Chapter 239 Who is it

In the activity room of the mit Radio Association, Professor Murray was staring at the content on the blackboard without saying anything.

Harvey asked curiously, "Professor? What's the matter?

However, Professor Murray didn't seem to hear it at all. He stepped forward and looked at it carefully for a while. Then he immediately picked up the paper of the measurement record in his hand, took a look at the record book, and then looked at the content on the blackboard.

At the beginning, he frowned deeply and kept comparing the content on the blackboard and manuscript paper, guessing why it was arranged like this.

After Harvey shouted once, he saw that his teacher did not respond, so he didn't say anything again.

He is very clear about Professor Murray's temperament. When he encounters something of interest, he will become particularly focused and automatically block any interference from the outside world.

What kind of data are those numbers written on the blackboard? How can you make the professor so fascinated?

Harvey also felt very strange.

Professor Murray is an authority on wireless communication. His achievements in this regard are at the forefront in the world. As his student, Harvey naturally knows this.

In those years, he started a business after he finished his graduate school. The field of entrepreneurship is also closely related to wireless communication. When he came back this time, he came back on behalf of the company and wanted to hire professors to give them honorary technical guidance, and strive to establish a close cooperative relationship with mit as a future. One of the R&D talent reserve bases.

Out of curiosity, Harvey also walked over and watched the content on the blackboard.

At the beginning, he was still a little confused when he saw the data. After all, he had not participated in this project, but when he saw Professor Murray matching the record book in his hand with the data on the blackboard from time to time, he immediately understood.

"Are these numbers on the blackboard the satellite communication channel code tablets measured by the students?"

Thinking of this, Harvey also looked at it seriously.

The content on the blackboard has completely attracted Professor Murray.

He found that all the data above was based on the observation data in his hand, and then selected some channel code pieces to write on the blackboard.

is not a simple excerpt, but a selection. Every distance, a continuous string of numbers will be selected.

Then, these numbers are formed into a matrix, and then after a specific transformation, it becomes another matrix.

Next, calculate the obtained matrix with another selected matrix, and then get a matrix that has been magnified many times.

Murray didn't know why he chose these data, but he was very shocked to see the results calculated on the blackboard!

Because at this point, he can see some of the laws contained in these numbers.

"This is actually a channel denoising algorithm!"

After dealing with radio communication and satellite communication coding for a long time, he can naturally understand what this process represents. That's why he was very shocked!

You should know that in satellite communication, the most important thing is the denoising algorithm, because the satellite is usually thousands of kilometers away from the earth, and it works with batteries. The emission power is impossible to be very high. It is sending signals to the earth, and it will also pass through the thick ionosphere and various artificial shields. When it reaches the earth, the signal power will decay to very small, and even be directly submerged in the background noise.

The antenna on the earth can still receive weak signals, but whether these signals can be distinguished is a great problem.

For example, they can actively amplify the received signal by 300 times by using the 1.8-meter dish antenna of the monitoring station, but this level of intensity still cannot meet the requirements.

These signals must also be specially processed.

First of all, the signal coding technology on the satellite cannot use ordinary coding methods, but must use a technology called spread spectrum communication.

For a long time, spread spectrum communication technology has been mainly used for military confidential communication and electronic confrontation systems, so this technology is extremely confidential and cannot be accessed by ordinary people at all.

Because of Professor Murray's special identity, he is qualified to access this technology, but he does not know who is the real inventor of this technology.

What Professor Murray can know is that this technology first appeared in the mid-1950s, when the U.S. Navy gave Hoffman Radio a patent to produce sonar buoys and radios accompanying aircraft for two-way communication between aircraft and sonar buoy equipment.

However, in that patent, the inventor's name was erased from the document, the information given was extremely confidential, and Hoffman Radio did not know who the patent was.

Spread spectrum communication technology is indeed a very unexpected but powerful technology.

It has many advantages, such as good anti-interference and strong concealment, which can improve the utilization rate of the frequency band.

Conventional communication coding technology, known as "narrowband communication technology".

A certain bandwidth is required to transmit any information. For example, the bandwidth of voice information is about 20hz~20000hz, and the bandwidth of ordinary TV image information is about 6mhz.

In order to make full use of frequency resources, the transmission bandwidth is usually compressed as much as possible. If the phone is a baseband transmission, people usually limit the bandwidth to about 3400hz.

However, spread spectrum communication technology does the opposite. It belongs to broadband communication technology, and the usual ratio of spread spectrum signal bandwidth to information bandwidth will be as high as hundreds or even thousands of times.

This technology is to exchange length for accuracy. The length of the information is lengthened, and then the specific encoding and decoding algorithm can be used to achieve the purpose of accurate communication with very small power.

For example, there is only one signal, representing the code, but in order to avoid this signal being completely offset by other interference noises in the space, it is usually necessary to expand the code to dozens of bits or even hundreds of bits.

In this way, even if a certain encoded fragment is lost, it is irrelevant for the whole. After decoding, the received part of the chip can still be restored to "".

When the signal is on the satellite, it is necessary to encode the spread spectrum according to certain rules. This process is equivalent to encrypting the data and inserting a lot of specific information on the original information to make its coded piece n times the original.

But after reaching the ground, it is necessary to operate in the opposite direction and decode.

This process is like wearing clothes in the order of underwear and then outerwear when getting out of bed, and taking off clothes in the order of outerwear and then underwear when going to bed.

However, it is not that anyone will take off his clothes, but to give him a decoding sequence, which is equivalent to a key. Only by using this sequence corresponding algorithmic operation can the original face be finally restored.

However, this key is confidential and is usually not told to you. The purpose of the project that Professor Murray is doing is to calculate the key by monitoring the satellites of Su Union or Mei, and then through a large amount of data operations.

As long as you get the key, it means that the satellite has been cracked.

However, this process is very complicated and difficult. It has been more than a year since the establishment of this project. Professor Murray has built dozens of mathematical models for this purpose, but he still hasn't touched the edge of the key.

However, today, he actually saw the dawn of the key on the blackboard of the activity room!

The digital matrix on the blackboard shows that it seems that after several matrix operations, the background noise has been greatly eliminated, that is to say, the original appearance of the signal has been restored to a certain extent in this way.

If it continues, it is likely to restore the real code!

At this time, Professor Murray has finished reading the contents of the blackboard, only half of the last number matrix, and all the following has been erased.

"Why did you erase it?" Professor Murray exclaimed, "Why erase it! Who wiped it!"

He was seeing the key point, but found that it was gone. This feeling was like being ooxx with his wife. When he was about to reach the peak, he was suddenly poured from his head to his foot by a basin of ice water, and the thin ** was about to fall to the freezing point.

The second half was the most critical part, but it was erased, which made Professor Murray feel very sorry and angry at the same time.

Professor Murray's eyes widened, looking forward to seeing the content from the faint traces left on the blackboard, but his expectation failed. The other party wiped it thoroughly, and even the slight traces were left.

In the face of this situation, he is a little crazy.

"Professor, these contents..." Harvey saw that the professor came to his senses and hurriedly said.

Before he finished speaking, Professor Murray said directly, "Harvey, don't you Qualcomm want to develop a commercial product in the field of satellite wireless communication? That's the key!"

"What?" Harvey's spirit was immediately shaken up when she heard the words, and then she was a little surprised!

He knows that his teacher is not the kind of talker. He said yes, that's for sure.

In fact, he came here for another purpose, which is to hope that Professor Murray can civilize the spread spectrum communication technology he has mastered.

However, Professor Murray has never nodded about this, because this technology is a confidential technology. He signed a non-disclosure agreement at the beginning. Although the government does not seem to be as strict as before, there is no clear document saying that the technology can be decrypted.

"Who wrote these contents on the blackboard?"

Professor Murray did not answer Harvey's words, but searched for possible candidates in his mind.

First of all, a member of the mit radio association, Bailey? Sophie? No, they haven't reached this level yet.

Other professors in the field of wireless engineering?

Professor Murray looked around in his mind, but he really couldn't find the right person.

In mit, he doesn't know who can be better than himself in this area.

Professor Murray re-examined the previous content several times, but he still couldn't see how these rectangles on the blackboard came from.

The author who wrote these contents omitted too many steps in the middle, as if the other party just wrote the answer here.

Who is

?