White-space spectrum is fast becoming a playground for what could be ground-breaking devices and services, and lessons learned from employing the technologies necessary to make white space commercially viable could also drive innovation over a host of other spectrum bands in time.
White-space spectrum sits between TV channels and is open for use with unlicensed TV Band Devices (TVBDs). Depending upon world region, the preferred spectrum generally falls somewhere in the 450-800 MHz range. In the United States, TV bands consist of six-megahertz channels primarily in the 470-698 MHz UHF band. Rural areas with few TV stations contain huge swaths of available white space.
In order to prevent interference with local TV broadcasts, most TVBDs in developed markets such as the United States must be able to communicate with a spectrum database to identify which channels are available at a given location, and they also need to employ cognitive radio operation, including spectrum sensing and management.
Envisioned applications for TV white space include public safety, smart grids, ad-hoc mobile networks, home networking, one-way and two-way video, rural broadband delivery and more.
While the idea of using TV white-space spectrum is novel enough, the enabling technologies allow for "the opportunistic use of spectrum" either through a combination of the database and sensing or just sensing by itself, explained Rick Rotondo, vice president of marketing for xG Technology, a developer of cognitive radio networks primarily for military and government applications.
"In TV white space, the database will tell you what channels you can use. Sensing will tell you what channels out of those you should use," said Rotondo, who also co-founded Spectrum Bridge, the first company to win FCC designation as a white-space database administrator.
Crunching the data
Spectrum databases for interference mitigation can be based upon time, frequency, power, distance or whatever parameters are appropriate for a given device or are mandated by a particular telecom authority. Ultimately, these types of databases could enable device manufacturers to produce more universal devices that work in different parts of the world, creating additional economies of scale.
"We not only see this as a U.S. activity but actually a worldwide future activity, and the future could be as early as tomorrow," said John Malyar, chief architect for interconnection solutions at Telcordia. The company, now owned by Ericsson (NASDAQ:ERIC), in March became the second certified white-space database administrator for TVBDs.
However, developing countries may have little need for white-space spectrum databases simply because their spectrum is considerably less encumbered, said Dan Lubar, external affairs director for the WhiteSpace Alliance. Developing nations can, "to a great extent, side-step the need to protect the primary users of TV spectrum," meaning spectrum databases would be optional, he said.
Countries with developing economies "want to use the sub-1GHz TV-band spectrum for broadband but are waiting for equipment to show up in volume," Lubar said, which may not happen anytime soon if developed economies have a different focus than broadband for TV white-space spectrum.
White-space spectrum "could be a licensed service instead of a shared service in some countries," said Jim Carlson, CEO and CTO of California-based vendor Carlson Wireless. "I imagine initially at least in some countries for five or 10 years, they might go with just a licensed service because there's a much greater need for using those frequencies in providing broadband."
Nonetheless, frequency databases developed for use with TV white space might eventually gain a new role in a broad range of countries with unencumbered as well as encumbered spectrum. Carslon suggests spectrum owners could use the services of database administrators to help them lease their frequencies to other users, with leasing terms based upon multiple parameters, including time, frequency, power and distance, which can be tracked by databases.
Gaining spectrum through agility
Aside from spectrum databases, the other key ingredients for putting white space to work are cognitive radio and dynamic spectrum allocation. "This is a good proving ground for that technology in general," said Malyar.
The use of frequency-agile radio technology, which enables a radio to tune itself based upon information received from an external source or even from itself, can help alleviate the spectrum crunch because it enables devices to operate on frequencies for which they may not have been originally purposed. "The big opportunity we have now is to more effectively utilize spectrum because you don't have to just sit on a particular band," said Malyar.
According to Rotondo, "You actually can utilize spectrum far better and increase your network capacity far more by using all that processing capacity in your cognitive radio to do interference mitigation." For instance, enabling devices to identify interference and then null it out allows them to continue operating on a channel full of RF pollution. Such an approach, he said, provides "a solution for the spectrum have-nots--the guys who don't own a lot of spectrum."
Rotondo and Malyar both suggest the 1755-1850 MHz band might eventually be ripe for dynamic spectrum allocation. The National Telecommunications and Information Administration recently called out 95 MHz of spectrum in that band, which could be repurposed for commercial wireless use and might even be shared between federal agencies and commercial users.
Carlson agrees that this approach appears feasible based on early successes using cognitive radio and frequency databases in TV white space. "I think that is working very well with the database administrators, and any frequencies in a reasonable range, from VHF to microwave, could be assessed fairly quickly and implemented," he said.