On aspects of indoor localization
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Date
2006-08-28T08:50:28Z
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Abstract
One of the key issues of emerging mobile computing and robotics is to
obtain knowledge of the position of persons, vehicles and objects in
an indoor environment. In order to enable a pervasive coverage, this
must be achieved at low cost. Due to the importance of this problem,
numerous solutions have been proposed. In this thesis two important
localization techniques are discussed and major improvements are
developed to address their weaknesses.
A common approach for the position estimation problem is hyperbolic
localization. This method is based on time difference of arrival
(TDOA) measurements of signals transmitted from the mobile unit,
i.e. the unit that is to be located, to a set of fixed reference
units. A key requirement of this technique is that the clocks of the
reference devices are synchronized. Unfortunately, if electromagnetic
signals are used that travel at the speed of light even a very small
clock deviation results in a tremendous inaccuracy of the computed
location. Therefore, a highly precise time measurement and
synchronization is mandatory for these systems. However, clocks
operating at the required resolution and precision are complex and
thus expensive. In this thesis, a localization approach based on TDOA
measurements that implies clock synchronization is proposed and
discussed. It allows for the usage of low cost oscillators that
operate at a moderate frequency in the order of 100 MHz. The impact
of short and long term instabilities like jitter or clock drift are
inherently delimited. The approach can be applied to radio or infrared
as well as ultrasound based systems. The main advantage of this
approach is that common synchronization mechanisms that require a
significant amount of processing and/or hardware resources can be
neglected. Hence, this method is well suited for applications where
the mobile unit must be very low cost and thus, of low complexity.
An alternative to hyperbolic localization is triangulation, which
requires the measurement of angles among fixed reference units and the
mobile target. In this work, an infrared detector array for angle of
arrival measurement is presented. The array consists of multiple
sensing elements that are orientated in different directions. First,
the arrangement is described by a sampling system. However, it is
shown that low cost integrated receivers yield various aberrations,
and thus the sampling approach fails. Subsequently, a new approach
named virtual filter interpolation is proposed and discussed. This
approach can handle individual sensitivity characteristics of each
sensor element and therefore outperforms the sampling approach. The
proposed technique is qualified for extremely low cost localization,
e.g. for robot navigation.
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Keywords
Indoor localization, Angle of arrival, Triangulation, Hyperbolic localization