  Target coverage problem in wireless sensor networks is concerned with
maximizing the lifetime of the network while continuously monitoring a set of
targets. A sensor covers targets which are within the sensing range. For a set
of sensors and a set of targets, the sensor-target coverage relationship is
assumed to be known. A sensor cover is a set of sensors that covers all the
targets. The target coverage problem is to determine a set of sensor covers
with maximum aggregated lifetime while constraining the life of each sensor by
its initial battery life. The problem is proved to be NP-complete and heuristic
algorithms to solve this problem are proposed. In the present study, we give a
unified interpretation of earlier algorithms and propose a new and efficient
algorithm. We show that all known algorithms are based on a common reasoning
though they seem to be derived from different algorithmic paradigms. We also
show that though some algorithms guarantee bound on the quality of the
solution, this bound is not meaningful and not practical too. Our
interpretation provides a better insight to the solution techniques. We propose
a new greedy heuristic which prioritizes sensors on residual battery life. We
show empirically that the proposed algorithm outperforms all other heuristics
in terms of quality of solution. Our experimental study over a large set of
randomly generated problem instances also reveals that a very na\"ive greedy
approach yields solutions which is reasonably (appx. 10%) close to the actual
optimal solutions.
