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eration approach is the envinronment fingerprinting
method (Jan and Lee, 2003), due to that for all the
rooms in a building a set of radio signal vectors (fin-
gerprints) is collected and saved in a central directory.
A device interested in its position will send its actual
signal vector to the central directory and the directory
will send the closest position to the provided signal
vector back to the device.
2.1 Positioning Accuracy of Mobile
Devices
Proximity detection in GSM networks could use the
Cell-IDs to estimate the position of a mobile device
(Kunczier and Anegg, 2004). The very low accuracy
of this systems in outdoor scenarios will be worser
in indoor scenarios, making them unsuitable for in-
door positioning or guidance applications. The accu-
racy for Cell-ID based approaches could be improved
by probability calculus (Borenovic et al., 2005), but
not in that matter to make them suitable for indoor
positioning. In (Krempels and Krebs, 2008) a new
approach for indoor positioning is proposed that is
based on geo-tagged WLAN access points and tri-
alteration. The proposed solution assumes that there
exists a WLAN infrastructure in that all access points
are tagged with their geographical position and mo-
bile devices will use this tags to estimate their posi-
tion. The accuracy of this system seems to be suit-
able for guidance and navigation applications inside
of large buildings.
Trilateration provides only a very low accuracy in
GSM networks, due to the large diameter of GSM net-
work cells (Kos et al., 2006). Thus, it is not very use-
ful for navigation or guidance systems in indoor envi-
ronments. One way to improve the positioning accu-
racy is to increase the density of antennas that would
increase the network operation costs. However, this is
not the objectiveof the network provider and operator.
The deployment of the trilateration approach in exist-
ing indoor network infrastructures like WLAN would
reduce the costs, but the position estimation becomes
difficult due to the different signal strengths of the
WLAN access points transmitter and multipath signal
propagation (Wallbaum, 2004). The positioning accu-
racy could be improved with the help of probabilistic
calculus, but this is also highly influenced by envi-
ronmental changes. Benchmarks regarding the posi-
tioning accuracy of famous wireless location systems
proposed in the past are discussed by Wallbaum and
Diepolder in (Wallbaum and Diepolder, 2005).
2.2 Mobile Device Positioning Costs
Wireless positioning systems based on proximity de-
tection in GSM networks using Cell-ID’s (Kunczier
and Anegg, 2004) (Borenovic et al., 2005) require a
directory on the network site that maps a Cell-ID to
the coordinates of the corresponding location. This
means, that a mobile device must either establish a
connection to this directory for each positioning re-
quest or must remain connected all the time. Both
cases would produce continous positioning costs. A
directory is also necessary for wireless positioning
systems in GSM networks that are based on trilater-
ation or fingerprinting causing also continuous costs
for the positioning of a mobile device.
Trilateration positioning systems for WLAN in-
frastructures proposed in the past are also directory
based (Wallbaum and Spaniol, 2006) (Wallbaum and
Diepolder, 2005). To determine its position, a mobile
device scans its vicinity for WLAN access points and
send this list to a directory server. The server pro-
vides the coordinates which are related to these ac-
cess points. If there is no positive match, the server
responds with an error and the client cannot deter-
mine its current position. The main drawback of di-
rectory based systems is that clients must establish a
connection to the directory server that would cause
high costs for the positioning information, which is
required very often for navigation and guidance ap-
plications.
The indoor positioning approach based on geo-
tagged antennas (WLAN access points) proposed in
(Krempels and Krebs, 2008) operates directory-less.
Therein, the central directory required by other ap-
proaches was removed in favour of reduced position-
ing costs for a mobile device. The approach is suit-
able for indoor and outdoor scenarios with an existing
WLAN infrastructure without GPS coverage.
3 DIRECTORY-LESS INDOOR
WLAN POSITIONING
In the directory-less indoor positioning approach
based on geo-tagged antennas (Krempels and Krebs,
2008) the Service Set Identifiers (SSID) of each
WLAN access point encodes the geographical coordi-
nates of the access point. A mobile device with an em-
bedded WLAN receiver will receive the broadcasted
SSIDs from a number of access points and could de-
code their geographical coordinates immediatly.
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