Regarding GPS jamming/spoofing:
https://www.sbg-systems.com/news/introdu...FpEALw_wcB
This unit uses more than three satellites to resist spoofing. It also recognizes "false" GPS data. This ability is typical of all manufactures "military grade" navigation systems. I suspect most "newer" commercial aircraft systems also have this capability. To be clear, the INS generates an autonomous "track" independent of any GPS data. The INS data can be "corrected" by adding in GPS "fixes" made along the track. If the GPS data exhibits an "impossible" discontinuity or deviates from the INS track by an impossible value, that GPS fix simply will be marked as invalid and not used. The GPS correction factor will remain as the last known valid GPS update. As the platform moves in 3D space the INS absolute position accuracy will degrade. Valid GPS updates cancel the accumulated error and restore the current accuracy of the INS track.
It would in theory be possible to "lead" a specific platform along a false track. If the spoofing agent has an actual radar fix on the intended target platform he could, in theory at least, transmit "believable" GPS signals that would incrementally draw the target along a false track. However, the inherent basic accuracy of the INS severely constrains that track. Once the intended GPS position is "too far" from the INS track, game over for the "spoof". Any other platforms not on the same track would see wildly wrong GPS data and detect the spoof much quicker. The main purpose of "spoofing" is therefore not to "fool" the nav system, but rather to deny the nav system the use of the GPS updates.
FWIW aircraft at relatively high altitudes are easier to spoof using a single transmitter than lower altitude (e.g. ground level) targets. A transmitter on a 70 ft tower can spoof an aircraft at 30,000 ft at a range of 357 km (193 nm). The same transmitter's range to targets on the ground is 19 km. To targets at 200 ft, like a cruise missile, the range is 44 km. Thus many transmitters would be needed to shield important targets in depth. Even a glide bomb that operates "for a while" at high altitudes would be pretty hard to jam with a single long range transmitter. The INS will still get it "close" to the target and once it gets below the horizon of the jammer it will get valid GPS again. This will often allow the glide bomb to achieve full accuracy. Multiple jammers with no 70 foot tower, but rather a 10 foot (or so) tower are therefore "better" at protecting most targets. Obviously, both are "nice to have".
GPS satellites orbit at a nominal altitude of 20,200 km. The transmitter power is 44.8 watts with an antenna gain of 12 dBi. Obviously a transmitter that is "only" 357 km away even with an antenna gain of 0 dBi (fully omnidirectional) has a massive advantage. A particularly high power transmitter is not needed. That said, it would be very easy to "lock on" to the spoofing signal and fly right to it.
Resisting GPS jamming is quite possible by using an adaptive array (like your home Wifi does). Unlike your Wifi, the adaptive array would configure itself to reject the "false" GPS signal(s). The depth of the null(s) so generated can be very deep, much deeper than the gain of a synthetic aperture pointing at the satellite would provide. Goodbye spoofer. The spoofer can lie to you about the timing (and thus the range) but it can't hide its actual bearing, which in general is not anywhere near the satellite's actual bearing. Eigenvalues to the rescue. Obviously, the bad news is that one needs several antennas to do this (3 or 4 "works", 8 is much better). Most glide bombs and the like don't presently have that. I suspect they soon will, at significant cost to the taxpayer.
https://www.sbg-systems.com/news/introdu...FpEALw_wcB
This unit uses more than three satellites to resist spoofing. It also recognizes "false" GPS data. This ability is typical of all manufactures "military grade" navigation systems. I suspect most "newer" commercial aircraft systems also have this capability. To be clear, the INS generates an autonomous "track" independent of any GPS data. The INS data can be "corrected" by adding in GPS "fixes" made along the track. If the GPS data exhibits an "impossible" discontinuity or deviates from the INS track by an impossible value, that GPS fix simply will be marked as invalid and not used. The GPS correction factor will remain as the last known valid GPS update. As the platform moves in 3D space the INS absolute position accuracy will degrade. Valid GPS updates cancel the accumulated error and restore the current accuracy of the INS track.
It would in theory be possible to "lead" a specific platform along a false track. If the spoofing agent has an actual radar fix on the intended target platform he could, in theory at least, transmit "believable" GPS signals that would incrementally draw the target along a false track. However, the inherent basic accuracy of the INS severely constrains that track. Once the intended GPS position is "too far" from the INS track, game over for the "spoof". Any other platforms not on the same track would see wildly wrong GPS data and detect the spoof much quicker. The main purpose of "spoofing" is therefore not to "fool" the nav system, but rather to deny the nav system the use of the GPS updates.
FWIW aircraft at relatively high altitudes are easier to spoof using a single transmitter than lower altitude (e.g. ground level) targets. A transmitter on a 70 ft tower can spoof an aircraft at 30,000 ft at a range of 357 km (193 nm). The same transmitter's range to targets on the ground is 19 km. To targets at 200 ft, like a cruise missile, the range is 44 km. Thus many transmitters would be needed to shield important targets in depth. Even a glide bomb that operates "for a while" at high altitudes would be pretty hard to jam with a single long range transmitter. The INS will still get it "close" to the target and once it gets below the horizon of the jammer it will get valid GPS again. This will often allow the glide bomb to achieve full accuracy. Multiple jammers with no 70 foot tower, but rather a 10 foot (or so) tower are therefore "better" at protecting most targets. Obviously, both are "nice to have".
GPS satellites orbit at a nominal altitude of 20,200 km. The transmitter power is 44.8 watts with an antenna gain of 12 dBi. Obviously a transmitter that is "only" 357 km away even with an antenna gain of 0 dBi (fully omnidirectional) has a massive advantage. A particularly high power transmitter is not needed. That said, it would be very easy to "lock on" to the spoofing signal and fly right to it.
Resisting GPS jamming is quite possible by using an adaptive array (like your home Wifi does). Unlike your Wifi, the adaptive array would configure itself to reject the "false" GPS signal(s). The depth of the null(s) so generated can be very deep, much deeper than the gain of a synthetic aperture pointing at the satellite would provide. Goodbye spoofer. The spoofer can lie to you about the timing (and thus the range) but it can't hide its actual bearing, which in general is not anywhere near the satellite's actual bearing. Eigenvalues to the rescue. Obviously, the bad news is that one needs several antennas to do this (3 or 4 "works", 8 is much better). Most glide bombs and the like don't presently have that. I suspect they soon will, at significant cost to the taxpayer.