T Mani Bhowmik Dated:

Transcription

1 T Mani Bhowmik Dated:

2 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 , 2.4 GHz, 2Mbps; b, 2.4 GHz, 11 Mbps a, 5 GHz, 54 Mbps g, 2.4 GHz, 54Mbps; n, 2.4 GHz, 100 Mbps

3 Location Refers to a place Position Refers to a place with some reference point Reference point is in general Earth s coordinate system consists of latitude, longitude and altitude A location is not always a position, but a position is always a location.

4 Received Signal Strength Positioning is calculated based on received signal power level Measured power levels are converted to distance estimates by using a simple propagation model Fingerprinting Pre-defined fingerprinting is also used to determine position Time of Arrival Time of Arrival Time of Arrival technique is used along with RSSI

5 RSSI Model or Propagation model Connectivity Contains underlying radio technologies, WLAN Establish links with stationary devices [at least three for horizontal position; four for three dimensional position] Measurement Contains methods to meter RX power level. Measuring RX power levels can by performed by a mobile device or stationary devices or both

6 Distribution Assisting information is exchanged between the mobile and stationary devices Consist of coordinates of stationary devices, floor plan, TX power levels, antenna gains, used frequencies and Other information that affects to the propagation model Computation Mobile based: Mobile device does the measuring and data processing to determine position Network Based: Stationary base station does the computaion

7 Computation (contd...) Phase One: Convert measured RSSI values a.k.a RX power to distance estimates RX power levels are converted to distance estimates Phase Two: Because measurements are corrupted by noise, individual measurement error is decreased by statistical mean and variance combination Phase Three: Convert distance estimate to position estimate Exploitation Show the position in a GUI application

8 Fingerprinting or Empirical model RF Map Creation A Radio Frequecy grid is created and stored into a database for reference Contains signal strength at each location from each access points Connectivity: Movile device gets connected to the access points. And access points grant access to the mobile device. Server and mobile connectivity is also established Measurements Mobile device measures signal strength received from all access points and send the information to the server

9 Database search Based on the received signal strength information server searches the database and finds the closest match and returns the information to mobile device

10 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 ii. A device can be identify based on fingerprinting [ b d f d f d Combine i and ii, position of an identified device is known

11 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 Tx Receiver calculates the distance by measuring the time dff difference of Tx and Rx and wave propagation velocity

12 Security WLAN is secure network. Position information is also secure Wired Equivalent Privacy [WEP] Wi-Fi Access Protection [WAP] Ease of use WLAN is everywhere Only aim is to build a measurement model to determine position

13 Short Range Positioning is confined to a small area or location Possibly high power consumption Pi Privacy is an issue because of wide range of usage of x standard Multipath propagation, uneven spreading adds more noise Fingerprinting g needs huge manual efforts: creation and constant update to the database

14 Fingerprinting wins the race, but that is because there is a huge effort to create predetermined RF map But, RSSI based model is mostly used with support of TOF [TOA and TDOA] techniques

15 To determine location of a property in a confined area of location To make a secure area of movements in industry or in airport Very few commercial offering

16 AAjCQkT /a/aa80211standard.htm tut applica tions_positioning.html wireless_fingerprinting_wisec08.pdf wisec08 pdf echnologies_introduction_spring_2010.pdfintroduction spring pdf 06-boeing-wlan-location-tracking.html