FCC Reveals Crucial Piece of TV Channel Repacking Method
(Note--the headline was modified to reflect updated information on the issue.) WASHINGTON – The Federal
Communications Commission has quietly revealed what amounts to its methodology
for repacking TV channels in the post-incentive auction spectrum band. The
agency released a new version OET-69 software that it intends to use for the
repacking, and is seeking input on its efficacy.
Issued by the commission’s Office of Engineering and Technology, OET
Bulletin-69 describes the calculations used to forecast the coverage area
and interference potential of full-power and Class A low-power TV station transmissions.
OET-69 is based on Longley-Rice, an analog-era methodology that yielded
short-comings when applied after the DTV transition.
The new version is dubbed “TVStudy.”
“The new software operates on modern computer systems, and it runs much faster,
provides greater accuracy in modeling and analysis, and is easier to use and
more versatile than the existing software,” the FCC’s Notice stated. “In
addition, the TVStudy software will allow us to perform the types of analyses
that are needed to support the proposed incentive auction.”
In giving the FCC the authority to hold incentive auctions, Congress directed
the agency to “make all reasonable efforts to preserve… the coverage area and
population served of each broadcast television licensee” using OET-69.
The commission notes that while OET-69 sets forth several values for predicting
signal propagation, including desired-to-undesired ratios, receiver antenna
performance, elevation plane transmitter antenna performance and more—it does
not provide specifications for developing software to implement the values, which can lead to disparate results. The
commission is aiming for consistent results by releasing TVStudy and reference
copies of the databases necessary to run it available to the public.
TVStudy was said to be developed in two parts. The first is a Java-based
graphical user interference that draws on data from the applicable databases.
The second is an analysis engine that does the coverage and interference
The OET is seeking comments on the software ranging from general observations
to identification of bugs. It also is soliciting input on additional
capabilities, including methods for identifying populations already subject to
interference, so that new interference is not created by the repacking.
The TVStudy software updates several parameters of OET-69, including population,
terrain, inaccuracies in the FCC database, antenna beam tilt, calculation of
depression angles, precision of geographic coordinates, establishment of cell
grids and treatment of internal Longley-Rice warnings.
With regard to population, the current OET-69 relies on data from the 1990 U.S.
Census. The 2010 count, used by TVStudy, indicates a 24 percent increase. The
new software also relies on one-arcsecond terrain data versus three-arcsecond,
meaning land elevations are reported at every one versus three seconds of
latitude and longitude, providing greater accuracy.
As for inaccuracies in the FCC database, the commission seeks feedback on how
to detect and correct them. Some examples given were negative beam-tilt values,
swapped values for mechanical beam-tilt and orientation, missing maximum values
for directional antenna patterns, missing or incorrect directional antenna
flags, and effective radiated power values entered in dBk instead of kilowatts.
Updating beam-tilt calculations, TVStudy uses beam-tilt values provided in the
commission’s Consolidated Database System, rather than a fixed value as OET-69
OET-69 Vers. 1 also contained an error in calculating depression angles—the
vertical value between a DTV transmitting antenna and a given receive site—that
caused this value to be calculated based on antenna height above ground, rather
than above mean sea level, creating errors in radiated power calculations. The
error is corrected in TVStudy, the commission said.
The new software also uses full-precision geographical coordinate data from the
U.S. Census, calculated to around 0.0004 seconds of latitude and longitude. The
old software rounded to the nearest second, possibly due to “computational limitations,”
the commission said.
The new cell-grid approach uses a global rather than a unique calculation
applicable to all cells so that interference impact can be predicted at the
Longley-Rice warnings occur when unrecognized terrain profiles are entered. The
Longley-Rice Irregular Terrain Model is based in part on signal path-loss
measurements made by the U.S. Commerce Department over several different
terrain profiles. The data was used to create generalized terrain models, but
those not represented are “flagged” as being “unusable or dubious,” the Notice
The old OET-69 software overlooked this in the DTV Table of Allotments used to
repack TV stations after the digital transition. Consequently, flagged areas
were presumed to have coverage, whether they actually did or not. The Notice
said this was found to be “typically not unreasonable,” even though the
methodology was modified for the Satellite Home Viewer Act.
The OET wants to know if it should continue assuming coverage in flagged areas
or apply some other method.
The new software is available at the commission’s website at http://data.fcc.gov/download/incentive-auctions/OET-69/. Installation and operating instructions
are included as separate files, as are links to the necessary correlative
The software was developed on an Apple iMac, but “it is expected that the
source code can be compiled on other Unix-like platforms,” the Notice states. “Compatibility
of the C source-code with Microsoft Windows-based compilers is not guaranteed,
but only minor modification would be expected. The Java code, which was
developed in Java version 1.6, is expected to be platform independent. In
addition to the source code, a fully-compiled version of the software is
supplied for use on Apple computers running OS10.6 or higher. The software also
requires certain MySQL client libraries, which can be obtained by installing
MySQL Community Server (available at no cost from Oracle). To ensure
compatibility, MySQL Community Server version 5.529 is recommended.”
Comments are due on the software update, ET Docket No. 13-26, March 21, 2013.
Replies are due Aril 5, 2013.
~ Deborah D. McAdams
June 20, 2011, “Congressman
Asks FCC to Explain its Spectrum Analysis Model”
John Dingell (D-Mich.) wants to know how many people would lose over-the-air TV
if broadcasters lose 40 percent of their spectrum. Dingell is calling on the FCC
to explain its method for redesignating 120 MHz of broadcast spectrum for
Nov. 23, 2009, “Digital
Coverage is Hot at IEEE Symposium,” by Doug Lung
Irregular Terrain with Obstructions Model (ITWOM) includes the use of clutter,
rather than diffraction, to calculate losses in the LoS range and on the far
side of obstacles. ITWOM does away with the averaging present in ITM, except
for Troposcatter paths. LoS and diffraction losses are determined on a
point-to-pixel basis, eliminating the "smearing" present in ITM.
Feb. 10, 2009, “Fixing
DTV Coverage Problems,” by Doug Lung
In December the
FCC released maps comparing stations' analog coverage with their DTV coverage.
They also offered some tools for filling in any holes in DTV coverage.
April 14, 2008, “Is
it Time to Replace Longley-Rice?” by Doug Lung
of the Longley–Rice propagation model used in FCC coverage and interference
studies have been known for some time.