Avoiding the Flip Ambiguities in 2D Wireless Sensor Localization by   Using Unit Disk Graph Property
  In this paper, we propose a range-based localization algorithm to localize a wireless sensor network (WSN) in 2D. A widely used algorithm to localize a WSN in 2D is trilateration, which runs in polynomial time. Trilateration uses three distance measurements to localize a node. In some cases, the lack of connectivity leads to a low percentage of localized nodes since a node's position can be fixed using three distance measurements. We propose an algorithm that finds the position of a node by using the absence of a distance measurement in addition to a third distance measurement. If two nodes are not able to sense each other, that means the distance between them is more than the sensing range. Therefore, our algorithm checks if the possible positions of an unlocalized node $u$ is inside the sensing range of a localized node $\ell$ that is not the neighbor of $u$. In such case, we eliminate one of the possible positions. 
Onur Cagirici
cs.NI