An automated calibration method for the Local Positioning System LOSNUS

Calibration of a Local Positioning System (LPS) is essential before the system can be used to localize static nodes or mobile devices. The authors have developed a cost efficient and high accurate Ultra Sound indoor positioning system called LOSNUS (LOcalization of Sensor Nodes by Ultra Sound), which is a type of locating system mainly used to localize static devices in a wireless sensor network (WSN) where multiple sensor/actuator devices are deployed. The system has transmitters that are permanently installed and mounted on the wall. Calibration of the system by manual measurements with common measurement tools would deliver high uncertainty of transmitter positions and reduce the overall accuracy. To determine absolute 3D positions of e.g. six transmitters of a test system in an automated calibration process, six coordinates of three transmitters are defined using a special procedure establishing the system coordinates of the room. The remaining 12 transmitter-coordinates are unknown. Four additional receivers with unknown positions are used as assistance for calculation of transmitter and receiver coordinates. In this paper the system configuration, the proposed calibration algorithm and its benefits explained.