Chapter 1012 Communication Relay Platform

Although Chang Haonan wrote in the document that communication relay is based on "ground stations", this is just a general statement to make it easier for superiors and comrades in brother units to understand.

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

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

And even if we take a step back, even if we don't consider this, the fixed relay station itself is a relatively vulnerable target in wartime and can easily be taken care of by the imaginary enemy.

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

One is the stratospheric airship led by Zhejiang University, which had a brilliant performance during the dike construction operation.

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 be completely connected to Chang Haonan's needs.

Even the overall architecture does not need to be modified too much, as long as the encoding-decoding function is added on the basis of the original simple reception-storage-forwarding.

Because its floating altitude is more than 20,000 meters, which is much higher than the general flight altitude of the early warning aircraft, it can be used as a simulated satellite unit in the test 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 much stronger than the real space-based communication.

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 let Zhang Weiyong make the satellite.

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

Compared with the stratospheric airship, its function is weaker and the clutter interference is stronger, but it can achieve "communication in motion", that is, communication while moving.

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

The vehicle chassis does not need additional research and development, and can be directly modified with the huge SX2190 truck.

If necessary, it can also be directly moved to other models.

As for the development of the entire vehicle-mounted relay station, Chang Haonan did not choose the 14th Institute of China Electronics Technology, which was responsible for the development of KJ-2000, nor the Space Technology Research Institute, which was responsible for the development of satellites.

Instead, he found the 54th Institute of China Electronics Technology, located in Shimen.

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

Because the 54th Institute is currently developing a series of satellite communication/scattering 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 more than 90%.

And the technology is interoperable.

Chang Haonan has no objection to this.

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

As long as the execution is strong enough and the learning ability is available.

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

So, about a month after the QC300 project was completed, one day in late May, Wu Wei, the head of the general department of the 54th Institute of China Electronics Technology, brought a core team of four people to Beijing to find Chang Haonan.

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

…

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

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

He said while carefully considering the sentence:

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

Communications have always been about standing high and transmitting far, so most of the ideas are to use aircraft in the sky to relay the ground.

This is the first time Wu Wei has heard of the reverse request in his life.

"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 the multi-hop network."

Looking at Wu Wei, whose eyes were almost popping out, he had to continue to explain:

"This kind of test, whether for confidentiality or to reduce the impact on normal production and life, must be far away from the city, so the test area is likely to be placed in the northwest, with a range of at most 200 to 300 kilometers. I have to ensure that at least three hops have passed in the middle, so the working range of the vehicle system basically meets the requirements... The airship has to reduce the power specifically."

The amount of information in this content took Wu Wei a few minutes to digest, and he completely 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 hand and pointed to the information in Wu Wei's hand:

"Turn two pages back and 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 the maximum rank distance code 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. ”

"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 At that time, we believed 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 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-route 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 delay... will be reduced!"