Integration of RFID, GNSS and DR for Ubiquitous Positioning in Pedestrian Navigation

Location determination of pedestrians in urban and indoor environment can be very challenging if GNSS signals are blocked and only pseudorange measurements to less than four statellites are avialable. Therefore a combination with other wireless technologies for absolute position determination and dead reckoning (DR) for relative positioning has to be performed. Radio Frequency Identification (RFID) is an emerging technology that can be employed for location determination of a mobile user in indoor and urban environment. RFID transponders (or tags) can be placed at known location (so-called active landmarks) in the environment and the user who has to be positioned can carry a RFID transceiver (or reader). Then the location of the user can be obtained using cell-based positioning or with trilateration if ranges to several tags are deduced. In this paper the use of active RFID in combination with satellite positioning and DR is investigated. For that purpose the integration with GNSS and other wireless technologies is discussed and the deduction of ranges to RFID tags is investigated. Test results show that the ranges to RFID tags can be deduced from signal strength observations to tags in the surrounding environment. Two different models that describe either a logarithmic or linear relationship between the measured signal strength and the distance to the tag are analyzed. In addition, if pseudorange observations to GNSS satellites can be measured then they can also be used with ranges to RFID tags to obtain the position fx. The absolute position can then be used to update the drift rates of the DR sensors which are used for continuous position determination. Different scenarios for the correction of the DR drift are described in the paper. The presented research is conducted in a new research project at the Vienna University of Technology.