Civil Engineering Reference
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For instance, WLAN-based tracking systems such as Ekahau are economical and
equipment deployment mainly consists of placing access points in the tracked area.
However, the area needs to be calibrated first (several sample points are required at
different locations) which is an arduous and often challenging task, in particular in
dynamic construction environments. Although the range of a typical 802.11 b
WLAN node is 100 m (Wang and Liu, 2005), the technology does not provide the
desired accuracy (1.5 to 2m) needed to locate mobile users and identify their spatial
context with high-precision.
On the other hand, UWB and Indoor GPS require significant time and effort to
deploy all required stations around the coverage areas, in particular on dynamic
construction sites. Additionally, both technologies are relatively expensive. For
instance, a full UWB system with four receivers (any antenna type), one processing
hub, four cables (150 ft) and eleven tags costs about $15 000. Individual receivers
(any antenna type) are $2195 each. The hub costs around $5195 and individual 1 Hz
tags are $40 each, and higher power tags range from $120 to $125 each. An Indoor
GPS system with four transmitters and one receiver costs up to $45 000 (trans-
mitters cost $10 000 each). While the Indoor GPS technology range (60 m) is better
than that of UWB (10 m), it depends on a clear line of sight and some calibration
points are needed unlike UWB. However, both technologies offer centimeter level
positioning accuracy, with Indoor GPS positioning offering significantly higher
precision.
6.5 Integration of GPS and inertial navigation
The main drawback of the aforementioned tracking technologies is their
dependency on pre-installed infrastructure and, in some cases, pre-calibration
for fingerprinting. In addition, most technologies are environment (outdoors
and indoors) specific. Such dependency makes them unreliable in dynamic
environments like construction sites due to constant changes in the site layout.
Furthermore, every potential environment cannot be expected to have pre-
installed infrastructure and pre-calibration done for fingerprinting. In applica-
tions such as post disaster reconnaissance, any pre-installed infrastructure may
itself be partially or completely damaged. It is therefore critical to have a
comprehensive location tracking system that can be used reliably irrespective
of the mobile user's environment and does not rely entirely on tracking
technologies that are dependent on pre-installed infrastructure and pre-cali-
bration techniques.
6.5.1 Personal dead reckoning (PDR) system
Personal Dead Reckoning (PDR) tracking systems are based on Inertial Navi-
gation and are independent of pre-installed infrastructure and calibration.
Although less accurate than WLAN, UWB and Indoor GPS, they provide
sufficient accuracy that degrades gradually with extreme modes of legged loco-
motion (Ojeda and Borenstein, 2007). The PDR system used in the research
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