Ultrasonic ranging transducer at low SNR and low sampling rates based on cross-correlation function. The specific method is as follows the ultrasonic signal sent by the transmitter is used as a reference signal, and the output of the receiver is immediately sampled at the end of each transmission of the ultrasonic wave, and the cross-correlation function between the sample value and the reference signal is calculated. If the cross-correlation function has a peak value, the sampled value is the echo signal received by the transducer, and the range time can be calculated according to the moment when the correlation peak appears. The correlation estimation method (also known as the match detector) utilizes both the amplitude of the echo signal and the shape of the echo signal. If the waveform of the echo signal is basically not distorted, and the noise superimposed on the echo signal is Gaussian white noise, then the delay estimation accuracy and sensitivity of the correlation estimation method are higher than the threshold detection method. In the past ten years, domestic foreign scholars have published many improved correlation estimation algorithms. The proposed fast delay correlation estimation algorithm based on interpolation principle can realize 256 point digital correlation calculation in lms by using ordinary digital signal processing chip (DSP), distance measuring transducer not only ensures the system's ranging accuracy but also improves the system's real time.
Firstly, an echo signal model is including delay parameters, linear frequency offset and additive noise is established, and then the maximum likelihood criterion is used to estimate the delay parameters in the model. Experiments show that even if the echo waveform has unknown distortion It also does not substantially reduce the accuracy of the delay estimation of the algorithm, which indicates that this model-based algorithm is better than the ordinary correlation estimation method. In addition,there are many other improvements or extended delay-related estimation methods. For example, the delay correlation estimation method based on Hilbert transform, the delay correlation estimation method of ultrasonic distance measurement sensor has the correlation delay estimation algorithm, the pseudo-random code based delay orthogonal correlation algorithm and the pseudo-random code delay two steps methods. These abnormal state correlation estimation algorithms can greatly reduce the influence of external interference on the accuracy of correlation method delay estimation.Many of these algorithms also consider the real time problem of system implementation.
The line analysis method uses a fast fourier transform (FFT) to perform spectral analysis on the echo signal to determine whether it exists.An echo signal has the same frequency spectrum as the ultrasonic wave transmitted by the transducer, and thereby determining the appearance timing of the echo signal. Under the condition of extremely low signal-to-noise ratio, the use of spectral analysis algorithm to detect echo signals helps to reduce false alarm probability. However, the spectrum analysis algorithm has a large amount of calculation, and it is not easy to obtain a high delay estimation accuracy. Therefore, the ultrasonic distance measuring transducer in the air medium is rarely applied.
The spectral analysis algorithm and the application of the adaptive enhancer in the underwater ultrasonic distance sensor are listed. Based on the same ranging and direction finding principles, these algorithms can be transplanted into the air sonar without modification. A quadratic frequency domain is adaptive to time delay estimation model and a time delay estimation algorithm is based on the model are proposed. In the case of low SNR, this adaptive algorithm in the frequency acoustic measurement system has good delay estimation ability.Another time delay estimation method with large computational complexity is the least mean square adaptive time delay estimation. The specific implementation method is as follows the ultrasonic signal transmitted by the transducer is used as a reference signal, and the echo signal (received signal) is added at the front end. A delay amount by continuously adjusting the amount is the variance between the echo signal and the reference signal after the LMS algorithm reaches a minimum value, and the delay amount at this moment is the range time. This algorithm is equivalent to the effect of eliminating the channel noise by the adaptive transversal filter, and plays an adaptive channel equalization function. It does not need to know the statistical characteristics of the channel noise in advance, ultrasonic liquid sensor transducer does not need to consider the distortion problem of the echo waveform. A better time delays estimation method. The well-known Matlab software also gives a simulation demonstration of the LMS is adaptive for estimation algorithm. The specific method is the reference signal after the LMS algorithm is compared with the echo signal, when the mean square error reaches the minimum, the transverse filter assumes that the delay amount is corresponding to the maximum value among the weight coefficients of the N delay links is the range time. There is no essential difference between the two delay estimation algorithms, both of which utilize the single-frequency characteristics of the ultrasonic wave, but the latter requires that the delay amount corresponding to the N delay links of the transverse filter must be greater than the range time.
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