Compared with the previous cooperation, the process of the dinner seems a little bland.

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

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

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

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

So overall, the atmosphere is still relatively warm.

After the dust settled, Xu Yang refused to join his colleagues at the computing institute, but said that he was ready to go directly back to the computing center of Beijing Airlines University, which is the current actual office location of the Torch Group.

Naturally, he 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 stopped talking.

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

"I wanted to contact you a few days ago, but I can't go into too much detail on my phone."

"The trajectory deception algorithm of the GPS positioning system, I have basically studied it, and I have initially tested it several times on the civilian GPS receiver, and the effect is good, but in terms of hardware implementation, there are still some problems."

One sentence suddenly made Chang Haonan, who was a little tired, come to his senses:

"Tell me about it?"

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

And in this direction has been studied for almost half a year.

If the results are achieved, it will be extremely resistant to equipment such as precision-guided weapons and autopilot systems that rely on satellite guidance.

In the "new three-attack and three-defense" policy, this technology can solve the two problems of "fighting cruise missiles" and "anti-precision guidance" at one time.

At least for some time to come.

Of course, the other side can also counteract by upgrading the system or replacing the algorithm, but electronic warfare, unless it is hard to kill, there is no one-and-done solution, and it is all one and the other.

It's pretty good to be able to maintain an advantage for a while.

Xu Yang organized the language for a moment, and then explained:

"A complete GPS navigation signal is divided into three parts: pseudo code, carrier and navigation message, and the military pseudo code for civilian use, and even a considerable part of the US allies, is the C/A code of rough capture, and the military precision capture code is the P code."

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

"I have tried this kind of generative jamming method, which can easily change the location coordinates in China to Africa, and even generate a complete false movement trajectory, so that the navigation equipment can work exactly according to our ideas."

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 to achieve navigation, it is completely possible to let these things listen to us?"

Don't look at what Xu Yang said lightly, as if you can interfere with the C/A code casually.

In fact, the real difficulty of this activity lies in the reverse calculation of the navigation message, so that the receiver constantly calculates the "wrong but reasonable" position information.

Otherwise, the GPS navigation device itself is not entirely stupid, and if you really let the location information keep jumping around, the relevant signal will be blocked immediately.

What Xu Yang said just now is "generating a complete false movement trajectory".

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

And, don't underestimate the interference with the C/A code.

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

"Theoretically, yes."

Xu Yang nodded:

"However, this requires our jamming signal to be much stronger than the satellite positioning signal, and it is best to be installed on an aircraft or vehicle to carry out approach jamming in the middle of the way."

"The drone is okay, if it is a guided weapon, wait until it approaches the target before starting to interfere, then even if the interference is effective, at most it will make the ammunition slightly off the target."

"And ......"

Speaking of this, Xu Yang's words changed:

"This method does not work for the P code, unless we can get the various parameters of the P code signal structure, or directly get a spaceborne signal transmitter, it is impossible to directly generate a navigation signal that is enough to mess with reality."

Chang Haonan is directly a sweaty soybean:

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

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

If you can even get the full parameters of the P code, then you don't have to think about any new three-fight three-defense now, and you can directly write a plan to land on the West Coast......

"To put it another way, it's forwarded jamming?"

Xu Yang has obviously thought about other technical routes as well.

"That's right."

Chang Haonan pulled the pen and paper with his hand and drew a simple schematic diagram:

"The pseudorange positioning principle of GPS is to receive satellite navigation signals transmitted by 4 or more satellites, and then calculate the pseudorange according to the signal transmission time, and finally solve the current position."

"Now since we can't forge the P code, we can let the jammer receive a completely real GPS signal, process the real GPS signal according to the relative position between the jammer and the target receiver and forward it, and the target GPS receiver captures and tracks the deception GPS signal and calculates the wrong navigation location."

"As for the specific deception method, just improve it on the basis of the algorithm you just mentioned, military signals and civilian signals are only different from the pseudo code, and the format and content of the navigation message data code are exactly the same."

"Of course, there will be a delay in the signal between multiple satellites, and our spoofing signal is sent synchronously, so we have to falsify the time information to control the time difference to ......"

Chang Haonan wrote down an equation on paper:

"Just keep this result to a positive number."

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

Of course, the degree of freedom of spoofing content is low, and things like replacing the target signal from China to Africa are more difficult to do.

But it is not difficult to generate a signal error of the order of 100 meters.

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

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

"Moreover, this requires a very high signal solving speed for the jammer, after all, the signal reception, solving, and forwarding must be completed by the jammer, and in the case of generative jamming, the jammer only needs to send a signal."

"There's no way around it."

Chang Haonan threw the pen aside:

"It would have been impossible to interfere with military code positioning by purely technical means, otherwise the Americans and Soviets would not have spent so much money on building a satellite navigation system."

"Fortunately, the positioning logic of GPS is passive positioning, and the positioning terminal only receives and does not send signals, so it is not so sensitive, anyway, the difficulty of getting a receiving terminal is definitely easier than sneaking into a NASA factory to dismantle a spaceborne signal transmitter, or stealing the complete characteristics of the P code."

"As for the speed of solving...... Actually, it's okay, I forgot where to read the data before, the GPS feature data is only updated every 12.5 minutes, so after obtaining the data code through any GPS receiver, there is still plenty of time for data processing......"

"The bigger problem is that the inertial navigation equipment normalizes the information square detection of the signal, and 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 a little impatient, had already picked up his bag and got up to leave:

"It doesn't matter, I've thought about this a long time ago."

"Normalized information squares are scalar values, and this detection can be circumvented by paying attention to the fact that each false signal only changes direction and does not change the distance when generating a spoofed signal."

"I'm going to contact the 14th Institute of Electronics, so that they can study the specific hardware design first, and before the receiving terminal gets it, you can use the C/A code navigation equipment to do a functional test."

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

"I'll report to the Commission of Science and Technology on the receiving terminal, this thing will have to wait for the opportunity......"

(End of chapter)