"Passive Wifi" created using an FPGA consumes uW of energy.

[Stonent]

This was a very interesting read on some innovative stuff they came up with at the University of Washington.

They were able to build an 802.11b wifi device in an FPGA without any analog hardware and were able to cut power consumption from 100's of mWs to uWs.

It seems to be centered around moving more functionality from the client, to the Access Point.  So that the wifi Access Point is doing the work of determining when it is ok for a device to start transmitting rather than the client monitoring doing the work.

They seem to be doing some of this passive communication in side areas of the wifi channels which won't have as much interference.

Story: http://www.networkworld.com/article/3037088/mobile-wireless/researchers-make-low-power-wi-fi-breakthrough.html
Published Paper: http://passivewifi.cs.washington.edu/files/passive_wifi.pdf

[nwvlab]

Very interesting indeed!

I hope that a standard will be set-up!

[scatha]

Pretty cool - it modulates a passive out-of-band CW by altering the antenna impedance to create backscatter. I'm surprised at the kind of ranges they're getting out of it.

[coppice]

Pretty cool - it modulates a passive out-of-band CW by altering the antenna impedance to create backscatter. I'm surprised at the kind of ranges they're getting out of it.

Remember that the range for 802.11b was pretty good compared to the modern 802.11 specs. There is a price to pay for greater bit rate, even when you use a more efficient transmission scheme. For the pretty optimistic case of the CW transmitter, sensor and receiving station sitting in a line the range doesn't look too bad, but for more general positioning its not so great. Those (d1^2)*(d2^2) losses really add up. They talk a lot about the power needed to transmit, but don't say much about receiving at the passive node. The power taken by receiving is quite considerable, and a node which cannot receive sounds rather limited. It must have been a very interesting project to work on, but I suspect it will have limited application.

[rrinker]

 I can see all sorts of uses for a transmit-only device - in things like sensors of all sorts. Door and window sensors, presence detectors, pretty much anything. Those sort of devices don't have to receive anything, and the lower the power they need to consume the better, as such devices are usually battery powered. If you can get near shelf life out of a set of batteries, it just makes using these as purely wireless devices that much better.

[Tinkerer]

Very fascinating.

I can see all sorts of uses for a transmit-only device - in things like sensors of all sorts. Door and window sensors, presence detectors, pretty much anything. Those sort of devices don't have to receive anything, and the lower the power they need to consume the better, as such devices are usually battery powered. If you can get near shelf life out of a set of batteries, it just makes using these as purely wireless devices that much better.

Put a small rechargable battery in there with something like a small solar cell and you are almost going to have unlimited power as long as it catches sun for a bit each day. Bet a small solar cell would generate 10x more energy than that thing uses at any given point.