In yesterday’s NAB wrap-up “NAB Reveals, And Revels In, 3.0 Progress,” one of the things I wrote about was the ATSC 3.0 Broadcast Pavilion at the back of the South Upper Hall at the Las Vegas Convention Center where the ecosystem for the next-gen TV system was on full display.
One of the booths in the pavilion was devoted to Layered Division Multiplexing (LDM) and for the story I spoke with Pablo Angueira, associate professor in the Department of Communications Engineering at the University of Basque Country, to unpack LDM a little bit for the readers.
In the story, the professor explained how LDM will allow the transmission of two signals on the same channel, one on top of the other -don’t confuse this to mean only two TV channels, such as a broadcaster’s main channel and one digital subchannel.
Rather, Angueira is talking about a robust service — one that can withstand low signal to noise (I like to think of a mobile service delivered to a viewer in a café at and a little below street level) and one that benefits from low noise and lots of signal to push oodles of data through the pipe, like Ultra 4K.
It’s up to the consumer receiver — an Ultra HD television, gateway or small mobile device of the future — to decide whether to decode one or both signals.
That’s where I left things in yesterday’s story, because I didn’t want to get too deep in the LDM weeds.
However, another important aspect of Angueria’s presentation focused on using the two services in a way that enables a network of stations in a geographical area, such as state, to transmit via an SFN common programming while giving them a means to reach their local audiences over the air with programming tailored to their individual markets.
In this scenario, broadcasters could put the less robust signal on top of the more robust signal, says Angueiraz. “The reason to take this approach is to enable the reception of local content on a single frequency network,” he says.
“Imagine Ohio State Television. All transmitters in Ohio will be transmitting the same channel on the same frequency at the same time, because they use one channel in spectrum,” he says. “But the big drawback is you can’t deliver local content to different cities in Ohio because with an SFN you need to send the same [precisely timed signal] to everyone.”
“With Layered Division Multiplexing, you can put the common content in the upper layer, so that every city in Ohio will get Ohio State Television, and if you live in Cincinnati the lower layer there would deliver the Cincinnati channel,” he says.
Akron residents, however, would get their local channel on the lower layer of the signal transmitted there, and so on throughout the state, he says.
I don’t cover television in Europe, so I am not very familiar with the nuances and peculiarities there, and I suspect the professor’s example may be more suited to Spain than Ohio because I doubt all of the public broadcasters in Ohio are on the same channel.
However, it seems to me that this strategy could be deployed by local broadcasters in a given market to deliver hyperlocal content to a geographic area that justifies doing so based on demographics or financial considerations while continuing to blanket their market with common TV service.
On the other hand, because ATSC 3.0 is IP-based and there has been lots of work done on developing that aspect of the next-gen TV standard, it might make more sense to offer hyperlocal coverage over the Internet.
Here’s the thing, ATSC 3.0 gives broadcasters so much to ponder about the services they offer, how they deliver them and where and how to make money, that there probably is no right or wrong approach. The answer more likely will be based on factors specific to individual stations.
But isn’t nice to know that there are so many options?
The LDM exhibit on the ATSC 3.0 Broadcast Pavilion was the co-creation of the Communications Research Center from Canada, the Electronics and Telecommunications Research Institute from South Korea, the National Engineering-Research Center from China and the University of Basque Country.