HD Picture Sharpens


HDTV isn't just a game for the big-boy national cable networks any more — now, it is going local. Lured by the prospect of one-upping their own broadcast competition, more and more local TV stations are starting to transmit their signals not just in digital but also in HD. While that content may be welcome news for cable operators trying to fill up their own HD content lineups, they face several challenges in giving their customers those pictures — not the least of which is how to bring in the signal and deal with the resulting bandwidth load.

Strategically, it's a hassle that may well be worth it for cable operators. By comparison, satellite competitors have a much harder time providing local signals — let alone HD signals — to their customers. So many MSOs see local HD channel additions as a key way to compete against the likes of EchoStar Communications Corp. and DirecTV Inc.

"It gives us a clear differentiation from what satellite does," said Kevin Hill, director of marketing for video services at Cox Communications Inc. "Currently and in the near future they are not going to be able to deliver local signals in the local markets, which means that we have hundreds of HD programs and events that they are not going to be able to show."

Meanwhile, more local stations are making the jump, and they are comprising a good percentage of cable MSOs' HD lineup. Late last month, KXAS-TV in Dallas/Fort Worth became the first station in that market to go high-def for cable, and Charter Communications Inc. picked up the HD feed for its digital service.

"They are going full speed ahead on this," noted Sylvain Riviere, marketing director for broadcast video services at BigBand Networks, a HD-bandwidth management-systems specialist. "Most of the lineup we are serving is at least 50% local broadcast."

To do so, the signal has to get from the TV station to the cable headend, and there are two general strategies being used. In some markets, fiber links installed between TV stations and cable headends can deliver the signal directly, but it can also be brought in via a good, old-fashioned VHF antenna on the roof.

Cox Communications Inc. has already invested in the conversion gear as it prepared for its HD rollouts. Toward the later part of 2002 and into 2003, where there was fiber available, Cox has tried to drive that transmission toward fiber. In some markets, both means are used.

"I would estimate that probably more than half receive fiber feeds," said Steve Watkins, Cox's manager of digital technology for the engineering multimedia technology group.

Either way the signal arrives, it must then be converted from its 8 Vestigal Side Band (8VSB) modulation into cable's 256 Quadrature Amplitude Modulation (QAM) channel. That conversion is a must because 8VSB takes up too much bandwidth to deal with in the cable plant.

"8VSB is not a great technology because it takes up a lot more space on a cable system," said Mark Hess, Comcast's vice president of digital television. "It's a great technology for them because it has got a lot of forward error correction, a lot of robustness to it, so when it is sent out over the airwaves it does very well. But for us it's just not practical from a standpoint of how much bandwidth it uses."

HD Launch Package

There is little shortage in gear to make that conversion. Motorola Inc. offers an HD launch package of gear, including an 8VSB receiver it resells, a QAM modulator and upconverter. The package, which takes up two rack units, costs less than $10,000.

Rival Terayon Communication Systems Inc. offers an HD off-air signal conversion system, and recently it has seen an uptick in sales for its CP 7585 converter box.

"It's really picking up. We are getting a number of orders from larger MSOs," said Mark Jeffery, Terayon's senior product line manager for digital video solutions. "I think that the operators are realizing this is the real differentiation, where they have the bandwidth and satellite doesn't — and that's how they are going to win."

But taking HD local signals means dealing with the added bandwidth load, and that is no small matter. Compared to a standard definition signal at an average 3.75 megabits per second, HD signals come in at a whopping 19.4 mbps. That means on a 256 QAM channel, cablers can multiplex just two signals, compared to upwards of 10 SD signals.

In some cases, cablers are choosing to funnel just one local HD signal on a single 6 megahertz channel. Even if two are multiplexed on the same channel, given the amount of HD programming coming on line, that may soon present a problem.

"Last year we were looking at three or four channels in a lot of our systems, and a lot of them were carrying even multiple east and west feeds. This time next year, I'm expecting there is going to be anywhere from 13 to possibly as many as 17 HD channels that we could be looking at trying to carry," Hill said. "So we're trying to figure out a way that we do not end up with having several 6 MHz channels having to be devoted to multiple and multiple HD networks."

To Mux or not to Mux?

There is a technology that can help shave down the bandwidth of HD signals, but it is by no means without controversy. Statistical multiplexing systems offered by Terayon, Motorola and BigBand Networks, among others, can compress the signals by taking out video elements largely imperceptible to the human eye. They also can dynamically adjust the bit rate allotted to each signal in a channel, so a high-action movie scene can temporarily "borrow" bandwidth from its more static news channel next-door neighbor.

But worries that might erode the video quality have cablers decidedly cautious about the practice, particularly when it comes to HD.

"We do not do any of what would be called stat muxing or rate shaping of the content that is being delivered by the local content providers," Hess said. "We give them the full 19.4 mbps bandwidth — it is the same amount that they would need. We do not do anything with their signal other than change its modulation scheme, which is better for us."

That doesn't mean Comcast will stick to that no stat-muxing policy in the future.

"We are always interested in being efficient, and as technology allows that, I think we might look into testing it perhaps and then sharing what we find with our content providers," Hess said. "But I don't think we would do any of that without full knowledge and a joint agreement to do that with the content provider."

Cox, meanwhile, is preparing to start stat-muxing HD signals later this year. While its quality is key, in terms of bandwidth, "we do believe it is going to be significant savings," Watkins said.

Trials are under way now and "they look very promising," Watkins said. "In fact, the trials look better than anticipated."

New technologies arise

The drive to make HD more bandwidth palatable without degrading the signal quality is the primary focus these days for BigBand Networks. In the past year or more, BigBand has been making the rounds to cablers and programmers alike, arguing that stat muxing and rate shaping of HD signals doesn't have to mean poorer-quality video.

"We've been working very hard explaining this, that with stat muxing you won't see the difference between your original source that you could get off air and your resulting cable service," Riviere said. "It's pretty much up to the cable operator to decide, and while they all have the stat mux capability, most of them are transitioning slowly to it to see what happens, to see that customers are not calling. But on the broadcasters' side it's pretty much 'you do what you want. I just want to be on the cable plant and get more people looking at my service.' "

Terayon, too, has been in the stat-muxing hunt, fielding its CherryPicker 6400 unit, able to combine multiple HD streams on one channel. It sees that, in the end, programmers including local broadcasters will have to accept the technology if they want access to cable's HD world.

"They realize that rate shaping is what I would call a necessary evil," Jeffrey said. "They don't want anyone compressing their content, and they put up for it because the operators are pushing for it, and they realize it is even more important when it comes to HD just because of the bandwidth."

Seeking order

But programmers are looking for some sense of order when it comes to handling the input of their content into the cable channel lineup, Jeffrey said. That was the case for one major programmer, who came in seeking a more coherent system for processing its network signals.

"He told me: 'We can't sit down with each operator or each headend and figure out and basically fine-tune it to fit us. We are going to have to come in and we're going to have to lay down some high-level requirements that yes, you can rate-shape but you cannot have more than three signals in 256 QAM, and these are the devices you can use to do it, and you won't put more than one sport or music video in with my content,' " Jeffrey noted.

But for Cox, creating set guidelines for how HD channels are mixed and shaped won't provide enough flexibility to fit local conditions.

"We're not going to put out guidelines that say these services must go together," Watkins said. "There's too much variance between the local broadcaster feeds and satellite feeds to really do that. What we are recommending our systems do is combine the signals and basically add in enough HDs such that you don't materially degradate the quality — keep the total bandwidth through the process of stat muxing beneath the maximum transmit that we have available, so that we don't actually start pegging into artifacts."