In this paper, we propose an MAC protocol for energy-efficient            and reliable data transmission in medical emergency monitoring of WBSNs. In addition to the energy-efficient aspect, another consideration is a reliable transmission of data collected from the sensor node to the sink node. Very urgent and important data, such as acute myocardial infarction, cerebral stroke, sudden changes in blood sugar, etc. should be transmitted within a limited time. For this, we consider a cluster-based network. In the proposed cluster-based network, all the nodes in the cluster select a head node. The selected head node always stays ON and detects emergency data transmission. Apart from the residual energy of each node, we consider the past head selection experience for the cluster head selection. As in a medical emergency monitoring application, a lot of data such as video signal transmission must be transmitted using the special control packet for slot-reservation and operational cycle expansion. Our protocol reduces the packet transmission delay and average node energy consumption in comparison to existing related MAC protocols.

WBSNs, MAC, energy efficiency, cluster, delay.