抄録
In order to develop an indoor, local positioning system and evaluate its ranging accuracy, range measurement experiments have been performed using spread spectrum sound waves at audio frequencies of 0.69, 3.0, and 10kHz, for which a relatively broad frequency response can be readily prepared by means of a pair of transmitter-receiver commercially available. A series of the experiments based on the demodulation of spread spectrum sound signals due to M-sequence (Pseudo Random Noise Code) with a 127-code length showed that the range measurement successfully yielded full-scaled ranging errors of less than 1% as the accuracy for the frequencies of 0.69 and 3.0kHz, and much smaller value of 0.037% for the full scale distance of 18m in the case of 10kHz. The capabilities of noise rejection to super-imposed white noise and signal discrimination between two different M-sequence codes have been also ensured for the phase shift keying modulation on longitudinal elastic waves. Discussions on the measurement precision are interestingly given in terms of the frequency of carrier wave and the traveling distance during the phase shift chip period as an analogy of pseudorange measurements in the global positioning systems.
