WIRED: The Future of Wi-Fi Is 10,000 Times More Energy Efficient

[Sean Lynch]

On Sun, Mar 6, 2016 at 12:04 AM, Cari Machet <carimachet at gmail.com> wrote:

> Engineering students have discovered a way to reflect Wi-Fi packets
> instead of broadcasting them.
>
> http://www.wired.com/2016/03/future-wi-fi-10000-times-energy-efficient/
>
Neat! It does seem like you're trading "pollution" of the band for power
consumption, though. Even ignoring the tone generated by the "plugged in
device", which is carrying energy but no information and much of which is
wasted, their modulation technique results in significantly more energy
outside of the passband of the receiver than inside. So overall power
consumption goes way up, even though it's not from the battery-powered
device. And then if a bunch of people start using these, the total amount
of energy you need to pump out will keep getting higher and higher due to
the added interference, which will cause battery powered devices to have to
use more power. Possibly surmountable, but still interesting. I suspect
(and I think you may have had this in mind as well) that backscatter
modulation will end up being more interesting for covert applications,
where you use a tiny device with a tiny (or no) battery that transmits by
reflecting some signal that is already in the environment, like an FM radio
station, and you use a receiver that is designed for receiving the
reflected signal including the "mirror image" and a couple of the extra
harmonics. You could see that as a kind of "free" spread spectrum.
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