Civil Engineering Reference
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have, and at the same time seamlessly maintain the connection between their node
and available access point(s).
In some situations, interactions with typical building objects can affect the
propagation of energy, and thus the range and coverage of the system. However,
WLAN is considered as appealing because it allows enhanced connectivity,
extended coverage, and is particularly useful when mobile access to data is
necessary. Additionally, user flexibility and portability can easily be reconfigured
while requiring no cable infrastructure. For the above reasons, WLAN was
investigated and implemented in the presented research (Section 6.4.1). A proper
WLAN architecture framework provides a structure to develop, maintain, and
implement an acceptable operation environment, and can support implemen-
tation of automated test bed experiments conducted to continuously track
mobile users.
Ultra-Wide Band (UWB), on the other hand, is a lower power solution that
benefits from causing minimal interference to other systems and UWB networks
operating in the same frequency bands, and even supports multiple independent
networks. UWB systems have, therefore, an inherent immunity to detection and
interception. Additionally, the low frequencies included in the broad range of UWB
frequency spectrumhave long wavelength, which allows UWB signals to penetrate a
variety of materials. For instance, Teizer
et al
. (2008) demonstrated how the UWB
wireless sensing technology is capable of determining three dimensional resource
location information in object cluttered construction environments. For the afore-
mentioned advantages, the proposed research tested and implemented UWB
technology (Section 6.4.2) for possible integration within an overall context-
aware application framework.
The last indoor tracking technology that has been investigated for possible use
in context-aware applications in construction is Indoor GPS. This system focuses
on exploiting the advantages of GPS for developing a location-sensing system for
indoor environments. As mentioned earlier, the GPS signal does not typically
work indoors because the signal strength is too low to penetrate a building.
Nevertheless, Indoor GPS solutions can be applicable to wide space areas where
no significant barriers exist. A GPS-like navigation signal is generated by a
number of transmitters. This signal is transferred through a wireless network
connection providing mobility to the operator (Aziz
et al
., 2005). Additionally,
Indoor GPS is a rugged technology offering superior operating ranges, with
accuracies in the range of few centimeters. Another key advantage of indoor GPS
is the 360
coverage.
As aforementioned, interpretation of a user's spatial context using position alone
results in an incomplete and imprecise interpretation of spatial context. Therefore,
available head orientation trackers were also investigated for possible use together
with position tracking systems. In the past, there have been a variety of head
trackers available (Ferrin, 1991).
Mechanical trackers, for instance, are capable of very good accuracy, resolution,
and interference immunity, but they have extremely limited range and tend to
encumber the user. The most common technology today is magnetic tracking,
which is convenient because it does not have the line of sight problems of optical
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