Global Positioning System Reference
In-Depth Information
BS
1
(x
1
,y
1
)
BS
2
(x
2
,y
2
)
ș
2
ș
1
MS
(x
m
,y
m
)
Fig. 3. The AOA localization method.
distance between an MS and a BS, the MS must lie on a circle centered at the BS. Employing
three or more BS's provides an estimate for the MS location.
RSS is well known for being drastically affected by multipath fading and shadowing
(multipath signals). The error caused by multipath signals can be reduced by using prior
knowledge available on the contours of the signal strength centered at the BS's Smith (1991).
However, such knowledge assumes a specific surrounding environment that can change due
to change in whether, moving objects, such as trucks, as well as new buildings and other
barriers.
4.1.5 Fingerprinting
This localization method is a pattern recognition, or pattern matching, technique. The
underlying concept of fingerprinting is that the radio signal propagation characteristics of
an MS are unique in terms of TOA, AOA, and RSS when captured at different BS's Chen
et al. (2006); Porretta et al. (2008). These characteristics can therefore be used as a signature to
indicate the location of an MS. The fingerprinting method has two phases: a training phase
and localization phase. In the training phase, a database is created to index the different
patterns in the characteristics of the radio signal propagation. In the localization phase, the
signature of the MS is matched with the patterns in the database. The challenging aspect of
this method is assuring that the system can distinguish between similar patterns that represent
different locations.
Of course, the more exhaustive is the training phase (i.e., recording a signature for every small
area in the environment), the more accurate is the MS location estimate. The main drawback
of this method is the requirement to continually update the database as the configuration of
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