Comment by namibj | Hacker News Reader

Comment by namibj | Hacker News Reader

Freifunk should work fairly easily; take 2-3 2X2 MIMO routers (like 20 bucks each), adjust the firmware for them, get the P2P directional link to either use existing satellite dishes (not sure what the easy orthomode splitter is, here, as you need same-source-spot signals for both horizontal/vertical or left/right polarization), or simple DIY'd axial helix antennas (made on plastic/cardboard tube of appropriate diameter, by winding an even spiral at the right "thread pitch", then fixing it in place with glue/tape, and weatherproofing the assembly) (one wound like a normal screw thread, the other like a reverse thread, and put side-by-side with a gap of like 5-10 tube diameters to not interfere with each other).

Use the router's switch ports to connect them with each other, and use one local router with stock antennas pointing straight up to serve local clients and mesh with possible nearby mesh nodes.

The electronic warfare resilience is going to involve hacking the collision avoidance techniques to be sufficiently less aggressive, and likely to get Freifunk to use encryption for the mesh links. If necessary, just set up P2P links with per-link encryption. Routing-table-affecting nodes in a mesh sadly need some inherent trust to be performant in the non-adversarial case, or at least, no one seems to have tackled that possible issue yet (to the point where you could just compile existing software for the router at hand and get something working by the end of next week).

Seconded, Freifunk is easy to use and pretty resilient, there is also a pretty large community of people with knowledge about it and the hardware requirements are as low as they will go.

Beware of some of the possible downsides: the default is for Freifunk nodes to be placed on a map and I'm not sure if this is a requirement or not but it might provide easy targeting information for the Russians. This will have to be taken into account, and if possible to be done without.

Also, Freifunk nodes are open enough that behind-the-lines enemy could use it to phone home without a trace, so likely you'll need some extra FOF kind of authentication mechanism.

People more versed at this than I am will most likely have a whole bunch of other concerns about setting up a system like this.

Finally, long haul is all about antenna tech, I would suggest to enlist the help of as many local HAMs as you can find.

While being placed on a map is clearly bad, commodity WiFi is not great for anything that shouldn't be located, as it is obviously radiating in RF and will be detectable some distance further than the signal can actually be decoded.

Tactical radios are specially designed for the problem. Eg using spread spectrum approaches, and plain not transmitting most of the time and only by the choice of the operator.

It's possible that open source SDR could be applied, but I guess that the Ukrainian side have been supplied with military radios by their allies.

I'm not very familiar with Freifunk, but if it interfaces like a normal WLAN to the user, then simply not advertising SSID and a basic password will go pretty far. This is obviously not secure against any sort of special operative, but eliminates it as a very easy convenient tool for e.g. a mobik with a cell phone, if this finds its way anywhere near a frontline.

An upside of highly directive, P2P links is that they can provide some protection against EW, simply by nature of having a constrained field of view. Also I'll note most consumer devices (laptops, cell phones) have pretty bad antennas, they're assuming you have a router right nearby. You might get much better coverage if you're also able to provide the user with a simple USB dongle that can attach to an external antenna (e.g. a 10dBi yagi-uda)

If there is need for any input on the antennas side, I'm more than happy to help (EM PhD, design antennas for a living). 2.4GHz is relatively forgiving, you can literally hand make antennas, with some attention to detail. If you have access to shipping (I really don't know the situation) they can be mass produced on PCB.

While not sure if it will help/matter for the OP, I'd like to confirm the idea/thought of using (ground-plane-having-for-back-lobe-suppressing) axial-firing helix antennas, in pairs, to do circular polarization MIMO on the point-to-point long-distance links. So one clockwise and one counter-clockwise helix, connected to the two antenna ports on a cheap 2.4 GHz router.

Gain seems to max out around 15 dBd, in that case, for a 90cm long antenna of ~5cm diameter. The beauty of circular polarization there is the independence of mounting angles/matching rotations, but I guess a small forest of H/V dual-polarization Yagi's (or, for routers with 3X3 MIMO, 3 equally-spaced polarization directions, assuming that works without breaking the workings of the Yagi) might be easier due to the potential for a solid metal center pillar to hold the elements.

A forest instead of a lone Yagi would be to increase gain more efficiently than by merely elongating a single Yagi, as the latter would quickly cause mechanical issues in wind.

I'm imagining access to an improvised spot welder to attach lengths of copper wire to a steel support pillar, then finished with some paint as an anti-corrosion coating. Or some more low-tech attachment process, like a styrofoam pillar with the wires pierced through in the right spots, mounted either indoors or in a drain pipe or such for weather protection.

Can you confirm that these approaches are appropriate for the situation/call some out that are not appropriate?

What do you think of Yggdrasil to handle mesh routing? I know it has "flapping" issues (connecting and disconnecting the root node rapidly), though that was somewhat mitigated, and need to control the root (compute/"mine" a suitable key) first.

Ideally, we'd have Wi-Fi NAN (Wi-Fi Aware/Neighbour Awareness Network) on all devices (including routers, smartphones), discovering devices close by and allowing Yggdrasil to work on top. That's very recent though. I blame Apple keeping AWDL proprietary.

Some of that can probably be approached by connecting handsets to multiple networks at once (the chips usually support it, but I don't know about the OS).

In the end, in this case it's probably better to ask a local ISP for cooperation (ask for a part of their spectrum, and put 4G antennaes and local 4G to Wi-Fi APs). It can still be meshed together.

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