Toward highly-available WSNs for assisted living

In response to the consistent increase of elder people living in their apartments, and the need for innovative non-obtrusive tools to connect elders to their caregivers, we started an initiative with the Institute of Gerontology at Wayne State University to explore the application of wireless sensor networks (WSNs) for the monitoring of elder people and the communication of potential emergency conditions to their remote caregivers. Motivated by the fact that sensor nodes are resource-constrained and error-prone on one hand, and mission urgency on the other hand, we argue that high availability is a vital requirement that viable WSNs for assisted living have to acquire. We propose the use of classical reliability theory techniques to tackle this issue in a systematic way. We develop analytical models of the WSN availability in terms of the availability of the underlying sensor nodes. These models help in planning for the required number of nodes and the way these nodes are scheduled ON and OFF Our preliminary results show that using node scheduling almost doubles the expected WSN total uptime.