Maximum lifetime connected coverage with two active-phase sensors

A sensor with two active phrases means that active mode has two phases, the full-active phase and the semi-active phase, which require different energy consumptions. A full-active sensor can sense data packets, transmit, receive, and relay the data packets. A semi-active sensor cannot sense data packets, but it can transmit, receive, and relay data packets. Given a set of targets and a set of sensors with two active phrases, find a sleep/active schedule of sensors tomaximize the time period duringwhich active sensors form a connected coverage set. In this paper, this problem is showed to have polynomial-time (7.875 + ε)approximations for any ε > 0 when all targets and sensors lie in the Euclidean plane and all sensors have the same sensing radius Rs and the same communication radius Rc with Rc ≥ 2Rs .