抄録
The fields of application for indoor positioning have expanded in tandem with advancements in our information-driven society. Compared to other positioning methods such as using radio waves, pseudolites or infrared rays, the systems based on ultrasonic waves have the advantages of low cost and comparatively high accuracy. However, these systems have weak noise resistance. Furthermore, the system takes a longer time to acquire data because they use a time-division multiplexed method with on-off keying (OOK), which becomes more cumbersome as the number of objects to be measured increases. To overcome these drawbacks, we have investigated a a real-time positioning system with spread spectrum (SS) ultrasonic modulation using general-purpose transducers, which is band-limited and utilized in the conventional systems with the OOK. In this paper, the measurement time, measurable range and measurement errors are compared with two modulation types (i.e., conventional OOK and proposed SS modulation) in a situation and an environment using a positioning system. In real-time measurements, improvement of angular dependence and ability for accuracy using SS modulation in conjunction with general-purpose transducers has been not discussed thus far. In the case of measurement for over 3 targets, the system with OOK takes more longer time to obtain a position than with SS, because of CDMA. The result with SS modulation presents the measurement accuracy and measurable range were improved. Therefore, in terms of accuracy, the SS modulation is more effective for indoor positioning than OOK.
