Solving energy issues for sweep coverage in wireless sensor networks.

Sweep coverage provides solutions for the applications in wireless sensor networks, where periodic monitoring is sufficient instead of continuous monitoring. The objective of the sweep coverage problem is to minimize the number of sensors required in order to guarantee sweep coverage for a given set of points of interest on a plane. Instead of using only mobile sensors for sweep coverage, use of both static and mobile sensors can be more effective in terms of energy utilization. In this paper, we introduce two variations in sweep coverage problem, where energy consumption by the sensors is taken into consideration. First, an energy efficient sweep coverage problem is proposed, where the objective is to minimize energy consumption by a set of sensors (mobile and/or static) with guaranteed sweep coverage. We prove that the problem is NP-hard and cannot be approximated within a factor of 2. An 8-approximation algorithm is proposed to solve the problem. A 2-approximation algorithm is also proposed for a special case. Second, an energy restricted sweep coverage problem is proposed, where the objective is to find the minimum number of mobile sensors to guarantee sweep coverage subject to the condition that the energy consumption by a mobile sensor in a given time period is bounded. We propose a (5+2)-approximation algorithm to solve this NP-hard problem.