Chapter 803 Laser Coding
The simplest example, if you want to destroy a bridge with many piers, the most ideal attack method is to use multiple ammunition to hit as many piers as possible at the same time.
In this case, the value of this requirement of the Air Force is reflected. After all, laser-guided bombs are free-falling. It takes time for each bomb to fall from hundreds or even thousands of meters in the air, and it will In the absence of ground illumination, the carrier aircraft must also maintain illumination guidance.
This is a very serious challenge for the survival of the carrier aircraft. If multiple bombs have to be thrown one by one, the situation will worsen, and the survival probability of the carrier aircraft under enemy air defense firepower will drop sharply.
Gao Zhendong had to lament that the minds of those in the Air Force were so quick that they even had a longer vision than the real inventor of laser-guided bombs, Citigroup. At the beginning, Citigroup didn't Consider this issue.
It's just that for Chunlei Factory, this kind of request is a bit beyond their capabilities. At first, their idea was quite simple. This is easy to handle. One bomb and one irradiation device. Isn't that good? Everyone goes their own way, and everyone just blows up what they want.
In fact, after they actually put into the experiment, they realized that the problem was not that simple.
——After the laser hits the target surface, it is diffusely reflected.
Diffuse reflection means that the areas of reflected laser light from multiple approaching targets overlap greatly. A bomb flying in the air will receive laser echo signals from multiple targets at the same time.
As the saying goes, one monk has water to eat, but three monks have no water to eat. For a bomb, if it receives multiple signals at the same time, it doesn’t know what to do, because apart from the difference in strength, these signals are all They are all the same, there is no way to tell them apart. If they all fly towards the strongest signal, things will get messed up.
The summary is that when multiple targets are illuminated in a small range at the same time and multiple bombs are instructed to strike, the behavior of the bomb is unpredictable.
The best situation is a repeated strike, that is, multiple bombs fly towards the target with the strongest signal. In this case, at least one target can be hit. Although the strike power is seriously overflowed, everything will not be harvested. Not.
The worst-case scenario is that no one can be hit, and the bombs fly this way and that way, and finally hit nothing, or the lasers interfere with each other, and the bombs don't know where to fly at all, and they have to follow. It's not impossible that it's like a free-falling bomb.
According to tests at Chunlei Factory, when multiple bombs hit multiple targets in the same area, the hit rate of the bombs will drop sharply.
"General Engineer Gao, what we are encountering now is this problem. You are the inventor of the laser, and you are much more in-depth about the application of lasers than we are. We invite you here this time just to see if there is a way to solve it. This question." Mr. Zhang's words were sincere.
"Have you tried solving it?"
"We tried, we wanted to use different wavelengths to solve this problem, but found that it was simply impossible. Multi-wavelength lasers and seekers are unacceptable in terms of cost, volume, and weight."
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The method that Mr. Zhang and his colleagues are thinking of is relatively straightforward wavelength division multiplexing, using different wavelengths to achieve multi-target guidance in the same space.
However, this method can be used in theory, but in fact, based on the current technical capabilities, it is theoretically okay but not engineeringly possible.
To realize this method, they currently have only one way, which is to install many lasers with different wavelengths on the illuminator, and then find a way to achieve wavelength selection on the seeker. Let’s not talk about whether it is technically possible. This method The price is simply too high to accept.
After Gao Zhendong understood his question, he thought for a moment. For him, if he didn't come up with a specific plan directly, he wouldn't have to search for information in his system for this problem, because for him, in theory, On one level, the answer is basically ready-made.
The reason why he wanted to think about it was mainly to consider how to explain this issue clearly to Mr. Zhang and the others.
"Mr. Zhang, this problem is not difficult to solve, especially since you can now use microcontrollers. In fact, you can do it without microcontrollers, but microcontrollers have relatively greater potential."
When Mr. Zhang heard that Gao Zhendong didn't even have 30 seconds, he told him that there was a way. He was very happy. Mr. Gao was still reliable. This technology and foundation were beyond words.
Thinking of this, he complained a little to the Air Installation Bureau. If you had made this request from the beginning, maybe Chief Engineer Gao would have solved it in the initial plan without making any detours.
Gao Zhendong wrote two words on the blackboard - "encoding".
"The easiest way to solve your problem is to encode the laser signal."
"Encoding?" "Yes, use a certain method to make the lasers of different illuminators have their own characteristics. The seeker can distinguish these characteristics through the parameters preset before launch, so that different seekers can only target Being interested in your own laser is like looking for a wife, everyone can only look for his own wife.”
Gao Zhendong's down-to-earth statement of "finding a wife" made the comrades present laugh. Chief Engineer Gao was quite humorous, but his idea made them suddenly enlightened. Yes, the wavelengths are inseparable. , then we separate the signals.
In fact, if there are comrades from the Institute of Communications or the Institute of Computing in their research group, they can basically find this idea quickly. Even if they can't find a specific solution for a while, there is no problem with the idea.
However, the comrades at Chunlei Factory were all bomb makers in the past and had made copies of SS.11. However, there is no such demand for SS.11. That thing just drags a thread and is as fast as Yue Lao's red thread. It is simply useless. There is no possibility of a signal "derailing".
"Mr. Gao, what specific method should be used?" asked Mr. Zhang from Chunlei Factory.
Since Chief Engineer Gao just said that this goal can be achieved with or without a single-chip microcomputer, it means that he must have one or even many plans in mind.
As expected, Gao Zhendong nodded: "Well, there are many ways. For you now, the simplest way is pulse width modulation."
"Pulse width modulation?" Another new thing.
"Yes, to put it simply, different pulse widths are used to distinguish different radiation sources. Let me give you an example." Gao Zhendong picked up the chalk and drew several square wave waveforms of different widths on the blackboard.
"For example, all laser signals use the same 30% duty cycle, but the pulse width of the No. 1 illuminator is 1ms, the pulse width of the No. 2 illuminator is 2ms...and so on. In this case, nothing is needed on the receiver side. Microcontroller, in the SZ61 series Finding a timer or other chip can solve the problem. You just need to set the pulse width parameter of that bomb before dropping it. Of course, this number is just a random example, you just need to understand what I mean."
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This is one of the simplest encoding methods. It can’t even be regarded as encoding. It can only be said to distinguish signals. The information it can carry is extremely limited. It only carries one piece of information - who does this signal belong to? There is no information.
"Really, using pulse width can easily distinguish signals."
"This method is good. Basically, the changes to the existing guidance system are very small. You only need to insert a pulse generator in the illuminator and a pulse width selector in the seeker."
However, some comrades are a little confused about the example Gao Zhendong gave, mainly because of why he chose that special duty cycle.
"General Engineer Gao, why does it have to be 30% duty cycle? Can't other duty cycles work? For example, the easiest to achieve is 50% duty cycle." Duty cycle, simply put, is the time when the signal is "1" , the ratio to the total signal cycle time, a 50% duty cycle, means that within a cycle, the time when the signal is "1" and the time when it is "0" are the same.
Technically speaking, a 50% duty cycle is the easiest to implement. It only needs to record a time and flip the signal when the time is up.
"Because the 50% duty cycle is still more likely to cause signal misjudgment when the pulse width is increased to an integer multiple. It may not be 30%, but it is not recommended to be 50%."
This is the first time for the comrades at Chunlei Factory to hear this little trick. After all, their previous understanding of digital circuits was very limited.
When they expressed their admiration and lamented that they had learned new knowledge, Gao Zhendong reminded them: "This method is simple and direct, and the cost is very small, but it is not without its flaws."
"Mr. Gao, what are the flaws?"
"In terms of reliability and system complexity, it is impossible to set many different pulse widths. For the system, an excessively large pulse width means a reduction in control response speed. If the pulse width is too large to a certain extent, it will lose practical significance. A pulse width that is too small will increase the technical difficulty of the pulse width identification circuit. Therefore, in practice, the number of guidance channels in this method is relatively limited. However, from the perspective of actual combat, the number of pulse width coding guidance channels can be satisfied. Required.”
The number of laser-guided bombs that need to be dropped simultaneously in the same area is actually not very large, so to say that it is enough, the pulse width coding is also enough.
Mr. Zhang nodded and took notes, but he was still interested in other coding methods. Maybe he couldn’t use them now, but he might be able to use them when a new weapon came out: “General Engineer Gao, what other coding methods are there? ?”
Gao Zhendong did not answer directly, but asked them: "Since we can identify signals through pulse width, think about it, is there any other way to distinguish signals? Even if it does not carry any information, it just distinguishes the signals. That’s it.”
(End of chapter)