The Military-industrial Scientific Research System of the Academic Master Chapter 1012

Chapter 1012 Communication Relay Platform

Although Chang Haonan wrote in the document that he relied on "ground stations" for communication relay, this was just a general term used to make it easier for superiors and comrades in fraternal units to understand.

In fact, the nodes responsible for communication relay do not need to stick to the formality.

After all, under the premise that low-orbit relay communication constellations will be planned in the near future, it would be a waste of resources to really spend a lot of money to build expensive fixed communication sites in border and coastal areas.

And to say the least, even if we don't take this into account, the fixed relay station itself is a relatively fragile target in wartime, and it is easy to be taken care of by imaginary enemies.

Therefore, after the project was officially approved, Chang Haonan actually invested in research and development, mainly on two platforms.

The first is the stratospheric airship, which was developed under the leadership of Zhejiang University and has performed brilliantly during embankment operations.

This is already a fairly mature technology, and Zhejiang University has not stopped upgrading and improving the equipment in recent years.

In addition, its original design purpose was to serve as a communication relay platform, which can be said to fully meet Chang Haonan's needs.

There is no need to make major changes to the overall architecture, as long as the encoding-decoding function is added to the original function of receiving, storing and forwarding.

Since its floating height is more than 20,000 meters, which is much higher than the general flight height of early warning aircraft, it can be used as a simulated satellite unit during testing to test the antenna performance of the upper hemisphere of the aircraft.

Of course, because the distance is closer, the signal strength and signal-to-noise ratio are definitely still much stronger than real space-based communications.

Moreover, the relay station itself is relatively static and cannot completely restore the scene of space-based communication.

This is why Chang Haonan had to ask Zhang Weiyong to build the satellite.

Another platform is a vehicle-mounted ground communication relay station.

Compared with stratospheric airships, its functions are weaker and it is subject to stronger clutter interference, but it can achieve "communication while moving", that is, communicating while moving.

It is used to test the antenna performance of the lower hemisphere, while simulating the constant motion of the satellite platform and the weak signal characteristics.

The vehicle chassis does not require additional research and development. It can be modified directly with the SX2190 truck, which has a huge inventory.

If necessary, you can also directly move it to other models.

As for the research and development of the entire vehicle-mounted relay station, Chang Haonan neither chose the 14th Institute of Electrical Engineering, which is responsible for the research and development of Air Police 2000, nor the Space Technology Research Institute, which is responsible for satellite research and development.

Instead, he went to the 54th Institute of Electrical Engineering in Shimen.

Or strictly speaking, it was the leaders of Electronic Technology Group who took the initiative to recommend them to Chang Haonan.

Because the 54th Institute is currently developing a series of satellite communication/scatter communication vehicles for military communication units and emergency rescue units.

Although it is not completely consistent with Chang Haonan's needs, the similarity is at least 90%.

And the technologies are similar.

Chang Haonan had no objection to this.

The technical difficulty of the hardware level of this communication relay vehicle is not high, and the core algorithm of the software is still developed by him, so it does not require the partner to have strong capabilities.

As long as the execution ability is strong enough and you have the ability to learn.

Moreover, as a network communications research institute, the 54th Institute is not an ordinary person.

So, about a month after the QC300 project was completed, one day at the end of May, Wu Wei, the head of the general department of the 54th Institute of Electrical Engineering, took a core team of four people to the capital to find Chang Haonan in person. .

The latter did not beat around the bush and stated his requirements straightforwardly.

In Chang Haonan's office, Wu Wei looked at the densely marked technical information in his hand and showed a somewhat embarrassed expression:

"Mr. Chang, using ground vehicles to relay communications for aircraft...technically it is not difficult to achieve, but..."

He said while carefully considering his words:

"But considering the size and power limitations of the vehicle platform, the range may not be particularly optimistic..."

Communication has always been a matter of standing high and transmitting far away, so most of the ideas are to use aircraft in the sky as relays on the ground.

This was the first time in Wu Wei's life that he had heard of a reverse request.

"It doesn't matter, this is the effect I want."

Chang Haonan's answer was even more shocking:

"If the transmission range is too wide, it will be inconvenient to test the theoretical throughput performance of a multi-hop network."

Looking at Wu Wei, whose eyes were about to pop out, he had no choice but to continue explaining:

"This kind of test, whether for confidentiality reasons or to reduce the impact on normal production and life, must be far away from the city, so the test area will most likely be placed in the northwest, with a maximum range of two to three hundred kilometers. I There must be at least three jumps in the middle, so the working range of the vehicle system basically meets the requirements...the airship has to specifically reduce the power.”

The amount of information in this paragraph took Wu Wei a few minutes to digest before he fully understood Chang Haonan's ultimate goal:

"So...the network coding technology you just mentioned is prepared for multi-hop communication?"

"That's right."

Chang Haonan nodded, then raised his finger and pointed at the information in Wu Wei's hand:

"If you turn two pages further, there will be relevant technical instructions." The latter quickly lowered his head and turned to the position he mentioned.

"Of course, there is nothing much to say about network coding technology itself. You are an expert in this field. You must have studied it...at least you have understood it."

At this time, Chang Haonan continued:

“The real core of our test is to use maximum rank distance codes to provide sufficient error correction capabilities for the network coding transmission process to ensure that information can still be transmitted accurately even under strong interference caused by opponents...or the natural environment. "

"What's the MRD code?"

Wu Wei put the information in his hand on the table and looked like he was thinking:

"When the scatter communication vehicle project was first established two years ago, I also studied this technology. It can detect and correct errors in the matrix data structure. The error correction efficiency can be improved by five orders of magnitude compared with the traditional low-density parity check code (LDPC). …”

Compared with Zhang Weiyong, who specializes in satellite systems, he obviously has a deeper understanding of this aspect.

"As long as you have done your research."

Chang Haonan put down the pen he was holding:

"Not only is it error correction capability, but technically speaking, MRD code is also an encryption technology that is almost impossible to crack, which can greatly improve communication stability and security."

The reason why he emphasized that technically speaking is because no encryption method can stop physical theft.

In a system, the most reliable and weakest link is always the people.

"But Mr. Chang, our research at that time was all completed on the supercomputer..."

Wu Wei's frowned brows still didn't relax:

"The encoding and decoding process of MRD codes relies on check matrices and generator matrices. It is very complex and its efficiency depends heavily on computing power. Even for supercomputers, the cycle to complete an encoding-decoding cycle sometimes has to be calculated in hours. , if you want to apply it to real-time communication, will the computing power requirements for the relay equipment be too high..."

Chang Haonan was not surprised by this result.

In fact, the reason why the maximum rank distance code, an artifact with incredible effects, was proposed as early as 1985 but has never been put into use is mainly because the encoding and decoding process is too complicated.

The technological breakthrough he achieved was precisely in this part.

"I think... what you were testing was the Gaby Dulin code?"

"Yes."

Wu Wei nodded:

"After all, it is the most classic maximum rank distance code."

"However, we have also tested several variants of Gaby Dulin codes. Generally speaking, the efficiency is improved compared to the original version, but it is not very obvious..."

"But the maximum rank distance code I want to test does not entirely rely on the concept proposed by Gabi Dulin..."

Chang Haonan picked up the pen he had just put down again:

"The technical details about this part... are too long and cannot be explained in one or two hours. I will give you a special technical document later..."

"But to put it simply, it is to introduce a new concept called the self-duality of the maximum rank distance code... uh... similar to the orthogonal concept of the matrix, that is, when an MRD code C and its dual code C⊥ are equal, We believe that it has self-duality. Under the premise of meeting certain conditions, an MRD code must be equivalent to a self-dual MRD code..."

"Combining this concept, we can design a fast decoding algorithm for Gaby Dulin code... Of course, it can also be a fast decoding algorithm for other MRD codes, that is, for the adjoint formula S and i=t, t-1, t-2... Calculate the matrix Mi and the determinant det(Mi) until the first occurrence of i=m such that det(Mi)≠0, where m is the rank of the error vector e..."

"Furthermore, we can let legitimate user A choose matrices S, Secret Matrix, so security can be greatly improved..."

Although it was "in simple terms", Chang Haonan still talked for almost half an hour.

This is based on the premise that Wu Wei has sufficient encryption algorithm foundation.

"In other words, we use traditional encryption methods to transmit the asymmetrically encrypted message itself, and then use asymmetric encryption to transmit the key required for decryption. This can reduce the amount of data that requires error correction by the relay station and ensure transmission efficiency?"

Wu Wei tentatively confirmed.

Chang Haonan nodded happily and leaned his upper body back on the chair.

Now, the latter at least understands the technical route part.

As for the specific algorithm level...

This can't be rushed.

Even he himself spent almost a month on this with the help of the system.

"I have tested this MRD code combined with network coding technology on a small-scale wired network."

Chang Haonan said lightly:

"The result is that in a four-router multi-hop network, the actual transmission capacity can be increased by about 15-20 times, but the processing delay is a little higher and has to be calculated in seconds."

"However, for satellite communications or space-to-ground communications, because the bandwidth is too low, transmission delay will replace processing delay as the dominant factor, and the actual displayed delay... will be reduced instead!"

(End of chapter)

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