Guarding an area of interest in sensor grids with unreliable nodes

We consider Wireless Sensor Networks (WSNs) deployed in the plane to guard against intrusion events aiming to access a specified area of interest. Sensor nodes of the network are assumed to be unreliable with known failure probabilities. In such an environment, system dependability is of prime importance. To aid in analyzing dependability, we formalize a network wide reliability measure that quantifies the likelihood that the network provides simultaneous detection and reporting of intrusion events. We refer to the problem of computing the defined measure as the breach path to target area reliability (BPTA-REL) problem. We show that the problem admits polynomial time solution on grid networks employing diagonal links where the width of a grid is limited but the length can be arbitrarily large. Such grid topologies are useful for border area protection applications. The result is notable since the BPTA-REL problem is #P-hard in general. We present numerical results that show the potential use of our devised algorithm as a network design tool.