RSSI - Received Signal Strength Indication

Fraunhofer IIS's self-contained Positioning Technology for Cities and Buildings

awiloc® Technical Solution

© Photo Fraunhofer IIS/Sven Mattes

Fraunhofer IIS’s awiloc® technology enables continuous localization by detecting the characteristic field strength distribution of existing WLAN stations and Bluetooth LE transmitters.

Mobile devices are able to determine their own position using what is known as a fingerprinting technique. This involves taking measurement values at reference points that include all detected WLAN base stations and Bluetooth LE transmitters as well as their corresponding transmission information. This information is limited solely to the signal strengths of the detected WLAN base stations and Bluetooth LE transmitters as measured at the reference point.

 

Positioning through signal strengths patterns

This fingerprint of transmission data is then stored in a database and serves as the basis on which mobile devices can determine their own position. This is achieved by using a localization algorithm developed by Fraunhofer IIS that autonomously compares recorded transmission data with reference data to calculate the current position. This means that the position is known only to the user.

The so-called MAC address serves for a technical distinction of measured signal strengths of wireless LAN stations. The SSID, assigned and possibly disabled by the user, is an uncertain information in terms of positioning. Therefore the positioning through awiloc® technology by Fraunhofer IIS is not hooked on the SSID as well as other information sent by wireless LAN stations, e.g. their encryption status – they are not needed and therefore not stored. A data exchange with the wireless LAN station is not performed. The position of the wireless LAN access point is unimportant and not determined.

 

Positioning in cities and buildings

Our stand-alone wireless LAN positioning in cities considers both commercial wireless LAN hot spots and private wireless LAN access points and works without registration or access to the data network.

A robust positioning algorithm ensures a high degree of immunity to distorting influences such as the addition, removal, or relocation of wireless LAN access points. Thus, positioning accuracy is totally unaffected by the addition of wireless LAN access points and it will be influenced only if the number of wireless LAN access points in a common city surrounding is reduced by more than 50%. While accuracy will be diminished if access points are moved, continuous positioning means that there will be no major errors or dropouts.

The solution developed by Fraunhofer IIS enables continuous positioning even in multi-story buildings or underground facilities. By the use of an environment model it is possible to integrate semantic information and to add functionality such as structural feature identification. Indoor positioning accuracy usually varies between 1 and 5 meters (depending on the type of environment, e.g. office building or production facility). Outdoors, positioning accuracy averages around 10 meters while also varying with the environment: The more densely built up an area, the better the performance of Fraunhofer IIS's wireless LAN positioning technology – a characteristic that makes this solution the ideal complement to GPS.

 

Implementation

awiloc® technology by Fraunhofer IIS for wireless LAN positioning is a purely software-based solution that can be easily integrated into mobile devices. Location Based Services are feasible both as local services on the mobile device and as network-based services.

 

Position Transfer Interfaces

For the position transfer the following socket-based interfaces are available:

  • Position information applications
    can request the position on the mobile device
  • Location information applications
    can request the logical position (e. g. room number) on the mobile device
  • Virtual GPS
    furnishes a virtual gps adapter