T863203
Mani Bhowmik
Dated: 23.04.2010
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WLAN
◦ Is a wireless local area network that uses high
frequency radio signals to transmit and receive data over distances of a few hundred feet; uses Ethernet ; protocol
◦ Standards Available
802 11 2 4 GHz 2Mbps;
x 802.11, 2.4 GHz, 2Mbps;
x 802.11b, 2.4 GHz, 11 Mbps x 801.11a, 5 GHz, 54 Mbps x 802.11g, 2.4 GHz, 54Mbps;
x 802.11n, 2.4 GHz, 100 Mbps
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Location
◦ Refers to a place
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Position
Refers to a place with some reference point
◦ Refers to a place with some reference point
◦ Reference point is in general Earth’s coordinate system consists of latitude, longitude and altitude
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A location is not always a position, but a
position is always a location.
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Received Signal Strength
◦ Positioning is calculated based on received signal power level
◦ Measured power levels are converted to distance Measured power levels are converted to distance estimates by using a simple propagation model
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Fingerprinting
◦ Pre-defined fingerprinting is also used to determine position
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Time of Arrival
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Time of Arrival
◦ Time of Arrival technique is used along with RSSI
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RSSI Model or Propagation model
◦ Connectivity
x Contains underlying radio technologies, WLAN
x Establish links with stationary devices [at least threeEstablish links with stationary devices [at least three for horizontal position; four for three dimensional position]
◦ Measurement
◦ Measurement
x Contains methods to meter RX power level.
x Measuring RX power levels can by performed by a
bil d i i d i b h
mobile device or stationary devices or both
◦ Distribution
f h d b h
x Assisting information is exchanged between the mobile and stationary devices
x Consist of coordinates of stationary devices, floor plan, TX power levels, antenna gains, used frequencies and x Other information that affects to the propagation
model
◦ Computation
x Mobile based: Mobile device does the measuring and data processing to determine position
data processing to determine position
x Network Based: Stationary base station does the computaion
◦ Computation (contd...)
Phase One:
x Phase One:
x Convert measured RSSI values a.k.a RX power to distance estimates
x RX power levels are converted to distance estimatesRX power levels are converted to distance estimates
x Phase Two:
x Because measurements are corrupted by noise, individual measurement error is decreased by statistical mean and y variance combination
x Phase Three:
x Convert distance estimate to position estimate
◦ Exploitation
x Show the position in a GUI application
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Fingerprinting or Empirical model
◦ RF Map Creation
x A Radio Frequecy grid is created and stored into a database for reference
x Contains signal strength at each location from each access points
◦ Connectivity:
x Movile device gets connected to the access points. And
access points grant access to the mobile device. Server and mobile connectivity is also established
Meas rements
◦ Measurements
x Mobile device measures signal strength received from all access points and send the information to the server
◦ Database search
d h d l h f
x Based on the received signal strength information server searches the database and finds the closest match and returns the information to mobile device
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Fingerprinting is the characteristic of the signal at various position in a network
◦ i. Postioning of a mobile device can be measured based on the fingerprinting
based on the fingerprinting
◦ ii. A device can be identify based on fingerprinting [
http://security.dso.org.sg/publications/wireless/wireless_fingerprinting_wisec08.pdf]
b d f d f d
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Combine i and ii, position of an identified
device is known
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TOA Model
◦ Mobile device transmits signal to the receiver along with Tx time. Signal strength is known.
◦ Receiver receives the signal and note the time of
◦ Receiver receives the signal and note the time of
◦ Tx Receiver calculates the distance by measuring the
d ff f d d
time difference of Tx and Rx and wave
propagation velocity
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Security
◦ WLAN is secure network. Position information is also secure
x Wired Equivalent Privacy [WEP]Wired Equivalent Privacy [WEP]
x Wi-Fi Access Protection [WAP]
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Ease of use
◦ WLAN is everywhere
◦ Only aim is to build a measurement model to determine position
determine position
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Short Range
◦ Positioning is confined to a small area or location
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Possibly high power consumption
P i i i b f id f
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Privacy is an issue because of wide range of usage of 802.11x standard
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Multipath propagation uneven spreading
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Multipath propagation, uneven spreading adds more noise
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Fingerprinting needs huge manual efforts: g p g g
creation and constant update to the database
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Fingerprinting wins the race, but that is
because there is a huge effort to create pre- determined RF map
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But RSSI based model is mostly used with
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But, RSSI based model is mostly used with
support of TOF [TOA and TDOA] techniques
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To determine location of a property in a confined area of location
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To make a secure area of movements in industry or in airport
industry or in airport
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Very few commercial offering
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http://answers.yahoo.com/question/index?qid=
20080609154640AAjCQkT 20080609154640AAjCQkT
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http://compnetworking.about.com/cs/wireless8 0211/a/aa80211standard.htm
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http://www tkt cs tut fi/research/daci/ra applica
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http://www.tkt.cs.tut.fi/research/daci/ra_applica tions_positioning.html
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http://security.dso.org.sg/publications/wireless/
wireless fingerprinting wisec08 pdf wireless_fingerprinting_wisec08.pdf
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http://www.tekniikka.oamk.fi/tl-
lab/tietoliikennejarjestelmat/Location/Location_t echnologies introduction spring 2010 pdf
echnologies_introduction_spring_2010.pdf
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