bob baxley

TV White Space

Current IoT devices operate in either licensed spectrum (e.g. cellular frequencies) or in unlicensed spectrum (e.g. 2.4GHz/5.8Ghz ISM). But a 15-year-old field of research called cognitive radio (CR) that is a hybrid of the licensed and unlicensed models is starting to be commercialized. The main driver for CR is the exploding demand for wireless services over the finite resource of radio spectrum, which is extremely expensive to license.

Generally, CR refers to a radio that is smart enough to autonomously access the radio spectrum in a way that does not degrade other users. The technology is not quite that far along, but the FCC has recently blessed a simple version of CR, where unlicensed devices (secondary users) can access licensed spectrum when the license holder (primary user) is not using it. In practice, this means that the secondary users utilize a whitespace database to determine if the spectrum is available. If the spectrum is available, the secondary user is free to use it. If not, the secondary user must wait until the spectrum becomes available.

In 2008, the FCC agreed to open TV whitespace in the UHF and VHF bands for unlicensed use. Later, in 2011 the FCC approved several companies for hosting a database of near-real-time spectrum usage information. The idea is that companies can provide wireless services in these white-space bands without having to buy a license to the spectrum. Because the bands are unused, it is a win-win. Google is one of the database providers and has a nice web interface/API that allows users to see which TV bands are unoccupied in a given location.

CRs can use this white-space database to access “beach-front property” spectrum without a license. White space devices in the TV bands are just starting to come to market (e.g. Agility Wireless Radio: FCC Docs).

There is a lot of federal momentum to open more spectrum to the sharing model. For instance, the President’s Council of Advisors on Science and Technology (PCAST) released a report in 2012 outlining a path forward on opening up more spectrum using spectrum-sharing models (disclosure: I contributed to that report). In addition to the VHF/UHF bands, which are shared with TV, the US government is also pushing hard to open up 150MHz in the S band (3.5 GHz) for spectrum sharing. As demand for wireless services increases, I am sure we will see more and more of the IoT utilizing CR white space technology. While this trend will create untold opportunity for commercial devices, it will also inevitably introduce new wireless vectors for malicious attacks. It will be fascinating to watch this quickly evolving space. Stay tuned!