
Now, I can see wifi signals - bane
https://imgur.com/gallery/jdNA6
======
Animats
Neat. The phenomenon is called Rayleigh fading, and is well known, but I've
never seen it mapped as clearly. Rayleigh fading is often viewed
statistically, and some article even call it "random". As shown here, it's not
random at all; it's deterministic and repeatable. It's determined by the
position of transmitter, receiver, and reflective and absorbent objects in the
environment.

This is why most WiFi devices have two antennas and a diversity receiver.

Spread-spectrum systems are resistant to Rayleigh fading, because multipath
nulls are frequency-specific; the two paths have to be half a wavelength
different in length to get cancellation. So it seems surprising at first to
see this with WiFi, which is a spread-spectrum system.

There's a reason for that. Cancellation becomes less of a problem as you get
further from a spread spectrum transmitter, because the phase difference is
related to the product of the frequency change times the number of wavelengths
along the path. (This really needs pictures.) Once you're far enough away that
the spreading moves the nulls at least a half wavelength, the effect is that a
fixed percentage of data is lost, and error correction deals with that. In
this demo, transmitter and receiver are very close, so the nulls are strong.

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ChuckMcM
That is _slick_. The wavelength of 2.4Ghz radio being 125 mm and 5Ghz being
62.5mm it looks like he is imaging standing waves in the 5Ghz spectrum. (if
the cube is 360mm x 360mm it would have ~6 waves of 5Ghz and ~3 waves of
2.4Ghz RF energy. There is an experiment to see the standing waves in a
microwave using chocolate - [http://morningcoffeephysics.com/measuring-the-
speed-of-light...](http://morningcoffeephysics.com/measuring-the-speed-of-
light-with-chocolate-and-a-microwave-oven/) which demonstrates the same sort
of thing, but frankly I think this is much cooler.

~~~
pervycreeper
He does mention that explanation for explaining the distance between
"features" in his visualization, however this does not explain their
particular shape, nor their general irregularity. It would be nice to see this
repeated outdoors in the desert to reduce reflections and possibly
interference.

~~~
DonHopkins
It would also be nice to see the chocolate experiment repeated in other
desserts.

~~~
gonzo
only if you extract the Theobromine. (hi don)

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jpmattia
This is a beautiful hack.

Because terrific work causes us to think of additional questions, I'd add: The
only thing I found missing is that there is more than one polarization. So to
accurately map the field, you'd need to perform multiple scans, with the
receiving antenna rotated 90 degrees for each one.

~~~
cheez
> Because terrific work causes us to think of additional questions,

I'm gonna steal this line.

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ianlevesque
Really cool, but I wonder how much his big metal testing rig is interfering
with the signal.

~~~
jakobegger
Not only the metal testing rig, but also the 60kg RF-absorbing sack of water
holding the device in the earlier experiments.

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darkmighty
Awesome. I'm not sure how to make this argument precise, but I think you could
sample the intensity function only every 12.5cm (wavelength at 2.4 Ghz), since
waves of a given wavelength are restricted to resonate and interfere at small
multiples of it's wavelength.

For reconstruction there should be some ideal interpolation, maybe a 3d sync
filter?

Another random interesting fact: if you capture not only the intensity but
also phase of only a 2D slice, and have some environmental information (i.e.
know how the signal propagates in your room), you can reconstruct the full 3D
intensity.

~~~
icegreentea
A naive application of Nyquist sampling theorem will say you have to sample at
twice the frequency of whatever you're trying to reconstruct - so for 2.4Ghz
you need to sample at at least every 6.25cm. The reason why you can't just use
the base frequency is cause... well, for example, imagine you have the worst
luck ever, and only ever sampled the nodes of the standing wave - it would
just look like no signal.

In practice... I have no idea. RF is too much for me.

------
frozenport
Unlike heat, E&M is a vector field, so the author should have rotated his
antenna at every point :-)

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devindotcom
This was done in a pretty spectacular way by Luis Herman a little while back:

[http://www.itsnicethat.com/articles/luis-hernan-digital-
ethe...](http://www.itsnicethat.com/articles/luis-hernan-digital-ethereal)

~~~
bithive123
Also see: [http://www.nearfield.org/2011/02/wifi-light-
painting](http://www.nearfield.org/2011/02/wifi-light-painting)

------
grannyg00se
Why is there so much variation in strength from such a small change of
position?

~~~
Sami_Lehtinen
Signal variance is nothing new. I remember personally noticing it in late 90's
that with my GSM (900MHz) phone, moving it on table just for about 5
centimeters could bring it down from full signal to no reception at all. Of
course with analog radios you also notice how easily signal changes with
location. If you've been ever playing with TV antenna in in bad reception and
so on. Moving your hand in other room might block TV signal or make it crystal
clear even if you would make there's no connection what so ever. With 2.4GHz
people often forget that interference from other sources can significantly
contribute. So signal quality and signal strength aren't same thing at all.
Getting to the root all these things require professional, which I'm not. So
one type of measurement defined as "signal strength" probably misleads you
badly. Is it a good idea to select a wifi channel that doesn't have any other
wifi boxes? Well, the reason might be that the channel is totally overpowered
by local wireless CCT or phones. That's the reason why nobody's using it for
WiFi and then you think it's a great idea to select a free Wifi channel? Radio
stuff is (truly) really tricky. With higher frequencies it's just like light.
Why some things are in shadows and some things are well lit?

~~~
tracker1
I'm in a relatively large appartment building.. I can see about 20 other wifi
options in my area on my laptop... fortunately, my signal quality is
significantly better (higher end asus, with shibby tomato) spent a fair amount
of time tweaking the settings a bit that seem to work very well for me... I
can keep signal on my phone across the parking lot (I'm facing the pool, which
is adjacent to outside parking) ... no wifi really gets into the garage
though, but cell phone signal does...

It's really wild how a foot or two difference could make all the difference in
the world...

------
DanAndersen
I'm curious if combining this with Google's Project Tango for accurate 3D pose
estimation would be useful for doing a handheld 3D mapping of an area. Add an
additional camera to the tablet, have it point at an array of these sensors,
and use it to sweep out regions of space quickly.

------
auxym
Pretty cool! Would be cool to add some sort of position sensor on, I guess GPS
wouldn't be ideal though. Maybe hack a roomba to map signal strength in your
house!

Anyways, reminds me of this:
[https://vimeo.com/20412632](https://vimeo.com/20412632)

------
rawnlq
Reddit comments:
[http://www.reddit.com/r/dataisbeautiful/comments/2vuvhf/prec...](http://www.reddit.com/r/dataisbeautiful/comments/2vuvhf/precise_3d_mapping_and_visualization_of_wifi/)

The author had a nice summary here:
[http://www.reddit.com/r/dataisbeautiful/comments/2vuvhf/prec...](http://www.reddit.com/r/dataisbeautiful/comments/2vuvhf/precise_3d_mapping_and_visualization_of_wifi/col4he6)

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jrockway
What is this measuring? RSSI, MCS level, observed throughput?

~~~
tonyarkles
I'd assume RSSI

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atamyrat
What about beamforming? Wouldn't signal strength depend on locations of
connected wifi clients?

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praseodym
Strap it onto a quadcopter and you have a portable solution to map every room
you could imagine.

~~~
acadien
There was a project several years ago to map a University's wifi using a self
driving RC car with a wifi detector on it. The goal was to identify weak spots
in the signal. I can't remember the name of the project and its not popping up
on google, anyone else remember this?

------
andyfleming
Here's a cool animation (supposed showing the "propogation" of wifi signal):

[http://gfycat.com/ImportantSafeBlackmamba](http://gfycat.com/ImportantSafeBlackmamba)

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VonGuard
This is brilliant, I wish it'd get more upvotes and attention. Wireless waves
are such nebulous, hard to understand things. It's great to see a visual
representation!

------
stolio
Awesome. A while ago somebody did something similar but with really hard math:
[http://arstechnica.com/gadgets/2014/08/mapping-wi-fi-dead-
zo...](http://arstechnica.com/gadgets/2014/08/mapping-wi-fi-dead-zones-with-
physics-and-gifs/)

It's always nice to see multiple approaches to the same problem.

------
kator
I have often wondered what Jordi's[1] vision would really be like.. Maybe this
is a peek into his world.

Imagine all these things, wifi, FM/AM Radio, iBeacons, cell towers etc.. It
must be so noisy in the radio spectrum..

[1]
[http://en.wikipedia.org/wiki/Geordi_La_Forge](http://en.wikipedia.org/wiki/Geordi_La_Forge)

~~~
TheSpiceIsLife
There was a Next Gen episode, I think, where Jordi's visor was displayed on
the main viewer on the bridge of the Enterprise with Picard commenting.

~~~
raldi
Argh why are you both spelling his name wrong!? It's right there in the URL!

~~~
TheSpiceIsLife
True. Oops. Wasn't thinking and just copied the other guy.

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noonespecial
Very directional antenna, fast scanning servo gimble, oculus rift... hmmm.

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k__
This with the hololens could be rather nice to debug.

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enthdegree
That is really cool. It would be cool to put it on an indoor UAV, and have it
fly around, mapping wifi signals around a building

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jszymborski
Write a paper!

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zan2434
I was really hoping this was going to be an AR hack for seeing WiFi, but this
is cool too!

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aceperry
Nice, I didn't know about this board. It looks pretty interesting.

~~~
linker3000
It's a real nice tinker toy for only a few pounds/dollars.

The default firmware uses modem-style 'AT' commands for control, but there is
an Open Source LUA implementation, and you can cross-compile in C.

[http://www.esp8266.com/](http://www.esp8266.com/)

[https://github.com/nodemcu](https://github.com/nodemcu)

[http://l0l.org.uk/2014/12/esp8266-modules-hardware-guide-
got...](http://l0l.org.uk/2014/12/esp8266-modules-hardware-guide-gotta-catch-
em-all/)

------
thomasfl
The most top ranked comment says; "PATENT THIS MOTHERFUCKER NOW, DO IT BEFORE
APPLE FIND OUT AND STEAL YOUR IDEA." Hope neither this will get patented or
Apple will steal it.

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mtgentry
Can I come over to your house and play?

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milesf
Yeah, I went there. And no, I'm not sorry :)
[http://imgur.com/9bnvWRm](http://imgur.com/9bnvWRm)

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iLoch
Now do it with my piece of shit Shaw router.

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tdicola
Neat hack but aren't there free tools to do this with a laptop and its wifi
adapter? [http://www.ekahau.com/wifidesign/ekahau-
heatmapper](http://www.ekahau.com/wifidesign/ekahau-heatmapper)

