The CDS test lab helps stations configure technology used to process both baseband and IP signals for their designated coverage area.
As more terrestrial television stations in the U.S. have been making the transition to ATSC 3.0 operations, the testing and compliance lab at Comark’s headquarters in Southwick, Mass., has been a busy place.
The lab is home to the Comark Digital Services (CDS) unit, a division of Hitachi Kokusai Electric Comark, which helps stations configure and install all of the technology required to process both baseband and IP signals for their designated coverage area—sometimes simultaneously. Southwick is also where Comark’s solid-state, high-power ATSC transmitters are manufactured and serviced.
To date, CDS has worked with dozens of stations to get them on air with an ATSC 3.0 signal, although these are still the early days of the transition and many engineers are confused by what’s actually required to operate a NextGen TV service to its fullest potential.
“ATSC 3.0 is a paradigm shift from what was once transport stream-based workflows [ATSC 1.0] to all IP,” said Joe Turbolski, Vice President of Sales & Marketing at Comark. “There’s a lot of complexity in setting the system up and making sure the separate components talk to one another correctly.”
He said a broadcaster could go out and buy all of the components separately and try and configure it themselves but Turbolski’s team has the experience (and the fully functioning lab) to put it all together and make it work seamlessly. The equipment packages they recommend to customers are pre-certified to interoperate and are backed up with Comark’s engineering support.
“There’s no learning curve for us, we’ve done this before,” said Turbolski, adding that the lab has everything from signal sources to encoding to reception devices (linear TV, set top boxes, mobile devices, in addition to test and monitoring) that are used for testing and interoperability compliance. In fact, they have the entire signal chain replicated in the lab that is based on prior experience with customers in the field.
“We’ve been broadcasting ATSC 1.0 and 3.0 live in our lab (from a small antenna to another small antenna) for three or four years,” said Turbolski. “The lab is our tool to test what our customers want and provide them with a way to make it all work cost-effectively. We’ve already navigated the learning curve on this technology, so we can save you time and money.”
Indeed, CDS was actually launched in the mid 1990’s, as the broadcast industry was making its first major transition from analog to digital service. That operation was headed by Mark Richer, who went on to serve as President of the Advanced Television Systems Committee (ATSC) until his retirement in January 2019. Today Tim Hosmer, Director of Comark Digital Services, is filling the lead role.
The mission for CDS is to help stations select the right equipment and suggest components (like the encoder, transports stream stack, and IP gateway), based on the “real world” testing it performs in their lab. The group’s signal distribution services are based around the ATEME TITAN Live software-based encoder, which supports a variety of outputs and is used by both ATSC 1.0 and 3.0 broadcasters to convert their SDI signals to IP.
After the TITAN encoder, stations must deploy an MPEG media transport protocol (MMTP) or ROUTE packager that feeds an IP broadcast gateway. The gateway is used to configure what’s going out over the air. In ATSC 3.0, you can not only send out linear programming but also adjust the signal that’s being broadcast to meet different levels of bit error rate requirements. These are called physical layer pipes (PLPs).
“Inside my 6 MHz channel I can stack multiple PLPs and I can assign each of those PLPs to be used in a different application,” said Turbolski. “If I am sending out a lot of HD or UHD signals, I need a pretty large pipe (bandwidth). So, you can adjust the modulation & coding in one of the PLPs to provide a high throughput but it’s not very robust in terms of receivability.”
He added then that stations can add another PLP in that same 6 MHz channel and change the modulation & coding so that it may not give you as much throughout but it’s much more forgiving on its signal-to-noise (SNR) requirement. You could have 1, 2, 3, 4 or up to 64 PLPs (although no one’s doing that right now). Most today use 2 to 4 PLPs.
The most typical package offered includes a TITAN Live encoder and an ATSC stack (from companies like Enensys Technologies, DigiCAP and Triveni Digital). These have all been tested in Comark’s lab in Southwick, Mass. and deemed well suited to ATSC 3.0 broadcasting.
TITAN Live provides MPEG-2 encoding for ATSC 1.0 and HEVC encoding for 3.0, simultaneously. It also provides a customer who wants to send the exact same stream over an OTT signal. The encoder can then be set up to output the HLS protocol signal. This in turn feeds an origin server that then feeds a content distribution network, which goes to the subscribed end user. Making it all work is part of CDS’s value.
“We try to make the process as easy as possible,” said Turbolski. “We work with each customer to find out which technologies make the most sense and then pre-configure it in our lab before sending it out to the customer. We can either send somebody to the site to install and commission it or we can complete final commissioning remotely from our lab in Southwick. (This was done a lot during the worst of the pandemic).”
Looking at the workflow of a typical TV station, you have program capture (cameras feeding master control and postproduction), which goes out to a playout system. It’s all baseband SDI processing at this point—it’s uncompressed HD SDI programming at 1.5 GB/s). The physical layer in ATSC 1.0 is an MPEG transport stream. In ATSC 3.0, everything is IP once you get into the encoder.
To broadcast over the air, whether that’s 3.0 or 1.0, the first thing you have to do is compress the signal to save bandwidth on the output. The encoder takes the baseband signal and reduces the amount of bits. Using MPEG-2 for ATSC 1.0., an HD signal can be reduced to 8-12 Mb/s. ATSC 3.0 uses H.265 encoding, which is 3x more efficient than ATSC 1.0’s MPEG-2 or H.264 compression scheme and can reliably send out good quality in IP at 4-6 Mb/s. In ATSC 3.0, once you get into the encoder, everything becomes compatible with an IP infrastructure.
“If you look at the workflow of a HD SDI signal, you have HD coming into the encoder, it gets compressed using H.265 HEVC,” said Turbolski. “Coming out of that is an IP stream at 4 to 6 Mb/s. In ATSC 3.0, it has to go through additional levels of processing before it arrives at the transmitter.”
The other common application used by stations today is mobile reception. Those environments are very difficult to receive in, so you need the smallest possible signal-to-noise (SNR) to receive those signals. Broadcasters tend to crank the bits down to ensure reliable reception in mobile devices. Even when those devices are in a moving car. Turbolski said this workflow allows a station to “pull the signal out of the noise,” and get good transmission results.
All of these desired signal requirements (and more) are set up by CDS using an IP broadcast gateway.
CDS’s cost structure include a one-time capital expenditure , depending upon the size and complexity of the system configuration. Stations can then enter into a service level agreement with CDS to obtain recurring software updates and on-site or remote maintenance when required.
CDS also offers customers signal monitoring systems, whether they be portable or rack-mounted, that can look at anything from the output of the encoder (analyzing multiple IP streams) to the output of the transmitter. Test and monitoring packages are available from under $5k to $60k depending on the feature set required by the end user.
“What’s happening is that the experience of the new generation of engineers is very different than those that had years of broadcast experience before them,” said Turbolski. “[The new guys] understand network engineering, Cisco switches and IP and Ethernet. They don’t necessarily understand the RF part. With the current generation of solid-state transmitters, CDS is probably a better fit for what’s happening now than it was 20 years ago, as transmission has gotten so much more complex. Broadcasters are having to do a lot more in today’s multi-platform world.”
To date, about 24 TV stations in the U.S. are now broadcasting an ATSC 3.0 signal, so the lab looks to be a lot busier in the months to come as more stations look to come online with NextGen TV. CDS also works with ATSC 1.0 broadcasters looking to make the move to IP as well.
“Everyone has different needs and we’re here to accommodate,” said Turbolski.
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