Chapter 1006 Maximum Rank Distance Code


    In fact, Zhang Weiyong’s earliest professional background was in communications technology.


    However, after he started serving as satellite chief engineer in the mid-to-late 1990s, his main focus was on the overall engineering aspect.


    ?Of course, even if he is still specialized in the original major, he may not have noticed the paper that proposed network coding in advance—


    At the beginning of the 21st century, we are catching up with the explosion of network communication technology. Not to mention every day, at least every month, new concepts and new technologies are proposed, and almost every proposer claims that their research can change the world.


    Even a research team with abundant resources cannot pay enough attention to every result.


    Not to mention that China’s aerospace research has always been focused on stability and is relatively conservative in the application of new technologies.


    But if it is a technology that has been proven in other industries...that is another matter.


    Therefore, after hearing Chang Haonan’s answer just now, Zhang Weiyong immediately sat up straight:


    “Mr. Chang still has research on information theory?”


    Data transmission and data compression are both categories of information theory.


    Chang Haonan has not had any research results in this area before.


    ?But after thinking about it, it seems that Chang Haonan has expanded into a new research field, which is not very surprising...


    “Although network coding does belong to information theory, I came into contact with this field purely from a mathematical perspective...”


    Chang Haonan smiled and explained:


    “You know, I have done some research on topology and topological structures...”


    “Cough cough cough—”


    ?At this moment, Zhang Weiyong just picked up the cup again and took a sip of wine, but was choked by Chang Haonan''s words.


    A person who solved the Poincaré conjecture and created a manifold learning algorithm.


    Say that you have “some research” on topology?


    ?That is really well researched.


    ?After a while, Zhang Weiyong finally calmed down and waved his hand to express that he was fine, and motioned for Chang Haonan to continue performing... uh... keep talking.


    "In short...some time ago, someone came to me to review a paper on nonlinear coding algorithms. I found that there were several very basic theoretical issues in his paper. It was definitely impossible to pass the paper, but the ideas proposed were indeed It’s very novel, so I stopped by to learn about the research background. ”


    ?Chang Haonan drank a small glass of red wine and did not continue. Instead, he got a thermos from somewhere and drank water instead.


    While talking, he also poured a glass for Zhang Weiyong.


    “So you’re going to study it in depth?”


    “Research is out of the question.”


    Chang Haonan shook his head:


    “Things in the field of information theory are okay at the theoretical level. If you really want to study engineering applications, you will need enough time and funds. At most, I have a little understanding..."


    At this moment, Zhang Weiyong finally understood.


    ?The other party went around in such a big circle because he originally wanted to apply for the project with me, and then take advantage of the resources at the Aerospace Port.


    After all, not to mention that Chang Haonan is only a half-step academician now. Even if he is really a big brother in the Dzogchen realm of academicians, it is impossible for the country to build a batch of satellites or build an entire dedicated network just by talking about it. Carry out technical verification.


    Must rely on some names.


    Of course, Zhang Weiyong would not believe even a single punctuation mark in such nonsense as "I just learned about it and haven''t studied it in depth yet."


    “Can you tell me more?” He asked calmly:


    “I mean, about that specific general code.”


    "certainly."


    ?Chang Haonan turned the piece of paper to the back:


    "We first simplify a multicast directed acyclic network with single source and dual sinks. All point-to-point links in the network have unit capacity. S is the source, T1 and T2 are sinks, and the rest are intermediate nodes... "


    As he spoke, he drew two schematic diagrams on the paper.


    "According to the ''maximum flow minimum cut'' theorem, in any directed graph, the maximum flow of information from the input node to the output node is equal to the capacity of the minimum cut set that separates the input node from the output node. Then the multicast network in the figure below The maximum theoretical transmission capacity is 2 bits/unit time..."


    "If we follow the traditional model in the picture on the left, since link CD is the bottleneck of the network transmission, it can only transmit 1 bit of information. As a result, node C must use the traditional queuing storage method to realize information transmission, resulting in the throughput of each sink node. The amount is only 1.5 bits/unit time..."


    "In the picture on the right, node C encodes the received message a and message b... For simplicity, we choose the simplest XOR logic. In short, the sink node can use the received message a or b, and the relationship between a and b. The encoded result simultaneously decodes another unreceived message bit, thus reducing the transmission of one information stream and increasing the throughput of each sink node to the theoretical upper limit of 2 bits/unit time..."


    "Of course, due to the existence of the Shannon limit, it is impossible for any technology to compress data infinitely, but this is just the simplest case. You and I both know that the more complex the information transmission network is, the difference between the actual throughput and the theoretical transmission capacity will be. The wider the gap, the more obvious the potential of this type of algorithm..."


    …”


    "Wait a moment…"


    Just when Chang Haonan was coming to the end of his speech and the paper was finally almost full, Zhang Weiyong suddenly stretched out his hand:


    "Mr. Chang, what you just said is based on the premise that the transmission process is error-free... If any of the nodes on the right has a coding error or transmission error, then the subsequent nodes will be infected, causing errors like a computer Like a virus, it eventually spreads to the entire communication node..."


    “Not to mention that such errors are very common in normal communications. Military satellites also need to consider the opponent’s electronic interference..."


    The latter’s concerns are naturally justified.


    The traditional information relay method repeatedly sends data. Although it will cause lags and delays, the correct information can still be sent.


    ??But for this new trick that Chang Haonan is planning to do, if something goes wrong in the intermediate encoding and decoding process, the relevant data may be wrong.


    ??Moreover, because errors propagate so quickly, it’s difficult to figure out which step caused the problem.


    In the end, you still have to send the data repeatedly, which will only make it more laggy.


    ?However, when faced with this problem, Chang Haonan acted as if it were a matter of course:


    “That’s why I said that in-depth research and technical verification are still needed...”


    “If I can come up with ready-made technology now, then there is no need to go to you, I can just go to Director Luan directly..."


    …


    ?Zhang Weiyong scratched his head and felt that it made sense...


    "In short, Mr. Zhang, you just mentioned that the focus of this technology now is to develop encoding algorithms with stronger compression capabilities. The second is to find ways to find an error correction mechanism for the information transmission process, so that even if the data is being transmitted If an error occurs, it can be corrected at the next node, ensuring that the error will not spread between different nodes.”


    ??Chang Haonan said, reaching out and tapping the paper lightly for emphasis.


    At this point, we enter a field that Zhang Weiyong is relatively familiar with:


    “For example…maximum rank distance code?”


    “MRD code is indeed possible.”


    ?Chang Haonan was a little surprised that the other party could directly give him the answer he wanted, but there was no change in his expression:


    “However, the current research on MRD is mainly focused on using it for data encryption, and the error correction function is only incidental...So if you want to achieve strong error correction capabilities, you must develop new MRD code technology.”


    "I can use the resources of the Torch Group to conduct some research and testing in the field of small-scale local area networks and aviation relay communications. However, these environments are still too mild compared to satellite communications. I definitely need a... or even It is a group of specialized satellites to conduct inter-satellite link testing to finally determine the feasibility of use in the aerospace field..."


    (End of this chapter)