Consumer electronics companies got an early Christmas present this year when the Federal Communications Commission (FCC) decided to grant unlicensed smart phones, computers and other wireless devices approval to connect to the Internet via vacant "white space" airwaves. Exactly which Christmas, however, is less clear—consumer electronics–makers wanting to take advantage of broadcast spectrum space abandoned as a result of last year's shift to digital television have much work ahead of them to meet the requirements laid out by the FCC.

In a formal ruling on September 23 the FCC assured broadcasters and incumbent users of the spectrum that they will be protected from interference by new, unlicensed wireless gadgets seeking to use white spaces. In a statement (doc) the agency called its move the "first significant block of spectrum made available for unlicensed use in more than 20 years."

In addition to the requirement that mobile phones, netbooks, tablets and other devices have access to the information needed to determine their position and consult an FCC-approved geographic database listing licensed broadcast spectrum users (in particular, TV stations) in their area, the FCC reserved two vacant UHF channels for licensed wireless microphones and other low-power auxiliary service devices in all areas of the country.

The FCC's decision is a boon for Internet addicts, who can look forward to faster, more reliable wireless connections via the broadcast spectrum. White space access is also a shot in the arm to makers of mobile devices (as well as the operating systems, apps and chips that these gadgets use) who covet the broadcast spectrum's low-frequency waves, which have strong propagation characteristics allowing the signals to reach farther than wi-fi and penetrate walls and other impediments (doc).

Spectral sensing suspended
The FCC eliminated the requirement that wireless devices have built-in spectral sensing capabilities that can detect whether a white space is being used before connecting to the Internet, as long as those devices have geolocation capabilities and access to the FCC-approved white space database (yet to be created). The agency has not ruled out the use of spectral sensing in the future, but it backed away from demanding such technology over concerns that it could not be done accurately at this time and that such a capability would be a serious drain on wireless device batteries.

There has been a swing away from the spectral sensing approach because it was deemed too difficult to do at this time, says Luke D'Arcy, head of cognitive radio at Cambridge Consultants, a company that stands to gain much by the FCC's ruling. Cambridge is developing a product called InCognito, a package of microprocessors, circuit design and software that makers of mobile phones, computers, set-top boxes and wireless base stations can use to enable their devices to find available white spaces by linking up to the free-spectrum database when it becomes available.

The InCognito platform, however, also supports spectral sensing technology, which can detect free spectrum when the database is not available (for example, when the white space device is not connected to the Internet). Part of the FCC's ruling lowers the spectral sensing requirements, making the design of the sensor significantly easier than originally expected, D'Arcy says. If the device does not have to work as hard to detect white space, such searches will be less of a threat to battery life.

Microsoft chose a different path, feeling "strongly" that a database lookup function was sufficient in lieu of a spectral-sensing capability that could probe white spaces to see if they are being used by an FCC-licensed user at any given time, says Dan Reed, head of Microsoft Research's eXtreme Computing Group. The argument is that, if the database indicates vacant white space in the area of a laptop or mobile phone, that device should be able to connect to the Internet via that white space without interfering with local TV stations or wireless mics.

The company has wasted little time preparing to fill the vacuum. Last year, Microsoft Research set up a wi-fi–like network on its Redmond, Wash., campus to transmit high-speed data signals over white spaces using a technology the company refers to as "WhiteFi." Engineers from Microsoft's Networking Research Group received permission from the FCC last year to test a live WhiteFi network stretching over a 2.6-square-kilometer area of the campus to determine whether wireless devices would be able to get a high-speed connection without interfering with the TV broadcasts and wireless mics used in nearby buildings. "We needed to see what such a network would look like in the wild," says Ranveer Chandra, a researcher with the group.

One scenario enabled by Microsoft's WhiteFi network is the ability to give wireless users Internet access while they ride the 220 shuttle buses and cars used to transport employees and visitors around the company's city-size campus. The researchers installed a wi-fi access point in one such shuttle. The access points get their wireless signals from WhiteFi antennas set up last October and then hand off the connection to mobile devices on the shuttle via wi-fi. They rely on a prototype database Microsoft created to find vacant portions of the broadcast spectrum.

Channel sharing
Microsoft Research continues to test its WhiteFi network. A particular area of interest moving forward is the WhiteFi's ability to divide spectrum channels so that a tablet PC, for example, could share that space with a wireless mic. Right now, this is a no-no—the FCC prohibits a white space device from sharing channels with wireless mics, even if that mic does not use the entire channel. The researchers are experimenting with ways to snag the unused portion of the channel for data transmission without interfering with that of the mic, Chandra says.

To ensure there is no interference, Chandra and his team are testing white space transmissions in an anechoic chamber, whose walls absorb sound to prevent echos and reverberations. In the chamber they record sounds via a wireless mic, at the same time exposing it to white space transmissions (they also make recordings without any white space transmissions). Then they analyze the quality of the recording using a set of standards known as perceptual evaluation of speech quality (PESQ), also used by phone-makers, network equipment vendors and telecom operators to assess voice quality. Their results show that vacating only a few 100 kilohertz of a six-meghertz TV channel is sufficient to avoid audible interference to wireless mics. The remaining spectrum can be simultaneously utilized for high-speed data communication.

Mobile phones, PCs and access points enabled for both wi-fi and white spaces could hit in the market in roughly two years, Reed says.

White space connectivity is needed, particularly as information technology reaches new heights—demand for wireless content will grow anywhere from five to 40 times what it is today within the next decade and a half, Reed says. The next big frontier is likely to be wireless video, which would let mobile phone users stream live video (a baseball game, for example) to their handsets with low latency. Wi-fi and cell networks are not prepared for this type of traffic, he says, adding, "Think about the challenges that carriers are facing now just to support smart phones."