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Comment by samstave | Hacker News Reader

Can you apply these theories to using a wifi AP to read the 3d layout of the room/space based on RSSI and its various interferences?

Could you make a 3D scanner app in conjunction with UBNT and see what could be done....

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Not only wave length, but also beam width. The laser is spatially very compact. Radio waves need larger antenna apertures to be that focused. It's hard to get tight spatial resolution with a beam that looks like a balloon animal.

Also, multipath and time-of-flight is difficult with radio waves, and the EM reflectance is weirder. Light is just much more convenient for this purpose. But - it's not outside of the realm of possible.

> Light is just much more convenient for this purpose

With RADAR you get phase information, which helps a lot, and now that 60GHz wifi is a thing the balloon animal has a manageable size :)

>It's hard to get tight spatial resolution with a beam that looks like a balloon animal.

Would compressed sensing help? It doesn't need the focus to be precise to reconstruct the scene from a single pixel detector.

No, compressed sensing only allows you to attempt to reconstruct the original signal from a limited subset of the data sampled in a specific way, as long as you can assume some kind of sparsity on the data in another domain.

Fundamentally, you cannot get something from compressed sensing that you wouldn't be able to otherwise normally.

You could build a ghetto imaging RADAR using RSSI and phase inference, sure, but once you started optimizing it past the parlor trick phase (pun intended), you'd quickly find yourself reinventing traditional imaging RADAR, which is very much a thing.

Fairly sure I've seen an MIT paper on passive wifi imaging; including seeing humans through walls.

Is this[1] the paper you're talking about?

[1]: https://www.mit.edu/~ty20663/SAR_files/Ralston_Charvat_Peabo...

I think it was actually https://people.csail.mit.edu/fadel/wivi/

I don't think the wavelengths involved would be the best choice for it. The question is how much reflection is exhibited at wifi frequencies with the surfaces in a room, probably not enough to be able to observe it.

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