You have probably heard a little about broadcaster plans to switch to a new generation of digital TV broadcasting, called “ATSC 3.0”.  But until recently, most of the details were closely held. In May, ATSC held a “boot camp” where the new technology was exposed in some detail. So now we know that carrying this new technology on cable systems will be quite a challenge.

The bottom line is that ATSC 3.0 is incompatible with today’s cable TV technology in almost all respects. That can be overcome by converting or transcoding from the new format to the cable system format. But who is going to do that conversion? The cable operator or the broadcaster? Will broadcasters trust the cable operator to do a high-quality conversion? Retransmission contracts are going to get a lot more complicated. 

Let’s look first at the physical layer. Broadcasters today use 8VSB modulation to achieve a data rate of about 19 Mbps in a 6 MHz channel. Cable operators today typically use 256QAM modulation to achieve about 38 Mbps, since the cable transmission environment is more benign than over-the-air transmission. There is no particular challenge in re-multiplexing broadcast signals to fit that scheme.  

The new ATSC plan calls for a higher data rate, perhaps 25 Mbps in 6 MHz. The new modulation method supports what are called “physical layer pipes” that can carry different signals using different levels of robustness. So, for example, the 6 MHz channel might carry three pipes: audio using very robust modulation (say QPSK), HD video using an intermediate robustness (say 16QAM) and Ultra HD (“4K”) video using a less robust modulation (say 64QAM). In this way, the audio pipe will have the greatest coverage area, the HD pipe less coverage, and the UHD pipe the smallest area.  

In that scheme, the cable system that receives the broadcast signal off-air might be close enough to the broadcast tower to receive the UHD pipe. But maybe not, maybe only the HD video can be received. In either case, the audio must be combined with (and synchronized with) the video before delivery on the cable system. Whose job is that?

ATSC 3.0 is going to include an advanced emergency alert system. There will be two levels of emergency alerts, “basic” and “enhanced.” The basic alerts might be text only, intended for less capable receivers. Enhanced alerts might include maps and other graphics, intended for “smarter” ATSC 3.0 receivers.

One possibility is that emergency alerts will be carried in the most robust physical layer pipe, the one that (in the above example) carries the audio. If so, there may be a need to combine not only the audio but also the emergency alert with the video before delivery on a cable system. Who carries the liability if that gets messed up?

ATSC 3.0 will be a combination of broadcast and broadband delivery. In fact, some elements of a program might be delivered off-air and other elements via broadband.  So, for example, English language captions might be delivered via broadcast and Spanish language captions delivered via broadband. Those off-air viewers without a broadband connection will receive only a part of the programming features.

Another challenge is that ATSC will deliver programming as files, rather than as MPEG Transport Streams as is done today. Cable systems today usually deliver video-on-demand as files, so that technology is understood. But broadcast TV and other linear video channels are delivered as streams. ATSC needs to define a way to convert these ATSC 3.0 files to streams that are compatible with today’s cable systems.

Closed captions will also be delivered as files, rather than (as today) embedded in the video streams. There are various specifications for “timed text” file formats that might be used in the ATSC 3.0 standard. But current practice in cable is that set-top boxes recognize the CEA-708 standard which defines a particular format for digital closed captions. And FCC Rules specifically point to CEA-708. It’s not yet clear how the ATSC 3.0 closed caption files will be formatted, and how they will be converted to CEA-708 format and embedded into video streams, and who will do that.

“Smart” ATSC 3.0 receivers might be both connected to a cable set-top box over an HDMI interface to receive video and audio, and connected to broadband to receive enhanced elements of a TV program. But the “smart” TV receiver is rendered “dumb” by the HDMI interface, which can pass video and audio but not system metadata. So ATSC is planning to use a scheme called “watermarking” to tunnel metadata in both the video and the audio streams. The watermark might, for example, identify the broadcast channel and the program. It might contain a URL to direct the receiver to retrieve enhancements such as interactive applications using the broadband connection. It might contain a program guide. It is not clear whether cable operators are required to carry the watermarks under existing FCC “must carry” regulations.

There are other ATSC 3.0 challenges for cable operators as well, but the biggest challenges face the broadcasters themselves. The transition from analog to digital ATSC 1.0 relied on broadcasters having a second TV channel. How will they transition to ATSC 3.0 without having that second channel?