Sentry Selection in Sensor Networks: A Sufficient Condition for k Single Covers

Wireless sensor networks are becoming increasingly popular due to their numerous applications and advances in microelectronics. One basic application is the surveillance or monitoring of large areas. Assuming n sensor nodes are randomly deployed and each sensor can cover a circular area of a certain radius r, a central question is what fraction the total area of interest can be expected to be covered (as a function of n and r). This question has been answered for certain cases. We present a recent result on a related problem, the so-called sentry selection problem. In practical applications, it is desirable to turn most of the sensor nodes off to conserve energy, while having a subset of nodes active acting as sentries. After a certain period of time, the sentry duty is moved to a disjoint set of nodes, and so on. Let the desired number of subsets be k. Then the sentry selection problem is the following: Find the minimum radius r such that there exists a partition of the node set into k subsets that each provide a (single) cover of the area of interest. Note that this is different from asking for k-coverage, since a k-cover may not be divisible into k single covers.