wireless ad hoc networking

Localization Techniques for Wireless Local Area Networks 263
in a network. They usually equip powerful equipments such as GPS or
high-powered transmitters. The APIT algorithm locates a node according
to the following steps: (1) Beacon exchange, (2) APIT testing, (3) APIT
aggregation, and (4) center of gravity (COG) calculation.
Initially, each anchor broadcasts beacons that include the location information
where the anchor is. A node who wants to know its location could
receive many beacons from the audible anchors. Then a node builds various
triangles from a set of the N audible anchors. Figure 9.8 illustrates
the APIT testing aims to determine whether a node is inside or outside the
triangular regions. The area of the maximum overlap is the most probable
area where a node is present during APIT aggregation. Figure 9.9 illustrates
the APIT aggregates of the outcome of the APIT testing through a
grid SCAN approach. The SCAN approach uses a grid array to represent
the maximum area where a node likely resides. Finally, the centroid of the
area is treated as the location of an MU.
9.2.2.3 Probabilistic Techniques
Deterministic techniques 2,3 store the scalar values of a measured RSS from
each access point for each predefined location in the radio map, i.e.,
(a)
(b)
Figure 9.8
(a) A node is inside a triangle. (b) A node is outside a triangle.
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Figure 9.9
Using SCAN approach to execute APIT aggregation.