http://www.tvtechnology.com/regulatory-&-standards/0012/a-look-inside-the-cleveland-futurecasts-atsc-30-transmission-test/276567
Inside the Cleveland Futurecast ATSC 3.0 Transmission Tests
Head-to-head comparison with ATSC 1.0 A/153
July 13, 2015
Broadcast Engineering Extra
By Bob Kovacs
Why This Matters
The future of television broadcasting may be at stake, and this is one possible
direction.
CLEVELAND- Work on a future ATSC 3.0 standard is moving swiftly, with officials
from GatesAir, LG and Zenith's research and development lab predicting that
there will be a "candidate standard" by the end of this year. And with an
experimental high-power ATSC 3.0 transmitter available for test broadcasts at
any time during the day, the GatesAir/LG/Zenith Futurecast proposal shows some
interesting data from recent tests in Cleveland.
Licensed as WI9X3Y in the Cleveland suburb of Parma, Ohio, and owned by WJW's
parent company Tribune Broadcasting, the full-power UHF station operates on
Channel 31 with an ERP of 430 kW. This was the digital broadcasting plant for
TV station WJW in Cleveland, which turned it off permanently during the analog
shutdown in July 2009.
Until May 2015, when the Futurecast team consisting of GatesAir, LG and Zenith
negotiated with WJM and the FCC to revive the digital broadcasting plant as a
test bed for proposed ATSC 3.0 technology. Since then, the Futurecast team has
conducted transmission tests of both ATSC 1.0 and ATSC 3.0 for extended hours,
to gain experience with the capabilities of ATSC 3.0 and compare it to the
existing standard.
A previous test of Futurecast was held last October in Madison, Wisc., where
three early morning hours were set aside for an ATSC 3.0 demo. The Cleveland
facility allows the same team to broadcast at any time without concern for
viewers or the station's schedule. The test participants said that some things
learned in the Madison tests were accommodated in Cleveland.
"In Madison, we learned a few things in terms of acquisition and tweaked that
for this test," said Wayne Luplow, vice president of Zenith's R&D lab.
75,000 DATA POINTS
To date, the Cleveland test has collected information from more than 75,000
data points. These include far more challenging conditions than those
experienced in Madison, including tall downtown buildings as well as
transmission near a large body of water (Lake Erie). John Taylor, vice
president for public affairs and communications for LG Electronics, said that
there was continual improvement since the Madison test, particularly with
software for mobile acquisition and improved multipath performance.
Some of the important findings so far have compared the Futurecast ATSC 3.0
technology with the current ATSC 1.0 A/153 mobile standard. The data collected
by the Cleveland team shows that Futurecast's semi-robust HD stream (720p) is
only a bit less robust than the A/153 mobile standard: Futurecast can get a
solid HD signal through about 78 percent of the time, while A/153 scores about
83 percent but with much lower-quality video. Futurecast's most robust mode
scores a solid reception score of 91 percent, and that is with a clean
DVD-quality SD video feed. The current ATSC A/153 mobile system has a video
feed that is sub-SD in quality. The modulation and encoding are such that the
most robust Futurecast signal can be received even if noise exceeds the signal
level by 1.2 dB.
The Futurecast ATSC 3.0 proposal uses OFDM modulation and HEVC encoding. The
modulation scheme means that a 6 MHz broadcast channel can carry about 26 Mbps
of data, while HEVC encoding-sometimes referred to as MPEG-5-means that video
streams have considerably more efficient encoding than the MPEG-2 encoding used
for ATSC 1.0.
As in Madison, the Futurecast broadcast consisted of three simultaneous
streams: 256QAM at 15.7 Mbps for a 4K stream, 16QAM at 1.25 Mbps for the
semi-robust 720p stream and QPSK at 0.59 Mbps for the ultra-robust 480p signal.
SWEEPING OUT THE COBWEBS
Prepping WJM's old digital transmitter for around-the-clock Futurecast testing
took more than just sweeping out the cobwebs from a facility that hadn't been
used in six years. The transmitter-which is not a GatesAir/Harris
product-needed two of its three IOT tubes replaced. Even with tube replacement
and other re-commissioning work, the transmitter can be finicky.
"When you turn it off for a couple of weeks, it's like starting from scratch,"
said Tribune Broadcasting's director of engineering operations Bill
VanDuynhoven. "We're still working on it."
In addition to a look at some of the data from Futurecast's tests, the
Cleveland presentation included a discussion of an advanced early warning
system called AWARN that is incorporated into the ATSC 3.0 proposal. With
AWARN, far more than just an emergency announcement crawl can be transmitted.
The warning information can include maps, detailed full-motion video weather
reports and other emergency information, even as the main broadcast continues
uninterrupted.
Another tantalizing possibility with Futurecast and AWARN is a "wake-up bit"
that can turn a TV on or switch it to emergency information in the event of an
imminent disaster. This is still being worked out, but the goal is to target
warnings by geography, so that TVs located 25 miles east of a transmitter
aren't affected by an emergency event 25 miles west of the transmitter.
Turnout for the Cleveland event-part of which was held at the Rock & Roll Hall
of Fame-was excellent, with more than 60 attendees. Many of them were engineers
from TV stations in or near Cleveland, and it was the first time many of them
had seen an over-the-air 4K broadcast.
Looking at the off-air signal on a 4K display, it didn't take long for some to
see the possibility in 4K broadcasts.
"The video encoding [in the Futurecast broadcast] is so much better than what
we have," said Karl Lahm, an engineer with a Univision broadcaster in Cleveland.
Other than a new encoder/modulator, Futurecast is designed to work with current
digital transmitters and all existing passive RF gear, such as antennas and
mask filters. The only other change to the transmitter is to reduce its power
slightly (by 0.5 dB or so) due to the higher peak-to-average ratio of
Futurecast's modulation.
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