TV white space has certain problems that make it unsuitable for extremely low-power applications. For one, the FCC requires you to periodically query a web serv

TV white space has certain problems that make it unsuitable for extremely low-power applications. For one, the FCC requires you to periodically query a web service to determine which channels are currently unoccupied at your location. If you are mobile, you need to query every so-many meters (~50, I believe, but don't quote me on that), which would mean querying every 40-odd seconds assuming an average walking speed of 1.2m/s. Even if you're not mobile, e.g. an environmental sensor or relay station, you will still need to periodically check to see if there isn't a wireless microphone or other device occupying the band you're transmitting on. Querying a web service over a 3G connection will cost you anywhere between 2-6 Joules depending on hardware, network conditions, network features (fast dormancy, state transition time-outs) etc. So for battery powered and/or low data rate applications, staying in an unlicensed band like 433, 868, 915, or 2.4 is still the best option by far.