[jessaustin]

I think we're at the stage where it would make sense to have an unlicensed band that allowed "smart" devices only, which followed a minimum set of rules.

Then we agree on the only point that matters.

The challenge here is getting someone to give up their spectrum.

That is indeed a challenge. In one case, this effort included updating every television in the nation. Yet still, five years after the digital transition, from the WIA Spectrum Policy [0] page:

Rural areas continue to be the most underserved market in terms of wireless reach and innovation. However, the abundance of white spaces in these regions provides a unique opportunity for rural wireless providers to use this unused spectrum to promote coverage through high-capacity service. While the advantages to expanding this expansion remain undisputed, firm action has not been taken as of yet in order to allow the operation of higher powered spectrum in these areas. At present, TV band devices are not permitted to operate at power levels greater than 4 watts EIRP, even though expanding this power limit would pose virtually no threat of interference to current broadcast bands. The delay in the advance of power limits only serves to hinder wireless progress in rural areas of the country.

That seems wasteful: usable white space was one of the selling points of the digital transition, and yet giant blocks remain unusable for no publicly-acknowledged reason. I mean, I hesitate to even ask what the military are doing with all their spectrum while this is still going on.

[0] http://www.wirelessinnovationalliance.org/index.cfm?objectid...

[rayiner]

The "virtually no threat of interference" claim needs to be taken with a grain of salt. Digital TV receivers are pretty dumb devices that aren't very good at rejecting interference.

I'm a big proponent of having minimum interference tolerance requirements for receivers, and there's work happening on that front: http://transition.fcc.gov/bureaus/oet/tac/tacdocs/WhitePaper.... But we'd be talking about another round of updating every television in the nation...

[jessaustin]

The "virtually no threat of interference" claim needs to be taken with a grain of salt. Digital TV receivers are pretty dumb devices that aren't very good at rejecting interference.

When I enter "Los Angeles CA" on the FCC reception map site [0], there are 23 green/strong broadcasters listed. When I enter the location of my home, there are two. Are we to believe devices that can handle the presence of 22 "competing" signals in one situation will be completely overwhelmed by the presence of one or two extra signals in the other situation?

[0] http://transition.fcc.gov/mb/engineering/dtvmaps/

[rayiner]

Those 23 broadcasters are all on different channels. We're talking about devices that could potentially be on the same channel as an exiting TV station. This is not a trivial problem to solve, because you need very sensitive detectors on the "smart" device to ensure that it correctly detects when there is an active station on a given channel: http://www.sharedspectrum.com/wp-content/uploads/2008-10_SSC....

One of the most complex aspects of doing this sort of thing is various permutations of the "hidden node" problem. Essentially, the problem is that a "smart" transmitter may not hear a dumb one, and use an in-use channel, interfering with a dumb receiver, which otherwise could hear the dumb transmitter. This tends to happen because geographic obstacles can cause individual nodes to have a different view of the spectrum environment.

[jessaustin]

Good point, but devices don't have to be able to sense broadcasts on a channel in order to avoid using that channel. Alternatively, the WISP WAP could just continuously broadcast (on known safe channels, as a part of the normal SSID etc. beacon) the list of currently safe channels, as configured and maintained by WISP personnel, and consumer devices could simply not transmit until they received the list.

Even if we were limited to listen-before-talk, the linked study recommended 10 W rather than 4 W, and that was in the urban context of Baltimore-DC, rather than out here in the hills where we rural people would like a choice in ISPs.