On Sun, Mar 6, 2016 at 12:04 AM, Cari Machet <carimachet@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.