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See also "Phasing Out GPS Reliance in U.S. Military Operations: An Imperative in the Face of Emerging Threats": > Global Navigation Satellite Systems (GNSS), s

See also "Phasing Out GPS Reliance in U.S. Military Operations: An Imperative in the Face of Emerging Threats": > Global Navigation Satellite Systems (GNSS), such as the American GPS, Europe's GALILEO, China's BEIDOU, and Russia's GLONASS, play an essential role in modern warfare. Despite their different technical specifications—like frequencies and orbits—these systems are designed to be compatible, allowing for greater positional accuracy. However, their signals are susceptible to various forms of interference, such as jamming and spoofing. While there are security measures like anti-spoofing in place, these are not foolproof. * https://www.realcleardefense.com/articles/2023/09/26/phasing_out_gps_reliance_in_us_military_operations_an_imperative_in_the_face_of_emerging_threats_981890.html https://www.realcleardefense.com/articles/2023/09/26/phasing...

londons_explore 3y ago
There are plenty of techniques the military could use to make jamming or spoofing almost impossible. For example, use a signal encrypted with a key not known to the enemy. That prevents spoofing. Jamming can be pretty much eliminated by using phased array antennas. They can reject signals coming from the wrong direction. To fully block a military unit receiving GPS, the enemy would need to have ~30 planes in the sky over the unit, between the unit and each GPS satellite, broadcasting the jamming signal. Pretty infeasible for them. There are other ways to make jamming far far harder. For example, if you are happy for your GPS receiver to be always on and have an atomic clock, you can make a new signal that replaces the 1024 bit PRN codes with multi-gigabyte codes which are secret. That effectively means rather than the enemy needing to overpower the real signal, the enemy needs to be billions of times stronger than the real signal to prevent you decoding it.
- hiatus 3y ago
  > To fully block a military unit receiving GPS, the enemy would need to have ~30 planes in the sky over the unit, between the unit and each GPS satellite, broadcasting the jamming signal. Pretty infeasible for them. How did you arrive at this number?
  - uoaei 3y ago
    It's approximately the number of GPS satellites in the sky from a given location on the ground. One plane per satellite. Of course this varies due to geography, orbits, etc. but is a good rule of thumb.
  - jabart 3y ago
    Number is a bit high but may be counting GPS, and EU GPS satellites you would have to block. You can "see" 4-12 GPS satellites at a time for one system. Assuming the EU system has the same style layout.
    - Jtsummers 3y ago
      You don't need to block line-of-sight to the GPS satellites to create a GPS jamming attack. You just need a more powerful emitter near enough your intended target. No need for 30 planes trying to interpose themselves between the target and satellites.
      - orangepurple 3y ago
        Such a powerful jamming emitter is also a wonderful automatic target for loitering munitions
        Jtsummers 3y ago
        If it's within a region that can be attacked and the opponent has those capabilities, yes.
        hef19898 3y ago
        If you ask "the internet", the answer is drones. Regardless of the question being asked...
        orangepurple 3y ago
        Recently huge drone swarms have been launched recently to increase the chance of mission success.
- wil421 3y ago
  Even with a key you can drown out the signal by blasting enough RF waves at the receiver or area. I’ve heard a Growler pilot describe what they do as shining a spot light in your face to blind you.
  - jabart 3y ago
    Yes but you would have to do that from top down. You can't shine a spot light on the back of a person's head to blind them. Not to mention the tricks they use to make RF signals directional to both send and receive.
    - TeMPOraL 3y ago
      > You can't shine a spot light on the back of a person's head to blind them. You can, if the spot light is strong enough, and the person in question isn't floating in deep space. Just keep adding power until the light reflected by the person's surroundings is strong enough to blind them. > Not to mention the tricks they use to make RF signals directional to both send and receive. Makes me wonder if there's an RF equivalent of getting permanently blinded by laser light scattering off random objects in your line of sight.
  - Hello71 3y ago
    that's called jamming and was addressed by the comment. if you wear very narrow blinders and point your face right at where you want to look, then the enemy needs to install their spotlight right ahead of you instead of just anywhere in front.
    - throw0101c 3y ago
      It is a mitigation that may help, but not foolproof: someone can jam or spoof from the sky. Current areas where jamming is being detecting. * https://gpsjam.org https://gpsjam.org
      - jhugo 3y ago
        This jamming isn’t from the sky though. Incidentally, there has been a recent escalation in this: over Iraq commercial airline pilots have been reporting increasingly successful GPS spoofing, with GPS positions being shifted by tens or hundreds of nm, the clock being shifted, etc. In some cases this has exposed bugs in aircraft software where it has not successfully recovered the GPS position even after leaving the affected area, leaving them with degraded navigation all the way to the destination. This is not as dire as it might sound, as there are plenty of other ways for an aircraft to determine its position, though it certainly reduces the margins for error in some cases. But it’s interesting because such spoofing should be extremely difficult to carry out successfully, especially on a moving target like an airliner.
- throw0101c 3y ago
  > There are plenty of techniques the military could use to make jamming or spoofing almost impossible. The US DOD is not as confident as you are, as they looking at backups/alternatives: > DOD primarily relies on GPS for accurate PNT data, which is essential to effective military operations. However, multiple threats can render GPS data unavailable or inaccurate. DOD recognizes the threats to GPS and is taking steps to address them by developing more robust GPS capabilities and alternative PNT technologies. GAO was asked to review DOD's acquisition of alternative PNT technologies. * https://www.gao.gov/products/gao-22-106010 https://www.gao.gov/products/gao-22-106010 > To fully block a military unit receiving GPS, the enemy would need to have ~30 planes in the sky over the unit, between the unit and each GPS satellite, broadcasting the jamming signal. Pretty infeasible for them. All GNSS signals live on a finite number of frequency bands: L5/E5, L2, E6, L1/E1: * https://gssc.esa.int/navipedia/index.php?title=GNSS_signal https://gssc.esa.int/navipedia/index.php?title=GNSS_signal * https://www.geospatialworld.net/blogs/gnss-frequency-bands-for-constellations/ https://www.geospatialworld.net/blogs/gnss-frequency-bands-f... * https://www.tallysman.com/gnss-constellations-radio-frequencies-and-signals/ https://www.tallysman.com/gnss-constellations-radio-frequenc... * https://en.wikipedia.org/wiki/Satellite_navigation#Frequency_allocation https://en.wikipedia.org/wiki/Satellite_navigation#Frequency... > The ITU have allocated the following L-band frequencies to GNSS (bold are aeronautically used): > *GPS, the centre frequencies are 1575.42 MHz (L1), 1227.6 MHz (L2) and 1176.45 MHz (L5). > *GLONASS operates as frequency divisional multiple access (FDMA) and there are two operational centre frequencies 1602 MHz (L1) and 1246 MHz (L2) and at 1207.14 MHz (L3). GLONASS over this decade will also introduce Code Divisional Multiple Access (CDMA) similar to GPS. > *GALILEO has a range of frequencies assigned in the L-band as follows: > ** E2 – L1 – E1 – Centre frequency 1575.42 MHz (band from 1559MHz – 1591MHz). > ** E5A – Centre frequency 1176.45 MHz (band from 1164 MHz – 1188 MHz). > ** E5B - Centre frequency 1207.14 MHz (band from 1188 MHz – 1215 MHz). > ** E6 – Centre frequency 1278,75 MHz (band from 1260 MHz – 1300 MHz). * https://pbnportal.eu/epbn/main/Overview-of-PBN/PBN-Concept---Unpacked/PBN-Infrastructure/Space-based/GNSS-Spectrum-Allocation.html https://pbnportal.eu/epbn/main/Overview-of-PBN/PBN-Concept--... A handful of planes (or drones) focussing on those few frequency ranges can do a lot of mischief. And this is not theoretical, but observed events: > Russia has been thwarting US-made mobile rocket systems in Ukraine more frequently in recent months, using electronic jammers to throw off its GPS guided targeting system to cause rockets to miss their targets, multiple people briefed on the matter told CNN. * https://www.cnn.com/2023/05/05/politics/russia-jamming-himars-rockets-ukraine/index.html https://www.cnn.com/2023/05/05/politics/russia-jamming-himar...
- DoctorOetker 3y ago
  How feasible would you estimate passive positioning systems? For example consider solar radio noise at frequencies that are partially reflected, partially transmitted by the ionosphere. Do you consider it possible for an SDR to geolocate by comparing multiple antenna signals say: 1: "direct signal" : sun -DOWN-> partial transmitted through ionosphere -DOWN-> antenna 1 aimed at sun 2: "geography / terrain fingerprinted signal" : sun -DOWN-> partially transmitted through ionosphere -DOWN-> reflection on Earth -UP-> partial reflection from ionosphere -DOWN-> antenna 2 Or any suggested variations? (reflection from moon for example). https://commons.wikimedia.org/wiki/File:Ionospheric_layers_from_night_to_day.png https://commons.wikimedia.org/wiki/File:Ionospheric_layers_f... i.e. can Western citizens prepare to still have geopositioning in case of an adversarial (successful) first strike against GPS and Galileo where the citizen refuses to rely on adversary positioning systems.
  - londons_explore 3y ago
    With a clock and a telescope, you can get super precise positioning the same as the 16th century way... Atomic clocks are now good enough to make those positions really good. You can do the same with radio frequencies and a phased array antenna if you like. I'm not sure if other approaches would perform better.
    - DoctorOetker 3y ago
      I mean without a clock, the reference being the direct path of noise from the sun. Telescopes are impeded by clouds. During night there is no line of sight to the sun, so I concede my rudimentary idea or question has similar drawbacks.
      - DoctorOetker 3y ago
        It would be interesting if precise time could be derived from imaging the night sky, so that the synchronized clock becomes unnecessary.
    - amalcon 3y ago
      I've actually heard of research into putting celestial navigation in guided missiles (from people who've worked on it -- so the idea that this is possible seems to not be a secret). Cameras and optics have become good enough to make this plausible with those kind of constraints. I don't know if it's been deployed, but I would not be surprised.
- 13of40 3y ago
  I was reading the specs for the GPS satellites vs. the GLONASS ones a while back, and it seemed like they transmit on a similar frequency but with a different modulation scheme and protocol. Pure speculation, but you could imagine a Tom-Clancy-esque scenario where their secondary role is to jam GPS when they need to.
  - londons_explore 3y ago
    To jam something, you ideally jam the same frequency, PRN code, and direction. If you don't know frequency, you need to jam a wide range of frequencies. Defences like frequency hopping make use of this. Bluetooth uses this for example, to prevent inadvertent jamming. In GPS, frequencies aren't secret. If you don't know the code, you need to jam with as much power as the benefit of the code. For GPS, thats a 10x 1024 bit code, which provides 43 dB of processing gain. This can be increased almost without limit, as long as you don't plan to move much during the code period. There are clever methods to make encryption keys double-up as PRN codes that the enemy doesn't know. For direction, it depends on the receiver. Your phone has an omnidirectional receiver, so the attacker is 'on par with' the real signal. A military directional phased array system might have 200 elements, and therefore 30db of gain. Add that up, and the enemy needs to use far far more signal power than the real signal to 'outshine' it. Turns out that's pretty much impossible - and if they get near to doing that, your biggest problem is probably being cooked by their jammer.
- KaiserPro 3y ago
  > Jamming can be pretty much eliminated by using phased array antennas. citation needed there. GPS typical signal strength is -125dBm. For ground based stuff, its pretty simple to overpower the band so that nothing can hear it.
  - sennight 3y ago
    This has been a solved problem for a very long time. The nice thing about GPS satellites is that you know where they should be, and where they shouldn't, so long as your RTC is properly set and you've got a compass. A GPS Digital Phased Array Antenna and Receiver (2000): https://apps.dtic.mil/sti/tr/pdf/ADA452307.pdf https://apps.dtic.mil/sti/tr/pdf/ADA452307.pdf
    - KaiserPro 3y ago
      yes, phased arrays, especially if you have a tight beam, can give you an extra 40db of SNR (see figure 9 https://www.analog.com/en/analog-dialogue/articles/phased-array-antenna-patterns-part1.html https://www.analog.com/en/analog-dialogue/articles/phased-ar..., also in the charts on your link) but thats still like -70dbm at best. That's about the level of being a few meters away from a wifi AP level of power. a 1 watt(RF) jammer is going to cast a large cone of non-GPS even with a phased array antenna.
      - sennight 3y ago
        You are forgetting about the phased nulling. Military GPS has been including jammer detection in the firmware for a long time. I remember my handheld unit constantly annoying me anytime the IED jammer (which was waaaay more than 1 watt of rf) went active... 2005ish - it would simply mask the signal coming from that direction and continue to provide positioning data.
      - londons_explore 3y ago
        Add in coding gain over 1 second (a code 10 million chips long), and that gives you an extra 70dB. Now it's getting hard to jam. Downside: This only works if your movement over the 1 second period is predictable, to a small part of a wavelength. If you're moving unpredictably, you'll have to give up a few db's of coding gain.
- ranger207 3y ago
  "The sky" covers 180°x180°, or more if you're in a plane. A jammer that can block out half of that can result in a significant reduction in accuracy
hef19898 3y ago
So, basically back to old school, "manual" stuff? Should be doable, if less convenient.
- throw0101c 3y ago
  The US Navy brought back celestial navigation (with sextants) as a backup: * https://www.usni.org/magazines/proceedings/2021/december/bring-celestial-navigation-21st-century https://www.usni.org/magazines/proceedings/2021/december/bri... * https://skyandtelescope.org/astronomy-news/u-s-navy-resumes-celestial-navigation-training-04042016/ https://skyandtelescope.org/astronomy-news/u-s-navy-resumes-...
  - hef19898 3y ago
    And all the other, old school stuff is still available anyway. Still, without GNSS, things are complicated.
- supertrope 3y ago
  Cell phone towers depend on GPS for timing and frequency precision. A lot of processes depend on GPS availability.
  - hef19898 3y ago
    Military navigation doesn't so. Sure, GPS makes things a ton easier but it is perfectly possible without it.

londons_explore 3y ago

There are plenty of techniques the military could use to make jamming or spoofing almost impossible. For example, use a signal encrypted with a key not known to the enemy. That prevents spoofing. Jamming can be pretty much eliminated by using phased array antennas. They can reject signals coming from the wrong direction. To fully block a military unit receiving GPS, the enemy would need to have ~30 planes in the sky over the unit, between the unit and each GPS satellite, broadcasting the jamming signal. Pretty infeasible for them. There are other ways to make jamming far far harder. For example, if you are happy for your GPS receiver to be always on and have an atomic clock, you can make a new signal that replaces the 1024 bit PRN codes with multi-gigabyte codes which are secret. That effectively means rather than the enemy needing to overpower the real signal, the enemy needs to be billions of times stronger than the real signal to prevent you decoding it.

hiatus 3y ago
> To fully block a military unit receiving GPS, the enemy would need to have ~30 planes in the sky over the unit, between the unit and each GPS satellite, broadcasting the jamming signal. Pretty infeasible for them. How did you arrive at this number?
- uoaei 3y ago
  It's approximately the number of GPS satellites in the sky from a given location on the ground. One plane per satellite. Of course this varies due to geography, orbits, etc. but is a good rule of thumb.
- jabart 3y ago
  Number is a bit high but may be counting GPS, and EU GPS satellites you would have to block. You can "see" 4-12 GPS satellites at a time for one system. Assuming the EU system has the same style layout.
  - Jtsummers 3y ago
    You don't need to block line-of-sight to the GPS satellites to create a GPS jamming attack. You just need a more powerful emitter near enough your intended target. No need for 30 planes trying to interpose themselves between the target and satellites.
    - orangepurple 3y ago
      Such a powerful jamming emitter is also a wonderful automatic target for loitering munitions
      - Jtsummers 3y ago
        If it's within a region that can be attacked and the opponent has those capabilities, yes.
        hef19898 3y ago
        If you ask "the internet", the answer is drones. Regardless of the question being asked...
        orangepurple 3y ago
        Recently huge drone swarms have been launched recently to increase the chance of mission success.
wil421 3y ago
Even with a key you can drown out the signal by blasting enough RF waves at the receiver or area. I’ve heard a Growler pilot describe what they do as shining a spot light in your face to blind you.
- jabart 3y ago
  Yes but you would have to do that from top down. You can't shine a spot light on the back of a person's head to blind them. Not to mention the tricks they use to make RF signals directional to both send and receive.
  - TeMPOraL 3y ago
    > You can't shine a spot light on the back of a person's head to blind them. You can, if the spot light is strong enough, and the person in question isn't floating in deep space. Just keep adding power until the light reflected by the person's surroundings is strong enough to blind them. > Not to mention the tricks they use to make RF signals directional to both send and receive. Makes me wonder if there's an RF equivalent of getting permanently blinded by laser light scattering off random objects in your line of sight.
- Hello71 3y ago
  that's called jamming and was addressed by the comment. if you wear very narrow blinders and point your face right at where you want to look, then the enemy needs to install their spotlight right ahead of you instead of just anywhere in front.
  - throw0101c 3y ago
    It is a mitigation that may help, but not foolproof: someone can jam or spoof from the sky. Current areas where jamming is being detecting. * https://gpsjam.org https://gpsjam.org
    - jhugo 3y ago
      This jamming isn’t from the sky though. Incidentally, there has been a recent escalation in this: over Iraq commercial airline pilots have been reporting increasingly successful GPS spoofing, with GPS positions being shifted by tens or hundreds of nm, the clock being shifted, etc. In some cases this has exposed bugs in aircraft software where it has not successfully recovered the GPS position even after leaving the affected area, leaving them with degraded navigation all the way to the destination. This is not as dire as it might sound, as there are plenty of other ways for an aircraft to determine its position, though it certainly reduces the margins for error in some cases. But it’s interesting because such spoofing should be extremely difficult to carry out successfully, especially on a moving target like an airliner.
throw0101c 3y ago
> There are plenty of techniques the military could use to make jamming or spoofing almost impossible. The US DOD is not as confident as you are, as they looking at backups/alternatives: > DOD primarily relies on GPS for accurate PNT data, which is essential to effective military operations. However, multiple threats can render GPS data unavailable or inaccurate. DOD recognizes the threats to GPS and is taking steps to address them by developing more robust GPS capabilities and alternative PNT technologies. GAO was asked to review DOD's acquisition of alternative PNT technologies. * https://www.gao.gov/products/gao-22-106010 https://www.gao.gov/products/gao-22-106010 > To fully block a military unit receiving GPS, the enemy would need to have ~30 planes in the sky over the unit, between the unit and each GPS satellite, broadcasting the jamming signal. Pretty infeasible for them. All GNSS signals live on a finite number of frequency bands: L5/E5, L2, E6, L1/E1: * https://gssc.esa.int/navipedia/index.php?title=GNSS_signal https://gssc.esa.int/navipedia/index.php?title=GNSS_signal * https://www.geospatialworld.net/blogs/gnss-frequency-bands-for-constellations/ https://www.geospatialworld.net/blogs/gnss-frequency-bands-f... * https://www.tallysman.com/gnss-constellations-radio-frequencies-and-signals/ https://www.tallysman.com/gnss-constellations-radio-frequenc... * https://en.wikipedia.org/wiki/Satellite_navigation#Frequency_allocation https://en.wikipedia.org/wiki/Satellite_navigation#Frequency... > The ITU have allocated the following L-band frequencies to GNSS (bold are aeronautically used): > *GPS, the centre frequencies are 1575.42 MHz (L1), 1227.6 MHz (L2) and 1176.45 MHz (L5). > *GLONASS operates as frequency divisional multiple access (FDMA) and there are two operational centre frequencies 1602 MHz (L1) and 1246 MHz (L2) and at 1207.14 MHz (L3). GLONASS over this decade will also introduce Code Divisional Multiple Access (CDMA) similar to GPS. > *GALILEO has a range of frequencies assigned in the L-band as follows: > ** E2 – L1 – E1 – Centre frequency 1575.42 MHz (band from 1559MHz – 1591MHz). > ** E5A – Centre frequency 1176.45 MHz (band from 1164 MHz – 1188 MHz). > ** E5B - Centre frequency 1207.14 MHz (band from 1188 MHz – 1215 MHz). > ** E6 – Centre frequency 1278,75 MHz (band from 1260 MHz – 1300 MHz). * https://pbnportal.eu/epbn/main/Overview-of-PBN/PBN-Concept---Unpacked/PBN-Infrastructure/Space-based/GNSS-Spectrum-Allocation.html https://pbnportal.eu/epbn/main/Overview-of-PBN/PBN-Concept--... A handful of planes (or drones) focussing on those few frequency ranges can do a lot of mischief. And this is not theoretical, but observed events: > Russia has been thwarting US-made mobile rocket systems in Ukraine more frequently in recent months, using electronic jammers to throw off its GPS guided targeting system to cause rockets to miss their targets, multiple people briefed on the matter told CNN. * https://www.cnn.com/2023/05/05/politics/russia-jamming-himars-rockets-ukraine/index.html https://www.cnn.com/2023/05/05/politics/russia-jamming-himar...
DoctorOetker 3y ago
How feasible would you estimate passive positioning systems? For example consider solar radio noise at frequencies that are partially reflected, partially transmitted by the ionosphere. Do you consider it possible for an SDR to geolocate by comparing multiple antenna signals say: 1: "direct signal" : sun -DOWN-> partial transmitted through ionosphere -DOWN-> antenna 1 aimed at sun 2: "geography / terrain fingerprinted signal" : sun -DOWN-> partially transmitted through ionosphere -DOWN-> reflection on Earth -UP-> partial reflection from ionosphere -DOWN-> antenna 2 Or any suggested variations? (reflection from moon for example). https://commons.wikimedia.org/wiki/File:Ionospheric_layers_from_night_to_day.png https://commons.wikimedia.org/wiki/File:Ionospheric_layers_f... i.e. can Western citizens prepare to still have geopositioning in case of an adversarial (successful) first strike against GPS and Galileo where the citizen refuses to rely on adversary positioning systems.
- londons_explore 3y ago
  With a clock and a telescope, you can get super precise positioning the same as the 16th century way... Atomic clocks are now good enough to make those positions really good. You can do the same with radio frequencies and a phased array antenna if you like. I'm not sure if other approaches would perform better.
  - DoctorOetker 3y ago
    I mean without a clock, the reference being the direct path of noise from the sun. Telescopes are impeded by clouds. During night there is no line of sight to the sun, so I concede my rudimentary idea or question has similar drawbacks.
    - DoctorOetker 3y ago
      It would be interesting if precise time could be derived from imaging the night sky, so that the synchronized clock becomes unnecessary.
  - amalcon 3y ago
    I've actually heard of research into putting celestial navigation in guided missiles (from people who've worked on it -- so the idea that this is possible seems to not be a secret). Cameras and optics have become good enough to make this plausible with those kind of constraints. I don't know if it's been deployed, but I would not be surprised.
13of40 3y ago
I was reading the specs for the GPS satellites vs. the GLONASS ones a while back, and it seemed like they transmit on a similar frequency but with a different modulation scheme and protocol. Pure speculation, but you could imagine a Tom-Clancy-esque scenario where their secondary role is to jam GPS when they need to.
- londons_explore 3y ago
  To jam something, you ideally jam the same frequency, PRN code, and direction. If you don't know frequency, you need to jam a wide range of frequencies. Defences like frequency hopping make use of this. Bluetooth uses this for example, to prevent inadvertent jamming. In GPS, frequencies aren't secret. If you don't know the code, you need to jam with as much power as the benefit of the code. For GPS, thats a 10x 1024 bit code, which provides 43 dB of processing gain. This can be increased almost without limit, as long as you don't plan to move much during the code period. There are clever methods to make encryption keys double-up as PRN codes that the enemy doesn't know. For direction, it depends on the receiver. Your phone has an omnidirectional receiver, so the attacker is 'on par with' the real signal. A military directional phased array system might have 200 elements, and therefore 30db of gain. Add that up, and the enemy needs to use far far more signal power than the real signal to 'outshine' it. Turns out that's pretty much impossible - and if they get near to doing that, your biggest problem is probably being cooked by their jammer.
KaiserPro 3y ago
> Jamming can be pretty much eliminated by using phased array antennas. citation needed there. GPS typical signal strength is -125dBm. For ground based stuff, its pretty simple to overpower the band so that nothing can hear it.
- sennight 3y ago
  This has been a solved problem for a very long time. The nice thing about GPS satellites is that you know where they should be, and where they shouldn't, so long as your RTC is properly set and you've got a compass. A GPS Digital Phased Array Antenna and Receiver (2000): https://apps.dtic.mil/sti/tr/pdf/ADA452307.pdf https://apps.dtic.mil/sti/tr/pdf/ADA452307.pdf
  - KaiserPro 3y ago
    yes, phased arrays, especially if you have a tight beam, can give you an extra 40db of SNR (see figure 9 https://www.analog.com/en/analog-dialogue/articles/phased-array-antenna-patterns-part1.html https://www.analog.com/en/analog-dialogue/articles/phased-ar..., also in the charts on your link) but thats still like -70dbm at best. That's about the level of being a few meters away from a wifi AP level of power. a 1 watt(RF) jammer is going to cast a large cone of non-GPS even with a phased array antenna.
    - sennight 3y ago
      You are forgetting about the phased nulling. Military GPS has been including jammer detection in the firmware for a long time. I remember my handheld unit constantly annoying me anytime the IED jammer (which was waaaay more than 1 watt of rf) went active... 2005ish - it would simply mask the signal coming from that direction and continue to provide positioning data.
    - londons_explore 3y ago
      Add in coding gain over 1 second (a code 10 million chips long), and that gives you an extra 70dB. Now it's getting hard to jam. Downside: This only works if your movement over the 1 second period is predictable, to a small part of a wavelength. If you're moving unpredictably, you'll have to give up a few db's of coding gain.
ranger207 3y ago
"The sky" covers 180°x180°, or more if you're in a plane. A jammer that can block out half of that can result in a significant reduction in accuracy

hef19898 3y ago

So, basically back to old school, "manual" stuff? Should be doable, if less convenient.

throw0101c 3y ago
The US Navy brought back celestial navigation (with sextants) as a backup: * https://www.usni.org/magazines/proceedings/2021/december/bring-celestial-navigation-21st-century https://www.usni.org/magazines/proceedings/2021/december/bri... * https://skyandtelescope.org/astronomy-news/u-s-navy-resumes-celestial-navigation-training-04042016/ https://skyandtelescope.org/astronomy-news/u-s-navy-resumes-...
- hef19898 3y ago
  And all the other, old school stuff is still available anyway. Still, without GNSS, things are complicated.
supertrope 3y ago
Cell phone towers depend on GPS for timing and frequency precision. A lot of processes depend on GPS availability.
- hef19898 3y ago
  Military navigation doesn't so. Sure, GPS makes things a ton easier but it is perfectly possible without it.