Sammendrag
The Global Positioning System (GPS) is the standard technology for outdoor positioning, but it cannot be used for accurate indoor positioning due to scattering and attenuation of GPS signals. A popular alternative is to use ultrasound for indoor positioning because of the high accuracy and low cost of these systems, but few such systems are readily available for users. This thesis presents a wireless ultrasonic indoor positioning system that is built using commercial off-the-shelf devices. This system is easily adaptable for different applications that require accurate positioning with room-level coverage and has a low deployment effort. The positioning system presented here is implemented using a wireless sensor network, and uses Micro Bit V2 microcontroller boards as the wireless node control units, which have an onboard ultrasonic microphone. This means that an ultrasonic transducer for transmission is the only external component needed, and the Murata MA40S4S transmitters are used for this purpose. The system estimates the ultrasonic time-of-flight (ToF) between transmitting and receiving wireless nodes which are synchronized using a radio communication link. By using four transmitter nodes with known positions and the estimated ToF distances to the receiving node, the receiver is positioned by applying multilateration. The results show a 90th percentile sub-centimeter accuracy and precision in ToF distance estimation, and achieved a mean positioning error less than 3 cm in the estimated 3D coordinates with a standard deviation less than 0.41 cm.