May/June 2012

Could 2012 be the year that finally sheds light on how “white spaces” are used to support new wireless communication services and support the rapidly growing demand for an increasingly connected world? Frequency spectrum is allocated for specific uses; however, not all of it is occupied for 100% of the time. In fact, usage across the UHF (ultra-high frequency) band is quite low; studies carried out by Shared Spectrum Co., between 2004 and 2009 revealed average usage varies between 7% and 18%. In the United States, the FCC set out rules for how TV white spaces can be used on a license-exempt basis. The main driver is free access to commercially attractive spectrum to support new services and to expand the capacity and reach of existing wireless systems.

“White spaces” is the name given to segments of frequency spectrum that are unused. In the 54-698 MHz UHF band, which mainly features TV and wireless microphone services, unused or available channels are known as TV white spaces. The transition from analog to more spectrally efficient digital television, which began in 2009, freed up additional spectrum for new services.

Segments of the TV band may be unused because they just don’t have wireless services occupying them or are adjacent to existing TV channels and intentionally lie fallow in order to protect TV services against interference. They can also appear to be unused because terrain or other obstacles are blocking signals. Usage can be quite fragmented in terms of time, frequency, and geography. Frequency usage varies from one location to the next, and wireless services may not be active for all of the time and used in the same way across an entire country. For example, TV transmitters may be switched off during the night and TV channel usage in Indiana might not be the same as in Illinois. Change also happens on a much faster basis, and new technologies need to dynamically adapt to the changing nature of white space spectrum.

These variances in how frequency spectrum is used create opportunities for new services. The rapidly growing demand for wireless connectivity has prompted regulators to examine new ways of supporting the myriad of devices and services coming on stream throughout the next few years. In the case of TV white spaces, the evolution has proved to be a long process. The main impetus for this has been the drive to make broadband Internet accessible for all by addressing the need for a solution that provides long-range rural wireless coverage. The 470-698 MHz portion of the UHF band is seen as the beachfront property of spectrum development—this is the sweet spot of spectrum, offering sufficient bandwidth to deploy high data rate ‘Super-Wi-Fi’-type services, yet support long-range and non-line-of-sight wireless connectivity.

How TV White Spaces Have Evolved
A decade ago, Dell, HP, Intel, Microsoft, and Philips approached the FCC to make more license-exempt spectrum available at frequencies less than 1 GHz. This helped lead to a notice of proposed rule-making regarding the unlicensed use of TV white spaces in 2004. A report and order was approved, allowing unlicensed use of TV band spectrum in 2008, and the final rules for unlicensed operation in the TV broadcast bands were released in February 2009. Microsoft developed a “WhiteFi” system in 2009 and deployed it as a test case across its Redmond, Wash., campus in 2010.

In July 2011, a new IEEE standard for cognitive wireless radio access network operation in the TV bands was released. In the U.K. that same year, Neul Ltd., a start-up based in Cambridge, developed, and is currently trialing, an M2M network using TV white spaces called NeulNET. It is also leading the charge in the development of a royalty-free and open network standard for wireless M2M communications called “Weightless.”

In December 2011, the FCC’s OET (Office of Engineering & Technology) approved a TV white space database system created by Spectrum Bridge and allowed it to begin providing services to devices starting in January 2012. The OET also approved a fixed-location TV band transceiver by Koos Technical Services (KTS) as the first product allowed to operate on a license-exempt basis on unused frequencies in the TV bands. The KTS device operates in conjunction with the Spectrum Bridge TV band database, and initial deployment has occurred in Wilmington, N.C., involving public Internet access and security camera feeds.

The market requirements for TV white spaces are still emerging and are inherently linked with this slowly evolving spectrum regulatory environment. However, these requirements are largely dictated by the protection measures that regulators apply to other services in the TV broadcast bands. Throughout the past decade, the primary method used to determine which TV channels are occupied was based on spectrum sensing; detecting usage based on the level of activity measured for each TV channel. This approach was plagued by uncertainty stemming from the detection apparatus itself and the inability to detect services shielded by terrain or man-made structures.

The added device costs associated with this sensing approach tended to deter market adoption. Following trials, the FCC set out rules for how TV white spaces can be used. These rules target the need to protect existing services in the UHF band. The primary condition is that devices must regularly consult an approved geolocation database in order to determine which frequencies are available in the device’s locality.

The attraction of a geolocation database approach is it removes the uncertainty of knowing whether or not a channel is in use by a TV or other primary service. This approach also helps to drive down the device cost because sensing is no longer a primary requirement. A geolocation database approach also enables TV channels to be added or excluded on an as-needed basis by the regulator or other approved body in order to expand and reclaim spectrum to cater to future changes and needs.

Connected Devices to M2M
Increasingly congested airwaves, the rapidly growing need for more wireless connectivity, and the growing data deluge means we must look at new ways of using spectrum. An exclusive-license approach is no longer considered tenable in the long term. The surge in connected devices also means existing license-exempt frequency bands based on uncoordinated or ‘free for all’ usage. In other words, the 902-928 MHz band only available in the U.S., will face an increase in potential interference from other users as congestion grows. The concept of flexible usage rights is set to become a prominent feature in future spectrum-regulation policies. A coordinated geolocation database approach is a step in the right direction; however, a number of challenges also remain.

First, the costs associated with adhering to the FCC’s rules must be driven down to allow TV white space communications modules’ costs to compete with GPRS/EDGE and RF mesh in the sub-$10 module cost range. The need to regularly query a geolocation database requires a direct or backchannel link, which may not always be available in deployment scenarios. The database also must be maintained to include any new primary services in order to minimize any potential interference scenarios.

Interference is still a concern—only primary services, e.g., TV and wireless microphones, are catered to in the database and the secondary opportunistic users will have to rely on additional detect and avoid techniques or further coordination to minimize the potential for interference.

Cellular technologies are targeting the UHF band also: 2G/3G cellular standards are evolving toward LTE (3.9G) and LTE-Advanced (4G). Spectrum auctions will continue, and the exploration of opportunities for LTE deployments in the UHF band is a major driver for cellular operators. Spectrum auctions are large revenue generators for the government and this can reduce the number of opportunities for license-exempt spectrum bands. In 2008, the FCC raised $19 billion through auctioning 52 MHz of spectrum in the 698-806 MHz frequency range, known as the “700 MHz band.” This was more than any other auction in the past 15 years. It is therefore likely that license-exempt opportunities will evolve toward using the spectrum scraps left over from future spectrum auction feeding frenzies.

The first TV white space services are now live in the U.S., and U.K., but compelling business cases and new vertical markets demonstrating the real commercial value of white spaces must be realized before significant market pull can be generated. In fact, 2012 may well be the year we see these emerge.


Keith Nolan is a research fellow with CTVR/The Telecommunications Research Centre, Dublin, Ireland, and leads various M2M and dynamic spectrum access communications commercialization initiatives. Reach him at keith.nolan@tcd.ie

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