On the reliability of backbone-assisted end-to-end transmissions in WSNs

Many anticipated deployment scenarios, in particular military, healthcare, and disaster-recovery applications, of Wireless Sensor Networks (WSNs) require reliable source to sink communication. Since transmission range of sensors is quite limited, to achieve higher end-to-end transmission reliability, WSNs generally employ intermediate backbone links (wired or wireless) that can deliver packets at larger distances. In this paper, we evaluate the reliability of backbone-assisted routing and dissemination in WSNs. In particular, we use reliability theory to investigate two important problems: a) if sensor node to backbone/gateway node ratio is fixed in a unit area, what is the maximum achievable reliability? b) How many wired hops or gateway nodes are required to achieve a given reliability? Finally we analyze the cost and benefit incurred by adding gateway nodes to a backbone-assisted WSN and observe that after a certain threshold adding more backbone nodes to the WSN provides negligible improvement in the overall end-to-end reliability.