HDTV RISING: Reception and Processing Lessons-Learned

Time Warner in Raleigh, N.C., and Cox in Las Vegas learned that high-definition TV demands extra care in signal reception and processing.

With the quantity of programming on the rise and the price of display monitors in decline, the stars are aligning over high-definition television (HDTV). Are cable engineers ready to play their role in deploying this new service?

The cases of two early-adopting cable systems—Time Warner in Raleigh, N.C., and Cox in Las Vegas—indicate that, with the right tweaks, HFC networks are ready to execute their role in HDTV transport and delivery.

While posing none of the complicated, two-way integration puzzles of video-on-demand (VOD), HDTV nonetheless demands attention, especially in the reception and processing of over-the-air signals.

HDTV pioneers

Raleigh, N.C., will figure in any historian’s account of HDTV, in large part because of Capitol Broadcasting’s WRAL-TV. A digital broadcasting pioneer, in 1996 WRAL received the Federal Communications Commission’s first experimental HDTV license. By 2001, it had begun broadcasting all of its newscasts in HD.

Having WRAL in the neighborhood gave Time Warner Cable’s Raleigh-Durham, N.C., system an opportunity to gain valuable, early experience in the handling of over-the-air HD signals. "I have to credit the fact that we have been dealing with HD much longer than any other marketplace because of the (FCC) pioneer preference afforded WRAL," Patrick Hourigan, vice president of engineering and technology in Raleigh, says.

In addition to WRAL, Time Warner Raleigh is receiving HD signals from the PBS, ABC, NBC and Fox affiliates. On the HD cable programming side, the system receives HBO and Showtime.

HD challenges

The delivery of HD to the Raleigh system presented some challenges. But again, the operator benefited from proximity to WRAL, which built transmitter towers for itself and other digital operators that lease space.

The challenge is that if too weak, a broadcaster’s digital signals can run into problems. "There are a lot of multipath problems associated with HD 8-VSB (vestigial sideband) technology," notes Hourigan.

In the case of the PBS affiliate (WUNC), which was lacking the funds to build its own transmitters, Time Warner Raleigh did a "kind of HD in reverse" by building an optical link into its studio, effectively accelerating WUNC’s deployment of HD (within the cable plant) by 18 months.

Once these sorts of reception issues are settled, usually through a digital upgrade on the broadcaster side and the cable operator’s installation of 8-VSB receivers, a second tier of issues surface within the cable plant.

Hourigan puts bandwidth concerns at the top of his list. Then there is the need to cope with format differences among broadcasters. "Not all support a full 1080i, 16 x 9 format," he notes. "That presents some challenges to us to get everybody in the format that they need to display the best possible picture quality.

A related challenge is dealing with daily format changes that occur within each HD broadcaster. "WRAL, for example, might at some point send us an 18 Mbps HD signal, and no multiplexes," Hourigan says. "Then at 6 p.m., they might decide to send a 12 Mbps HD signal, a 3.75 Mbps NTSC digital signal, and a 1.5 Mbps radar signal."

Mix, and pass through

So far, the Raleigh system’s approach to HD has been to avoid compression. While operators are treating this issue differently—and vendors are accommodating them with a range of solutions—a safe starting point is Hourigan’s reminder that "the whole point (of HDTV) is to provide higher quality."

Instead of compressing, Hourigan simply combines his digital programming. "In our case, it goes to a statistical multiplexing system," he says. "It used to be Cisco; now it’s BigBand."

More specifically, before these HD streams hit the Scientific-Atlanta DNCS, the Raleigh team gets into the multiplexer and begins clicking and dragging. "I take one 18 Mbps HD signal and add to that several other standard definition (SD) signals of unrelated video programming to fill up that QAM as best I can," Hourigan says. "Then I move onto the next HD signal, and to my next QAM."

As for better handling a broadcaster’s daily format changes, Hourigan depicts any solution as elusive. "We’ve had conversations with several vendors about how we can more closely automate the process. And it’s difficult, very difficult."

One problem stems from concatenated formatting data. "If (the broadcasters) decide to do something different, I can certainly work with them to make the technical adjustment to make that happen," Hourigan says. "But guess what: the guide doesn’t work."

That raises the topic of program and system information protocol (PSIP), a category that vendors such as Triveni Digital aim to master. The importance of navigation on the digital tier only underscores the need to help operators integrate PSIP with other guide data.

Cox deploys in Vegas

Las Vegas is the second Cox system to deploy HDTV. First place goes to Cox’s system in Omaha, which modestly launched the service in April 2000. But the Las Vegas system picked up the HDTV banner about a year ago and pushed hard.

At the time, Las Vegas was facing DirecTV’s imminent launch of local-into-local, which it saw as a threat. The idea of countering with HD sprang from a chance to field test S-A’s Explorer 3100 set-top and the simultaneous discovery that the HD market was heating up.

"We talked to the local Circuit Cities and Best Buys and the local electronics vendors, and they were selling 500 or so HD sets a week," Will Lundstrom, Cox’s vice president network operations in Las Vegas, says.

Satisfied with the Explorer 3100, Las Vegas launched HDTV last July, evidently thwarting the competition in the process. "We only had a 0.1 percent direct-to-home growth in our market in all of 2002," Lundstrom notes.

More modest challenges

As in Raleigh, both the reception and processing of HD in Las Vegas created technical issues. Unlike Raleigh, only three of its eight HD channels come from broadcasters (PBS, CBS and ABC), with CBS coming in via a direct fiber link using the C-COR.net (previously ADC) DV6000 optical transport system.

The relative scarcity of programming—a complaint heard among HDTV subs in Raleigh—apparently has figured in the business plans of some Las Vegas broadcasters. "They just don’t have enough content coming down to justify the equipment to get it out in HD," Lundstrom says.

So how’s over-the-air reception? "It seems to be pretty good," Scott Weiss, master telecommunication center (MTC) supervisor, says. "(But) I will say that I had to upgrade some of my antennas…to get a reliable 8-VSB."

As in Raleigh, adjustments to broadcast HD content continues in the headend, where a broadcaster’s sometimes arbitrary switches from a single HD to multiple SD channels make the viewing experience potentially confusing for the sub.

"We can carry all of that, but what channels do we put it on? How do we identify it? What happens when they’re not there?" Weiss asks. "All those issues need to be resolved." Their lack of resolution, however, isn’t shutting down this service.

As to whether PSIP data is cable-friendly, for instance, Weiss gamely says that some is and some isn’t. "We can work with it."

Monitor, then mux

While not quite as dogmatic on leaving HD untouched as Time Warner’s Hourigan, Weiss effectively ends up in the same camp.

First, Weiss monitors the incoming signals. He has found that they rarely exceed 16 Mbps, with only one (PBS) clocking in at the "true" 19.4 Mbps. Then he multiplexes, as in Raleigh, using BigBand’s BMR.

"I found that running at 256-QAM, we get about 38 Mbps. So I can take two 15 Mbps HD and one or two 3.2 Mbps SD signals and combine them together on one QAM carrier," Weiss says. "I’ll lock the two up at 3.2, and then I’ll prevent the HD signals from exceeding 15 Mbps."

Because Weiss has found that HD runs most of the time at 10-11 Mbps, the opportunity for rate shaping—actually reducing the number of HD bits—is rare.

"It would have to be like planets lining up at the right time," he explains. "Both of them would have to exceed 15, at the same time, and the other two would have to exceed their 3.2."

Technology alignment

"Alignment of stars" might describe the HDTV deployment as a whole. As mentioned at the outset, it awaited the arrival of a critical mass of HD programming and the reduction in display-monitor costs from their astronomical heights.

On the technology front, suppliers also have circled into view. Motorola’s original sidecar HD boxes, which Comcast has deployed in Philadelphia, are now giving way to an integrated DCT 5100. Looking three years out, S-A CTO Bob McIntyre wonders why HD silicon chips won’t be in every set-top (which are likely to populate ever more retail outlets.)

Meanwhile, the BigBand BMR has given multiplexing a big bang. But Terayon has responded in kind with its Network CherryPicker DM 6400, in the process provoking debates over the relative merits of digital signal processor (DSP), application specific integrated circuit (ASIC) and field programmable gate array (FPGA) technologies.

Charter has selected the DM 6400 for several of its networks and aims to work it hard. "We want to do 3 HD in one 6 MHz channel, using 256-QAM at 38.8 Mbps," Pragash Pillai, Charter senior digital engineer, says. "We want to manage the bandwidth and use it more efficiently."

Whether basic or advanced multiplexing philosophies win out, vendors in the HDTV food chain expect to have products ready, "no matter how the pendulum swings," says Ned Mountain, executive vice president for Wegener Communications, a manufacturer of 8-VSB receivers.

In terms of its reception, processing and even installation, HDTV deserves a "handle with care" sticker. While working anew with broadcasters and testing options on the multiplexing and formatting fronts, engineers also must beware of challenges in bandwidth management that the success of this service will bring.

Jonathan Tombes is executive editor of Communications Technology. Email him at [email protected].

BOTTOMLINE

Prepare for Your HDTV Launch

HDTV is hot; be careful how you handle it.

* Talk to local broadcasters about their implementation of HDTV.

* Ensure that your 8-VSB signal reception is loud and clear.

* Anticipate variable formats and arbitrary changes in HD vs. SD programming.

* Monitor the incoming signals (few off-airs hit the "true" 19.4 Mbps rate).

* Assess HDTV in terms of bandwidth constraints.

* Consider advanced multiplexing/grooming, if simpler techniques come up short.

Is 8-VSB Robust Enough?

Debate over 8-VSB transmission still surfaces in technical circles, but Pat Hourigan, vice president of engineering and technology at Time Warner Cable in Raleigh, N.C., finds objections both counterproductive and irrelevant.

Hourigan doesn’t get "warm and fuzzy" when the talk turns to changing the HD standard again. "(That’s) kept a lot of the broadcasters from embracing and moving forward with HD purchases," he says.>

Yet he admits that 8-VSB’s reflection issues (manifested as multipath) create problems that broadcasters have difficulty managing at current power levels.

"In very urbanized areas, the multipath bouncing off buildings is pretty difficult to overcome. They also do not have, because they are generally UHF frequencies, the power outputs necessary to be equal to their original broadcast channel," he says.

Once the cable plant has secured these HD feeds, however, 8-VSB’s characteristics become moot. Why? "Because I serve all of those holes: the downtown multipath hole, the rural, I-don’t-get-that-far-with-my-HD-signal hole," Hourigan says. "I serve all those folk."

Can Your Techs Handle Home Theater?

While HD signals demand special treatment at the headend, technicians on the subscriber side of this service are finding other challenges.

"When we first launched, our installs averaged around one-and-a-half hours, because you’re running into these high-end TV sets and surround-sound stereo systems," Will Lundstrom, vice president of network operations for Cox’s Las Vegas system, explains.

Looking to quicken its pace, the system worked with its local training center and created manuals and processes for its in-house technicians, contractors and customer service reps. The upshot was a doubling of efficiency, with conversions of standard digital to HD now taking 45 minutes, Lundstrom says.

As HDTV merges with VOD to create what nCUBE CTO Greg Thompson has described as "neighborhood theatre," operators will want to help techs interface with their gold-plated subs’ fancy electronics gear.

Cox executives in Atlanta seem to have already realized this. "Corporate adopted our training plan after we got done with it," Lundstrom says.