Lessons for China to learn from Ukraine conflict for Taiwan scenario

FairAndUnbiased said:

You don't need to know exactly where the receiver is located. In 3D all that is known is the azimuthal and polar angle to the source, and the magnitude of the signal from the source.

A satellite and an aircraft could have the same azimuthal and polar angle from a given point on the ground, as long as it's not directly overhead. Given that multiple GPS satellites are required for triangulation in 3D, it is likely that not all of them will be directly overhead and in fact may be on the horizon where a distant aircraft would be.

A jammer on the aircraft can emit a signal of equal frequency and equal or greater magnitude as that would be received from the satellite.

a signal of same frequency, magnitude, polarization, azimuthal angle and polar angle is indistinguishable from another signal with these characteristics.

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Yes, in your scenario, the aircraft is in the line of sight between the satellite and the receiver

But that is not going to happen, because you have 3 elements moving very fast, namely:

1. Multiple satellites overhead
2. Being able to keep an aircraft exactly between a satellite and the receiver below
3. Multiple GPS receivers below

It's just not feasible, even for just 1 satellite and 1 GPS receiver
Then consider the huge number of line-of-sights between [overhead satellites x GPS receivers below]

Plus in the case of China, it's easy to program in that only GPS satellites (and other GPS transmitters) in the direction of mainland China are valid.

AndrewS said:

If you go back to high school physics, remember the light/water experiments showing the patterns of constructive/destruction wave interference? How would a third-party (sitting at a different angle and to the side) be able to generate the waveforms to cancel out the signal located at the receiver?

Theoretically it is possible, given the hideous constraints above.

But in order for a jammer to send out the perfect set of signals to destroy the real GPS radio waveform, you would have to know the exact location of the GPS receiver to be targeted.

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No one implied generate a perfectly opposite radio signal to cancel the GPS signal. We are talking about injecting signals within the frequency range make decoding the original signals impossible (Some 1’s become 0’s and some 0’s become 1’s)

AndrewS said:

Yes, in your scenario, the aircraft is in the line of sight between the satellite and the receiver

But that is not going to happen, because you have 3 elements moving very fast, namely:

1. Multiple satellites overhead
2. Being able to keep an aircraft exactly between a satellite and the receiver below
3. Multiple GPS receivers below

It's just not feasible, even for just 1 satellite and 1 GPS receiver
Then consider the huge number of line-of-sights between [overhead satellites x GPS receivers below]

Plus in the case of China, it's easy to program in that only GPS satellites (and other GPS transmitters) in the direction of mainland China are valid.

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what's the angular velocity of a GPS satellite? angular bearing changes are all a receiver can see.

you also don't need perfectly destructive interference, only enough interference to distort the signal, which occurs for any in band interference which is not perfectly constructively interfering.



the only things you can possibly know about an arbitrary RF signal are 1. magnitude 2. frequency 3. angular bearing 4. polarization 5. phase. There's no other parameters with which to describe an RF signal. an RF signal of comparable magnitude, equal frequency, similar angular bearing, equal polarization and any non-perfectly constructive interfering phase, would result in signal distortion as measured at the receiver. This isn't exactly controversial.

FairAndUnbiased said:

what's the angular velocity of a GPS satellite? angular bearing changes are all a receiver can see.

you also don't need perfectly destructive interference, only enough interference to distort the signal, which occurs for any in band interference which is not perfectly constructively interfering.

the only things you can possibly know about an arbitrary RF signal are 1. magnitude 2. frequency 3. angular bearing 4. polarization 5. phase. There's no other parameters with which to describe an RF signal. an RF signal of comparable magnitude, equal frequency, similar angular bearing, equal polarization and any non-perfectly constructive interfering phase, would result in signal distortion as measured at the receiver. This isn't exactly controversial.

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I think it's worth clarifying jamming versus spoofing.

Given that civilian telecoms equipment (consumer-grade Wifi 6 home routers and commercial-grade handheld directional GPS signal locaters) already have the ability to determine the direction of a signal, spoofing a military-grade GPS receiver given the scenarios previously outlined would be very difficult if not impossible.

So that leaves jamming and distorting the weak GPS signal.

Yes, a jammer will produce signal distortion on a single receiver.

But when you have multiple receivers, you can determine the direction and characteristics of all the signals through some signal processing. That gives you the original signals to work with in the software.

AndrewS said:

I think it's worth clarifying jamming versus spoofing.

Given that civilian telecoms equipment (consumer-grade Wifi 6 home routers and commercial-grade handheld directional GPS signal locaters) already have the ability to determine the direction of a signal, spoofing a military-grade GPS receiver given the scenarios previously outlined would be very difficult if not impossible.

So that leaves jamming and distorting the weak GPS signal.

Yes, a jammer will produce signal distortion on a single receiver.

But when you have multiple receivers, you can determine the direction and characteristics of all the signals through some signal processing. That gives you the original signals to work with in the software.

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The signal distortion exists at all points in real space for in band interference. If the in band interfering signal is strong enough then it doesn't matter how many real emitters there are.

A WiFi signal is also far stronger than a GPS signal so you have much more SNR.

I'm not familiar with the specific technologies of any given receiver or transmitter, I only know the basic physics. Unless you are a subject matter expert in electromagnetic waves and signal processing, I'd rather consult an EE here, of which there are many.

FairAndUnbiased said:

The signal distortion exists at all points in real space for in band interference. If the in band interfering signal is strong enough then it doesn't matter how many real emitters there are.

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And my point is that the signal processing (machine learning algorithms) are now good enough to still pick out the real GPS signals, because the GPS signal itself will reach the different antenna are different times

So let's look to the real world in Ukraine. Military grade GPS systems and Starlink systems are still operating on the frontlines in Ukraine.
GMLRS rockets are still being launched by Ukraine and hitting their targets deep in Russian territory.

If it was as easy to jam GPS signals (as you make it out like), then why haven't the Russians done this?
It's been 9 months now, which is more than enough time for the Russians to develop an effective long-range GPS jammer, if it was technically feasible to do so.

AndrewS said:

And my point is that the signal processing (machine learning algorithms) are now good enough to still pick out the real GPS signals, because the GPS signal itself will reach the different antenna are different times

So let's look to the real world in Ukraine. Military grade GPS systems and Starlink systems are still operating on the frontlines in Ukraine.
GMLRS rockets are still being launched by Ukraine and hitting their targets deep in Russian territory.

If it was as easy to jam GPS signals (as you make it out like), then why haven't the Russians done this?
It's been 9 months now, which is more than enough time for the Russians to develop an effective long-range GPS jammer, if it was technically feasible to do so.

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Because Russians can't fly a slow EW plane over Ukraine without getting shot down. They can barely fly fighters or helicopters.

FairAndUnbiased said:

Because Russians can't fly a slow EW plane over Ukraine without getting shot down. They can barely fly fighters or helicopters.

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The US have exactly the same problem.

They can't fly slow EW planes (and in any case, they would need a lot of them to cover so the angles) close enough to Taiwan to prevent Chinese GPS systems from working

AndrewS said:

The US have exactly the same problem.

They can't fly slow EW planes (and in any case, they would need a lot of them to cover so the angles) close enough to Taiwan to prevent Chinese GPS systems from working

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Chinese GPS is Beidou which is already much harder to jam since there's almost 2x more satellites visible on average at any given point on the earth, which eliminates many possibilities such as spoofing a low on horizon satellite, and increases general signal strength.

FairAndUnbiased said:

Chinese GPS is Beidou which is already much harder to jam since there's almost 2x more satellites visible on average at any given point on the earth, which eliminates many possibilities such as spoofing a low on horizon satellite, and increases general signal strength.

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Yes. China operating twice as many Beidou satellites as US GPS satellites also indicates:

1. the importance that the Chinese military places on satellite navigation
2. that they believe they can use those satellite navigation signals, despite attempts by the US to jam or spoof the signals

On the flipside, it means the US can also operate with the exact same logic with regards to their GPS satellites

And indeed, we see more investment in GPS guided munitions from the US in their latest spending authorisation, which includes 100K GLMRS rockets guided by GPS/INS

If we assume that both the US and China can use satellite navigation most of the time, remember that favours China in a Taiwan scenario. I reckon China would have a minimum of 10K aimpoints and possibly a maximum of 50k aimpoints. And Taiwan is close enough that large numbers of cheap GPS munitions can be delivered by the Chinese military.

In comparison, due to the distance to Taiwan, the US can deliver far fewer munitions to China