The second time around
Apr 1, 2008 12:00 PM, BY CRAIG BIRKMAIER
In his book, “Defining Vision: The Battle for the Future of Television,” reporter Joel Brinkley tells how the drive for advanced television has its roots in an FCC proposal from the '80s, which required broadcasters to share additional broadcast white spaces with the land mobile industry. In an effort to hang onto their precious frequencies — and inspired by Japanese HDTV experiments — the broadcasters struck a new plan.
They said they needed the underutilized spectrum space for HDTV. Brinkley's book describes the discussion that ensued at that NAB meeting in 1986. An unidentified participant in the meeting reportedly raised a concern, “Yeah, but what if we really get it?”
Wish granted
Ultimately broadcasters did get the opportunity to deliver HDTV to the masses. Rather than using two 6MHz channels, as broadcasters originally proposed, the DTV standard that was adopted by the FCC in 1997 loaned each broadcaster a second channel for the new digital service.
After a simulcast transition period — now scheduled to end Feb. 17, 2009 — broadcasters will return the spectrum used for NTSC broadcasts, and the TV bands will be compacted into channels 2 through 59, freeing up the 700MHz spectrum for new applications.
Auctions of the 700MHz spectrum ended in March. Based on the bidders, this spectrum will be used primarily for wireless telephony and data services, as well as TV broadcasts optimized for mobile and handheld devices.
Broadcasters got two more decades of virtually exclusive use of this beachfront spectrum. Channels 14 through 20 are still shared with land mobile services. Medical telemetry devices share several channels. And wireless microphones used by TV broadcasters and production companies operate in this spectrum. These are typically licensed applications, though many users never apply for those licenses.
So here we are 22 years later, and broadcasters are finally facing the end of the analog TV era. However, the debate over appropriate uses of the white spaces in the compacted broadcast TV spectrum (channels 2 through 59) still rages on.
It's like déjà vu
Several factors have historically contributed to the need for the broadcast white spaces. First and foremost, the use of high-powered TV transmitters on tall transmission towers cause signals from these transmitters to radiate into adjacent TV markets.
This is particularly true for geographic areas with high population density and multiple adjacent markets, such as the northeast corridor between Washington, D.C., and Boston, as well as in Southern California. Many channels cannot be used in adjacent markets because of interference considerations, and this legacy has been perpetuated with the new DTV service.
Second, the RF design of legacy analog TV receivers was limited in the early days of broadcasting. The lack of sensitivity in early TV tuners often required that several adjacent channels not be used to protect the one channel carrying a TV broadcast. Modern TV tuners offer improved sensitivity, as evidenced by the ATSC recommended practice A-74, which details minimum receiver performance guidelines.
And finally, the propagation properties of certain frequencies in the TV bands, and reserved use for other applications, such as radio astronomy (channel 37), require the designation of additional taboo channels.
Let's open up
In 2004, the FCC issued a notice of proposed rulemaking (NPRM) that would open up the white spaces for new uses. The commission proposed to classify unlicensed broadband devices to be used in the TV bands into two general functional categories.
The first category would consist of lower power personal/portable unlicensed devices, such as Wi-Fi cards in laptop computers or wireless in-home LANs. The second category would consist of higher power fixed/access unlicensed devices that are generally operated from a fixed location and may be used to provide a commercial service such as wireless broadband Internet access.
Unlicensed permission
In October 2006, the FCC issued a report and order and further notice of proposed rulemaking (FNPRM) for new uses of the white spaces. (See “Web links” on page 20.) This order authorizes the fixed/access unlicensed devices mentioned above. Service may begin Feb. 18, 2009. After the first NPRM was issued, the IEEE began work on a standard for these fixed point-to-multipoint systems. The IEEE 802.22 standard is currently going through the final phases of documentation and adoption. (See “Web links.”)
The FNPRM extended the opportunity for comments and testing of portable devices that would detect the availability of unused channels allowing their unlicensed use in the TV bands. Two such prototype devices were tested last year with mixed results. A second round of tests are currently underway with four prototypes.
Yea vs. nay
Predictably, the NAB and the MSTV strongly oppose the use of unlicensed portable devices in the TV bands. (See “Web links.”)
Several organizations are pushing for the unlicensed use of the white spaces. The New America Foundation has issued several reports and has filed comments with the FCC in response to the white spaces NPRM. (See “Web links.”) And several influential information technology companies have formed the White Spaces Coalition, promoting the unlicensed use of the white spaces and developing the prototype devices that the FCC is testing. Members of the coalition include Dell, Earthlink, Google, HP, Intel, Microsoft and Samsung.
These organizations counter the assertions of the NAB, the MSTV and other companies that oppose the unlicensed use of the TV bands, claiming that it is imperative that the commission consider the enormous social and economic opportunity costs of accommodating the unnecessarily restrictive (and spectrally inefficient) recommendations of self-interested spectrum incumbents.
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