The aging population and the high expectations towards quality of life in our society lead to the need of more efficient and affordable medical systems and monitoring solutions. The development of wireless Body Sensor Networks (BSNs) offers a platform to establish such a healthcare monitoring systems. However, BSNs in the healthcare domain operate under conflicting requirements. These are the maintenance of the desired reliability and message latency of data transmissions (i.e. quality of service), while simultaneously maximizing battery lifetime of individual body sensors. In doing so, the characteristics of the entire system, especially the Medium Access Control (MAC) layer, have to be considered. For this reason, this chapter aims for the optimization of the MAC layer by using energy-saving techniques for BSNs. The fact that the IEEE 802.15.4 MAC does not fully satisfy BSNs requirements highlights the need for the design of new scalable MAC solutions, which guarantee low-power consumption to the maximum number of body sensors in high density areas (i.e., in saturation conditions). In order to emphasize IEEE 802.15.4 MAC limitations, this chapter presents a detailed overview of this de facto standard for Wireless Sensor Networks (WSNs), which serves as a link for the introduction and description of the here proposed Distributed Queuing (DQ) MAC protocol for BSN scenarios. Within this framework, an extensive DQ MAC energy-consumption analysis in saturation conditions is presented to be able to evaluate its performance in relation to IEEE 802.5.4 MAC in highly dense BSNs. The obtained results show that the proposed scheme outperforms IEEE 802.15.4 MAC in average energy consumption per information bit, thus providing a better overall performance that scales appropriately to BSNs under high traffic conditions. These benefits are obtained by eliminating back-off periods and collisions in data packet transmissions, while minimizing the control overhead.
An efficient GTS allocation scheme for IEEE 802.15.4 MAC layer