

Ambient Backscatter: Wireless Communication Out of Thin Air [pdf] - interconnector
http://homes.cs.washington.edu/~gshyam/Papers/amb.pdf

======
WestCoastJustin
Whoa -- _We present the design of a communication system that enables two
devices to communicate using ambient RF as the only source of power. Our
approach leverages existing TV and cellular transmissions to eliminate the
need for wires and batteries, thus enabling ubiquitous communication where
devices can communicate among themselves at unprecedented scales and in
locations that were previously inaccessible._

p.s. just pasting a couple lines of text from the article, for those who are
wondering what this is after looking at the comments, my typical "use case".

~~~
StandardFuture
Whoa -- not to be a buzzkill but there is some massive overhype on this. Not
to even begin to mention what happens when the FCC gets involved. Spectrum is
bought and owned, you know. And zero unnatural interference is tolerated.
Sure, you can argue it won't interfere with any towers but lawyers will argue
some other points I'm sure.

~~~
chockablock
Reading the paper, what do you think is 'massive overhype'? They demonstrate
working devices on the 1-2 foot scale.

The regulatory question is certainly an interesting one. Is it 'interference'
to reflect very modest amounts of an existing signal? Multipath is already a
very real phenomenon; if these devices do not appreciably affect transmission,
then are they truly interfering?

Put another way, are the regulations written from the point of view of effects
(degraded transmission for the spectrum licensee), or in absolute terms (no
communication at a given frequency?)

~~~
StandardFuture
I would say that the regulatory question is the only question left. It's
obvious that this works; but how well will it 'cooperate' in an environment?

>Reading the paper, what do you think is 'massive overhype'? They demonstrate
working devices on the 1-2 foot scale.

To be a more effective network device the one thing you will have to do is (at
least) try to increase this signal efficiency. That spells future regulatory
problems.

>Multipath is already a very real phenomenon.

Again, interference management is already handled within devices. But now you
want to add more interference into the environment? See what I mean by: good
luck with that in a court.

>if these devices do not appreciably affect transmission, then are they truly
interfering?

Yes, they are still interfering. And the problem only grows as you scale this
"new" network.

...

And to answer the final question: Again, you would have to see what lawyers
will try to argue.

~~~
chockablock
Well, I hope you'd agree that it's OK to leave the lawyers out of the
discussion at this very early stage. (And technical workarounds might well
exist: e.g. a TV channel's worth of spectrum in a major metro might be given
over just to providing remote power to devices.)

A little relevant data from the paper: They do a somewhat crude experiment in
the paper looking for corruption of TV signal, and find no effects except when
the TV antenna is within a few inches of the device.

Which of course shows that these devices do indeed interfere with the normal
reception of the signals they are parasitizing.

~~~
StandardFuture
The legal statement about the FCC clause is there to try to cover their asses
on the research that went into this and to try to market the possibility of a
wide adoption of these types of devices. I'm guessing they did not bother
testing inside a screened room then if they believe that? Maybe? Maybe not?

EDIT: I am guessing not. I imagine they used real-world backscatter to test
this out.

------
willscott
The basic thought here is that there's a ton of energy in our environment,
specifically in the form of high-amplitude RF waves from TV broadcasts, and we
should be able to use that energy to do work.

This project is trying to figure out what the equivalent of an rfid tag looks
like with that power model. They come up with a scheme of being able to absorb
versus reflect the ambient signal to communicate between unpowered tags. Maybe
the most productive way to think about this is as a step into the larger
research area of how to effectively harvest energy and do useful stuff with
devices that don't need batteries.

~~~
femto
When I was at university, there was a final year undergraduate project that
used similar technology. In this case, the student was trying to build a
passive radar jammer, which modulated the reflected radar signal in a way that
the driver of a car could select what speed they wanted to appear on a traffic
radar.

The method was to build a corner reflector out of three orthogonal conducting
sheets, but to connect one of the sheets to ground via a PIN diode switch. By
turning the diode on and off, the reflection coefficient of the corner
reflector could be modulated, in turn modulating the reflected signal.

~~~
jevinskie
Do you have a link? That is fascinating! Did it end up working?

~~~
femto
I don't have a link. It got written up as an undergraduate thesis in about
1991, but as far as I know the University of Sydney doesn't keep copies of
such documents.

I'm not sure what the outcome was, though it must have gotten to a certain
point of success, since I've memories of a car driving around with a corner
reflector on it.

The same student was experimenting with using a plasma as the modulated
reflector, but that one ended when he connected the wrong end of the vacuum
pump to his gear, accidentally pressurised it, and blew it up!

------
qwerty_asdf
Pretty cool, although, not entirely a new concept:

[http://en.wikipedia.org/wiki/Crystal_radio](http://en.wikipedia.org/wiki/Crystal_radio)
(no battery needed for wireless reception)

Using that concept to also produce transmissions is the kicker here.

Now, "the walls have ears" takes on an entirely new meaning in "The Internet
of Things"...

~~~
GeorgeTirebiter
Tesla was interested in this, eh? I did this sort of thing in 1967 when I put
a capacitor on the output of my crystal set, and was able to (very weakly)
light a standard panel lamp. Nothing is new, only the details change.....

~~~
chockablock
Unwarranted grumpiness. Harvesting power from radio transmisssion is indeed
not new.

What they demonstrate, however, is transmission from the 'receiver' to
additional devices by modulating how much power is absorbed or reflected.

This is fundamentally different from just using the harvested power to run a
second transmitter, because modulating backscatter is 'orders of magnitude'
more efficient.

------
zw123456
Yes, this is being very over hyped, RF backscatter is the same basic mechanism
that RFID uses, there are a ton of good tutorials online. There are a number
of ways to increase the range of backscatter systems like RFID such as spread
spectrum. One of the other problems is multiple access, how can you tell if
back scatter is coming from source 1 or 2 or 3, that has also been worked out
in RFID using a coding scheme (eg. PN codes). Basically these guys
rediscovered RFID technology and got kind of excited. This is not to say that
there are not interesting applications, two passive devices can communicate
between each other given a strong enough source signal. But the applications
are limited, usually, if you have 2 devices that need to communicate between
each other, you want to do something with the information being exchanged,
maybe light an LED or something, that would take way more energy than you can
harvest from ambient RF. Once you realize you need a battery, then it is just
easier to put a simple 802.11 or 802.15 transceiver in.

------
ricardobeat
This is a great step towards the _internet of things_. The main roadblock for
attaching sensors to everything right now is power. Even with month or even
year-long battery life the maintenance burden and cost makes it much less
attractive.

If you could just stick a rice-sized sensor wherever you want and not worry
about battery life we'd all have 'smart houses' by now.

~~~
StandardFuture
This could not be used for 'smart houses' .. willscott had it right when he
mentioned RFID stuff. You cannot have 'ultra-low power' and have a transmitter
powerful enough on a WLAN.

~~~
ricardobeat
I'm not sure what you mean. This thing is not a transmitter, it piggybacks on
existing waves by modulating their reflections - that's the whole point of the
paper. It won't have to compete with a WLAN.

Presumably range can be increased, specially if the principle is adapted to
use that WLAN's 2.4ghz stronger signal instead of VHF.

------
chockablock
The key feature of this approach that many other commenters seem to be
missing:

They are not harvesting power from ambient RF and using it to power a second
transmitter. Instead, they are _using that harvested power to_ communicate
with other nodes by modulating their device's reflection of ambient RF, a
process that they claim is ~100x more power efficient.

Not an RF engineer, can't judge novelty, but this seems really, really clever.

EDIT: added text in italics above to make my post clearer.

~~~
StandardFuture
Sorry, but that is wrong. Figure 3 explains everything.

EDIT: I should say that yes the technique is using analog conditioning
circuitry to get the job done without storing power in a battery.

~~~
chockablock
There is indeed a block in that diagram labeled 'Transmitter', but it is not a
transmitter in the colloquial sense of converting onboard power into RF
energy. Instead, the 'transmitter' modulates the amount of ambient RF energy
that is backscattered, by modulating the antenna impedance.

This appears to be the major innovation in the paper. As lots of commenters
have pointed out, harvesting power from ambient RF is nothing new (whether or
not a battery is involved).

(Section 3.2): "By modulating the electrical impedance at the port of the
antenna one can modulate the amount of incident RF energy that is scattered,
hence enabling information to be transmitted."

(Section 8a): "backscatter communication is two orders of magnitude more
power-efﬁcient than state-of-the-art radio communication")

~~~
StandardFuture
Yeah, it's a cool technique. But it still has no room to scale as far as I can
tell. At least not for transmitting inside licensed frequencies ... maybe they
should try it out on 2.4 GHz or 3.5 GHz??

------
dfc
If you do not want ugly borders around links in latex:

    
    
      \usepackage[hidelinks]{hyperref}
    

[http://tex.stackexchange.com/questions/823/remove-ugly-
borde...](http://tex.stackexchange.com/questions/823/remove-ugly-borders-
around-clickable-cross-references-and-hyperlinks)

------
Selfcommit
Much of this is over my head, but 1kb/s across 2.5 feet seems like a very
small step.

Is the significant value in this it's ability to function at low power?

~~~
ajkjk
I think it's significant because it's a huge increase over '0'.

------
yalogin
One thing stands out, how do they address noise? Is Backscatter somehow
different from an unintentional noise or interference? If this is all low
power it would mean the impact of noise or interference will be high and it
will only multiply with the number of devices using it nearby. Is there a risk
of it becoming something similar to tuning to an AM radio station while
traveling in a remote area?

------
frankydp
They need to talk to these guys.

[http://www.thmoray.org/](http://www.thmoray.org/)

------
leot
Ultra-cheap mesh network, anyone?

------
phalanx101
This changes everything.

