Data transmission strategies for event reporting and continuous monitoring applications in wireless sensor networks

Wireless Sensor Networks (WSNs) can be typically used to achieve Continuous Monitoring (CM) or Event-Detection inside the supervised area. In CM applications each sensor node transmits periodically its sensed data to the sink node while in Event-Detection Driven (EDD) applications, once an event occurs, it is reported to the sink node by the sensors within the event area. Applications using both continuous monitoring and event driven reporting can also be considered. In this paper, we investigate such hybrid WSNs. Specifically, we propose two different strategies that explicitly assign a time period for the event reporting data by means of the NP-CSMA random access protocol. Both strategies take advantage of the clustered based architecture which assign a TDMA schedule for the continuous monitoring data transmission. By doing so, the continuous monitoring clusters are also used for the event reporting. Hence, no extra energy is consumed for separate event clusters. The performance of these strategies is analyzed for low and high event rate occurrence. These strategies are compared to both continuous monitoring protocols (such as LEACH) and event driven reporting protocols (such as TEEN).