We address a classical problem concerning energy efficiency in sensor networks. In particular, we consider the problem of maximizing the lifetime of coverage of targets in a wireless sensor network with battery-limited sensors. We first show that the problem cannot be approximated within a factor less than <inline-formula> <tex-math notation="LaTeX">$\ln n$ </tex-math></inline-formula> by any polynomial time algorithm, where <inline-formula> <tex-math notation="LaTeX">$n$ </tex-math></inline… CONTINUE READING