Multifrequency CW-based time-delay estimation for proximity ultrasonic sensors

With conventional pulse-echo ranging approaches it is difficult to obtain an accurate range measurement needed by a proximity ultrasonic sensor system owing to the limited bandwidth of the transducer. A continuous-wave multifrequency ranging method is presented to accurately measure the proximity distance for an ultrasonic distance sensor system. A novel time-delay estimator is derived based on a nonlinear least-squares-fitting criterion for the case where the received signal amplitude is non-negative owing to the acoustically hard reflection. To minimise the highly oscillatory cost function an efficient two-stage estimation algorithm is proposed. Numerical results show that the estimation algorithm can approach the Cramer-Rao bound as the signal-to-noise ratio increases