Service preemptions for guaranteed emergency medium access in Wireless Sensor Networks

Wireless Sensor Networks (WSNs) recently find extensive applications in remote disaster and health monitoring, where traffic prioritization is extremely essential for timely dissemination of critical information to the first responders. Though several resource control standards exist for general wireless networks, supporting differentiated traffic services (Quality-of-Service (QoS)) at the Medium Access Control layer for sensor networks need exclusive investigation and significant improvements. Particularly, the network treatment for disaster or medical emergencies needs to be exclusive (deterministic guarantees) rather than probabilistic guarantees as in most wireless QoS standards. In this paper, we introduce channel service preemptions during random medium access in WSNs. In the context of time-critical sensor applications, emergency traffic will have the privileges to interrupt the services of other routine traffic in the network to guarantee the lowest possible channel access latencies. We design our methodology within the QoS framework of the popular 802.11e EDCA standard and demonstrate the importance of service preemptions for emergency reporting. The performance analysis predicts close to 50% uniform decrease in emergency medium access delays when using our Channel Preemptive-EDCA (CP-EDCA) as compared to EDCA. The results also depict that CP-EDCA guarantees the lowest delay bounds and immunity to the presence of other lower priority traffic, for emergency frames, even under high network loads. The cost, however, is increased delays for routine traffic, which is acceptable during emergency sensor reporting.