On Sun, Mar 6, 2016 at 12:04 AM, Cari Machet <[1]carimachet@gmail.com>
   wrote:

     Engineering students have discovered a way to reflect Wi-Fi packets
     instead of broadcasting them.
     [2]http://www.wired.com/2016/03/future-wi-fi-10000-times-energy-effi
     cient/

   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.

References

   1. mailto:carimachet@gmail.com
   2. http://www.wired.com/2016/03/future-wi-fi-10000-times-energy-efficient/