As the presence of wireless mobile devices increases a whole new aspect of
services that can be provided to users emerge. Real world contexts such as
position play only a marginal role in traditional computing since the user
is all but bound to a single fixed location but are very prevalent in mobile
computing where the user's position might change from one moment to the
next. The number of services that can be offered to the users of mobile
devices based on position is endless, from locating the origin of a distress
call to finding friends and relatives.
In this thesis, a system for positioning users in a wireless network using
only the existing network infrastructure is presented. The wireless network
infrastructure is made up by access points, or base stations, which function
as bridges between wireless devices and the regular wired network. By
analyzing the degradation of the signal broadcasted from these access points
the approximate distance between the access point and the mobile device can
be created. The set of this information from all detectable access points at
a specific position is called a signal space location and is a unique
fingerprint for every real world location. By inserting these signal space
locations into an undirected graph the system becomes aware of the
surroundings.
Autonomy is a central concept to this method. For a positioning system to be
usable in a global context instead of just a local one it needs to be able
to independently analyze and adapt to new surroundings as well as detect any
changes to the signal space of a building. It also needs to be able to adapt
to errors, such as an access point malfunctioning. Basically, autonomy
represents the ability to independently handle any situations that might
change the system's view of the surroundings.
Empirical tests of the method yielded discouraging results. Due to the
complex nature of indoor radio wave propagation the signal fluctuated,
making it di...
