Chapter 803 Laser Coding

The simplest example is that if you want to destroy a bridge with many piers, the ideal attack method is to use multiple shells to hit as many piers as possible at the same time.

In this case, the value of the Air Force’s requirement is reflected. After all, laser-guided bombs are free-falling objects. It takes time for each bomb to fall from hundreds or even thousands of meters in the air. In addition, in the absence of ground illumination, the carrier aircraft must continue to illuminate and guide.

This is a very severe challenge to the survival of the carrier aircraft. If multiple bombs have to be dropped one by one, the situation will be further aggravated and the probability of survival of the carrier aircraft under enemy air defense firepower will drop sharply.

Gao Zhendong couldn’t help but sigh that those people in the Air Force were really quick-witted. Their vision was even longer-term than that of the real inventor of the laser-guided bomb, the Citigroup. The Citigroup didn’t consider this problem at the beginning.

However, for the Chunlei Factory, this requirement was 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 this just right? Each one goes his own way and bombs his own thing.

In fact, when they actually started the experiment, they found that the problem was not that simple.

——After the laser hits the target surface, it is diffusely reflected.

Diffuse reflection means that the reflected lasers from multiple close 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 drink, three monks have no water to drink. For a bomb, if it receives multiple signals at the same time, it doesn’t know what to do, because these signals are the same except for the difference in strength. It is impossible to distinguish them. If they all fly towards the strongest signal, things will be a mess.

To sum up, when illuminating multiple targets in a small area at the same time and instructing multiple bombs to strike, the behavior of the bombs is unpredictable.

The best case scenario is repeated strikes, that is, multiple bombs fly towards the target with the strongest signal. In this case, at least a target can be hit. Although the power of the strike is seriously overflowing, it is not a case of getting nothing.

The worst case scenario is that the bomb won’t hit any target. It will fly this way and that way and ultimately hit nothing. Or the lasers will interfere with each other and the bomb won’t know where to fly at all. It’s not impossible that the bomb will be like a free-falling bomb.

According to the tests conducted by the Chunlei Factory, when multiple bombs hit multiple targets in the same area, the bombs’ hit rate will drop sharply.

“Chief Engineer Gao, this is the problem we are facing now. You are the inventor of the laser, and you know much more about the application of lasers than we do. We invited you here to see if there is any way to solve this problem.” Mr. Zhang spoke sincerely.

“Have you tried to solve it?”

“We tried to solve this problem with different wavelengths, but found that it was impossible. Multi-wavelength lasers and seekers are unacceptable in terms of cost, volume and weight.”

The solution that Mr. Zhang and his team came up with is a relatively direct wavelength division multiplexing, which uses different wavelengths to achieve multi-target guidance in the same space.

However, this method can be used in theory, but in reality, from the current technical capabilities, it is theoretically feasible but not possible in engineering.

To achieve 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. Not to mention whether it is technically feasible, the cost of this method is simply too high to be accepted.

After Gao Zhendong understood his question, he thought about it. For him, if he didn’t need to come up with a specific solution directly, he wouldn’t need to search for the information in his system for this question, because for him, on a theoretical level, the answer was 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 others.

“Mr. Zhang, this problem is not difficult to solve, especially now that you can use single-chip microcomputers. In fact, you don’t need single-chip microcomputers, but single-chip microcomputers have relatively greater potential.”

When Mr. Zhang heard that Gao Zhendong didn’t even have thirty seconds, he told him that there was a way. He was very happy. Chief Engineer Gao was indeed reliable. His skills and foundation were impeccable.

Thinking of this, he felt a little resentful towards the Air Equipment Bureau. If you had raised this requirement at the very beginning, perhaps Chief Engineer Gao would have solved it in the initial plan, and there would have been no need to take a detour.

Gao Zhendong wrote two words on the blackboard – “coding”.

“The easiest way to solve your problem is to encode the laser signal.”

“Encoding?” “Yes, we 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 are only interested in their own laser beams. It’s like looking for a wife. Everyone can only look for his own wife.”

Gao Zhendong’s down-to-earth “finding a wife” statement made all the comrades present laugh. Chief Engineer Gao is quite humorous, but his idea made them suddenly realize something. Yes, if the wavelengths cannot be separated, then we can separate the signals.

In fact, if there are comrades from the School of Communications or the Institute of Computing in their research group, they can basically find the idea quickly. Even if they cannot find a specific method for the time being, there is no problem with the idea.

However, the comrades at the Chunlei Factory used to make bombs and had imitated the SS.11. However, there was no such demand for the SS.11. That thing simply dragged a wire, and was tied as tightly as the red wire of the matchmaker, so there was no possibility of the signal “going off track”.

“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 a set, or even many sets of plans in mind.

As he 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 irradiator No. 1 is 2ms, and that of irradiator No. 61 is ms… and so on. In this case, there is no need for a single-chip microcomputer on the receiver side. A timer or other chip in the SZ series can solve the problem. All you have to do is set the pulse width parameter for that bomb before dropping it. Of course, this number is just an example I gave casually. Just understand what I mean.”

This is one of the simplest encoding methods. It cannot even be considered encoding. It can only be said to distinguish signals. The information it can carry is extremely limited. It only carries one message – who the signal belongs to, and no other information.

“Really? Using pulse width can easily distinguish the signals.”

“This is a good idea. Basically, the changes to the existing guidance system are very small. We only need to insert a pulse generator in the illuminator and a pulse width selector in the seeker.”

However, some comrades did not quite understand the example given by Gao Zhendong, mainly why he chose that special duty cycle.

“Chief Engineer Gao, why must the duty cycle be 30%? Are other duty cycles not possible? For example, the easiest to achieve 50% duty cycle.” Duty cycle, in simple terms, is the ratio of the time the signal is “1” to the total signal cycle time. A 50% duty cycle means that in one cycle, the time the signal is “1” is the same as the time it is “0”.

Technically speaking, a 50% duty cycle is the easiest to implement. It only requires recording a time and flipping the signal when the time comes.

“Because a 50% duty cycle is more likely to cause signal misjudgment when the pulse width increases by an integer multiple. It can be different from 30%, but 50% is not recommended.”

This little trick was the first time that the comrades at Chunlei Factory had heard of it. After all, their understanding of digital circuits was very limited.

When they clapped their hands in admiration and expressed their gratitude for learning something new, Gao Zhendong reminded them: “This method is simple and direct, with low cost, but it is not without flaws.”

“Mr. Gao, what is the defect?”

“From the perspective of reliability and system complexity, it is impossible to set many different pulse widths. For the system, a pulse width that is too large means a reduction in control response speed. A pulse width that is too large will lose its practical significance, while 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 for this method is relatively limited. However, from the perspective of actual combat, the number of guidance channels for pulse width coding can meet the requirements.”

The number of laser-guided bombs that need to be dropped simultaneously in the same area is actually not very large, so if we say it is enough, the pulse width coding is also sufficient.

Mr. Zhang nodded and took note of it, but he was still interested in other coding methods. Maybe they were not useful now, but maybe they would be useful when a new weapon was developed. “Chief Engineer Gao, are there any other coding methods?”

Gao Zhendong did not answer directly, but asked them: “Since we can identify signals by pulse width, think about it, is there any other way to distinguish the signals? Even if it does not carry any information, just distinguishing the signals will be enough.”

(End of this chapter)