A hybrid MAC protocol for emergency response wireless sensor networks

Keywords: MAC protocol Wireless sensor networks Fire emergency a b s t r a c t We introduce ER-MAC, a novel hybrid MAC protocol for emergency response wireless sensor networks. It tackles the most important emergency response requirements, such as autonomous switching from energy-efficient normal monitoring to emergency monitoring to cope with heavy traffic, robust adaptation to changes in the topology, packet prioritisa-tion and fairness support. ER-MAC is designed as a hybrid of the TDMA and CSMA approaches, giving it the flexibility to adapt to traffic and topology changes. It adopts a TDMA approach to schedule collision-free slots. Nodes wake up for their scheduled slots, but otherwise switch into power-saving sleep mode. When an emergency occurs, nodes that participate in the emergency monitoring change their MAC behaviour by allowing contention in TDMA slots to achieve high delivery ratio and low latency. In its operation, ER-MAC prioritises high priority packets and sacrifices the delivery ratio and latency of the low priority ones. ER-MAC also guarantees fairness over the packets' sources and offers a synchronised and loose slot structure to allow nodes to join or leave the network. Simulations in ns-2 show the superiority of ER-MAC over Z-MAC, a state-of-the art hybrid MAC protocol, with higher delivery ratio, lower latency, and lower energy consumption. When a cluster of nodes in the network detects fire, nodes with ER-MAC deliver twice as many high priority emergency packets and four times faster than Z-MAC. This is achieved by ER-MAC with only one fifth as much energy as Z-MAC. Wireless Sensor Networks (WSNs) for emergency applications , such as fire, flood and volcano monitoring, must be traffic and topology adaptive. The communication protocol can be delay tolerant during normal monitoring and designed for energy efficiency. However, when an emergency event occurs, energy efficiency is less important than high packet delivery ratio and low latency, and the communication protocol should adapt in response. The protocol must also be able to prioritise high priority packets , as they normally contain important sensed data and require timely delivery. In addition, the protocol must support fairness over the packets' sources. Fairness is important when a hazard occurs, so the sink can receive complete information from all sensor nodes in the network to monitor the spread of the hazard. Some traffic and topology adaptive Medium Access Control (MAC) protocols have been designed. S-MAC [1], T-MAC [2], B-MAC [3] and X-MAC [4] …