CLEVELAND—The latest field testing of ATSC 3.0 from the NAB-CTA-sponsored experimental Next Gen TV station, Tribune’s WJW Fox affiliate in Cleveland, successfully demonstrated the ability of 3.0 to deliver SHVC-encoded LDM base and enhancement layers for mobile and high-quality UHD HDR fixed receivers, respectively.
“The test was an immense success. We assembled a commercial system to show ATSC 3.0’s ability to support enhanced over-the-air services in challenging urban environments,” said Alan Stein, VP of Technology Development and Standards at Technicolor.
Several use cases with a variety of test scenarios were tested in Cleveland, he said. Among them were carrying a 1080p Layer Division Multiplexing (LDM) base layer and an LDM enhancement layer with 4K and Technicolor’s SL-HR1 high dynamic range data; a 540p base layer and 1080p/HDR enhancement layer; and two high-quality SHVC services.
“When we did the HD and the 4K, the core PLP [physical layer pipe] was QPSK [modulated] 7/15ths [bits per symbol] code rate. That was the video base layer and audio,” said Stein. “The enhancement layer was 64 QAM, 9/15ths code rate, and that carried the SHVC enhancement layer data and the SL-HDR1 metadata.”
For that configuration, the core PLP capacity was 4.5Mb/s, while that of the enhancement PLP was 17.5Mb/s, he said.
SHVC, or scalable high efficiency video coding, is a particularly useful technology when combined with LDM because it enables broadcasters to enhance the bits delivered in the core layer to create the highest quality images on fixed receivers while preserving more bandwidth for additional services, such as mobile.
Although not nearly as robust as the core layer, the enhancement layer has a much higher throughput, capable of carrying the heavy data load needed to build the 4K UHD HDR image in a fixed receiver.
The Cleveland test demonstrated that despite being less robust, the enhancement layer—as well as the core layer—could be received downtown at the offices of test participant Osborn Engineering, an environment in which the transmitted signal was subject to reflections off adjacent buildings, which creates multipath interference.
“At the video coding layer, the enhancement layer is about 3x to 4x more bits, when we think about how the video encoder is set up,” said Stein. “But that is mitigated by having less physical layer robustness. The FEC [forward error correction] coding and using QPSK versus using QAM at the physical layer, the overhead is actually quite less.”
To test the ability of 3.0 to handle two high-quality signals, the test organizers worked from the assumption that a Next Gen TV signal in a 6MHz channel can carry 20Mb/s to 25Mb/s. With that in mind, PLP configurations were set to stay around 10Mb/s of total capacity. “The idea was we could have two services each taking 10Mb/s of capacity and have a multicast of two high-quality services,” he said.
That required the video bit rate to be reduced. For the core layer, it was reduced to 1Mb/s and the enhancement layer was set to 4Mb/s, “where the physical layer parameters gave us an aggregate of 10Mb/s capacity,” he explained.
Rather demanding test footage of a Washington Capitals hockey practice supplied by NAB was used. The footage was “fairly challenging” because of the ice, the ice spray from players stopping short, the players’ bright, saturated red and blue practice jerseys and the fast edits in the piece, he said.
“Subjectively, the quality delivered was acceptable, even at those very challenging bit rates and even with a first-generation SHVC card,” said Stein.
To make the test happen, organizers assembled a team of 3.0 vendors and experts, including: Technicolor, which encoded content with its SL-HDR1; ETRI, the South Korean-government funded research institute, which supplied LDM technology and a professional 3.0 receiver; Kai Media, which provided a professional HEVC and SHVC and SL-HDR1 decoder; and LG, which supplied a consumer OLED 4K/UHD/HDR TV. Technicolor also provided its Intelligent Tone Management (ITM) technology to convert source content from SDR to HDR using equipment provided by Cobalt Digital.
The Cleveland test isn’t the first for Technicolor, Stein said. A few years ago, it worked with Sinclair Broadcast Group to test mobile reception of a 3.0 signal transmitted from a Sinclair experimental station on board a train from Baltimore to Washington, D.C.
However, a lot has happened since then. “We are really happy to see this [3.0] commercialized,” said Stein.
Kelly Williams, senior director of Engineering and Technology Policy at NAB, is pleased with the testing for another reason. “The ability to deliver multiple broadcasts of enhanced video—in this case content encoded with Technicolor SL-HDR1—on a single channel will help to transform the economics of the broadcast industry, and meet the high expectations that consumers have today,” he said.
For a comprehensive source of TV Technology’s ATSC 3.0 coverage, see ourATSC3 silo.
