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Q. Fu, G. Retscher:
"Active RFID Trilateration and Location Fingerprinting Based on RSSI for Pedestrian Navigation";
The Journal of Navigation, 62 (2009), 2 (April); 323 - 340.

In the work package `Integrated Positioning´ of the project UCPNAVI (Ubiquitous Carthograpy for Pedestrian Navigation) alternative location methods using active RFID (Radio Frequency Identification) are investigated for positioning of pedestrians in areas where no GNSS position determination is possible due to obstruction of the satellite signals. In most common RFID applications positioning is performed using cell-based positioning. RFID tags can be installed at active landmarks (i.e., known locations) in the surroundings and the user who is equipped with an RFID reader can be positioned using Cell of Origin (CoO). The positioning accuracy, however, depends on the size of the cell defined by the maximum range of the signal. Using long range RFID for positioning the cell size can be quit large, i.e., around 20 m. Therefore, the paper proposes two new methods for positioning, i.e., trilateration und location fingerprinting based on received signal strength indication (RSSI) if more than one RFID tag are visible. The trilateration approach is based on the deduction of ranges to the RFID tags from RSSI. An iterative approach to model the signal propagation will be introduced, i.e., the ITU (International Telecommunication Union) indoor location model that can be simplified to a logarithmic model, and a simple polynomial model are employed for the signal strength to range conversion. In a second attempt, location fingerprinting based on RSSI is investigated. In this case, RSSI are measured in a training phase at known locations inside the building and stored in a database. In the positioning phase this measurements are used together with the current measurements to obtain the current location of the user. For the estimation of the current location different approaches are employed and tested, i.e., a direction-based approach, a tag-based approach, a direction-tag-based approach and a heading-based approach. Using trilateration or fingerprinting usually positioning accuracies on the one to few meter level can be achieved. The concept and the iterative approach of the different methods and test results are discussed in this paper.

http://journals.cambridge.org/repo_A48Q721F

Project Head Georg Gartner:
Ubiquitäre Kartographie für Fußgängernavigation