U.S.
Broadcasters Adopting
Some Elements of DVB
American
broadcasters are moving toward adopting European
broadcasting standards, but the efforts remain limited at
best.
by Judah Ken Freed,
"America Watch" columnist in
Euromedia.
The
more things change, the more they stay the
same.
A specialist group
within the Advanced Television Systems Committee (ATSC)
is now working to coordinate the DTV Applications
Software Environment (DASE) middleware standard with the
OpenCable Applications Platform (OCAP) middleware
standard for cable set-top boxes, based on the Multimedia
Home Platform (MHP) middleware specification developed in
Europe for Digital Video Broadcasting (DVB).
In separate
standards development efforts, ATSC is incrementally
moving toward the European model of single frequency
networks, integral to the design for DVB terrestrial
broadcasting systems.
In a conference
call during the week of August 11, members of the ATSC
Technology Group on Distribution (T3) discussed the
combined "D-CAP" standard that combines DASE and OCAP.
Without revealing details of the discussion, ATSC
president Mark Richer said the draft likely would not be
ready for candidate status in time for T3's September 10
"due process" meeting, but it may be ready by the
November T3 meeting.
"No decision was
made in that group about D-CAP," said Richer, noting that
an effort has been underway for a year and half to
harmonise the DASE and OCAP standards.
When completed,
D-CAP will allow compliant interactive TV content to be
carried by both digital cable and digital terrestrial
systems, including widescreen High Definition Television
(HDTV).
"Discussions are
going on about various elements of the draft
specification," Richer said. "We've made tremendous
progress in developing a unified standard, and there is
very strong support for it. We hope to see ballots going
out this fall."
Among the elements
still being discussed is D-CAP support for both
declarative XTML content and procedural Java-based
content for enhanced and interactive TV applications.
Both formats are already present within DASE and OCAP,
Richer said, but the question is what the consumer
electronics manufacturers will support. "We cannot
predict what the marketplace will do."
Support from
consumer electronic manufacturers is crucial. Long
accustomed to renting set-top boxes to subscribers at a
tidy profit, American cable operators are now required to
offer set-top boxes in the retail environment. OCAP was
developed initially to insure interoperability among all
the digital boxes, so a unit purchased for accessing a
cable system in Philadelphia would work just as well if
the consumer moved to Los Angeles.
While CE
manufacturers like Motorola and Panasonic are gearing up
for the retail cable box, if the manufactures of
terrestrial DTV receivers and analogue-digital converter
boxes do not support the D-CAP interactive content, all
of the ATSC development efforts could be in
vain.
While more than 65
percent of all U.S. households receive their free-to-air
local broadcast channels only through subscription cable,
if the CE manufacturers do not support the advanced
services offered by digital terrestrial broadcasters,
many consumers will be left out of the loop. Those most
likely to be disenfranchised, in fact, will be those in
the lower-income brackets who cannot afford to pay for
cable or satellite services.
According to Glenn
Adams, chair of the T3/S17 DTV Application Software
Environment specialist group, the challenges facing D-CAP
often are more economic and political and than technical,
such as making sure that it's feasible or cost-effective
to build set-top boxes or DTV receivers that can handled
all the different kinds of content possible under D-CAP.
"There are big
differences between DVB, ATSC and American cable," he
said. "For instance, OCAP and MHP and voluntary technical
specifications, not legally required standards written
into the law like ATSC."
Because D-CAP has
to go through formal due process under the rules of ATSC,
he said, he added, the specifics of D-CAP development are
kept private to give all the parties room to negotiate
without being prematurely locked into public positions.
"Discussions sometimes can turn on a dime, so that's why
I really can't go beyond saying that D-CAP likely will be
approved within six months."
"On the face of
it," said Peter MacAvock, Executive Director, DVB Project
Office in Europe, "ATSC's DASE and DVB's MHP are quite
similar. Both are based on Java. Both have a presentation
engine and both target broadly the same iTV market. While
the technical details of D-CAP have yet to be resolved,
there is no doubt that MHP will be the focal point of
this harmonisation.
To facilitate this
process, he explained the DVB office has worked closely
with CableLabs to develop the first version of GEM
(Globally Executable MHP), which includes OCAP. "It is
perfectly conceivable that future versions could include
links to other standardisation body's efforts, such as
ATSC in the United States or ARIB in Japan."
MacAvock added,
"The ultimate aim of middleware platform harmonisation is
the
interoperability of
iTV content. Wouldn't it be great if a small content
developer could produce content to GEM specifications,
and be sure that it could run in Europe, North America
and elsewhere?"
Another area of
overlap between ATSC and DVB is development within the T3
group of standards for distributed single-frequency
networks. European DVB broadcasters use this approach for
distributing one television signal regionally and
nationally.
Richer said the
focus within ATSC was creating the candidate standard
CS/110A for synchronising the transmitters within a
distribution network (available as a PDF file download at
ATSC.org).
He noted that
transmitter manufacturer Axcera already has implemented
the candidate standard, and others like Harris have
compliant transmitters in development. "A prototype
distributed network is now up and running in
Pennsylvania," he said, "and we expect to be doing more
on this in the future."
MacAvock observed
that DVB-T transmission is based on COFDM modulation
scheme, which was adopted in 1995 specifically "to
facilitate the deployment of the spectrum saving concept
of single frequency networks deployed on national or
regional levels. In-home repeaters are now on sale in
Europe which boost the DVB-T signal to facilitate set-top
antenna reception in areas where this might be difficult
due to low signal strength. Singapore, Sweden and Spain
operate wide-area single-frequency-networks very
successfully."
COFDM as rejected
in the United States by the Federal Communications
Commission after a controversial field test comparison
with the single carrier modulation scheme called 8VSB,
mandated for ATSC. Critics of 8VSB reception, such as
Sinclair Broadcasting, charged that the wrong type of
equipment was used for COFDM reception, and therefore the
test findings were invalid. Nevertheless, the findings
provided the basis for the FCC ruling against COFDM, a
decision backed by consumer electronics manufacturers,
who were already tooling production lines to produce 8VSB
receivers.
As for using
enhanced 8VSB for single-frequency networks, MacAvock
said, "With appropriate and costly measures, it is
possible to install a type of on-channel repeater.
However, a single carrier system such as 8VSB was never
designed for this type of operation, so it is
questionable how technically viable such solutions will
be."
He concluded, "The
US terrestrial broadcast industry has made a number of
decisions about technologies and business models which
are embodied in the ATSC digital broadcasting standards.
Whilst these are not in line with the thinking in the
rest of the world, we must respect the decisions taken.
After all, the aim of all digital television
standardisation bodies is to promote digital the benefits
of DTV. Each market has its own key to unlock the
potential of DTV." 
.
