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Due to energy constraints in individual sensor nodes, extending the lifetime is an essential objective in wireless sensor networks (WSNs). Several proposals have aimed at that objective by designing energy efficient protocols at the physical, medium access, and network layers. While the proposed protocols achieve significant energy savings for individual sensor nodes, they fail to solve topology-related problems; an example of such problems is that sensor nodes around the base station become bottlenecks and deplete their battery energy much faster than other nodes. A natural solution to such a problem is to have multiple mobile base stations so that the load is distributed evenly among all nodes. Only few proposals have followed that direction. In this paper we propose a mobile base station placement scheme for extending the lifetime of the network. In our scheme the life of the network is divided into rounds and base stations are moved to new locations at the beginning of each round. While previous work has focused on placing the base stations at predefined spots (e.g., the work in ) or at the boundary of the network (e.g., the work in ), we define and solve a more general problem in which a base station can be placed anywhere in the sensing field. We formulate the problem as an Integer Linear Program (ILP) and use an ILP solver (with a constant time limit) to find a near-optimal placement of the base stations and to find routing patterns to deliver collected data to base stations. Our experiments show that our scheme makes significant extension to the lifetime of the network.
Date of Conference: 15-18 Dec. 2007