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Comment by leonidasrup | Hacker News Reader

Because GPS and other GNSS have only a very weak signal strength there are no jam resistant frequencies, you can jam them all very efficiently, or you can jam them very efficiently in selective way (jam BeiDou, but not GPS).

GPS was jammed even as early as Iraq war.

"Coalition troops also got a glimpse of GPS’s greatest weakness during the Gulf War. Iraqi forces installed jammers, for example, on top of landmarks such as Saddam Hussein’s palaces to prevent them from being hit, Mastalir says. This helped the military realize early on that it would have to further develop its laser-guided munitions and other weapons that acquire targets when GPS is unavailable"

https://web.archive.org/web/20160208233555/http://www.scient...

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A lot of work is being done to make GPS more jam resistant, and - just as important - more spoof resistant. The latest batch of satellites has a whole raft of countermeasures to help a receiver to identify whether the received signal is genuine or whether it was spoofed. Receivers too can do a lot to detect spoofing by just observing the signal (for instance: unrealistic power levels on reception, impossible response to vehicle movement and others besides), but quite a few of those are unrealistic or too expensive for regular (non military) applications. Jam resistant frequencies do not exist as you already mentioned, from a physics perspective. But GP might mean this to refer to the new M-Code signal, and these are sent out on different frequency offsets from the main carrier, so effectively different frequencies.

Jam resistance and spoof resistantance are very different.

What work is done to make GPS more jam resistant?

https://gps.stanford.edu/research/current-and-continuing-gps...

Single element antennas, adaptive antennas, beam steering antennas. Basically attempting to pull good RF while avoiding bad RF.

(this has been applied in the Russo-Ukrainian war in modified Starlink equipment)

GPS antenna mods make Starlink terminal immune to jammers - https://news.ycombinator.com/item?id=39616417 - March 2024 (72 comments)

https://olegkutkov.me/2023/11/07/connecting-external-gps-ant...

The Russian response to directional antennas is to mount GPS jammers on satellites

https://www.gpsworld.com/todd-humphreys-russian-satellites-a...

If Russia’s proof of concept moves to active use, those satellites (Kosmos 2546 and any others) will need to be removed from service with anti satellite technology (either munition or X-37B equivilent). Clearly Russia is attempting to shield an overt military capability behind the satellite’s early warning launch detection primary mission to dissuade attempts to disable it. Remove the orbital capability, deny them access to replace it.

Ongoing Ukrainian strikes against Rassvet satellite production and launch sites contribute to further impairment of Russia's ability to get any new or replacement satellites to orbit.

https://ua.news/en/war-vs-rf/video-ukrayina-atakuvala-golovn...

https://en.wikipedia.org/wiki/Kosmos_2446

https://arxiv.org/html/2606.03673v1

https://www.youtube.com/watch?v=cRiOkQ1ngAM

L5 is considered to be more jam resistant, but it is still in the process of being rolled out and most receivers do not have that capability. It will take the better part of a decade to be rolled out completely but the space side should be done by 2027 so if you need it you can get it but you'll need a completely new receiver.

https://insidegnss.com/onenav-l5-direct-technology-enables-d...

For obvious reasons hard information about all this is tricky to come by, you can read what is available from non-classified sources though and you can glean quite a bit from there.

https://en.wikipedia.org/wiki/GPS_signals#L5

The third edition of 'Kaplan' is still excellent reading on the subject even though it is 10 years old now.

> L5-band signals are 30x harder to jam and interfere with compared to L1, and they offer superior performance in difficult-to-navigate areas such as urban canyons and tree-covered regions.

Impressive performance.

I think Starshield (Starlink for the military) is going to use lasers as the means of communication (and location). Those are highly directionaly, and likely not possible to jam. Though I'm not sure how resistant are they to atmospheric interference, and the sats need to know where your receivers are, which I can't imagine the military is too happy about.

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