Robustness enhancements of time-of-flight measurements in a CDMA ultrasonic channel of an opto-acoustic indoor positioning system using MEMS microphones

For quality assurance systems in manual assembly opto-acoustic indoor positioning systems provide sufficient accuracy. In this paper we examine an opto-acoustic indoor localization system, where the 3D position and orientation is calcultated with multiple ultrasonic piezotransducers attached to an object and measuring unilateral distances to multiple room-fixed receivers, followed by a multilateration. In the industrial working environment large disturbances are expected and due to the narrowband property of the used ultrasonic channel and the code division multiple access environment, the robustness of the unilateral distance measurements needs to be increased. This is done by including MEMS microphones with a higher bandwidth to record the binary-phase-shift-keyed (BPSK) signal more accurately. Two modeling approaches of the ultrasonic channel including the MEMS microphones are proposed. Experimental validation of the improved robustness is provided and distance measurements of an yet disturbance free measurement setup show positioning accuracies with a mean error below 1cm independent on distance and transmission angle.