Ambient Backscatter: Wireless Communication Out of Thin Air [pdf]

Whoa -- <i>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.</i><p>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 &quot;use case&quot;.

The basic thought here is that there&#x27;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.<p>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&#x27;t need batteries.

Pretty cool, although, not entirely a new concept:<p><a href="http://en.wikipedia.org/wiki/Crystal_radio" rel="nofollow">http:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Crystal_radio</a> (no battery needed for wireless reception)<p>Using that concept to also produce transmissions is the kicker here.<p>Now, &quot;the walls have ears&quot; takes on an entirely new meaning in &quot;The Internet of Things&quot;...

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.

This is a great step towards the <i>internet of things</i>. 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.<p>If you could just stick a rice-sized sensor wherever you want and not worry about battery life we&#x27;d all have &#x27;smart houses&#x27; by now.

The key feature of this approach that many other commenters seem to be missing:<p>They are not harvesting power from ambient RF and using it to power a second transmitter. Instead, they are <i>using that harvested power to</i> communicate with other nodes by modulating their device&#x27;s reflection of ambient RF, a process that they claim is ~100x more power efficient.<p>Not an RF engineer, can&#x27;t judge novelty, but this seems really, really clever.<p>EDIT: added text in italics above to make my post clearer.

If you do not want ugly borders around links in latex:<p><pre><code> \usepackage[hidelinks]{hyperref} </code></pre> <a href="http://tex.stackexchange.com/questions/823/remove-ugly-borders-around-clickable-cross-references-and-hyperlinks" rel="nofollow">http:&#x2F;&#x2F;tex.stackexchange.com&#x2F;questions&#x2F;823&#x2F;remove-ugly-borde...</a>

Much of this is over my head, but 1kb&#x2F;s across 2.5 feet seems like a very small step.<p>Is the significant value in this it&#x27;s ability to function at low power?

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?

They need to talk to these guys.<p><a href="http://www.thmoray.org/" rel="nofollow">http:&#x2F;&#x2F;www.thmoray.org&#x2F;</a>

Ultra-cheap mesh network, anyone?

This changes everything.