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US Army Developing Encrypted Radar Waveform (thestack.com)
An anonymous reader writes: The U.S. army is working on an innovative technology for masking radar emissions in contested territory and environments with heavily congested radio bands. Effective radar system performance is critical in military operations, yet remains a challenge in locations under attack or in areas of high traffic density. Army researchers have now developed a noise-encrypted radar waveform called Advanced Pulse Compression Noise (APCN), which can be tuned in real-time to allow users to adjust radar performance depending on their surroundings. Research scientist, Mark Govoni explained: 'Having the ability to transmit a radar waveform that's continually changing, one that never repeats itself, and looks like noise, is extremely difficult to intercept....and remains anonymous to radar detectors.'
Catching speeders.... since vehicle radar detectors won't work for attempting to detect the the encrypted radar signal.
How can they mask the signal if a detector has a larger bandwidth? Part of your spectrum is going to have more energy, even if it is digitally smeared. However if they are also doing something tricky with multiple transmit locations and a random phase array effect a snooper can't even be sure what time period a section of the spectrum belongs in. So not only is your signal dancing around on different frequencies it is also dancing around in space and time so only the receivers with the correct key to track the random sequences can make use of the reflected signal off the targets. So yeah you could really encrypt a radar signal, but they didn't describe what I just did did they? :-)
It's not just frequency hopping.
Radars have a pattern called Staggered PRF Frame, which is a repeating pattern. and this, along with frequency, pulse width and PRI is used to identify a radar.
We already have frequency agile radars. We can identify them because the other characteristics are still constant.
If you make the frame look like random noise then it just looks like clutter. VERY hard to spot.
This is important because you don't just waste HARMs firing at random clutter, and you certainly don't want to accidentally fire on an unexpected friendly.
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It's been a long time since I was involved with Army radar and encrypted communications (in my case, merely humble air traffic control equipment), but the article intrigued me enough to do a very quick lookup. This article isn't very technical, but I can see how it's not simple spread-spectrum radio.
Remember that the information conveyed by radar microwaves is limited; we're primarily interested in reflections (this is "primary radar"; "secondary" radar actually does transmit information; IFF is a type of secondary radar). For a simple radar we know the radar echoes are ours because they come back to our own dish, and match the frequency that we transmitted. They're also incredibly easy to jam.
Frequency hopping on its own makes things harder to jam because the frequencies change in a cryptographic pattern. They can still be jammed if your broadcast a lot of noise over the entire spectrum, but then you limit your own communications. If you can detect the point source, though, you can broadcast a point source over the entire spectrum and still jam them.
What I think I understand about this is that it’s not merely frequency hopping, but the signal modulation is encrypted in a way to evade detection. With a receiver I can detect a typical radar’s 3.4 Ghz signal at -200db (numbers are made up), even if spread across the spectrum, because I know what a 3.4 GHz square wave looks like against the background noise, even if it only appears intermittently on the narrow frequency I’m scanning.
I could try to modulate the signal a different way; maybe a sawtooth, maybe a sine, but a repeating, predictable signal is observable, even with frequency hopping. However if I broadcast noise (and my receiver knows the noise’ pattern), then any listening equipment shouldn’t be able to pick out my microwave pattern from the background.
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Staying out of other people's countries more like it.
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If a spread spectrum signal is below the noise floor, there's no way of telling that it's even there unless you know the pattern.
Even the summary says that isn't going to happen.
What "masking radar emissions in contested territory" tells me is that they intend to change their newspeak so that they aren't technically in a war zone but rather in a contested territory. Clearly the Geneva convention doesn't apply to contested territories.
It worked perfectly well for the "illegal combatants". Just invent a new expression and no treaties or laws have direct references to them.
Well, at least they aren't even trying to mask the imperial mindset anymore. I wonder how long it takes before they start taking slaves.
I think this is, at best, an ignorant comment. While I think the US is excessive in their military presence around the world, sometimes it's justified and even welcome. Europe is definitely better off for the Americans entering into WWII. While we can debate whether nuclear weapons should have been used against Japan, there was ample reason to fight a war in the Pacific as well. China, an American ally, was under attack by Japan. In the present day, we provide military protection to Japan and South Korea. They are our allies and our presence is welcome. Japan and South Korea face a very real threat from North Korea. I suspect the technique described would have value in Japan and South Korea because of the high traffic density and, in the case of South Korea, hiding the radars from North Korea. Does the US abuse military intervention? Absolutely! But are there countries where the US military presence is welcome? Definitely! And would the technique have value in some of those countries? I'd bet it does. And besides, there's really no way to know where the US military might really be needed in the future.
Even signals below the noise are detectable since any signal will raise the noise level somewhat. So if the noise level is higher at a specific direction for no natural reason occams razor would give that it's something there. And since it's now known that a radar technology exists with this kind of pattern it is detectable. It may take some time to detect it, but it's not impossible.
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Will this avoid lock? Probably not. I would imagine that attackers will just lock onto maximum noise rather than maximum signal. May make attacking radars harder though. And I suppose standing near an arcing power line in a war zone might be a bad idea if this becomes common.
BTW, are these things going to play hell with other radio communications?
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Will this avoid lock? Probably not. I would imagine that attackers will just lock onto maximum noise rather than maximum signal. May make attacking radars harder though. And I suppose standing near an arcing power line in a war zone might be a bad idea if this becomes common.
BTW, are these things going to play hell with other radio communications?
Won't it make identification problematic though? The big misconception about RW (Radar Warning) sensors is that it they only identify hostile radiation sources when in reality you want to know exactly what is lighting you up even if it is friendly. This has led to some unfortunate incidents. During the Iran-Iraq war the Iranians actually lost some F-14s to Iraqi fighters because the Iranian F-14s had a standard NATO RW unit that did not register the radars of Iraqi Mirage fighters and their Super 530 BVR missiles as a threat. In Europe this was OK since French fighters were not a threat but in the gulf, not so much. I expect the Iranians quickly figured out to change the threat classification of French radar signatures to 'Hostile'. The consequence is that firstly, once all radiation sources on the battle field look like noise, all you'll be able to tell after that situation becomes the norm, is that you are being lit up by an unusually strong source of radio noise. You won't be able to tell if it is friendly or not. Secondly I expect the current crop of anti radiation missile can be fired at a radar source and then lock onto another one if the primary target goes dead or the missile gets confused. For that purpose it would have to do some form of IFF, presumably based on the output of some derivative of a bog standard aircraft RW sensor, like those Iranian F-14s had, so that it does not accidentally choose a friendly radiation source when it picks it's alternate target so if radiation sources, friendly or hostile, all look like noise and the AR missile just gets locked onto strong sources of noise it would be unable to identify the operator of any alternate radiation source and thus unable to choose an alternate target without risking a blue-on-blue incident. I expect that the ROE for engaging radiation sources would be tightened up pretty severely, especially when firing AR missiles at AWAC aircraft.
I think you're responding to a different story.
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It's a spread-spectrum post.
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Geneva convention only applies to the loser of a conflict. It's a tool used by the victor to do a little more damage, charge people with war crimes, etc. It doesn't apply to the victor even when they break/ignore them. Because of course there's the old argument when you tell them to stop: "Oh yeah, who is going to make me stop? You and which army?"
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