While technologies such as software-enabled radios may in the future permit federal, nonfederal, and commercial entities to share the same bands of radio spectrum, policymakers should focus in the near term on freeing airwaves for commercial broadband networks, a panel of experts said July 16.
For the last several months, top officials within the Commerce Department's National Telecommunications and Information Administration (NTIA) and the Federal Communications Commission have been in deep discussions about spectrum sharing, which is seen as one way for wireless carriers to meet the increasing consumer demand for smartphones and tablet computers. Such devices require more spectrum to carry their data transmissions--significantly more than what is needed to carry cellular calls.
The problem, however, is that the technologies might not be ready for commercial application until 2020 at the earliest.
“Many licensed frequency bands are underutilized, including those used by federal government agencies, which creates theoretical opportunities for sharing,” said Peter Rysavy, a wireless engineer and consultant, during a Capitol Hill luncheon briefing hosted by the industry group Mobile Future. “But history has shown that every attempt to share spectrum has been much more complicated and time-consuming than anyone originally anticipated.”
In a new report released at the briefing, Spectrum Sharing: The Promise and the Reality, Rysavy presents myriad options for spectrum sharing, most of which are fraught with complexity and would not solve what has been termed the “spectrum crunch” anytime soon.
“Sharing is a long-term process, and we are at day one of a long journey,” Rysavy said.
Currently, there are three sharing models:
• Geographic sharing, in which a wireless carrier may use a federal agency's frequencies only in certain geographic areas;
• “Temporal” sharing, in which a wireless carrier may use a federal agency's frequencies only during certain times of the day or year; and
• Technology-based sharing, in which wireless carriers and a federal agency would each use a cognitive, or “smart,” radio device that can search wide swaths of a spectrum band for “quiet,” or unused, frequencies over which to transmit and receive data.
To Rysavy, there are still too many unanswered questions to definitively conclude whether sharing will be workable for the wireless industry, such as: Who will share with whom? If wireless carriers must share spectrum that is licensed to federal government agencies, who retains priority access? What are the rules for the wireless carriers when they are using spectrum licensed to the federal government?
“We don't know yet what spectrum is available and what the constraints are,” Rysavy said. “That's just a big question mark right now.”
Rysavy said the simplest way to share spectrum is to create geographic “exclusion zones” around which a commercial entity would make use of spectrum licensed to a federal government agency. The more complex approach, Rysavy said, would be to establish a primary- and secondary-access system in which users would coordinate with one another through a database. The FCC already uses a database to identify when and where the unlicensed spectrum in between TV channels--known as “white spaces”--is being used, so that those wanting to transmit their signal can select the right frequency without creating interference with others.
Technology-based sharing would be the most complex, Rysavy said, even though it has precedent in a technology with which most consumers are familiar--Wi-Fi. Operators of Wi-Fi use what is known as “dynamic frequency selection” to avoid interference with federal radar systems.
“We've now been at this for six years, with the FCC, the Department of Defense, and the FAA [Federal Aviation Administration], and I would say that we have yet to perfect the art of this particular sharing case,” said Mary Brown, director of government affairs at Cisco, of Wi-Fi sharing. “It is much harder than we thought when we went in. Most of it is working and it's working great, but we're still having challenges with certain radars … . It is very, very tough.”
Commenting on calls for broader spectrum sharing, Brown added that “no one in the world has ever tried to have a mobile technology share with some kind of federal systems.”
“We need to throw anything and everything we have at the 'spectrum crunch,’ ” Brown said. “One thing that's very clear is that we're not going to be able to solve it without additional spectrum.”
By Cisco's estimates, by 2016 almost 50 percent of mobile devices will be smartphones and, Brown says, they will be more powerful, which will require more spectrum.
David Redl, counsel on the House Energy and Commerce Committee, said the foremost challenge is “definitional,” as sharing can “encompass almost anything.”
“We need to make sure everyone is speaking the same language,” Redl said of the House Commerce Republicans' spectrum-related initiatives.
He also tried to tamp down enthusiasm for a spectrum-sharing technology called “dynamic spectrum access,” which would essentially allow consumer mobile devices to look for, and then transmit data over, unused frequencies in a spectrum band.
The technology, he said, is not ready to be deployed on a wide scale.
“We've got a short-term need for more spectrum in the commercial space,” Redl said. “While dynamic spectrum access is something that we should absolutely be looking at, it's got a long-term time line before it's going to be ready for prime time. Finding ways to do both clearing and allocation, as well as sharing, is something we're looking at as an all-of-these-should-be-options approach.”
The research firm Yankee Group estimates that by 2015, consumer use of wireless applications and services will be nearly 60 times today's volume.
The FCC has set a goal of freeing 500 MHz for commercial mobile broadband networks by 2020, and has championed the concept of “incentive” spectrum auctions, in which the agency would reclaim airwaves from television broadcasters and auction them off to mobile network operators, sharing some of the proceeds with the TV stations that volunteer to cease broadcasting and, ultimately, give back their spectrum to the government.
In March, NTIA concluded in a much-anticipated report that while it is possible to reallocate 95 MHz of government-held spectrum in the 1755 MHz to 1850 MHz band for commercial mobile broadband and similar applications, some federal licensees, such as the Department of Defense, “could remain in the band indefinitely.”
The NTIA has already identified 115 MHz--in the 3550 MHz to 3650 MHz and the 1695 MHz to 1710 MHz bands. The agency, however, still must free an additional 380 MHz by 2020.
To read Peter Rysavy's report, visit http://mftr.org/spectrum-sharing.
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