Tech Push May Ease Cables HDTV Entry3/21/1999 7:00 PM Eastern
A number of technology initiatives are under way that could
facilitate cable's delivery of high-definition television services on a much sounder
business basis than is possible now, without waiting until next year for outstanding
issues to be resolved.
The efforts fall into three general categories: securing
signals, encouraging broadcasters to adopt more efficient means of using bandwidth and
facilitating delivery over analog systems without waiting for digital set-tops.
One of the biggest issues that cable operators face in any
efforts to serve the early market of HDTV customers is the possibility that the newly
standardized approach to delivering secure signals from set-top boxes to HDTV sets will
not be on the market in time to meet operators' launch schedules.
"There's quite a bit of sensitivity over the
[unresolved] copy-protection issue between the owners of the content and the companies
that want to build the hardware, and we feel like we're caught in the middle,"
said Michael Hayashi, vice president of advanced services for Time Warner Cable.
Industry sectors reached a landmark agreement late last
year on the use of IEEE 1394 wiring technology -- also called "fire wire" and
other names, depending on applications -- as a means of passing HDTV signals from set-tops
to TV sets.
But the battle over what type of copy-protection system
should be incorporated into the chip sets that will process the signals delivered by fire
wire to the TV sets has proved more intractable than parties to the debate had
TV and set-top manufacturers had hoped to deliver
fire-wire-based equipment by the end of this year, but the delay in resolving the
copyright-protection issue is threatening to push hardware implementation well into 2000.
As a result, an expensive interim cable set-top solution
that vendors began talking about last fall has suddenly moved to the front burner.
Time Warner, especially, hopes to have a version being
developed by Scientific-Atlanta Inc. available for a handful of deployments to early
buyers of HDTV sets as soon as field tests that are currently under way are completed,
The issue isn't so much whether cable operators are
enthusiastic about promoting HDTV or not in the early rollout phase, said Bill Wall,
technical director for subscriber networks at S-A.
"If a good customer plugs in a new HDTV set and
can't get signals over the cable plant, this can become a significant
public-relations problem for cable," Wall said.
Time Warner and S-A said the new "HD-2000" box
will address two key needs for operators:
Delivering digital signals using QAM (quadrature
amplitude modulation), which is more bandwidth-efficient than the VSB (vestigial-sideband)
modulation used in over-the-air transmissions; and
Securing signals, which are currently delivered in
the clear, over the few cable systems where HDTV from broadcast and cable-network sources
The HD-2000 is a version of the "Explorer 2000"
digital set-top containing a circuit board that decodes HDTV signals.
When fire wire is ready for set-tops and HDTV sets, the
costly decoding process will reside in the TV sets. This will allow the signal to be
demodulated from QAM at the set-top and passed in compressed form at 19 megabits per
second over the shielded twisted-pair fire-wire connection.
The HD-2000, to be manufactured in limited quantities, will
cost in the same range as the modular receiver/decoders that come with HDTV monitors,
which can run anywhere from $1,800 to $3,000, Wall said.
General Instrument Corp. is developing a separate box, the
"HD-D100," which, when used in conjunction with the "DCT-2000" digital
set-top, would perform essentially the same functions envisioned by the S-A single-box
"The signal will be decrypted in the DCT-2000 and
delivered to the HD-D100, where it will be decoded and sent out the back to the HDTV
monitor," said Dwight Saduma, director of consumer products and services in GI's
The cost of the GI add-on "could run a little south of
$1,000," Saduma said. The HD-D100 will be available sometime in the third quarter, he
For cable companies like Time Warner and Cablevision
Systems Corp., which are moving immediately to deliver HDTV signals, it's important
to be able to secure signals that are currently being delivered in the clear.
With Home Box Office subscribers, for example, who
typically pay around $10 per month for the service, it could cause problems if
HDTV-equipped customers get the high-definition version of the service free-of-charge.
Moreover, said Wilt Hildenbrand, senior vice president for
technology and engineering at Cablevision, many programming components have to be
copy-protected by virtue of the agreements with the original program suppliers.
"When I start talking about delivering HBO in HDTV, or
certain things from the Garden [Madison Square Garden, which is supplying HDTV coverage of
sporting events to Cablevision customers in Long Island, N.Y.], not all of those signals
can be passed around for free," Hildenbrand added.
That means being able to deliver both free elements and
secured elements through the same set-top. But for Cablevision, the QAM piece of the
equation is not as vital as it might be for other MSOs.
"At some point, I'd like to have the signal on
QAM as a more efficient use of bandwidth," Hildenbrand said.
But he quickly added that Cablevision has learned that it
can transmit in VSB over analog systems directly to HDTV sets, which have VSB demodulators
This avoids the costs of adding QAM demodulation at the
premises, so long as there is plenty of bandwidth available above 550 megahertz to
accommodate a guard band and delivery of the VSB signals in the "high 600s" MHz
The VSB signals "can be aligned together,"
avoiding the need for additional guard bands, Hildenbrand noted.
In any event, however the interim approach is undertaken,
"it's necessary that it be done," Saduma said.
"The interest in these solutions is universal among
operators," he added.
Along with spearheading efforts to reach agreement on the
1394 hardware specification, Cable Television Laboratories Inc. has been quietly pursuing
advances that will help to improve carriage efficiency, starting with how broadcasters
multiplex their signals, CableLabs CEO Richard Green said.
"We're working on a method of variable-bit-rate
encoding that allows the broadcaster to multiplex an SDTV [standard-definition digital
signal] with the HDTV signal," Green added.
Broadcasters almost universally have been using fixed-rate
encoders, which consume the full 6 MHz of available bandwidth to compress the HDTV signal
to 19 mbps. But they are extremely interested in a more efficient solution, said Peter
Smith, vice president for technology at NBC.
"In days to come, when we can actually provide an HDTV
program and a second channel that may be in standard-definition, there's a possible
use for that in terms of alternative programming," Smith said.
This could include "the kind of news activities that
we do today," as well as data channels supplementing the Internet with specialized
fare tied directly to the broadcast programming, he added.
VBR encoding, of course, is standard to the encoding method
that cable will apply at the headend and in set-tops, but it would help if broadcasters
apply it in conformance with how it's done in cable, which would eliminate one of the
steps in processing the off-air signals.
Moreover, a uniform approach to VBR that uses intermediate
bits in the MPEG-coding stream to eliminate redundant information would help cable to
apply statistical multiplexing across all signal streams, Green noted.
Stat muxing looks at all of the signal streams of a
multiple-service feed into a 6-MHz channel, arranging the flow so that "fat"
portions of one feed are synchronized with "thin" portions of another, thereby
maximizing the number of feeds that can be delivered over the channel.
In this way, cable hopes to get three HDTV channels over
the 6-MHz channel, or even four, if the more-bandwidth-efficient 720-progressive format is
used, rather than the 1080-interlaced approach.
"We're having technology discussions with
broadcasters about how you achieve more efficiency without hurting the picture
quality," Green said.
In addition, CableLabs is issuing a request for information
from vendors, seeking input on solutions to remultiplexing digital advertising signals so
that they can be readily spliced into the video bit streams, Green said.
While this effort does not directly interface with those by
broadcasters, "I'd think that they would be looking to do the same thing,"