Using Wi-Fi to Get 3D Images of Surrounding Location

Interesting research:

The radio signals emitted by a commercial Wi-Fi router can act as a kind of radar, providing images of the transmitter's environment, according to new experiments. Two researchers in Germany borrowed techniques from the field of holography to demonstrate Wi-Fi imaging. They found that the technique could potentially allow users to peer through walls and could provide images 10 times per second.

News article.

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Posted on May 16, 2017 at 6:08 AM • 7 Comments

Comments

Clive Robinson • May 16, 2017 8:49 PM

The idea is far from new and the waveforms emitted by modern WiFi are praticularly suited to this sort of thing.

You can look at it as a variation of offset radar where the radar pulse is transmitted from one point but it and it's reflections are received at one or more other points. In effect you end up with a series of triangles where the sides are measured as time to get distance.

Unlike the old idea of radar which is to send pulses on a narrow beam of known direction to make the process of imaging much simpler, this uses an omnidirectional signal and you need to use a bit more in the way of mathmatics to get an image.

By moving their receiver antenna across several wavelengths of distance, they in effect gather data from very many points which increades the resoloution of the final image.

To improve the system image rate they could use a line of receivers and sweep those, or a grid of receivers in a stationary plane normal to that of the signal emitter. However to improve resolution they would be better using IQ antenna through receiver and demodulator to get the best phase/amplitude information.

Clive Robinson • May 17, 2017 11:33 AM

@ Albert,

Might be useful for detecting Christians.

But how do you filter out the Satanists?

Or just those who have read to much Vampire fiction ;-)

Jim Lux • May 20, 2017 9:53 PM

While such "through the wall" radars can fairly easily detect motion, actually resolving the location of the moving thing or imaging is very difficult. The FINDER victim detection radar detects the 1mm motion from the heartbeat of a victim buried 10s of feet in rubble, but all it can do is detect the presence, not the location, and not even close to imaging.

The problem is that the walls and furniture all cause the radio waves to be reflected, refracted, and altered. So a radar needs to essentially do a kind of radar tomography to determine the propagation characteristics of the surroundings, the walls, the furniture, etc., before it can form an image. At the current time, this is very, very difficult - it's computationally intensive (but fast computers are easy to come by), and it requires a lot of observational data: measurements from 3 or 4 or a dozen points won't be sufficient to resolve the propagation effects

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