Application of ambiguity function to ultrasonic signal recognition

The ambiguity function (AF) is proposed to represent the ultrasonic signal for its modulus' independence of time shift and frequency shift, which avoids the effect of center frequency and arriving time of the ultrasonic signal on feature extraction. Moreover, the K-L transform is considered to extract features from the ambiguity plane, and the effect of signals to noises on validity of ambiguity features is analyzed. Furthermore, we discuss the performance of recognizing ultrasonic signals at different center frequencies and different arriving time based on ambiguity features. Experimental results show that the features extracted by the K-L transform (KLT) are immune to noises, and can recognize ultrasonic signals effectively in a lower dimensional space.