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Singing the digital must-carry blues

Fri, 10/31/1997 - 7:00pm
Jeffrey Krauss, Pushing the Cable Signal Carriage and President of Telecommunications and Technology Policy
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By Jeffrey Krauss, pushing the cable signal carriage and President of Telecommunications and Technology Policy

But one thing is certain—the industry is relying on the NCTA to take the lead in lobbying these important techno-political issues at the FCC, but I've heard disturbing rumors that the NCTA is thinking about eliminating its Science & Technology Department. That would be a mistake.

When Congress amended the Communications Act in 1992, it required most cable systems to allocate up to one-third of their capacity to carry broadcast signals. And it established "retransmission consent," which allows TV stations and broadcasters to negotiate a private deal for carriage. The idea was that cable would have to pay for access to these TV channels; either cash or non-cash deals are permissible. But only commercial stations can choose to negotiate a retransmission consent deal; non-commercial stations must be carried under the must-carry regime.

You remember that in 1993 some TV stations chose retransmission consent, but couldn't reach agreement with cable operators, and were dropped from some cable systems. Temporarily. Eventually, all the stations that demanded retransmission consent payments, and all the cable systems that refused to pay, were able to come to some agreement.

The digital difference

Starting in 1998, TV stations will begin broadcasting a second channel, using digital techniques. They may decide to broadcast a single high definition (HDTV) program, or a multiplex of four to eight standard definition (SDTV) programs, or some combination of video broadcasting and data broadcasting. For some period of time, probably 10 years or more, TV stations will continue transmitting their analog programming on one channel while they simultaneously transmit digital programming on another channel.

Broadcasters will use a digital modulation method called 8-VSB, while cable systems will use 64-QAM. Products have been announced that will convert ("transcode") from 8-VSB to 64-QAM, so compatibility isn't an issue. But 64-QAM allows a higher data rate to be carried in a 6 MHz channel than 8-VSB, which is consistent with the more friendly propagation characteristics of a cable system compared with over-the-air broadcasting. So the simple and inexpensive approach of transcoding a broadcast signal from 8-VSB to 64-QAM might result in wasted capacity.

Remultiplexing

Under existing analog must-carry rules, the cable operator is required to pass the video and audio through to subscribers without degradation. The data signals in the vertical blanking interval that are associated with the video programming, such as closed captioning, must also be passed through. But the cable operator is permitted to strip out other VBI data signals and replace them with different data signals. The same concept would apply to digital video.

Digital TV signals are very flexible. They consist of one or more video, audio and data streams multiplexed together. And the different program streams can be broken apart and recombined. In order to capture the benefits of 64-QAM modulation, a cable operator can pick out parts (maybe just a single SDTV stream) and can remultiplex these parts together (maybe four different SDTV streams from four different broadcasters might wind up as part of the same 6 MHz channel), and then apply 64-QAM modulation. Remultiplexing is not only technically feasible, but in fact, it makes efficient use of channel capacity. But I imagine that broadcasters will complain. The big techno-political question is whether the FCC can be convinced that it's a good idea.

And then there is scrambling. Fox Broadcasting asked the Advanced Television Systems Committee (ATSC) to develop standards for a scrambling system for broadcasters. It clearly wants to broadcast some premium programming on an SDTV program stream and charge money for it. Fox envisions a smart card or PCMCIA card slot in the TV set, and wants standards so that viewers won't need to swap cards as they change channels. (Unfortunately, a standardized scrambling system creates a more inviting target for piracy. And a plug-in card, as opposed to embedded circuitry, makes vulnerable signal paths more physically accessible.)

In the early years, most TV viewers won't have digital TV sets — they'll still be using their analog NTSC TV sets. Cable subscribers will be able to use a cable box to convert the digital signal to analog. The cable box will play an important role in speeding the transition from analog to digital, because it will make the digital programming available to a larger audience than those few who have purchased new TVs. And the cable box will be particularly important for feeding the second TV set in a home. So in addition to the policy question of whether must-carry rules will apply to scrambled SDTV programming, there are technical and operational questions about compatibility between cable boxes and broadcast scrambling.

Should cable operators be forced to carry scrambled broadcast programming? No. Should cable operators and broadcasters negotiate private deals for carrying scrambled broadcast programming? Yes. Will there be big fights over digital must-carry policies? You bet!

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