Civil Engineering Reference
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enable the design of applications that have the capability to identify a user's
location and modify their settings, interfaces, and functionality accordingly
(Pateli
et al
., 2002).
Global Positioning System (GPS), being a satellite-based navigation system,
works very well outdoors but lacks support indoors and in congested areas (El-
Rabbany, 2002). In addition, unlike outdoor areas, the indoor environment
imposes different challenges on location discovery due to the dense multipath
effect and building material dependent propagation effect (Xiang
et al
., 2004). In
contrast to the outdoor positioning technologies that are capable of identifying the
location of an object or person in open areas, indoor positioning technologies
typically set the constraint of a limited coverage range, such as a building or other
confined spatial area. These technologies are, therefore, not dependent on any
external network. They are dependent on a set of technologies used for transmitting
wireless data in closed environments.
The first indoor positioning systems that were developed used infrared sensors.
Infrared (IR) systems (Aitenbichler and Muhlhauser, 2003) are known for their
inability to penetrate walls or other opaque materials. A computing device with an
infrared receiver uses these signals to determine its current position. Location of
tagged devices determines where receivers should be placed. These devices emit IR
light, and if the tagged device is in the same room as a receiver, its position is
known. However, for these systems to be effectively used there must be receivers,
connected using special wiring, in every room where an asset might be located,
which is time consuming and expensive. Additionally, IR-based systems fail to
function if the IR signal gets blocked. IR-based location systems are subject to
restrictions, such as line of sight limitations or poor performance with fluorescent
lighting or in direct sunlight. Therefore, as intervening objects can easily block
infrared signals, IR systems were not considered in this research.
A close competitive technology to IR systems is Bluetooth (Kodde, 2005) and,
unlike infrared, the line of sight it provides can penetrate through walls or
obstacles. Bluetooth, providing ranges of up to 100 meters, is also low power and
low processing with an overhead protocol, which makes it ideal for integration
into small battery powered devices. However, Bluetooth positioning technology
posessomedownsidesandproblems,suchasthedatarateandsecurity.Itonly
offers data rates of 1 MBps, which provides low rates for data transfer. For this
very reason, IR systems are considered by many to be the complimentary
technology to that of Bluetooth. The greater range and radio frequency (RF)
of Bluetooth make it much more open to interception and attack. On the other
hand, Bluetooth still remains the best for short range wireless technology but it
lacks efficiency in data transfer and for long range applications, and, therefore,
was not suitable in this research. Radio-based positioning has emerged as a more
attractive alternative.
A radio-based technology used for identifying and tracking objects within a few
square meters is Radio Frequency Identification (RFID). An RFID (Ayre, 2004)
system integrates an antenna with electronic circuitry to form a transponder that,
when polled by a remote interrogator, will echo back an identification number.
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