delay, sinks may visit only a few selected rendezvous points (RPs) (Kansal et al., 2004; Xing et al., 2008, 2007), where sensor readings of all data sources are ...