Chapter 723 Matched Filtering
"Mr. Gao, I remembered that this method can improve multi-target processing capabilities! Once the pulse width is compressed, it means that the echo signals of two adjacent targets can be clearly distinguished. In this way, Later, the original multi-target processing capabilities have also been improved.”
Gao Zhendong smiled: "Well, yes, it does have this effect."
In fact, this is basically the benefit brought by the improved resolution. If the resolution is low, the error will be large, so it is naturally impossible to distinguish two adjacent signals, and vice versa.
Mr. Liu thought more deeply than his comrades.
"General Engineer Gao, can this kind of pulse compression be able to pick out the echo signal from the white noise? Can it greatly improve the system's ability to resist errors caused by white noise?"
Gao Zhendong nodded, still very old-fashioned: "By the way! This is also a very important point. White noise is very uniform, but the amplitude of the compressed signal will greatly exceed the amplitude of white noise. Naturally, the amplitude of white noise will increase. was picked out”
There is a very interesting thing about radar signals. Sometimes the white noise seems to have a larger amplitude than the echo signal, as if it cannot be separated at all. However, appropriate digital signal processing technology can transform the echo signal from Pick them out from the white noise and process them individually.
Generally speaking, the energy of the echo signal is certain, and the pulse width is compressed, which means that the amplitude is increased, and obvious signal peaks will appear, which is easy to deal with.
"Yes! This idea is really amazing, and it can have this effect."
"Well, the benefit just now is incidental, this benefit is independent."
"Pulse compression! Great, I'll do it when I get back."
"..."
He said he would do it when he got back, but how? This question is actually no simpler than the previous one.
There are many solutions in principle, which look good, but once you enter engineering practice, you will find that it is not as simple as imagined.
"The question is, how to compress it?" Some comrades raised this question, which suddenly seemed to pour cold water on the heads of the comrades who were in high spirits just now.
We all know that pulse compression is good, but how to compress pulses?
This thing is not like a ball of cotton, which can be compressed into one piece by pinching it. It is invisible and intangible.
Everyone began to think hard. Although Gao Zhendong was smiling and confident, it seemed that he had a solution, but everyone still wondered if they could come up with a solution. After all, they couldn't wait for food for everything, and Chief Engineer Gao Feeding enough.
But they thought about it for a long time and couldn't think of any good way. Use analog devices for compression? Or use digital signal processing? No clue.
"General Engineer Gao, let's talk about it. We have no clue about this thing at the moment." Mr. Liu gave up quickly. It's not worth wasting time here.
As expected, Gao Zhendong was very confident about this matter.
"For pulse compression, a method called a matched filter is used."
After speaking, Gao Zhendong walked to the blackboard and picked up the chalk.
Chief Engineer Gao is going to draw a circuit diagram! Everyone is very excited. What are you doing in a daze? Get ready to memorize it! Everyone opened their notebooks.
But to everyone's surprise, Gao Zhendong didn't draw a single circuit diagram. Instead, he wrote mathematical formulas on the blackboard and explained them while talking.
"...Here, the output signal is composed of two parts: signal and noise..."
"...by Fourier transform, and then convolving the signal in the time domain..."
"...It can be seen that the signal energy is the accumulation of the square of the mode of the spectrum expression..."
"...according to Schwartz's inequality...eventually we will find that after processing, the signal-to-noise ratio has nothing to do with the waveform, and is only related to the ratio between the signal energy and the intensity of the white noise..."
Some comrades listened with great enthusiasm, while some comrades simply did not understand.
Although there is not much mathematics involved, after this sequence, some people still feel like they are listening to a book from heaven.
But comrades who understand it are truly a treasure.
Finally, Gao Zhendong threw away the chalk: "Well, that's probably the principle. Matching filtering is like this. I don't know if you understand it."
Even if comrades don't understand, they are too embarrassed to say, "Mr. Gao, please tell me again." Why are you so arrogant?
Fortunately, there are always people who understand, and some who understand partially. "Mr. Gao, what is the specific circuit design of the matching filter?" Some comrades were anxious and wanted to know the final result.
Hearing this question, Gao Zhendong was not easy to say. He just looked at Mr. Liu with a smile, "This... your person, you can solve it."
Mr. Liu had a look of hatred on his face: "Didn't we just finish talking about it? What more circuits do we need?"
Gao Zhendong then smiled and said: "This matched filter is actually a digital filter. You send the sampled signal to the digital signal processor. According to the mathematical principles and processing methods just mentioned, It’s done, no special circuit required.”
This is where digital signal processing technology excels. As long as the signal is sampled with a certain accuracy, the rest is purely mathematical calculation, and no additional circuits are needed.
Therefore, the weight of Lao Maozi's "Flanker" reversal artifact is calculated in tons due to its poor digital signal processing technology, but Citigroup's PD radar of the same period only needs to be calculated in terms of hundred kilograms.
The comrade who asked this question blushed, but the other comrades were secretly frightened. General Engineer Gao's method was really amazing!
Not only can it solve the problem, but what is rare is that it can also greatly simplify the system complexity, reduce the system weight, improve the adaptability of the radar, and it is expected that the reliability and maintainability can also be greatly increased.
Mr. Liu asked Gao Zhendong some things that he did not understand when Gao Zhendong explained it just now. After listening, he said cheerfully: "Mr. Gao, we will come here first today. Thank you very much. Your words have completely solved the problem of detection range and accuracy of our pulse radar. Let’s go back and digest it first. If there are any new questions, we will come back to you.”
For them, the biggest stumbling block, the contradiction between detection range and accuracy, has been solved. They have no interest in other problems, or they have not encountered them yet. The top priority now is to go back and apply the technology given by Gao Zhendong. When it comes to actual projects, Gao Zhendong seems to think this thing is very simple, but if they want to use it well, they still need to spend a lot of effort.
Gao Zhendong smiled and nodded: "You are welcome to come and communicate at any time."
——
Gallic chicken, Le Goff took a note and walked towards Mr. Senna's office with a happy face. This time the Eastern request would probably make Mr. Senna very happy.
"Mr. Senna, the Orientals have made a somewhat special request to us."
After speaking, he handed the note document in his hand to Senna.
"What else do they want to show off to us?" Mr. Senna muttered as he took the document.
After opening the file and taking a closer look, Senna's eyes were indeed filled with joy, just as Legoff expected.
"Hahahaha! They finally asked us for some serious high-tech products." Senna felt that he had a feeling of "turning over and singing".
Except for some military technologies for exchange, the Easterners seem to have no interest in the high-tech products provided by their own side. For more than a year, the other side has treated them like farmers, which makes Mr. Senna very dissatisfied. .
This time, the other party didn't know what the purpose was. As if they had enlightened themselves, they finally made a purchase request that at first glance represented high technology.
But the situation seemed to be somewhat different from what he expected.
"Rifamycin? They said it's something from the country of leather shoes? Damn it, they even like things from the country of leather shoes, so why don't they consider buying something from us?"
"Mr. Senna, I have verified that we have a certain influence on rifamycin. In other words, you can barely make sense of it as ours." Le Goff shrugged.
"Oh? My dear Le Goff, please tell me carefully." After hearing Le Goff's words, Mr. Senna's face looked a little better.
"The earliest sample of this antibiotic that is still under research comes from the soil in our pine forest. Therefore, with this drug, we can exert a certain influence on Leather Shoes. Although this antibiotic is still under experiment, their Patent protection has been completed, so they are very happy to cooperate with the sale of a certain number of samples or experimental chemicals. After all, it is a good thing to have someone to test with them. At the same time, no matter what others use it to do, they have to go to the leather shoes to buy it. Everyone can make money.”
Legoff was so well prepared that he had even mastered the shoe-leather man's attitude.
After listening to Legoff's words, Senna's expression softened a little. This could barely be regarded as something from his own country. After all, it came from the land of Gaul.
"Then what do you think the Easterners want to do by taking this kind of thing back?"
"I think it should be used to treat some disease. The health situation there is very pessimistic." Le Goff said with a smile.
"Legoff, your joke is not funny at all. The sanitary conditions here are actually not very good. We have no right to make fun of others."
The Seine, like the Thames, is notorious for pollution, perhaps even more so.
"Well... I think you are right, my husband. But do you think this business can be done?"
"Do it, why not do it? They can only buy it through us. If you can make money, why should you give up? And if you are more relaxed about medicine, I think it will win the favor of Eastern people." Senna's mind is very clear.
(End of chapter)