FCC Defines Unlicensed Use of TV Bands
The FCC's proposed reallocation will earmark prized spectrum for license-exempt use.
Author: Stewart Schley
For several years now, a quiet hope has been building around the idea of delivering high-speed Internet signals over freely available frequencies tucked away within the over-the-air TV spectrum. Now, there may be reason to crank up the volume. .
The source of the optimism: the U.S. government. As the Federal Communications Commission reshuffles the deck on prized swaths of over-the-air TV spectrum in the 600 MHz band, the commission has reserved several slices that can be used by entrepreneurs, established companies and local communities to deliver high-speed Internet signals wirelessly, without requiring expensive spectrum licenses
Proponents say a finalized ruling on license-exempt spectrum is exactly what's needed to encourage more interest in the category of using TV White Spaces (TVWS) for an assortment of applications including rural broadband.
TV's changing channels
The FCC Report and Order affecting TVWS is part of a bigger effort to repurpose airwaves that have been dedicated since the 1940s to analog television broadcasting in the U.S. To free up more spectrum for digital data transmission, the FCC is inviting TV station operators to turn in their licenses in exchange for the promise of money. Depending on how much spectrum broadcasters contribute, the 2016 spectrum auction scheduled to begin March 29 could fetch tens of billions of dollars.
Most of the spectrum the FCC hopes to reclaim from the television industry will be auctioned off to big players in telecommunications that want to fortify their cellular voice and data services. Mobile communications providers AT&T, Verizon and T-Mobile are expected to be among the more aggressive bidders for licenses. Interestingly Google has indicated it will not participate as it did in previous auctions. Large U.S. cable and satellite companies also may take part.
From the TVWS perspective, the proposed approach is meaningful because it guarantees at least some spectrum in the over-the-air TV band will be allocated to license-exempt use – in other words, free access to spectrum – in every U.S. market.
Per the FCC Report and Order “Expanding the Economic and Innovation Opportunities of Spectrum through Incentive Auctions” released on August 11, 2015, unlicensed TVWS device access will be maximized while protecting licensed users from harmful interference. The amount of spectrum made available and the technical requirements on how it can be used will vary based on location, the desired frequency of operation and whether the device is fixed or mobile. Under all circumstances TVWS devices will access a white space database for available channels in their location prior to operation and work within the constraints of maximum transmit power and antenna height.
The following describes the slices of TVWS spectrum the FCC has allocated to unlicensed usage:
- In the TV Band spectrum unused by television broadcast services with technical constraints including maximum transmit power and antenna height determined by the amount of contiguous spectrum available. It is anticipated that rural areas will have more TVWS spectrum than large urban areas.
- In the two vacant channels above and below channel 37 which were originally reserved for wireless microphone use.
- In the duplex gap between the wireless uplink (cellphone transmit) and downlink (base station transmit) bands.
- In Channel 37.
- In the guard bands between the TV and wireless service downlink bands.
- In the 600 MHz service band allocated for new wireless services outside the wireless licensee’s service area.
That’s enough to support multi-megabit-per-second Internet services over frequencies that can penetrate buildings and deliver signals across large distances. Channel bonding of available contiguous and non-contiguous spectrum is also allowed which enables data rates higher than what would be available with a single channel. This technique is used by cable TV companies to provide broadband data rates in the multiple hundreds of megabits to their customers.
There’s probably more to come. Additional unlicensed channels could emerge as broadcasters relinquish channels outright or use new spectrum-sharing technologies to squeeze two TV channels into the space previously occupied by just one.
Uniform approach
For TVWS proponents, this allocation is welcome because it will help to bring certainty and uniformity to the TVWS category, which has seen scattered experimentation since the FCC adopted rules allowing case-by-case TVWS implementations starting in 2010. “It’s a common statement that professional investment will be very skittish about getting involved with the TVWS until the incentive auction is worked out,” says Jim Carlson, the CEO of Arcata, Calif.-based Carlson Wireless Technologies, a developer of radio technology for TVWS.
Currently, broadband networks that make use of TVWS spectrum work on an ad-hoc basis, using specialized “cognitive” radios that probe dynamic databases to find out what unused channels are available where. It works well enough in localized implementations, but there are large variations among markets that make scaling the medium tough. Across much of the Los Angeles broadcast TV market, for example, there’s only one 6 MHz channel available for license-exempt use, according to Google’s Spectrum Database. In Fargo, N.D., at the other extreme, there are 21.
If implemented as planned following the auction, the proposed FCC rules should bring greater certainty and uniformity to the nascent broadband-over-TVWS industry, potentially triggering larger investments in technology by equipment makers and network operators.
In turn, that could help bring about a long-promised benefit of TVWS: Providing an economical way to extend broadband Internet connectivity to rural areas of the U.S.
But don’t expect standalone TVWS networks to spring up immediately after the FCC rules take hold, cautions Carlson, whose company has worked with Google and others on TVWS trial deployments. He thinks one likely market entry path for TVWS, at least in the U.S., will be to serve as an adjunct to existing Internet delivery systems that use high-frequency microwaves. These fixed microwave systems currently provide high-speed Internet service to around 2.5 million to 3 million U.S. homes, but can’t reach an additional 15% of households in their range because signals are blocked by line-of-sight obstacles like trees and buildings, Carlson says. TVWS, with its superior signal propagation, could be a solution to extending the reach of these networks.
Others agree with the notion of an incremental role for TVWS. Rouzbeh Yassini, the Executive Director of the University of New Hampshire’s Broadband Center of Excellence and the technologist who is widely known as the “father of the cable modem,” thinks TVWS is better-suited as a means to manage point-to-point communications – for example, from a base station to a community library or school – than for a one-to-many consumer Internet delivery architecture. West Virginia University has adopted this same thinking in an early TVWS trial implementation that uses TVWS to deliver high-speed connectivity to public transit stations, rather than individual residences.
Other possible applications for TVWS include connecting data sensors over wide areas for agricultural and industrial monitoring or other “Internet of Things” implementations that could spark innovations beyond traditional consumer Internet delivery.
“License-exempt spectrum is a key driver of growth in the global economy," said the Dynamic Spectrum Alliance’s Executive Director Hyacinth Nwana . “It powers Wi-Fi in homes, schools, and businesses; it enables broadband delivery in rural and underserved areas; and it powers the growing Internet of Things.”
Some big players like where the FCC is going. Google public policy executive Aparna Sridhar said Google is happy with the FCC’s plan, even though the FCC isn’t allocating as much spectrum for unlicensed use as the company recommended.
Work-in-progress
Still, there’s lots of work left to be accomplished before TVWS is ready for prime time on the broadband stage. Shared Spectrum’s CEO Tom Stroup notes that the databases used to sniff out available TVWS channels don’t adequately assess the real-time state of the RF environment, which can be compromised from noise generated by wireless microphones and other unlicensed devices. As a result, some TVWS channels might be highly unstable, even though they show up as available. Also, performance can be uneven. A TVWS trial deployment in Durham, N.H., conducted by the UNH BCoE, found wide variations in throughput at network end points, with downstream speeds ranging from unimpressive sub-megabit speeds to 8 Mbps in a single channel. The UNH BCoE trial also illuminated difficulties that may arise in pinpointing optimal antenna placement, partly because of insufficient spectral data and partly because of the absence of adequate network management tools.
As of June 2014, only the U.S. and Finland had formalized rules allowing license-exempt access to TVWS, although other nations are studying the possibility. On the technology side, the nascent industry is mostly made up of smallish developers including Adaptrum of San Jose and Carlson Wireless. Bigger players have largely stayed on the sidelines out of concern that a uniform national delivery fabric might not take shape. But there is demonstrated interest. Google and Microsoft Corp. are among prominent technology companies that have experimented with broadband-over-TVWS deployments outside the U.S. And in the U.K., a prominent 2011-12 TVWS trial brought together more than 20 players in communications technology, including Alcatel-Lucent, Microsoft, Nokia and Samsung.
Standards are progressing, too. In February 2014 the IEEE announced amendments to the IEEE 802.11 standard that allow wireless local area networks to be used in RF white spaces. The amendments establish a global standard allowing users worldwide to make use of unused or underused spectrum, based on location and time of day, by querying geo-location databases.
The development of TVWS and the regulations that will shape the category has been an “iterative” process that has sometimes tested the patience of participants, says Carlson. But thanks to the new FCC ruling, TVWS appears to be closer to a long-sought goal – the guaranteed availability of at least some license-exempt spectrum in the U.S. in the TV and 600 MHz bands.
The slow pace of the broadcast auction process – FCC Chairman Tom Wheeler extended the deadline as one of his first big decisions after taking the job – “has caused some havoc,” Carlson acknowledges. But he sees a new era looming. With the promise of new spectrum allocation on the horizon, says Carlson, “We’re ready to push this market to the tipping point.”
