Measurement accuracy on indoor positioning system using spread spectrum ultrasonic waves

This paper describes significant factors on spatial error distribution measured in a given indoor space with a local positioning system which utilizes spread spectrum ultrasonic waves generated by narrow directional ultrasonic transmitters. The positioning error has interestingly been discussed from the viewpoints of the dilution of precision (DOP) and the ranging error due to the transmitter directional characteristic, mainly. The indoor 3-D position is calculated by means of an algorithm using distances from the transmitters located at the four corners of the ceiling to a mobile receiver. From the result of these experiments, it has been usefully found that the positioning error can be more largely influenced on the DOP of vertical direction than it of horizontal direction and that its average is of 3.43[cm] rms for all 3-D measurable points. These findings obtained from the work imply that the 3-D indoor positioning can be realized with an acceptable centimeter-order of precision. Moreover, they suggest that it has to be considered from the viewpoints of not only the ranging error, which could be yielded by the distance measurement, but also the DOP, which is inevitably obtained by a geometrical arrangement relative to the transmitters and receiver.