Hybrid MAC protocol design in wireless sensor networks becomes vibrant research field for the pastseveral years. The ubiquitous plug and play characteristics of commercially available open source hardwarepaved way for the development of smart wireless sensor network. Wireless sensor networks can be termed asa new generation of distributed embedded systems that has a capability of meeting broad range of real-timeapplications. Examples includehome automation, industrial automation, power plant monitoring, radiationmonitoring, fire monitoring, pipeline monitoring and control, border surveillance, medical care etc. Wirelesssensor networks that are deployed in time critical or mission-critical applications with highlydynamicenvironments have to interact with the physical phenomenon under stringent timingconstraints and severeresource limitations. The proposed hybrid ET-MAC (Emergency Threshold MAC) protocol targets advancedhome automation which require careful MAC protocol design for safety critical low latency, reliability and endto end delay as a primary concernand secondary concern can be given for parameters like residual energy,energy efficiency etc. Supportingreal-time QoS faces severe challenges due to the wireless nature, limitedresource, low node reliability, distributedarchitecture and dynamicnetwork topology.This paper presents thedesign, implementation and performance evaluation of a hybrid ET-MAC protocol with prioritization ofnodeswhich adopts a TDMA approach to schedule collision-free slots during emergency periodand CSMA/CAapproach during normal operation conditions in time/mission critical applications to avoid collision andto havelow latency. The proposed MAC protocol is simulated in NS2 environment and from the results, it is observedthat proposed protocol performs better than conventional MAC protocols in terms of energy efficiency andoffering low latency.
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