OPTIMUM PSEUDO RANDOM SEQUENCE DETERMINING METHOD, POSITION DETECTING SYSTEM, POSITION DETECTING METHOD, TRANSMITTER, AND RECEIVER

摘要

The propagation time of a direct wave which reaches first from an ultrasonic sound source without being affected by the reflected wave of an ultrasonic signal is allowed to be accurately calculated. A plurality of ultrasonic signals generated on the basis of a plurality of different M sequences from one another are transmitted from the transmitting side to the receiving side. The receiving side generates the model waveforms of the M sequences, executes the correlation processing between each of the model waveforms and the waveform of each of the ultrasonic signals, detects the secondary peak of the correlation value appeared when the both waveforms are partially matched, and determines an M sequence in which the minimum secondary peak out of the secondary peaks detected in all the correlation processings has occurred as the optimum M sequence. The transmitting side sends out an electromagnetic wave signal and an ultrasonic signal modulated by the optimum M sequence generated under the initial condition of the optimum M sequence to the receiving side. The receiving side calculates the correlation value between the ultrasonic signal and the model waveform of the ultrasonic signal modulated by the optimum M sequence, detects the first main peak of the calculated correlation value, and calculates an ultrasonic propagation time from the point at which it has received the electromagnetic wave signal and the point at which it has detected the main peak.