An energy efficient implementation of on-demand MAC protocol in medical Wireless Body Sensor Networks

This paper presents an energy-efficient implementation of a real-time on-demand MAC protocol for medical wireless body sensor network (WBSN). Medical WBSN is focused on pervasive healthcare and medical applications, such as monitoring vital signs, making basic drug delivery, etc. The sensor nodes in the heterogeneous WBSN generally require different data rates, due to their differing functions. Additionally, because of the strict resource constraints, the sensor nodes must be ultra-low-power. Thirdly, low-rate treatment-function nodes must also ldquowork-on-demandrdquo to prove proper activities in the slave nodes such as stimulus and drug delivery. These three requirements cannot currently be satisfied simultaneously in commonly-used single channel implementations because the channel monitoring consumes too much power for long-term use. In the proposed implementation, a secondary channel is introduced in, which is used for channel listening only. Benefiting from the secondary channel, the node can achieve both real-time ldquowork-on-demandrdquo and zero idle power, by means of recovering energy from the ldquodemand tokenrdquo. An elaborated energy-harvesting RF module achieves monitoring the secondary channel. The prototype system of sensor nodes is expected for the zero-idle-power and the response time of less than 2 ms.