Wireless Sensor Networks: Passive Mobility Models
As we saw in the previous chapter, WSNs find application in very diverse user scenarios. Although in many scenarios there is no mobility involved, applications of WSNs where mobility plays a role do exist. We can distinguish three different kinds of mobility in WSNs: (i) mobility of the sensor nodes; (ii) mobility of the sink node(s); and (iii) mobility of a monitored event/object. The first kind of mobility occurs when at least part of the sensor nodes is mobile. Examples of sensor node mobility are when sensor nodes are dispersed and free to move in the monitored region (e.g., sensor nodes floating on the surface of the ocean), or when they are installed on animals for wildlife tracking and monitoring. The second kind of mobility refers to a situation in which sink nodes are able to autonomously move in the monitored region, with the purpose of collecting data from the sensor network. Finally, the third kind of mobility occurs when a WSN is used for monitoring or tracking purposes, and works under the event-driven data model. In this case, modeling the occurrence and mobility of an event to be monitored (e.g., a gas leak and movement of the resulting gas plume) is useful for understanding the resulting data traffic pattern in the WSN. Similarly, when the WSN is used for target tracking, modeling target movement is useful for estimating the amount and pattern of data generated in the WSN during target tracking.