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In this project, the objective was to use measured signal strengths of access points to locate either the positions of the access points or a smartphone. To do this, smartphones are used to collect data at various positions, which are determined by the GPS-functionality provided by the phone, about measured signal strengths for access points in range. This data is then aggregated and used to estimate the positions of the access points. These calculated positions can then, in connection with measured signal strengths, be used with the same method to determine the position of the smartphone.

The system is designed following the client-server model, with the server being responsible for saving collected data from clients, using this data to determine the positions of access points, and providing the results for the clients. The client is a smartphone app responsible for collecting the signal strength and GPS information, sending this data to the server, requesting estimated positions of surrounding access points from the server, calculating its own position on the basis of the available access point positions, and visualizing the data.

For determining the positions, the signal strengths are first converted to distances according to a simplified log-distance path loss model. The model takes into account the frequency, the received signal strength, and the transmitted signal strength, which is assumed to be the maximum value for the frequency. These distances are then used with the position data (either from GPS or calculated access points) and a technique called Multilateration to devise a overdetermined system of linear equations. This system is then solved according to a least-square algorithm to estimate the position.





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Felix Henze
Amir Alchikh