The military-industrial scientific research system of the academic master.

Compared with the previous cooperations reached, the process of the dinner seemed a bit dull.

Of course, this "mundane" is for Chang Haonan.

A large part of the people invited to attend the National Technology Awards are "young scientists" in the traditional sense.

That is, researchers between the ages of 30-45.

Not everyone can be like Chang Haonan, who has already experienced hundreds of battles in his early twenties and has seen a lot.

So overall, the atmosphere is quite warm.

After everything was settled, Xu Yang refused to go with his colleagues from the Computing Institute, but said that he planned to go directly back to the Computing Center of Beihang University, which is the current actual office location of Torch Group.

Naturally, I got into Chang Haonan's car.

In fact, during the dinner just now, Chang Haonan found that the other party wanted to say something to him several times, but he hesitated.

Sure enough, after the car took the two to the computing center, Xu Yang followed Chang Haonan directly upstairs and entered the office:

"I wanted to contact you a few days ago, but I couldn't give you too many details on my phone."

"I have basically researched the trajectory deception algorithm of the GPS positioning system. I have tested it several times on civilian GPS receivers and the results are good. However, there are still some problems in terms of hardware implementation."

One sentence immediately cheered up Chang Haonan, who was already a little tired:

"Tell me more specifically?"

Of course he knew that since the effect of the electronic jamming pod was verified, the other party's research interest has shifted to jamming, or in other words, deceiving the satellite positioning system.

And we have been researching in this direction for almost half a year.

If it can produce results, it will be equivalent to developing extremely high resistance to equipment such as precision-guided weapons and autonomous driving systems that rely on satellite guidance.

In the "new three attacks and three defenses", this technology can solve the two problems of "attacking cruise missiles" and "preventing precision guidance" at one time.

At least for some time to come.

Of course, the opponent can counterattack by upgrading the system or changing the algorithm, but in electronic warfare, unless hard kills are carried out, there is no one-and-done solution.

Being able to maintain an advantage for a period of time is already quite good.

Xu Yang organized the language a little, and then explained:

"A complete GPS navigation signal is divided into three parts: pseudo code, carrier wave and navigation message. The pseudo code corresponding to civilian use, and even the military pseudo code of a considerable number of U.S. allies, is a crude capture C/A code, while the military precision capture The code is P code.”

"The C/A code is completely open to the world, so it can be directly based on the real satellite signal format to forge a spoofing signal that is similar to the real signal, modify the position information in the satellite navigation message, and then send it to the spoofing target."

"I have already tried this generative interference method. It can easily change the location coordinates in China to Africa. It can even generate a complete false movement trajectory, allowing the navigation equipment to work exactly as we want."

To be honest, this research progress surprised Chang Haonan:

"In other words, if the opponent's drones or precision-guided weapons use C/A codes for navigation, can these things listen to us?"

Don't look at Xu Yang's understatement, it seems that he can interfere with the C/A code casually.

In fact, the real difficulty of this task is to reversely solve the navigation message, allowing the receiver to continuously calculate "wrong but reasonable" position information.

Otherwise, the GPS navigation device itself is not completely stupid. If you really let the location information keep jumping around, the relevant signals will be blocked immediately.

What Xu Yang just said was "generating a complete false motion trajectory."

It shows that this algorithm is quite reliable in terms of calculation accuracy, stability and speed.

Moreover, don’t underestimate the interference with C/A code.

Not to mention other countries, even within the US military, there are many devices that use civilian code positioning.

"Theoretically yes."

Xu Yang nodded:

"But this requires our interference signal to be much stronger than the satellite positioning signal. It is best to install it on an airplane or vehicle and perform close-in jamming midway."

"The drone is fine. If it is a guided weapon, if it starts to interfere until it is close to the target, then even if the interference is effective, the most it will do is make the ammunition slightly deviate from the target."

"and……"

At this point, Xu Yang changed the subject:

"This method will not work for P codes. Unless we can obtain various parameters of the P code signal structure, or directly obtain a satellite-borne signal transmitter, it is impossible to directly generate a navigation signal that is realistic enough. "

Chang Haonan is just a sweaty soybean:

"Then let's just change our thinking..."

The military code signal structure of satellite positioning systems in various countries is top secret. Not to mention making it public, even allies have to guard against it.

If the complete parameters of the P code can be obtained, then there is no need to think about the new three-on-three-defense, and we can just write a plan to land on the West Coast and be done with it...

"If you think about it differently, is it forwarding interference?"

Xu Yang has obviously also thought about other technical routes.

"Yes."

Chang Haonan grabbed the pen and paper and drew a simple diagram:

"The principle of pseudo-range positioning of GPS is to receive satellite navigation signals transmitted by four or more satellites, then calculate the pseudo-range based on the signal transmission time, and finally calculate the current position."

"Now that we can't forge the P code, we can let the jammer receive a completely real GPS signal, process the real GPS signal and forward it based on the relative position between the jammer and the target price receiver, and the target GPS receiver captures and tracks the spoofed GPS signal. , to calculate the wrong navigation position."

"As for the specific deception method, just improve it based on the algorithm you just mentioned. Only the pseudo code part differs between military signals and civilian signals. The format and content of the navigation message data code are exactly the same."

"Of course, there will be delays in the signals between multiple satellites, and our spoofing signals are sent out simultaneously, so we have to forge the time information to control the time difference within..."

Chang Haonan wrote a formula on the paper:

"Just control the result to a positive number."

This idea is not complicated, Xu Yang understood it after just a little thought.

Of course, the degree of freedom of deceptive content of forwarding jamming is relatively low. For example, it is more difficult to replace the target signal from China to Africa.

But it is not difficult to generate a signal error on the order of hundreds of meters.

However, this idea still faces similar problems at the hardware level.

"But even so, we still need a device that can receive and decipher the P code, otherwise the signal forwarded will still only be the C/A code."

"Furthermore, this requires a very high signal processing speed for the jammer. After all, signal reception, processing, and forwarding are all completed by the jammer. In the case of generative interference, the jammer actually only needs to send signals."

"There's nothing we can do about it."

Chang Haonan threw the pen aside:

"It would have been impossible to interfere with military code positioning through purely technical means. Otherwise, the Americans and the Soviets would not have spent so much money building satellite navigation systems."

"Fortunately, the positioning logic of GPS is passive positioning. The positioning terminal only receives but does not send signals, so it is not so sensitive. In any case, it is definitely more difficult to get a receiving terminal than to sneak into a NASA factory to dismantle a satellite signal. transmitter, or it’s easier to steal the complete characteristics of the P code.”

"As for the calculation speed...it's actually not bad. I read the information somewhere before. The characteristic data of GPS is only updated every 12.5 minutes. Therefore, after obtaining the data code through any GPS receiver, there is still There is relatively sufficient time for data processing..."

"The bigger problem is that the inertial navigation equipment performs normalized information square detection on the signal. If the gap between the navigation signal and the inertial navigation signal is too large, it will be automatically filtered out..."

Xu Yang, who was quite impatient, had already picked up his bag and stood up to leave:

"It doesn't matter, I have already considered this."

"The normalized information square is a scalar value. As long as you pay attention when generating deception signals, each false signal only changes the direction and does not change the distance to avoid this detection."

"I'm going to contact the 14th Institute of Electronics and ask them to study the specific hardware design first. Before getting the receiving terminal, I can use the C/A code navigation device to do a functional test."

Chang Haonan also stood up and sent the other party to the door of the office:

"I'll report the receiving terminal to the Science and Technology Commission. This thing will have to wait for an opportunity..."