Civil Engineering Reference
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While these technologies are capable of streamlining tracking, data access and
retrieval processes, their performances differ from the manufacturers' specifica-
tions when used on construction sites because of issues such as interference, data
reading range, data accuracy, inter-operability of hardware and software, and
memory limitations (Kiziltas
et al
., 2008). In addition, although these technologies
can save time and effort, they can also add new tasks that need to be performed
prior to, during, or after the use of a technology in the field. Hence, a thorough
understanding of both the technological capabilities and process implications of
these technologies is needed to be able to use them effectively during construction,
inspection and maintenance of facilities.
6.3.1 WLAN-based user position tracking
A WLAN is a flexible data communication system implemented as an extension to
or as an alternative to a wired LAN. The technology consists of a set of access points
communicating wirelessly, using electromagnetic waves, to any WLAN-enabled
device (Figure 6.3).
One set of experiments conducted to obtain location information in this study
was based on a WLAN-based position system called Ekahau, manufactured by the
Finnish company Ekahau Inc. (Ekahau, 2007). The underlying approach used for
determining users' position in the Ekahau tracking system is the fingerprinting
technique (Figure 6.4).
As shown in Figure 6.4, location fingerprinting consists of two phases: “training”
and “positioning” (Li
et al
., 2006). The objective of the training phase is to build a
fingerprint database. To generate the database, sample reference points (RPs) must
first be carefully selected. Locating a mobile user (MU) at one RP location, the
Received Signal Strengths (RSS) of all the access points (AP) are measured. From
such measurements, the characteristic feature of that RP (its RSS) is determined,
Figure 6.3 User localization with WLAN technology
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