For the identification and tracking of everyday objects we decided to develop a positioning system based on active RFID technology that allows indoor detection ranges of up to 30m from each antenna.
The following figure shows the schematic layout of the installation with 4 antennas at the corners of the building. Our first approach was to measure the field strength of transponders on all 4 antennas and compute their 2D position (x, y) using triangulation methods. But tests showed that environmental changes had serious influences on the calculated positions. To overcome the fluctuation in the field strength we recorded sample values for different positions within the building. This method proved to be robust against environmental changes and delivered adequate accuracy for object location within buildings. Nevertheless the high calibration effort has to be mentioned.