Date Added: Jan 2012
Many applications of wireless sensor networks such as object tracking, environment and habitat monitoring, intrusion detection, and geographic routing rely on the location information of sensor nodes. To provide accurate position information of sensor nodes, each sensor node can be equipped with GPS. In many applications, however, it is not possible that all sensor nodes are equipped with GPS economically and technically. For examples, GPS signal hardly reaches to all nodes when wireless sensor networks are deployed in underground structure or underwater environments, where a sensor node must estimate its position from various information of other nodes that are possibly equipped with GPS or estimate their positions from others as well.