Basics of Wireless Locationing
Mikko Asikainen, Msc
University of Eastern Finland
Department of Computer Science
Outline
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Wireless personal area networks (WPAN’s)
Wireless locationing in a nutshell
Received Signal Strength -locationing
Time of Arrival -locationing
Angle of Arrival -locationing
Research problems
Current issues at CI group
Wireless personal area networks
• Developments over the last decade have made
it possible to create miniatyrized electronic
devices with wireless connectivity.
• These devices can form ad-hoc networks and
utilize multi-hop routing to form strong and
useful wireless networks.
• These networks are commonly known as
sensor networks, smart dust or Wireless
Personal Area Networks (WPAN’s)
Common WPAN applications
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Building automation
Smart spaces
Sensor technologies
Logistics
Tracking and locationing
Entertainment
Research
Your imagination is the limit, really.
Different devices for different needs
Wireless locationing
• “Wireless locating is a category of
technologies to determine the actual location
of an entity by means of wireless
transmission.“ –Wikipedia
• By analyzing the properties of the signal sent
by mobile devices (nodes hereafter) we can
make certain assumptions on the location of
said devices.
The foundation of locationing
• For locationing of a mobile node, we also need nodes
which’s position on a XYZ grid is known to us. These are
known as landmark nodes.
• If we can make accurate enough assumptions on the
distance the transmission has traveled or the angle of
arrival, we can calculate the location using
triangulation, multilateration etc.
• These geometric
princibles are old indeed,
but new technolgies bring
new applications nobody
has thought about before.
• For example, acoustic
princibles are of use in
wireless transmissions.
Angle of Arrival
• With specialized antennas
the direction the
transmission comes from can
be determined.
• This is difficult to use in
WPAN-networks.
• AoA-locationing is used in
old school triangulation and
radar systems.
Signal travel time
• A radio wave is transmitted through space at the
speed of light, which means the wave travels 30
centimeters in one nanosecond (the billionth of a
second).
• Estimation of the time it has
taken for the signal to travel
requires very precise clocks.
•Time-of-Arrival locationing is
used in GPS systems.
Signal Strength
• The attenuation of a radio signal over a distance can be
modeled using, for example the log-normal path loss
model:
• Pl is the signal loss in dB between the transmitter and the
receiver, PL0 is the signal loss on the reference distance, γ is
the loss exponent, d is the distance between the
transmitter and the receiver in meters, d0 is the reference
distance in meters and Xg is a zero-mean gaussian random
variable.
• With models such as this, it is possible to approximate the
distance the weakened signal has traversed.
Received Signal Strength locationing
• Received signal strength locationing is the
subject of much research and many projects
because the components needed for RSS
calculation are both cheap and can be found
in most radio devices.
• RSS is especially important in indoor
environments since GPS doesn’t reach there.
That’s all fine in theory, but…
• The actual behavior of a radio wave in indoor
environments is extremely difficult to model
accurately.
• When the wave comes into contact with an obstacle,
part of the energy of the wave is scattered and
reflected, and a part continues through the medium
weakened. Predicting this has caused generations of
researchers a lot of trouble.
Tell me about it.. -
Line of Sight and multipath
propagation problems ahoy!
We wouldn’t research this stuff if it
would already be solved, though.
• At the moment, indoor locationing is not very
accurate.
• A reliable indoor locationing system reaching
<1 meter accuracy has a big demand.
• Indoor locationing is one of the subjects the CI
group researches.
The Smart Technology project
• The agricultural industry would greatly benefit from accurate indoor localization. A
working system would allow to study the behavior and status of animals.
• In the Smart Technology project we develop a locationing prototype system to track
free roaming dairy cows in an intelligent cowshed environment.
• A cowshed is a very difficult environment to deploy a
wireless system in. If we can make it work here, we can make
it work virtually anywhere.
Theses!
There’s a lot to study and research about in sensor
networks, wireless locationing etc. Contact me!
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Think of a possible subject
mailto:mikko.p.asikainen@uef.fi
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Bsc, Msc, Profit!
The images in this presentation have been blatantly stolen from the
net. Please don’t sue me!