Date Added: May 2009
Wireless sensor networks have been used in a wide range of applications such as military surveillance, environmental monitoring, and target tracking. In all these applications, the information collected by sensor nodes is useful only when coupled with the nodes' physical locations. How to obtain the location information of the sensor nodes or the target of interest correctly and efficiently becomes very important. Global Positioning System (GPS) is a widely used location services. However, the cost and nice environment requirement of GPS makes it not applicable in many sensor network applications.