Localization (Position Estimation) Problem in WSN

In a network of thousands of nodes, usually densely deployed, it is unlikely that the designer will determine the position of each node. To process sensor data, however, it is necessary to know where the data come from. Equipping every node with a global positioning system (GPS) is currently a costly (in volume, money, and power consumption) solution. Instead, we can estimate node positions relying only on measurements of distances between nodes and other similar connectionimposed proximity constraints. In this model, only a few nodes (anchors) have known positions (perhaps equipped with GPS or placed deliberately) and positions of the remaining nodes are computed from knowledge about communication links. The distance information can be based on time-difference of arrival, received signal strength, and other criteria.