  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.
