7 ms·

U.S. army developing encrypted radar waveform

60 points by chewymouse 11y ago

deleted 11y ago
[deleted]
whatnotests 11y ago
But does it have a back door? Hopefully not "end to end" encryption, at least. /s
- dfc 11y ago
  Please do not make posts like this.
  - TallGuyShort 11y ago
    Please do not make posts like this.
- whatnotests 11y ago
  Wow - what's with the downvotes? IMHO what's good for the goose is good for the gander.
msravi 11y ago
So this is spread-spectrum CDMA applied to a radar pulse?
- vonmoltke 11y ago
  My reading, based mainly on what they called it (Advanced Pulse Compression Noise), is no. I think what they are doing is adding an extra step that convolves the transmitted signal with a random noise signal before transmission, then deconvolves it when received as part of the normal convolution step in pulse compression. They may also be randomly shifting the center frequency and chirp bandwidth in top of this. Frequency-hopping radar is not a new idea.
  - dhimes 11y ago
    So direct sequence + frequency hopping? Interesting. Makes it hard to detect.
    - wrigby 11y ago
      Sounds exactly like direct sequence to me. Pretty neat.
rocky1138 11y ago
Anti-radar devices will have to go the Russian route and just blast the shit out of every frequency to disrupt radar. It won't help that the radar is shifting frequencies over time if every channel and frequency is filled with strong noise from a jammer.
- vonmoltke 11y ago
  Barrage noise jammers (to which you refer) have always been the most difficult jammers to deal with in the sensor. The usual countermeasure to them is "region blanking", where the sensor simply stops listening for returns on the azimuth of the jammer. Fortunately, barrage noise jammers are the easiest to deal with using AGM-88 HARMs. Edit: Also, I should note that barrage noise jammers have limited bandwidth, and have to trade off bandwidth for power. If the APCN system keeps its operating frequency sufficiently masked it may require multiple jammers to actually interfere with the system sufficiently.
  - wlesieutre 11y ago
    > The AGM-88 High-speed Anti-Radiation Missile (HARM) is a tactical, air-to-surface missile designed to home in on electronic transmissions coming from surface-to-air radar systems. Figured that's what it was, but I'll save everyone the googling.
- dogma1138 11y ago
  Well not really.... 1) Jammers are a realy good target for anti-radiation missiles. 2) Jammers are also limited in power and frequency you can't make a jammer that can saturate every frequency multi-spectrum jammers allow you to jam different frequencies but usually not at the same time because you are power limited. So even if you have a jammer with say 50 different physical transmitter if you operate all of them each transmitter will operate at 1/50th of the peak transmission power. Wide spectrum jamming is usually done using timing, radars send pulses based on some specific cycle so what you do is attenuate your jammer to the cycle and frequency which allows you to "effectively" jam multiple radars because you don't have to be transmitting all the time to create false signals. So this (#2) is what this whole new "encrypted radar" concept is supposed to combat which is cheap and effective wide spectrum radar jammers because today anyone with an SDR and a hacked TV dish can make quite an effective jammer.
dfc 11y ago
Does anyone know what non-traditional radar could mean?
- vonmoltke 11y ago
  It's "non-traditional radar waveform". They are referring to waveforms and modulation techniques not traditionally applied to radar signals. Radar typically has a very regular waveform. So regular, in fact, that a receiver can tell what type of radar is sending the signal by recording the overall signal pattern and deriving radar parameters from that (center frequencies, chirp bandwidths, scan patterns, and such). The type of obfuscation they are doing here is more typical of communications systems.
- nabla9 11y ago
  It looks like it combines features from pulse-Doppler radar and noise radar. It amplitude and phase modulates a complex pulse-linear FM waveform (linear chirp) using pseudo-noise. I'm not familiar with this particular research. ACPN is not something US army just discovered. Agile beam, agile frequency, pulse compression and pseudo-noise waveforms are the direction military radars are going towards.
- wnewman 11y ago
  At a guess, it includes things like the tricks in http://dtic.mil/dtic/tr/fulltext/u2/a456960.pdf http://dtic.mil/dtic/tr/fulltext/u2/a456960.pdf ("DETECTION AND JAMMING LOW PROBABILITY OF INTERCEPT (LPI) RADARS") but (1) it's obviously not a very precise term and (2) it would be surprising if all of the relevant techniques were available in an unclassified review from 2006.
nradov 11y ago
In the future military radars will increasingly look like directed white noise emissions rather than any sort of steady waveform on a particular frequency. This will make it much harder for targets to apply countermeasures, or even reliably detect when they are being illuminated. High speed signal processing makes it possible to reassemble radar returns that seem almost random into an accurate picture.
- hatsunearu 11y ago
  Yup. In fact, if you use a technique called spread spectrum emissions you can have your signal below the noise floor but have it still be possible to pick it up because it carries so much redundant information across a massive bandwidth. https://en.wikipedia.org/wiki/Spread_spectrum https://en.wikipedia.org/wiki/Spread_spectrum I can't find much information about using SS to go below the noise floor on wikipedia but it is a thing.
  - wiml 11y ago
    GPS is below the noise floor at the receiver, IIRC. UWB radar is also a thing.
vlehto 11y ago
As soon as someone learns to detect F35 radar signal, more than half if it's stealth advantage melts away. So far U.S. has only made air-to-ground anti-radiation missiles, but the Russians have tried also air-to-air version. https://en.wikipedia.org/wiki/Anti-radiation_missile https://en.wikipedia.org/wiki/Anti-radiation_missile All this has not gone unnoticed in the Pentagon, so radars like there have probably been in the works for quite some time. F35 sales pitches are probably warming up right now, so news like this are expected. The only surprise for me is that this comes from the army and not the air force or navy. They probably need to worry about enemy droids. And if they worry about those droids using radar, they need to worry about enemy anti-radiation missiles. This is probably part of larger picture of U.S. armed forces to avoid using Infra Red Search and Track (IRST). Because that makes stealth planes look bit silly, when you go past ~0,07m^2 radar cross section. At that point you would get parity with detection ranges of common radars and modern IRST sensors, which would be something like 80km for fighter jet sized object. But this would mean no operations in enemy airspace, as flight ceilings are typically around 20km. F35 has RCS 0,01 and F22 RCS 0,001 which is just great for operating in enemy airspace, if the enemy can't detect their radars and lacks IRST. Currently it seems the best USAF can do about IRST is to pretend it doesn't matter. So if there is any coordination between the branches, the army has to get their own stealth radar against enemy drones. After two decades and gazillion dollars, we probably see subsonic F40-cool-skin, with reflecting mirror finish aluminum body, that eliminates this problem. And power projection and proceed uninhibited. Why mirror finish aluminum? Current IRST sensors can detect current fighters from tens of kilometers away from sun heated surfaces radiating at IR spectrum. Having orthogonal plates means that sun glare doesn't hit the IR sensor directly, the mirror finish prevents excessive heating and smooth aluminum has very small IR emissivity naturally. Conveniently aircraft are already made from aluminum. Right now we don't hear about this aluminum shit, because U.S. is still funding some weaponized lasers. Airborne lasers smelled like "overspending" before, but it's really going to smell like bluff when reflecting surfaces increase power requirements some 400%. They already suffer from bad power/weight ratios. But once naval laser "close-in weapon system" has been fielded (because any chance is a good one when you're desperate) we can go back to airplane design. Sorry, this is bit long. I've had this autistic streak about this subject for past two weeks.
- 11y ago
__mbm__ 11y ago
This relates closely to the [Darpa Spectrum Challenge](http://archive.darpa.mil/spectrumchallenge/ http://archive.darpa.mil/spectrumchallenge/) that I participated in a couple years ago. The goal was to transmit information in a congested and contested RF environment. I think that they wanted to develop rapid spectrum-aware sensing as well as hard-to-jam signals.
- lsaferite 11y ago
  I was literally talking about this yesterday with a friend in the context of military robotics and their control systems. He said those C&C systems would be a huge IW/EW target and my counter was that DARPA was already addressing that through things like the Spectrum Challenge.
kylehotchkiss 11y ago
Nice! sounds like recent LIDAR innovations https://youtu.be/30Jc0GpYKYI https://youtu.be/30Jc0GpYKYI
ivan_ah 11y ago
Interesting progress; It's like CDMA for radar. For those who have one hour available, check out this amazing talk about the early history of silicon valley, back when the first tech sector was radars for WWII: https://www.youtube.com/watch?v=ZTC_RxWN_xo https://www.youtube.com/watch?v=ZTC_RxWN_xo

60 points by chewymouse 11y ago

deleted 11y ago

[deleted]

whatnotests 11y ago

But does it have a back door? Hopefully not "end to end" encryption, at least. /s

dfc 11y ago
Please do not make posts like this.
- TallGuyShort 11y ago
  Please do not make posts like this.
whatnotests 11y ago
Wow - what's with the downvotes? IMHO what's good for the goose is good for the gander.

msravi 11y ago

So this is spread-spectrum CDMA applied to a radar pulse?

vonmoltke 11y ago
My reading, based mainly on what they called it (Advanced Pulse Compression Noise), is no. I think what they are doing is adding an extra step that convolves the transmitted signal with a random noise signal before transmission, then deconvolves it when received as part of the normal convolution step in pulse compression. They may also be randomly shifting the center frequency and chirp bandwidth in top of this. Frequency-hopping radar is not a new idea.
- dhimes 11y ago
  So direct sequence + frequency hopping? Interesting. Makes it hard to detect.
  - wrigby 11y ago
    Sounds exactly like direct sequence to me. Pretty neat.

rocky1138 11y ago

Anti-radar devices will have to go the Russian route and just blast the shit out of every frequency to disrupt radar. It won't help that the radar is shifting frequencies over time if every channel and frequency is filled with strong noise from a jammer.

vonmoltke 11y ago
Barrage noise jammers (to which you refer) have always been the most difficult jammers to deal with in the sensor. The usual countermeasure to them is "region blanking", where the sensor simply stops listening for returns on the azimuth of the jammer. Fortunately, barrage noise jammers are the easiest to deal with using AGM-88 HARMs. Edit: Also, I should note that barrage noise jammers have limited bandwidth, and have to trade off bandwidth for power. If the APCN system keeps its operating frequency sufficiently masked it may require multiple jammers to actually interfere with the system sufficiently.
- wlesieutre 11y ago
  > The AGM-88 High-speed Anti-Radiation Missile (HARM) is a tactical, air-to-surface missile designed to home in on electronic transmissions coming from surface-to-air radar systems. Figured that's what it was, but I'll save everyone the googling.
dogma1138 11y ago
Well not really.... 1) Jammers are a realy good target for anti-radiation missiles. 2) Jammers are also limited in power and frequency you can't make a jammer that can saturate every frequency multi-spectrum jammers allow you to jam different frequencies but usually not at the same time because you are power limited. So even if you have a jammer with say 50 different physical transmitter if you operate all of them each transmitter will operate at 1/50th of the peak transmission power. Wide spectrum jamming is usually done using timing, radars send pulses based on some specific cycle so what you do is attenuate your jammer to the cycle and frequency which allows you to "effectively" jam multiple radars because you don't have to be transmitting all the time to create false signals. So this (#2) is what this whole new "encrypted radar" concept is supposed to combat which is cheap and effective wide spectrum radar jammers because today anyone with an SDR and a hacked TV dish can make quite an effective jammer.

dfc 11y ago

Does anyone know what non-traditional radar could mean?

vonmoltke 11y ago
It's "non-traditional radar waveform". They are referring to waveforms and modulation techniques not traditionally applied to radar signals. Radar typically has a very regular waveform. So regular, in fact, that a receiver can tell what type of radar is sending the signal by recording the overall signal pattern and deriving radar parameters from that (center frequencies, chirp bandwidths, scan patterns, and such). The type of obfuscation they are doing here is more typical of communications systems.
nabla9 11y ago
It looks like it combines features from pulse-Doppler radar and noise radar. It amplitude and phase modulates a complex pulse-linear FM waveform (linear chirp) using pseudo-noise. I'm not familiar with this particular research. ACPN is not something US army just discovered. Agile beam, agile frequency, pulse compression and pseudo-noise waveforms are the direction military radars are going towards.
wnewman 11y ago
At a guess, it includes things like the tricks in http://dtic.mil/dtic/tr/fulltext/u2/a456960.pdf http://dtic.mil/dtic/tr/fulltext/u2/a456960.pdf ("DETECTION AND JAMMING LOW PROBABILITY OF INTERCEPT (LPI) RADARS") but (1) it's obviously not a very precise term and (2) it would be surprising if all of the relevant techniques were available in an unclassified review from 2006.

nradov 11y ago

In the future military radars will increasingly look like directed white noise emissions rather than any sort of steady waveform on a particular frequency. This will make it much harder for targets to apply countermeasures, or even reliably detect when they are being illuminated. High speed signal processing makes it possible to reassemble radar returns that seem almost random into an accurate picture.

hatsunearu 11y ago
Yup. In fact, if you use a technique called spread spectrum emissions you can have your signal below the noise floor but have it still be possible to pick it up because it carries so much redundant information across a massive bandwidth. https://en.wikipedia.org/wiki/Spread_spectrum https://en.wikipedia.org/wiki/Spread_spectrum I can't find much information about using SS to go below the noise floor on wikipedia but it is a thing.
- wiml 11y ago
  GPS is below the noise floor at the receiver, IIRC. UWB radar is also a thing.

vlehto 11y ago

As soon as someone learns to detect F35 radar signal, more than half if it's stealth advantage melts away. So far U.S. has only made air-to-ground anti-radiation missiles, but the Russians have tried also air-to-air version. https://en.wikipedia.org/wiki/Anti-radiation_missile https://en.wikipedia.org/wiki/Anti-radiation_missile All this has not gone unnoticed in the Pentagon, so radars like there have probably been in the works for quite some time. F35 sales pitches are probably warming up right now, so news like this are expected. The only surprise for me is that this comes from the army and not the air force or navy. They probably need to worry about enemy droids. And if they worry about those droids using radar, they need to worry about enemy anti-radiation missiles. This is probably part of larger picture of U.S. armed forces to avoid using Infra Red Search and Track (IRST). Because that makes stealth planes look bit silly, when you go past ~0,07m^2 radar cross section. At that point you would get parity with detection ranges of common radars and modern IRST sensors, which would be something like 80km for fighter jet sized object. But this would mean no operations in enemy airspace, as flight ceilings are typically around 20km. F35 has RCS 0,01 and F22 RCS 0,001 which is just great for operating in enemy airspace, if the enemy can't detect their radars and lacks IRST. Currently it seems the best USAF can do about IRST is to pretend it doesn't matter. So if there is any coordination between the branches, the army has to get their own stealth radar against enemy drones. After two decades and gazillion dollars, we probably see subsonic F40-cool-skin, with reflecting mirror finish aluminum body, that eliminates this problem. And power projection and proceed uninhibited. Why mirror finish aluminum? Current IRST sensors can detect current fighters from tens of kilometers away from sun heated surfaces radiating at IR spectrum. Having orthogonal plates means that sun glare doesn't hit the IR sensor directly, the mirror finish prevents excessive heating and smooth aluminum has very small IR emissivity naturally. Conveniently aircraft are already made from aluminum. Right now we don't hear about this aluminum shit, because U.S. is still funding some weaponized lasers. Airborne lasers smelled like "overspending" before, but it's really going to smell like bluff when reflecting surfaces increase power requirements some 400%. They already suffer from bad power/weight ratios. But once naval laser "close-in weapon system" has been fielded (because any chance is a good one when you're desperate) we can go back to airplane design. Sorry, this is bit long. I've had this autistic streak about this subject for past two weeks.

11y ago

__mbm__ 11y ago

This relates closely to the [Darpa Spectrum Challenge](http://archive.darpa.mil/spectrumchallenge/ http://archive.darpa.mil/spectrumchallenge/) that I participated in a couple years ago. The goal was to transmit information in a congested and contested RF environment. I think that they wanted to develop rapid spectrum-aware sensing as well as hard-to-jam signals.

lsaferite 11y ago
I was literally talking about this yesterday with a friend in the context of military robotics and their control systems. He said those C&C systems would be a huge IW/EW target and my counter was that DARPA was already addressing that through things like the Spectrum Challenge.

kylehotchkiss 11y ago

Nice! sounds like recent LIDAR innovations https://youtu.be/30Jc0GpYKYI https://youtu.be/30Jc0GpYKYI

ivan_ah 11y ago

Interesting progress; It's like CDMA for radar. For those who have one hour available, check out this amazing talk about the early history of silicon valley, back when the first tech sector was radars for WWII: https://www.youtube.com/watch?v=ZTC_RxWN_xo https://www.youtube.com/watch?v=ZTC_RxWN_xo