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> given the low transmit powers, local wireless jammers should be relatively easy to implement. Not true. Both the transmitter and receiver (in both directions
by dkbrk 3y ago
> given the low transmit powers, local wireless jammers should be relatively easy to implement.
Not true. Both the transmitter and receiver (in both directions) utilize phased arrays. This means the receiver is very good at rejecting noise angularly separated from the expected location of the transmitter. Geometry dictates that jamming could be somewhat effective against upload (i.e. if the jammer is located roughly within the size of a spot beam from the transmitting dish), but is almost completely ineffective in the download direction.
This is all fairly theoretical since much of the details aren't publicly available; but as evidence I point to the fact that Russia has poured a huge amount of money into EW and, despite having considerable motivation to deny Starlink access, has consistently failed to prevent its widespread use by Ukrainian troops on frontlines mere kilometers from its own forces.
- ale42 3y agoThis is in ideal condition, but how good is the rejection of other signals by the beamforming circuits in the receiver? Intuitively, I'd think that a powerful enough local jammer (I really mean local, not at some kilometers, EM fields weaken with the square of distance, so very quickly) would manage to create interferences despite the beamforming.
- lxgr 3y agoI agree that jamming Starlink’s existing (dish-based) service might not be that easy, but mobile phones do not use phased arrays, and that’s what TFA is about.
- geraldhh 3y agoMU-MIMO implies a phased array no?
- lxgr 3y agoThey are conceptually related, and the more antennas you add ("massive MIMO"), the more you get into the "phased array" domain, especially on the base station side, which is where MU-MIMO is exploited. But on common mobile devices, you only have two or four antennas, so the beamforming gain is much more limited. Having more than one antenna there is mostly done to leverage multipath propagation in a non-line-of-sight environment for capacity gains as far as I understand it, and in a line-of-sight environment, you only get very moderate steering gains of a few dB (and practically no steering/beamforming effect). Satellite communication is primarily line-of-sight, though. So while the satellite can steer its beams towards a given mobile device (both for transmit and receive), and this allows for higher spectral efficiency and better use of the satellite's transmit power and better noise rejection, the mobile device can't do the same and will easily be overwhelmed by a jammer at least in the downlink path, as far as I understand.