JPH08240656A - Signal processing system - Google Patents

Abstract

PURPOSE: To prevent the deterioration of an S/R ratio in a system which extracts a signal by a peak hold processing in regard to a signal to be processed. CONSTITUTION: A high-pass filter 50 and a low-pass filter 60 are provided before a peak hold processing part 70 in regard to an input signal from an input sensor 10. A signal of a prescribed pulse width is passed and thereby the signal of a long pulse width and the one of a short pulse width are cut. By this system, the deterioration of an S/R ratio to be caused by a peak hold processing is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing system for signals received by various sensors such as acoustic and optical sensors, and more particularly to a signal processing system for extracting signals from noise.

[0002]

2. Description of the Related Art In the prior art, a peak hold circuit is used alone. In an application example of sonar echo detection, the received signal has a sampling period of 25, for example.
If the output from the phasing device is μs, the screen resolution of the display unit is 1000, and the sweep cycle is 1 second, this is 1 ms in terms of time resolution conversion value, which is 1 ms / 25 μs = 40 times compared with the sampling cycle. There is also 1m as it is
When resampled with s and displayed, there is a 39/40 probability of missing a signal. Therefore, in order to increase the display probability of the signal, the peak hold is designed to detect and display the maximum level in the period section every 1 ms.

Although this process seems to be rational at first glance, there is a problem that the probability of echo detection is improved and at the same time the probability of false alarm of reverberation and noise is increased. FIG. 6 and FIG. 7 show the probability distribution after the peak hold and the false alarm probability when the probability distribution of the reverberation before the peak hold is assumed to be the Rayleigh distribution.

[0004] In this case, the probability density function p (x ₁₎ of the detection output x ₁ of the reverberation is given by the number 1,

[0005]

[Equation 1]

The false alarm probability p _fa (x ₁ ) is given by the equation 2.

[0007]

[Equation 2]

On the other hand, the probability density function p (x ₂ ) of the peak hold output x ₂ is obtained as follows. The value of the detection output x ₁ with Rayleigh distribution is the peak hold output x ₂ is n
The probability density function p (x ₂ ) of the peak hold output is obtained by differentiating the probability of crossing over by x ₂ , and therefore, Equation 3 is obtained.

[0009]

(Equation 3)

The false alarm probability p _fa (x ₂ ) is given by the equation 4.

[0011]

[Equation 4]

Here, R ² is the variance of reverberation, and n is the number of peak hold data.

The peak hold has a problem as described above, and since the maximum value during a certain period is held, the signal level does not change before and after the peak hold, but the reverberation level becomes the maximum value during this period, so the original effective value is obtained. And the ratio of the target signal level in the reverberation to the reverberation level S /
Degradation of R occurs. From the definition of S / R, if the signal level is s, the average value of the noise level is x _r , and the effective value of the reverberation is σ _r , then Equation 5

[0014]

(Equation 5)

The average reverberation level x _r and the effective value σ _r take different values before and after the peak hold, while the signal level s
Is constant before and after the peak hold, so the S / R deteriorates.

FIG. 9 shows the results obtained by substituting the signal level before and after the peak hold, the noise average level, and the effective value of noise into the equation (5). This is the average value r = 0.886 and the effective value σ = of the Rayleigh distribution before the peak hold.
It can be obtained by back-calculating from 0.463. The number of samples of the peak hold was two, 40 and 4. From the figure,
In case of peak hold (40), input S / R = 15dB
In the following, the deterioration of the output is large, and the output S / R = 0 dB when the input S / R = 10 dB. Also, input S / R = 20d
It can be seen that the output S / R becomes larger than the input S / R at B and above.

From the above, the peak hold processing is
It can be seen that in the case of small signal input, the S / R ratio is deteriorated.

[0018]

In the prior art, since the peak hold is the maximum value within a certain period, the signal level does not change and the reverberation level becomes the maximum value during this period, and the S / R ratio of the input signal is increased. Is low, the deterioration of the S / R ratio is large.

An object of the present invention is to prevent the deterioration of the S / R ratio.

[0020]

The above object is to add a high-pass filter and a low-pass filter before the peak hold circuit in order to save the signal level and suppress the reverberation level, and apply the constant of the filter to the input signal to which the filter is applied. It is achieved by setting a pulse width corresponding to the reference pulse width of (1), inputting the signal passed through the filter to the peak hold circuit, and performing peak hold processing.

[0021]

When the above means is used, the input signal is composed of a signal having a constant pulse width and a reverberation having a random pulse width. When this signal passes through the high pass filter and the low pass filter, the signal level is preserved and the reverberation level is kept. Work to suppress. By inputting the output of this high pass filter and low pass filter to the peak hold circuit,
A peak hold output in which the S / R ratio is stored is obtained, and S
The / R ratio can be improved.

[0022]

EXAMPLES The present invention will be described below with reference to examples.

FIG. 1 shows an overall block diagram. In the figure, 10 is an input sensor, 20 is a preamplifier, 30 is an AD converter, 40 is a phase adjuster, 50 is a high pass filter, 60 is a low pass filter, 70 is a peak hold processing unit, 80 is a display control unit, and 90 is a display unit. Is.
The input signal 401 is the received reverberant sound when ultrasonic waves are periodically transmitted in water with a constant pulse length. FIG. 3 shows an outgoing signal (a) and a received signal (b).

FIG. 8 shows the high-pass filter 5 in FIG.
0 and the waveform of the signal 401 before the peak hold and the signal 701 after the peak hold when there is no low pass filter 60. FIG. 9 shows the input S with respect to the waveform of FIG.
It shows the relationship between the / R ratio and the output S / R ratio. As can be seen from these, the peak hold input S / R ratio is 1
The peak hold output S / R ratio is improved at 5 dB or higher, but the peak hold output S / R ratio is reduced at 15 dB or lower.
It can be seen that the R ratio is deteriorated.

On the other hand, as described above, the waveform 601 and its peak hold output 701 'when the high-pass filter 50 and the low-pass filter 60 are added are shown in FIG.
5 shows the relationship between the input S / R ratio and the output S / R ratio of the peak hold. As can be seen from these, by adding the high-pass filter 50 and the low-pass filter 60, the output S / R is reduced in the portion where the input S / R ratio is 15 dB or less.
The R ratio is improved.

High-pass filter 50 with improved S / R ratio
The low-pass filter 60 is a kind of pulse shaping filter, and has a property of passing a signal having a certain pulse width and cutting a signal having a longer pulse width or a signal having a shorter pulse width.

FIG. 2 shows a block diagram of a filter obtained by combining the high-pass filter 50 and the low-pass filter 60.
These difference equations are composed of, for example, first-order recursive digital filters, where an input signal code string is x _n , an output signal code string is y _n , and filter coefficients are k ₁ , k ₂ , and k ₃ .
It is shown in Equation 6.

[0028]

(Equation 6)

As an application example of the present invention, in the peak hold circuit, the target echo pulse length is geometrically elongated in correspondence with the target distance and the angle of inclination so as to match the target echo pulse length. A method of switching the filter constant according to the distance and the corner angle can be easily realized.

In the peak hold circuit,
In the absence of a filter, the peak peak value of noise generally does not have a Rayleigh distribution, but a method of switching the filter constants to approximate the Rayleigh distribution can be easily realized. In this case, a constant false alarm suitable for the Rayleigh distribution that is generally used. There is an advantage that processing is available.

[0031]

According to the present invention, it is possible to prevent the deterioration of the S / R ratio in the peak hold processing by selecting the constants of the high pass filter and the low pass filter according to the characteristics of the input signal.

[Brief description of drawings]

FIG. 1 is an overall block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of a filter according to an embodiment of the present invention.

FIG. 3 is a waveform diagram of a transmission signal and a reception signal.

FIG. 4 is an input signal waveform diagram after passing through a high pass filter and a low pass filter.

FIG. 5 is a graph showing a relationship between an input S / R and an output S / R after passing through a high pass filter and a low pass filter.

FIG. 6 is a graph of a probability density function graph of reverberation.

FIG. 7 is a graph of false alarm probability before and after a peak hold.

FIG. 8 is an input signal waveform diagram when there is no high-pass filter or low-pass filter.

FIG. 9 is a graph showing the relationship between input S / R and output S / R when there is no high-pass filter or low-pass filter.

[Explanation of symbols]

10 ... Input sensor, 20 ... Preamplifier, 30 ... AD converter, 40 ... Phase adjuster, 50 ... High pass filter, 60 ... Low pass filter, 70 ... Peak hold processing unit, 80 ...
Display control unit 90 ... Display unit.

Claims (3)

[Claims] 1. A signal processing method of a received signal in a sonar which transmits an ultrasonic wave in water and searches for a target from its echo sound, in an input sensor, a preamplifier, an AD converter, a phase adjuster, and a high pass filter. , A low-pass filter, a peak hold processing unit, a display control unit, a received signal processing system consisting of a display unit, the high-pass filter and the low-pass filter in the preceding stage of the peak hold processing unit, a signal of a constant pulse width, A pulse shaping filter that cuts a signal having a longer pulse width and a signal having a shorter pulse width than that, and a signal that has passed through the pulse shaping filter is input to the peak hold processing unit to perform peak hold processing. Processing method. 2. The signal processing method according to claim 1, wherein the filter constant of the pulse shaping filter is set so as to match the echo pulse length corresponding to the target distance and the corner angle of the sonar search. 3. The signal processing method according to claim 1, wherein the filter constant of the pulse shaping filter is set so that the peak hold output of the peak hold circuit has a Rayleigh distribution.