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

1.12 GENERATING MOBILE WIRELESS SENSOR AND ACTUATOR NETWORKS

A lot of research has been conducted on fixed sensor networks, where connectivity is normally demanded. However, a number of applications require mobile sensors. Mobile sensors and mobile actors may not preserve connectivity and often the application itself involves sporadic connectivity. Examples include vehicular networks where cars can be seen as sensors carrying information or actuators with possible actions such as changing speed, lanes or roads. People or wild animals can also act as actuators.

The model based on social network theory (Musolesi and Mascolo, 2007) views networks as collections of disconnected clusters. Each cluster is a connected network and nodes may move occasionally from one cluster to another (social movement), according to attractive “virtual forces” from other clusters. This is illustrated in Figure 1.10.

Some applications are based on harsh environmental conditions, such as underwater sensor networks of seals. In this application, batteries are impossible to change and could be lost since seals change their fur periodically. Networks can be very sparse. Seals can meet in clusters but then, they rarely meet at sea. There is no human pattern of day or night behavior.

It is worthwhile to mention that a collection of real mobility traces in various wireless networks is maintained at http://crawdad.cs.dartmouth.edu/.