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Going all-digital

Thu, 07/31/2003 - 8:00pm
Jeffrey Krauss, Digital Interpellator and President of Telecommunications and Technology Policy

By Jeffrey Krauss,
Digital Interpellator
and President of Telecommunications and Technology Policy
At SCTE Cable-Tec Expo last May, Dave Fellows said that Comcast would consider going all-digital if an inexpensive digital-to-analog converter were available to supply signals to legacy NTSC receivers. In June at the National Show, both Pace and Motorola were showing low-cost boxes to do just that. These devices raise policy issues, both for cable and for broadcasting.

The cable business implications are obvious. For a system that now carries 70 standard definition analog channels, they could be digitally coded at, say, 4 megabits-per-second so that about 10 would fit into a 39 Mbps 256-QAM channel. That means that seven channels would be needed to carry the 70 programs, thereby freeing up 63 channels for other uses. But let's look at the policy implications.

First is the must-carry issue of signal degradation. Section 76.62(b) of the FCC Rules requires that television broadcast signals must be carried without "material degradation." Because the cable operator would be receiving the broadcasters' analog signals off-air and digitally coding them, some broadcasters might be expected to complain that a 4 Mbps coding rate is inadequate, and constitutes material degradation of the picture quality.

There is no standard that specifies what MPEG data coding rate is adequate for NTSC television. Experts have not been able to agree on any objective test of digitally-coded picture quality. There are subjective tests, where viewers are asked to rate the picture quality of a program segment, but there are no automated, objective tests that give reproducible results, and no scale to convert a coding data rate to a picture quality rating.

So maybe the cable and broadcast industries can get together and negotiate some agreement. Or maybe the FCC will have to make a decision. And I can foresee variations from one encoder design to another, so that a Brand X MPEG encoder might require 8 Mbps to achieve the same picture quality that a Brand A encoder can achieve in 6 Mbps.

But make no mistake about it–broadcasters are very sensitive about picture quality with digital video. Some broadcasters are already complaining about degraded picture quality, now that cable operators are using "bit grooming" to carry HD broadcasts at 15 Mbps, rather than the off-air rate of 19 Mbps.

Oh, did I just mention HD? What about HD?

The device that Pace is planning to deliver has two QAM tuners, two MPEG decoders, and two NTSC outputs on channel 3 or 4, so that a subscriber can watch one channel on an NTSC receiver and record a different channel on an NTSC VCR. But, the MPEG decoders in the Pace device can handle only standard definition MPEG programming. They don't have the speed or frame memory to handle HD. The same goes for the Motorola device.

So long as the local broadcasters keep their NTSC signals on the air, and the cable system's only obligation is to carry a broadcaster's NTSC signal, these low-cost devices might be fully adequate. But HD signals are a problem for the low-cost devices, and adding the necessary processing horsepower and memory raises the cost.

When the broadcasters' NTSC broadcasts are eventually turned off, and only the digital broadcasts remain, that's when the big disputes will arise. Regardless of what the FCC finally decides about a cable operator's obligation to carry one or all of a multiplex of SD programs, we all agree that cable operators will be required to carry the digital HD broadcasts when they occur. But in order to deliver them to NTSC receivers using these low-cost devices, the HD signals will have to be downconverted to SD at the headend and dual-carried on the cable system. That's when the disputes over "material degradation" will really take place.

What about the implications for broadcasters? Years ago, when the FCC adopted its digital TV rules, there was an expectation that low-cost converter boxes would become widely available to convert the off-air digital 8-VSB signal to an analog NTSC format to feed NTSC receivers. It didn't happen. The consumer electronics industry never developed those devices, because there weren't many digital TV stations on the air until recently.

The QAM tuners in the Pace and Motorola boxes could easily be replaced by 8-VSB tuners. If so, it would have big policy implications for closing the analog TV loopholes I wrote about in my March 2003 column. The shutdown of analog NTSC broadcasting can't occur until 85 percent of households in a market have access to digital TV signals. The statutory provision where this occurs, Section 309(j)(14) of the Communications Act, says that a household has access to digital TV signals if at least one NTSC TV set is equipped with digital-to-analog converter technology. Presumably a Pace or Motorola digital-to-analog converter with an 8-VSB tuner would qualify. Or maybe not, because they lack HD capability. The FCC proceeding I mentioned in my March column asks for comments on that point.

But it's hard to see how these devices will be deployed for broadcast reception. While cable operators have a business incentive to deploy them in order to reclaim their analog spectrum, broadcasters have no such incentive. Or maybe the mobile radio side of Motorola will subsidize the 8-VSB converters, since they've been lusting after the broadcast frequencies for years.

Have a comment? Contact Jeff via e-mail at: jkrauss@cpcug.org

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