An accurate distance measurement by calibration of doppler-shift for ultrasonic sonar sensing

Ultrasonic distance measurement with the pulse-echo method is based upon the determination of the time of flight of ultrasonic waves. The pulse-compression technique, which involves the calculation of the cross-correlation function between the transmitted and the reflected waves, is the conventional method for improving the resolution of the measurement. The calculation of a cross-correlation operation requires high-cost digital signal processing, however. This paper presents a new sensor signal processing method of the pulse-compression technique using a delta-sigma modulated single-bit digital signal. The proposed method consists of three parts: an analyzing operation of the doppler-shifted frequency, a cross-correlation operation by single-bit signal processing, and a smoothing operation accomplished by a moving average filter. For the pulse-compression technique, this method reduces the calculation cost of digital signal processing. Since the frequency of the linear chirp signal is doppler-shifted, the distance from the moving transmitter to the moving object cannot be accurately measured in the pulse-compression technique. To solve this problem, the analyzing operation of the doppler-shifted frequency is used to calibrate the transmitted ultrasonic wave, thus effectively improving the accuracy of the measurement.