7 ms·

You seem to describe satellite uplink jamming: perturbing the link going from the content provider to the satellite. I would expect this uplink would be redunda

by ovi256 14y ago

You seem to describe satellite uplink jamming: perturbing the link going from the content provider to the satellite. I would expect this uplink would be redundant and encrypted in some way. Maybe even using optical communication for it, which would enable having a very narrow uplink receiver. Thinking about it, jamming the downlink in a large area to get the same effect seems to be much harder than jamming the uplink.

davidcuddeback 14y ago
Encryption doesn't counter jamming, because jamming happens at the physical layer (RF).
- mturmon 14y ago
  In this case, I'm sure you're right. But it might be worth noting that you can use spread-spectrum techniques (http://en.wikipedia.org/wiki/Spread_spectrum http://en.wikipedia.org/wiki/Spread_spectrum) to overcome jamming. Spread spectrum has some similarities to an encryption scheme, because the method used to smear the signal around uses a pseudorandom sequence which is known to the encoder and the decoder. CDMA (http://en.wikipedia.org/wiki/Code_division_multiple_access http://en.wikipedia.org/wiki/Code_division_multiple_access) cell phones use this idea. As you note, this type of encryption takes place at the RF level.
  - JosephRedfern 14y ago
    Surely the "jammers" could just broadcast their jamming signal over a large range of frequencies?
    - InclinedPlane 14y ago
      Of course, but that raises the amount of resources necessary for jamming all that much higher, perhaps taking it out of the realm of feasibility.
      - mturmon 14y ago
        Right, and you now have variables under your control to drive their power requirements arbitrarily high -- namely, the better your timing, the higher your effective S/N ratio (because your spread-spectrum signal can be, in effect, very-very narrowband, but hopping all over). You increase your timing accuracy by 10x, and the jammer's power requirements increase by 10x (crudely speaking -- not a 1:1 trade, but directly linked).
        dhimes 14y ago
        That's a different kind of spread-spectrum. That's a frequency-hopper, where the carrier changes frequency (the first SS- an idea attributed to Hedy Lemarr in the lore). We're talking about direct sequence, which increases the bandwidth of the signal but keeps the same carrier. To jam that (theoretically) you need large power through the entire band.
        mturmon 14y ago
        I was talking about both -- for the purposes of explanation, frequency-hopping is more intuitive. (I was trying to be responsive to @Redfern above, who mentions frequency-domain jamming.) Both frequency-hopping and direct-sequence spread energy over a larger bandwidth. Direct-sequence does not explicitly frequency-hop, but the time-domain switching it uses will spread the energy out in Fourier space.
- dhimes 14y ago
  This kind does: http://en.wikipedia.org/wiki/Direct-sequence_spread_spectrum http://en.wikipedia.org/wiki/Direct-sequence_spread_spectrum DS Spread Spectrum spreads the signal over a larger frequency range- because power is conserved it can even hide behind ambient noise. When un-spread, the noise is spread out and the signal is "collapsed" back to the original bandwidth.
  - deleted 14y ago
    [deleted]
  - rauar 14y ago
    I wonder if it still resistent to jamming when someone does so on each used DSSS channel...
    - dhimes 14y ago
      It take a huge amount of power to cover the whole spectrum at jamming levels. That's the beauty of the technique.
- xlevus 14y ago
  Jamming can happen at all layers. The most basic of jamming is to drown out all other communications with high-power noise. But in the case of illegal/covert activities this isn't ideal as your transmitter will be pretty easy to find. So then you have to pretend to look like a legitimate signal. Which is where encryption and modulation can help. But then application level encryption isn't going to help against basic jamming.
makomk 14y ago
You might expect so, but apparently a lot of satellites are just dumb repeaters. Remember that they have a low power budget and you can't upgrade the hardware once they're in the sky. If you design something that relies on a particular modulation scheme it's going to become obsolete once everyone moves to a beeter one.
jcr 14y ago
To jam the downlink, you'd need to be between the satellite and the ground receiving dish, or have line-of-sight to the receiving dish and a ton of power. This only disrupts the one receiving dish, so the attack is isolated. Jamming the uplink is much easier. All you have to do is over-power the signal from the transmission station(s) up to the satellite. Encryption doesn't do you any good. Having redundant uplinks also doesn't do much good since the resources of the satellite are limited, and the amount of power you can get here on the ground is more or less unlimited by comparison. There are multiple uplink transponders (chunks of spectrum used as carrier frequencies), and you can allocate them in a redundant fashion, but it's expensive due to the limited resources on the sat. The interesting, and undisclosed, question is whether or not the attack is only affecting the BBC? If so, then it's a more sophisticated attack targeting just the carrier frequencies (uplink transponders) being used by the BBC. A high power wide-band attack is crude but easier to perform, and would jam all of the channels broadcast from the satellite since it would over-load all of the uplink transponders. Sadly, there are still a lot of old and poorly designed satellites still in use; it's kinda like finding unfixable Win95 systems on your network infected with malware. Since they're in orbit and cost a whole lot of money, fixing or replacing them aren't a viable options. The only good news for older satellites is both the uplink (to satellite) and the downlink (to ground receivers) often have somewhat adjustable footprints. If you can identify the ground location of the jamming signal, you might be able to exclude its region from the uplink footprint. The trouble is, if the satellite is also being used for things like sat-phones, then you just cut off all customers in the excluded area of the uplink footprint. By the fact that this was made public, there's probably nothing that can be technically done about the jamming.
- knowaveragejoe 14y ago
  According to the press release, it's not just the BBC being affected.
- BlackNapoleon 14y ago
  how do you learn this stuff?
  - jcr 14y ago

by ovi256 14y ago

davidcuddeback 14y ago

Encryption doesn't counter jamming, because jamming happens at the physical layer (RF).

mturmon 14y ago
In this case, I'm sure you're right. But it might be worth noting that you can use spread-spectrum techniques (http://en.wikipedia.org/wiki/Spread_spectrum http://en.wikipedia.org/wiki/Spread_spectrum) to overcome jamming. Spread spectrum has some similarities to an encryption scheme, because the method used to smear the signal around uses a pseudorandom sequence which is known to the encoder and the decoder. CDMA (http://en.wikipedia.org/wiki/Code_division_multiple_access http://en.wikipedia.org/wiki/Code_division_multiple_access) cell phones use this idea. As you note, this type of encryption takes place at the RF level.
- JosephRedfern 14y ago
  Surely the "jammers" could just broadcast their jamming signal over a large range of frequencies?
  - InclinedPlane 14y ago
    Of course, but that raises the amount of resources necessary for jamming all that much higher, perhaps taking it out of the realm of feasibility.
    - mturmon 14y ago
      Right, and you now have variables under your control to drive their power requirements arbitrarily high -- namely, the better your timing, the higher your effective S/N ratio (because your spread-spectrum signal can be, in effect, very-very narrowband, but hopping all over). You increase your timing accuracy by 10x, and the jammer's power requirements increase by 10x (crudely speaking -- not a 1:1 trade, but directly linked).
      - dhimes 14y ago
        That's a different kind of spread-spectrum. That's a frequency-hopper, where the carrier changes frequency (the first SS- an idea attributed to Hedy Lemarr in the lore). We're talking about direct sequence, which increases the bandwidth of the signal but keeps the same carrier. To jam that (theoretically) you need large power through the entire band.
        mturmon 14y ago
        I was talking about both -- for the purposes of explanation, frequency-hopping is more intuitive. (I was trying to be responsive to @Redfern above, who mentions frequency-domain jamming.) Both frequency-hopping and direct-sequence spread energy over a larger bandwidth. Direct-sequence does not explicitly frequency-hop, but the time-domain switching it uses will spread the energy out in Fourier space.
dhimes 14y ago
This kind does: http://en.wikipedia.org/wiki/Direct-sequence_spread_spectrum http://en.wikipedia.org/wiki/Direct-sequence_spread_spectrum DS Spread Spectrum spreads the signal over a larger frequency range- because power is conserved it can even hide behind ambient noise. When un-spread, the noise is spread out and the signal is "collapsed" back to the original bandwidth.
- deleted 14y ago
  [deleted]
- rauar 14y ago
  I wonder if it still resistent to jamming when someone does so on each used DSSS channel...
  - dhimes 14y ago
    It take a huge amount of power to cover the whole spectrum at jamming levels. That's the beauty of the technique.
xlevus 14y ago
Jamming can happen at all layers. The most basic of jamming is to drown out all other communications with high-power noise. But in the case of illegal/covert activities this isn't ideal as your transmitter will be pretty easy to find. So then you have to pretend to look like a legitimate signal. Which is where encryption and modulation can help. But then application level encryption isn't going to help against basic jamming.

makomk 14y ago

You might expect so, but apparently a lot of satellites are just dumb repeaters. Remember that they have a low power budget and you can't upgrade the hardware once they're in the sky. If you design something that relies on a particular modulation scheme it's going to become obsolete once everyone moves to a beeter one.

jcr 14y ago

To jam the downlink, you'd need to be between the satellite and the ground receiving dish, or have line-of-sight to the receiving dish and a ton of power. This only disrupts the one receiving dish, so the attack is isolated. Jamming the uplink is much easier. All you have to do is over-power the signal from the transmission station(s) up to the satellite. Encryption doesn't do you any good. Having redundant uplinks also doesn't do much good since the resources of the satellite are limited, and the amount of power you can get here on the ground is more or less unlimited by comparison. There are multiple uplink transponders (chunks of spectrum used as carrier frequencies), and you can allocate them in a redundant fashion, but it's expensive due to the limited resources on the sat. The interesting, and undisclosed, question is whether or not the attack is only affecting the BBC? If so, then it's a more sophisticated attack targeting just the carrier frequencies (uplink transponders) being used by the BBC. A high power wide-band attack is crude but easier to perform, and would jam all of the channels broadcast from the satellite since it would over-load all of the uplink transponders. Sadly, there are still a lot of old and poorly designed satellites still in use; it's kinda like finding unfixable Win95 systems on your network infected with malware. Since they're in orbit and cost a whole lot of money, fixing or replacing them aren't a viable options. The only good news for older satellites is both the uplink (to satellite) and the downlink (to ground receivers) often have somewhat adjustable footprints. If you can identify the ground location of the jamming signal, you might be able to exclude its region from the uplink footprint. The trouble is, if the satellite is also being used for things like sat-phones, then you just cut off all customers in the excluded area of the uplink footprint. By the fact that this was made public, there's probably nothing that can be technically done about the jamming.

knowaveragejoe 14y ago
According to the press release, it's not just the BBC being affected.
BlackNapoleon 14y ago
how do you learn this stuff?
- jcr 14y ago