Accuracy Enhancements for Positioning of Mobile Devices in Wireless Communication Networks

Joao Figueiras

Research output: PhD thesis

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Abstract

Positioning of mobile devices in wireless communication networks is nowadays being intensively
investigated due to the combined benefit of location information and communication. Typical solutions
for such scenario rely on robust algorithms that estimate position from indirect measurements
of the physical length of the communication links. Since these solutions do not require integration
of additional hardware into the mobile nodes, they are cheap and simple to implement. As
a price to pay, accuracy is typically lower in comparison to dedicated positioning systems. Thus,
an important challenge to solve, that this dissertation aims at, is to enhance the accuracy of position
estimation in wireless communication networks without the use of additional hardware. To
reach this goal, the adopted approach is divided in three phases: (i) give a deeper insight on the
problems by analyzing current solutions; (ii) propose solutions for enhancing accuracy of position
information; and (iii) exploit the potential of such position strategies in cooperative schemes within
wireless communications.
The dissertation starts by analyzing common localization and tracking solutions generally used in
positioning systems. Since the measurement sampling is also important for tracking moving devices,
the first analysis concerns the latency time for obtaining location information in short-range
ad-hoc networks. Bluetooth is the elected technology since it is an actual example of such kind
of networks. Simulations of the communication protocols defined in the specifications tell us that
typical mechanisms present in current wireless communications, such as collision avoidance, can
deeply influence the latency time. For accuracy analysis an experimental indoor setup was implemented,
as a typical scenario where short-range communications are used in. The physical length
of the communication links was estimated by using the measurements of signal strength permitted
by the Bluetooth specifications. The final results lead us to the conclusion that due to the high
noise measurements and its inherent low frequency of fresh measurements, tracking wireless devices
is a challenging problem. In order to get better results, we propose a solution which restricts the
movement models of the mobile devices. This restriction, by relying on the assumption that users
typically move in segment-wise linear trajectories, outperforms the standard solutions.
Additionally, this dissertation develops the idea of mobile cooperative positioning. Instead of localizing
mobile devices in cellular networks in an individualist manner, the proposed solutions exploit
the physical proximity of other mobile devices. By fostering the cooperation and subsequent communication
among users, cooperative positioning strategies aim at localizing devices as a group
and not as individuals. In order to reach this goal it is necessary to combine measurements from
two domains: device-to-device links and cellular links. Since this combination of information is not
a straightforward task, this dissertation proposes two different solutions for solving the problem.
The main approach is to use a Bayesian filtering framework design in such a way that both types
of measurements can contribute in a balanced manner to a single estimation of positions for each
cooperative device. While in the first approach all the measurements are combined in a single
estimation procedure, in the second approach, the short- and long-range are separately treated and
combined in a subsequent step. The proposed solutions of combining additional information given
by the device-to-device links with the cellular links, results in considerably higher performance than
standard non-cooperative solutions.
Original languageEnglish
Place of PublicationAalborg
Publisher
Print ISBNs87-92078-38-9
Publication statusPublished - 2008

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