Chapter 535: Retransmission Satellite Positioning Interference
Compared with several previous cooperations, 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 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 has experienced hundreds of battles in his early twenties and has seen a lot.
So overall, the atmosphere is quite warm.
After everything 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 Beijing Hang University, which is the current actual office location of Torch Group.
Naturally, I got into Chang Haonan's car.
Actually, 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 sent the two to the computing center, Xu Yang followed Chang Haonan directly, went upstairs and entered the office:
“I wanted to contact you a few days ago, but there was no information on my phone. The method is too detailed. ”
“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, in terms of hardware implementation, There are still some problems."
One sentence immediately cheered up Chang Haonan, who was already a little tired:
"Can you 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 once.
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.
It is already quite good if we can maintain our advantage for a period of time.
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, which corresponds to civilian use. Even the military pseudocode used by a considerable number of U.S. allies is the C/A code for rough capture, while the military precision capture code is P code. "
"The C/A code is completely open to the world, so it is completely open to the world. It can directly forge a spoofing signal that is similar to the real signal based on the real satellite signal format, 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 position 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, Chang Haonan was a little surprised by the progress of this research:
“In other words, if the opponent’s drone or precision-guided weapon uses C/A code to achieve navigation, it can be completely Do these things listen to us?”
Don’t look at Xu Yang’s understatement, as if he can interfere with the C/A code casually.
In fact, the real difficulty of this task lies in the reverse interpretation of 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.
Also, 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 codes for positioning.
"Theoretically yes."
Xu Yang nodded: "But this requires that our interference signal is much stronger than the satellite positioning signal. It is best to be installed on an airplane or vehicle, and it can be used midway. Carry out approach jamming. "
"The drone is fine. If it is a guided weapon, it will wait until it is close to the target before starting to jam. Even if the jamming is effective, the ammunition will only be slightly smaller. Off 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 Signal transmitter, otherwise 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..."< br>
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 attacks and three defenses, and we can just write a plan to land on the West Coast and be done with it...
"To change the idea, it is forwarding interference. ?”
Xu Yang has obviously also thought about other technical routes.
“That’s right.”
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 4 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 fake it P code, then the jammer can 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 receiver, and the target GPS receiver captures and tracks the spoofed GPS signal, and calculates the wrong navigation position. "
"As for the specific deception method, just improve it on the basis of the algorithm you just mentioned. The only difference between military signals and civilian signals is the pseudo code part. The format and content of the navigation message data code It’s exactly the same.”
“Of course, there will be a delay 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... ”
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 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 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 forwarded signal will still only have the C/A code."
"Furthermore, this is not suitable for jammer signals. The resolution speed is very high. After all, signal reception, resolution, and forwarding must be completed by the jammer. In the case of generative interference, the jammer only needs to send signals.”
“There is no way. "
Chang Haonan threw the pen aside:
"It is impossible to interfere with the positioning of military codes through pure technical means, otherwise the Americans and the Soviets would not have spent the time. So much money is spent on 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 would be easier to steal the complete characteristics of the P code."
"As for the calculation speed...it's actually not bad. I forgot where I read the information, the GPS characteristic data. It is only updated every 12.5 minutes, so after obtaining the data code through any GPS receiver, there is still enough time for data processing..."
"The bigger problem is the inertial navigation equipment. Perform 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. Standing up and preparing 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 kind of detection."
"I will follow you now. Contact the 14th Institute of Electronics and ask them to study the specific hardware design first. Before getting the receiving terminal, they can do a functional test with the C/A code navigation device. "
Chang Haonan also stood up. , sent the other party to the door of the office:
"I will report the receiving terminal to the Science and Technology Committee. This thing will have to wait for an opportunity..."
(End of this chapter )