A Channel-Sharing Proposal for ATSC 3.0

How TV stations can get to the future without sacrificing the past July 8, 2016

JOHNSTON, IOWA—One of the questions that has been on my mind and the minds of many of my colleagues around the country is, how does ATSC 3.0 become a viable broadcast standard? Given the relatively short history of ATSC 1.0 compared to the NTSC standard it replaced, it will already be a challenge in the consumer market space given the number and relative newness of the televisions that have been purchased over the last few years.

Add to the mix, the uncertainty of the spectrum auction, the associated quiet period and just when stations will be able to talk to each other again and what will they be able to say. However, planning for the future is a requirement, not an option and not an indication of whether a station is participating in the auction or not. Remember that participation doesn’t guarantee a station that their offer will be accepted and if it is not accepted, they still have to deal with the future as a television station.

So for whatever reason or reasons, here I am working for a television station in a market with other television stations that are still on the air and we all believe that ATSC 3.0 is the future television broadcast standard. So we are all dealing with the same question, how do we get to the future without sacrificing the past? More succinctly stated, how do we get to the new mobile audience without disenfranchising the traditional fixed audience? Remember that for the foreseeable future, the traditional audience is either directly or indirectly paying the bills.

One proposal I have come up with is that one of the stations in each market should become the initial ATSC 3.0 facility and partner with some or all of the other stations in the market in a channel-sharing arrangement. I will use the Des Moines, Iowa market as my hypothetical example.

Iowa Public Television’s KDIN currently broadcasts an HD stream, two, potentially three SD streams and an audio-only service. For KDIN to make the jump to ATSC 3.0, we would have to be able to continue to supply our existing services to our audiences. No single ATSC 1.0 partner station would have the capacity so it would require multiple partners each carrying a service, possibly two.

Fig. 1: Within a few kilometers of the KDIN transmitter site are six additional full-power television stations. This map shows the FCC contours with the projected coverage for each station is pretty similar with one exception.
Click on the Image to Enlarge

Within a few kilometers of the KDIN transmitter site are six additional full-power television stations. As you can see from the map (Fig. 1) that I have generated that shows the FCC contours, the projected coverage for each station is pretty similar with one exception. Even the exception is not intolerable when I factor in that Iowa Public Television is a statewide network of nine full-power stations and in the areas where the coverage from the exception is less, there is another full-power IPTV station supplying the same content as KDIN.

Actually more of a concern would be the station that is showing the greatest FCC contour as it is a low-band VHF station that has much lower signal density in the near field than the other high band VHFs and UHFs. I realize that rather than using FCC contours I would want to use more accurate computer models to evaluate coverage but as I said, this is a hypothetical example and a whole lot more science and engineering need to be factored into the process before any commitment could be made, but based on the material presented, the concept seems valid.

As a starting point I will use what I consider to be the worst case scenario where the partnership requires four additional stations. A simple arrangement would be that all five partners have an HD simulcast service on the ATSC 3.0 transmitter. Simultaneously, the IPTV bouquet of services is spread across the four partner stations with one taking the HD and the other three taking one each of the SD services.

Based on the information gathered in the 2014 channel-sharing study commissioned by the CTIA, using the latest encoder technologies, the study demonstrated that by making some judicious decisions, encoding multiple HD streams on a single ATSC 1.0 channel is quite feasible; so is adding additional SD services. So while not minimizing the challenge of working with four partners to carry all of KDIN’s services, there doesn’t seem to be a technological roadblock to making the concept work.

What I would be most concerned about is the PSIP data for KDIN. The CTIA study did show that two stations could combine on to a single channel and still maintain their unique station identity in PSIP; I am proposing that a single station’s PSIP data would be spread out over four distinctly different RF channels. So I reached out to my friend Dr. Rich Chernock, chief science officer for Triveni Digital and his colleague Kota Buddharaju, also with Triveni Digital.

After explaining my concept, the questions were pretty simple. Will spreading the PSIP data for a single station over multiple RF channels work? Will the station be able to maintain a cohesive identity at the consumers’ receiver?

The answer to the first question is yes. PSIP allows for the management of major and minor channel numbers and the appropriate channel labels. So that is great news. The answer to the other question is a little less cut and dried as it would depend on how the receiver manufacturer implemented PSIP in their devices.

Ideally, you would hope that as a viewer channels up or down, when they reach Channel 11, which is KDIN RF and virtual channel, the appropriate major and minor channels would sequence in the appropriate order. However, it is conceivable that there may be implementations of PSIP in receivers where this may be too complex, and the receiver itself may just ignore some or all of the PSIP data and the KDIN service could end up sequencing as part of the channel array on the host station.

We encountered something similar to this when we implemented a reading for the blind audio-only service on our digital multicast. The service originally went out with no identifying data to associate it with a major or minor channel. These services in the past were exempted from paying copyright fees based on the fact that they originally went out on a subcarrier of an FM transmitter that could not be received by conventional FM radios, but instead required a modified receiver that was fixed tuned to the host station’s frequency and incorporated the subcarrier demodulator necessary to receive the reading service.

The concept for incorporating this in the television digital bitstream included a fixed PID and special set-top boxes that were again locked on the host station’s channel and tuned to the specific PID for the reading service.

While this worked great, we quickly discovered that almost every digital television receiver on the market did not ignore this unassociated audio stream but instead received and demodulated it as part of the DTV service. Some receivers labeled it as .4 or -4 while others made it .99 or -99. Some associated it with the RF channel while others associated it with the virtual channel. Virtually none of the receivers on the market ignored this theoretically ambiguous data stream. Long story short, I would love to see some testing done to see how receivers in the field react and display single station PSIP data that is distributed among multiple RF channels.

So conceptually what I am presenting is an idea on how stations in a market could cooperatively develop the ATSC 3.0 audience while minimizing the initial impact to the ATSC 1.0 audience. However, it is vital to go into an idea like this with a long-range view. An arrangement like this would have to have the flexibility to recognize that over time, members of the group would want to cease operations in ATSC 1.0 in favor of 3.0. They may want to migrate some service from 1.0 to 3.0 while still maintaining other services on a 1.0 host station or a partner station may decide to simply cease all 1.0 in favor of 3.0. My idea isn’t a perfect solution but it conceptually provides a migration path to 3.0 without companion channels.

One real wildcard in all of this is the consumer product manufacturers. At CES and most recently at NAB, I saw a number of silicon implementations of ATSC 3.0 tuners. While they are still early versions, the ones I saw were ATSC 1.0 and 3.0 capable. Very soon, South Korea will begin test broadcasting an ATSC 3.0 service with an expected full implementation sometime in 2017. WRAL-TV in Raleigh, N.C. commenced ATSC 3.0 experimental broadcasts last week.

I suspect in the not too distant future, the digital television sets available in the U.S. will have ATSC 3.0 capability so the consumer marketplace may become ATSC 3.0 enabled without really knowing about until they do a channel scan.

Another interesting consumer technology is the gateway device that incorporates this same ATSC 1.0/3.0 tuner into the home Wi-Fi router and enables the delivery of ATSC services to devices running appropriate apps connected to the home network. It is not inconceivable to think that the home infrastructure for ATSC 3.0 may actually lead the rollout. In the words of The Great One, Wayne Gretzky, “I skate to where the puck is going to be, not where it has been.”

For more on this subject, visit our ATSC 3.0 silo.

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