Monday, 26 August 2013

Ambient backscatter radio

It seems that some folk at U. Washington have managed to implement an idea that I've been playing around with for a while - ambient backscatter. Now what we need are far, far better reflectors - their system only really works well at distances of 2-3 feet in free air, and really what we need is something that can get through walls.

On the other hand, if their aerials can be made smaller, they could reflect WiFi signals, which have much higher local intensities than distant TV transmitters and whose reflection characteristics are fairly well known thanks to all the folk doing diversity with them.

I wonder if a semi-intelligent aerial which spots beacon frames in h/w is a good thing to have - on the one hand, it provides a known timing reference for the receiver to try and wake up to, but on the other you will have all of the distance-related wakeup window issues.

The other thing one can do over the UW study in a home hub environment is, of course, to have a pulsed interrogation transmitter - notably if you operate in 868MHz or 2.4GHz that transmitter can be on the same frequency as your ambient radio, so you can work in a wait_for_reflect-pulse-wait_for_result mode, which allows you to get quite high power intensities without interfering too much with WiFi (particularly if you are listening to the WiFi and know when its slots are).

This (in some form) is obviously the right technology for things like window sensors - now you only need to change batteries in one room, not one every sensor.

Anyway, have a link - it's an interesting read: