Basics of Wireless Locationing Mikko Asikainen, Msc University of Eastern Finland Department of Computer Science

Outline 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 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, PL 0 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, d 0 is the reference distance in meters and X g 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! 1: Think of a possible subject 2: 3: ??? 4: Bsc, Msc, Profit! The images in this presentation have been blatantly stolen from the net. Please don’t sue me!