Last July I wrote about the Google database that shows the availability of white space radio spectrum in the US. This is spectrum that has been used for years by UHF television stations. In some rural places it was never used and in others it has been freed up as stations have moved elsewhere.
I’ve been hearing about this spectrum a lot lately so I thought I’d talk a little more about it. There are now several trials of the spectrum going on in the US. The first test market was the City of Wilmington NC who implemented this in their municipal network in 2010. They use it to control traffic lights, for public surveillance cameras and other municipal uses. Probably the biggest US test so far is a campus-wide deployment at West Virginia University in Morgantown that launched in July 2013. There only look to be a few dozen of these trials going on worldwide.
So what are the pros and cons of this technology and why isn’t it being deployed more? Consider some of the following:
- It’s not available everywhere. That’s why Google and others have put together the maps. Where there are still TV stations using some of the bandwidth, only the unused portion of spectrum is available. There are still large areas around most major metros that have some use in the spectrum.
- This is still a trial provisional spectrum and the FCC has to approve your trial use. I’m not sure why this is taking so long, because the Wilmington test has been going on since 2010 and supposedly has no interference issues. But I guess the FCC is being very cautious about letting WISPs interfere with television signals.
- We are at that awkward point that happens with all new uses of spectrum, where there is equipment that will work with the spectrum, but that equipment won’t get really cheap until there is a lot of demand for it. But until that demand is believed by a manufacturer, not much happens. It was this equipment cost barrier that killed the use of LMDS and MMDS spectrum in the 90s. There is no equipment on the market yet that would let white space be used by laptops, cell phones or tablets. Instead it must feed a traditional WiFi router.
- One use of the spectrum is that it can make a better hotspot. I don’t think most people understand the short distances that can be achieved with hotspots today. A 2.4 GHz WiFi signal can deliver just under 100 Mbps out to about 300 feet. But it dies quickly after that and there may 30 Mbps left at 600 feet and nothing much after that. If they put whitespace receivers into laptops this spectrum can deliver just under 50 Mbps out to 600 feet and 25 Mbps out to 1,200 feet. And there is an additional advantage to white space in that it travels fairly free through walls and other barriers.
- The real potential for the spectrum is to extend point-to-multipoint radio systems. With white space you can deliver a little less than 50 Mbps up to about 6 miles from the transmitter. That’s easily twice as far as the distances that can be achieved today using unlicensed spectrum and a 12-mile circle around a transmitter can make for viable economic returns on an investment. Physics limits this to about 45 Mbps of total bandwidth meaning that a product of 40 Mbps download and 5 Mbps upload is possible. That is certainly not fiber speeds, but it would be a great rural product. The problem comes in in the many places where part of the spectrum is still in use, and in those places the radios would have to work around the used spectrum and the speeds would be correspondingly slower.
It seems like this is a spectrum with a lot of potential, especially in rural places where there are no existing uses of the spectrum. This could be used for new deployments or for supplementing existing WiFi deployments for WISPS. There is equipment that works on the spectrum today and I guess we are now waiting for the FCC here and regulatory bodies around the world to open this up to more use. The US isn’t the only place that used this spectrum for TV and much of the rest of the world shares the same interference concerns. But if this is ever released from the regulatory holds I think we would quickly hear a lot more about it.