Event reliability in Wireless Sensor Networks

Ensuring reliable transport of data in resource constrained Wireless Sensor Networks (WSNs) is one of the primary concerns. The two reliability mechanisms typically used in WSNs are packet reliability and event reliability. Packet reliability requires all packets from all the sensor nodes to reach the sink that can result in wastage of sensors´ limited energy resources. The sensing regions of densely deployed sensor nodes often overlap with one another and data from nodes that are in close proximity tend to exhibit high level of spatial locality. This introduces the concept of event reliability where a reliable transfer of event data from each sensing region in a sensor network is sufficient. This paper proposes the Event Reliability Protocol (ERP) that enables reliable transfer of packets containing information about an event to the sink while minimizing similar redundant packets from nodes in the vicinity of one another. ERP builds on the spatial locality condition and employs an implicit acknowledgement (iACK) mechanism with region-based selective retransmissions. The performance of ERP is evaluated and compared against a commonly used iACK scheme to show that ERP significantly improves event information delivery and network scalability, thus maintaining good coverage of events in the sensor network.