TECH SPOTLIGHT

Mobile DTV Repeater Shows Promise

A test of a single-frequency repeater in Washington this summer and fall indicates that it may be what broadcasters need to fill in coverage gaps in their mobile DTV service when they roll it out next year. "I'm cautiously optimistic," says OMVC's Sterling Davis (left).

From May to October this year, broadcasters’ Open Mobile Video Coalition conducted a live trial of their mobile DTV service in Washington, primarily to gauge consumer interest in the service and to learn something about how to market it when the commercial service rolls out late next year.

But the five-and-a-half-month effort also served as a test bed for a single-frequency (SF) repeater, a technology that mobile DTV proponents hope will improve mobile coverage.

Data from the experiment is still being evaluated, but Sterling Davis, VP of technical operations at the Cox Media Group and chair of OMVC’s Technical Advisory Group, said preliminary results suggest that repeaters may be the answer to spotty reception.

“It can definitely help mobile,” he said. “I’m cautiously optimistic.”

Victor Tawil, SVP of the Association for Maximum Service Television, who managed the experiment, said it was conducted “to help us understand better how feasible [the SF repeater technology] is, what you need to do, what are the pros and cons, how to design SF networks.”

He deferred to Davis for any comment on the results, but said that he fully expects broadcasters to use repeaters in certain circumstances, even though it will “cost some money.”

BRAND CONNECTIONS

The Washington trial involved nine stations broadcasting 23 different mobile programs, including simulcasts of the regular broadcast services of the Fox and NBC O&Os (WTTG and WRC) and several cable networks, including Fox News, MSNBC, CNBC, MTV and Comedy Central.

For the repeater experiment, OMVC chose WNVC, a full-power station operating on ch. 24 under a construction permit from a tower in suburban Virginia, about 14 kilometers west of downtown Washington.

The station is owned by noncommercial Commonwealth Public Broadcasting Corp., which does business as MHz Networks. It and sister station, WNVT (ch. 30), offer a variety of foreign news services.

In an effort to improve reception of WNVC’s service in downtown Washington, particularly indoors, the OMVC experimenters built a low-power repeater operating on the same channel at WRC, the NBC O&O in Northwest Washington.

According to Tawil, Harris and SPX Communications Technology (formerly Dielectric) supplied the transmitter and antenna, respectively. Richland Towers, which owns the tower on the site and leases space to WRC, provided space for the repeater antenna. The Communications Research Centre Canada loaned test-and-measurement gear.

Although the Harris transmitter operated at just one kilowatt, mounting the antenna 153 meters off the ground boosted the ERP to 4 Kw, Tawil said.

Intel and Dell were deeply involved in the test, but they are more interested in mobile DTV reception indoors on portable netbooks than they are on walk-around smart phones and tablets, Tawil said.

In general, coverage of the mobile DTV signals during the trial was “pretty good,” Davis said. But it was not blanket coverage, he said. “You do lose certain stations in certain places just as you do with the fixed service. That’s not unusual.”

Davis said that broadcasters have high hopes for repeaters as “gap fillers” that will minimize lost signals. They inject stronger signals in “geographically challenged” areas where main signals are blocked by the terrain or buildings or other man-made structures.

The single-frequency repeater uses the same channel as the main station and its signal is synchronized as closely as possible with the main channel. Reception is made possible by the ability of digital TV receivers to reject multipath interference caused by signals on the same frequency hitting receivers at slightly different times.

In analog broadcasting, multipath caused by echoes of signals bouncing off buildings caused ghosting in the pictures. In digital broadcasting, such interference can cause pictures to freeze, pixelate or disappear entirely.

One alternative to SF repeaters are TV translators that operate on different channels. But there are drawbacks, Davis said. First, because they are on different channels, the receiving devices would have to retune to the new channel and that could take up to 10 seconds, he said. “That’s a more awkward solution from a consumer point of view.”

Second, he said, licenses for translators are not always readily available. The mobile provider would have to buy them, lease them or apply for new ones at the FCC.

And applying for a translator may be tough, involving finding a frequency and making sure it doesn’t infringe on anybody’s else’s signal, he said.

By contrast, he said, “You can get a license for [a SFN repeater] easily because you are interfering with yourself.”


Comments (8)

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Colin MacCourtney says:

December 16, 2010 at 1:12 pm

This sounds a lot like the “Synchronous Boosters” that some FM radio stations have used successfully for 10 years.

Christina Perez says:

December 16, 2010 at 9:17 pm

How about Zenith’s proposal of a few years back to enhance the main ATSC standard so that it would work with mobile and stationary sets? Occam’s Razor and all that. I get the impression this ATSC M/H is a scheme to turn mobile broadcast TV into pay TV — instead of growing the OTA audience share for the only powerful mass advertising medium in the nation.

mike tomasino says:

December 17, 2010 at 12:04 pm

Yes, there are some broadcasters that have looked at making mobile a pay service. I believe that if that is the case that mobile will suffer the same fate as FLO-TV.

    Christina Perez says:

    December 17, 2010 at 1:21 pm

    My post exactly, Snap. “But the big fools say, ‘Push on.'” (Courtesy, Pete Seeger.)

Ellen Samrock says:

December 17, 2010 at 3:04 pm

From what I’ve read concerning Mobile DTV the intent has always been to provide a mix of free and premium pay TV channels. The advantage broadcasters have is that they can learn from the mistakes Qualcomm made with FloTV and avoid them.

    Christina Perez says:

    December 17, 2010 at 6:02 pm

    So why not say so? All broadcast stations/affils free and clear, no price of entry whatsoever, and pay channels optional, via authorization/activation. They won’t say so because they are tempted to charge a basic subscription fee, IMO. If they declared that all OTA channels would be free, they’d cut any competition off at the pass. They won’t say it because they think they can get away with charging for what the public always has gotten for free. And if they try to charge for broadcast channels, mobile broadcast WILL go the way of Flo TV, because only the crazies will watch a movie on a tiny screen. Once broadcast stations are freely available over any device, broadcasting will experience a second Golden Age. If this mobile coalition tries to impose a basic subscription fee, the people and Congress will yell and holler. Who’s advising this bunch?

    Ellen Samrock says:

    December 17, 2010 at 6:55 pm

    But I believe they have said it. Read some of the information on the OMVC website.

Derwin Cox says:

December 17, 2010 at 9:24 pm

It’s true, a booster is certainly one way to cover the troubled areas. It may be necessary, however, to initiate a slight delay of the main signal so that there is a smooth transition through the entire coverage area of both the main and the booster. Otherwise their may be an area of conflicting signals because of timing or phasing which tend to confuse the tv receiver. We have limited experience with digital phasing conflicts but will likely work out these solutions considering the considerable advantages offered.


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