  In this paper we address the problem of prolonging the lifetime of wireless
sensor networks (WSNs) deployed to monitor an area of interest. In this
scenario, a helpful approach is to reduce coverage redundancy and therefore the
energy expenditure due to coverage. We introduce the first algorithm which
reduces coverage redundancy by means of Sensor Activation and sensing Radius
Adaptation (SARA)in a general applicative scenario with two classes of devices:
sensors that can adapt their sensing range (adjustable sensors) and sensors
that cannot (fixed sensors). In particular, SARA activates only a subset of all
the available sensors and reduces the sensing range of the adjustable sensors
that have been activated. In doing so, SARA also takes possible heterogeneous
coverage capabilities of sensors belonging to the same class into account. It
specifically addresses device heterogeneity by modeling the coverage problem in
the Laguerre geometry through Voronoi-Laguerre diagrams.
  SARA executes quickly and is guaranteed to terminate. It provides a
configuration of the active set of sensors that lifetime and coverage
requirements of demanding WSN applications, not met by current solutions.
  By means of extensive simulations we show that SARA achieves a network
lifetime that is significantly superior to that obtained by previous algorithms
in all the considered scenarios.
