Evaluation of position and velocity measurement for a moving object by pulse compression using ultrasound coded by preferred-pair M-sequences

The pulse-echo method based on transmission of an ultrasonic pulse and time-of-flight determination of a reflected echo is one of the typical methods of ultrasonic distance measurement. To improve the SNR of the reflected echo, pulse compression using an M-sequence is employed in the pulseecho method. In the case of a moving object, however, the echo is modulated owing to the Doppler effect The Doppler-shifted M-sequence modulated signal cannot be correlated with the reference signal corresponding to the transmitted M-sequence modulated signal. Therefore, Doppler velocity estimation by spectrum-pattern analysis of a cyclic M-sequence modulated signal and cross correlations with Doppler-shifted reference signals corresponding to the estimated Doppler velocities has been proposed. Meanwhile, in the case of measurement using multiple transducers, the airborne acoustic image can be formed from multipath cross-correlation functions. Then, the position of the object can be determined from the airborne acoustic image. When different ultrasound are simultaneously transmitted, preferred-pair M-sequence codes are typically used for coding ultrasound to avoid the crosstalk. In this paper, the position and velocity of the moving object are measured by using two loudspeaker and three microphones. Then, the effect of interference of two M-sequence modulated signals are evaluated by comparison between simultaneous-transmission and non-simultaneous-transmission.