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".
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.
Fortunately the authors have addressed this in the paper:
"Legality:
In general, it is illegal to broadcast random signals on
spectrum reserved for TV (or cellular) channels. However, battery-free backscattering devices (e.g. RFID tags) are unregulated and not tested by FCC because the emission levels from such devices is very low [7] and because they are only modulating their reflection of a pre-existing signal rather than actively emitting a signal in re-served spectrum. Ambient backscatter also falls into this category, and would therefore be legal under current policies."
And the tolerance levels are not set at _zero_, but at a specific decibel level on a specific measuring setup. (I've been researching this professionally lately, especially ETSI EN 389-401). Pretty much all high-speed digital electronics in plastic cases will be radiating on the TV band, but at an extremely low level that passes the regulations.
This system modulates by switching its antenna between grounded and ungrounded. At no point does it inject transmission power into the antenna. Your house is already full of small metal objects that are slightly resonant in the TV band - such as cutlery. You could probably replicate this experiment by attaching a switchable ground to a fork and holding it _right next_ to a TV antenna. Thanks to the inverse square law the effect is so weak that it really does have to be right next to the antenna; in the paper they report no detectable effects at a distance of more than a few inches.
Agreed, StandardFuture. This is impressive, but TV channels and signals are owned by TV broadcasters. So:
* Not only the FCC, but the NAB [National Association of Broadcasters] will be on this pronto.
* So, consider either:
___o Allowing the FCC to retain a channel for a few years of ambient backscatter experimentation and evaluation (funding a set of transmitters for a while, experimenting with what transmitter signal structure might allow wider ambient backscatter bandwidth and node-to-node distances), then offer it as a tax-supported service ( as with GPS ), or sell it, else
___o Having the FCC allow an interested private owner of TV channels privately experiment with ambient backscatter engineering as proposed (locally, multipoint-piggybacked over 8VSB TV), develop the technology, then license it.
* In no way am I intending to cast aspersions on the authors' achievements here; instead I am very, very impressed! It shows indefinitely durable (battery-less) RF networking having practical applications drawing only half a microwatt for 'transmission,' carrying a general purpose programmable microcontroller on board, using a passive method to modulate an ambient RF signal with a man-made signal below the by the intended (TV) signal. And using analog components where they give significant power advantages, while retaining programmability sufficient to support a networking stack. Wow.
Disclosure: I work in support of the Broadcast TV Industry
Edits: (1) Tax-supported is not 'free' (2) Clarify that ambient backscatter is multipoint, 12 orders-of-magnitude lower power, and distributed, in contrast to the single point of origin of the 8VSB TV transmission
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?)
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.
Interestingly, the authors claim in the paper that batteryless backscattering devices are not regulated by the FCC, citing FCC regs.
"Legality: In general, it is illegal to broadcast random
signals on spectrum reserved for TV (or cellular) channels. However, battery free backscattering devices (e.g. RFID tags) are unregulated and not tested by FCC because the emission levels from such devices [7] ... Ambient backscatter also falls into this category, and would therefore be legal under current policies.
[7] New policies for part 15 devices, FCC, TCBC workshop, 2005."
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.
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.
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".