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Publications of Wolfgang Effelsberg

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Artikel

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Forschungs Papier

  • Thomas King, Thomas Haenselmann und Wolfgang Effelsberg. , Technical Reports. 2007 Key Factors for Position Errors in 802.11-based Positioning Systems Mannheim, . 07-003
    Indoor positioning systems based on 802.11 and fingerprints offer reasonably low position errors. We study the key factors for position errors by systematically investigating (1) the number of access points, (2) the number of samples in the training phase, (3) the number of samples in the position determination phase, and (4) the setup of the grid of reference points. Further, we squeeze out the best of the positioning system by selecting advantageous values for these parameters. For our study, we utilize a test environment with a size of about 312 square meters that is covered with 612 reference points arranged in an equally spaced grid.
  • Thomas King, Thomas Haenselmann und Wolfgang Effelsberg. , .Praktische Informatik IV, Fakultaet fuer Mathematik und Informatik, Universitaet Mannheim 2007 On-Demand Fingerprint Selection for 802.11-based Positioning Systems , .
    Fingerprinting is a popular technology for 802.11-based positioning systems: Radio characteristics from different access points are measured at various positions and stored in a database. The database is copied to all mobile devices, and when a position is needed, the devices compares its currently measured radio characteristics with the database entries. In this paper, we present two on-demand fingerprint selection algorithms to avoid the cumbersome and time-consuming approach of manually copying all fingerprints. Our algorithms only request those fingerprints from the database that are currently required to compute a position. The two algorithms differ in the way they shape the region for which fingerprints are requested. On-demand selection also allows storage-restricted mobile devices to utilize the positioning system. We carefully evaluate our algorithms in a real-world experiment. The results show that our algorithms do not harm the position accuracy of the positioning system. In addition, we analyze the space requirements of our algorithms and show that the typical constraints of mobile devices are met.
  • Thomas King, Hendrik Lemelson, Thomas Haenselmann und Wolfgang Effelsberg. , . 2007 Loc{lib,trace,eva,ana}: Research Tools for 802.11-based Positioning Systems , .
    802.11-based positioning systems are a hot topic in research. However, no standardized set of tools has been established to facilitate the researc process. In this paper, we contribute our research tools to the community. The benefit for the community is considerable: (1) Standardized tools reduce the amount of work each researcher has to spend to build software to collect signal strength samples and process this data. (2) The confidence in the correctness of the tools increases because everybody is encouraged to submit bug-fixes. (3) A unified evaluation process makes results mutually comparable. (4) We hope other researchers contribute to our tools.
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