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

1.4 EVENT-DRIVEN, PERIODIC, AND ON-DEMAND REPORTING

There are three types of applications for WSNs and each has its corresponding data communication modes: event-driven, periodic, and on-demand reporting. In the event-driven mode, sensors report the sensing data to the sink once a specified event (e.g., fire) has been detected. In the periodic reporting (or time-driven) mode, sensor nodes gather information from the environment at predetermined times and periodically send the data to the sink. In the on-demand (or query-driven) mode, users decide when to gather data. They send instructions to the WSN indicating that they wish to receive data and then wait for the required type of data to be sent in the requested format. Users may even specify the future reporting periods; subsequent reports would then be sent in periodic reporting mode.

Target or event detection and tracking is a typical example of applications in event-driven reporting. Its purpose is to detect, classify, and locate specific targets or events, as well as track the targets or events over a specified region. Once there is an event or a target emerging in the area, the sensor nodes around the target or event gather the required information and report back to the sink. One characteristic of event-driven reporting is its real-time requirement. This means that data transmission latency is one of the key problems in these applications.

Targets can be divided into two categories: targets in the first category are individual ...