DTS May Hold The Key To Mobile DTV

Distributed transmission systems, the cellphone approach to broadcasting, could give a boost to mobile DTV as broadcasters attempt to reach on-the-go viewers with rock-solid signals.

"DTS is just going to be required [for mobile DTV]," says David Neff, president of Axcera, a Pittsburgh-based transmitter manufacturer. "It's not going to work any other way."

Mobile requires "a good, reliable over-the-air signal that has to be ubiquitous," he says. "If you want to have reliable coverage you really are more compelled to do a service that broadcasts from multiple sites and multiple transmitters."

DTS, otherwise known as single frequency networks, was conceived nearly a decade ago as an alternative the tall tower approach that broadcasters have been using for the past 90 years.

DTS comprises a network of transmission sites -- antennas on relatively short towers driven by low-power transmitters and interconnected via microwave, landline or satellite.

With the advent of digital TV receiver technology, such networks can make use of a single frequency to cover a market just like conventional big-stick broadcasting.

The FCC authorized use of DTS in February 2009 and 17 stations have filed applications to build systems, including a few that had been experimenting with the technology for years.

However, DTS pioneers are finding that DTS is not practical for conventional broadcasting.

"It still costs way too much to implement," says Russell Rockwell, chief engineer of Penn State's noncommercial WPSU State Colleage, Pa., the first experimental DTS in the country.

Rockwell is using DTS to feed to fill in coverage in the challenging Nittany Valley terrain around State College, conceding that some viewers who could see WPSU's analog signal cannot see its digital one.

But he shelved the idea of using DTS to cover the Altoona market 45 miles from the main transmitter site because it would cost about $500,000 to link the transmitter sites.

"The promise is there but I believe the manufacturers need to reach a point where they can put up a distributed transmission site for the cost of a translator -- $20,000-$25,000," he says.

Costs are such a concern that many broadcasters won't even consider DTS, says an engineer with a national broadcast firm speaking on background.

"There's not a willingness to go out on a limb and try this technology in places other than where you have mountain ridges between transmitters," he says.

Still, in spite of the costs, many see DTS as the key to mobile DTV where having blanket coverage is critical since viewers will not tolerate having their pictures fizzle as they walk down the street or ride along in a car.

"You need very high field strengths over your entire service area to attain reliable network service," says Merrill Weiss, president of Merrill Weiss Group, and a longtime DTS proponent and patent holder. "If anything, mobile will be the driver for using single-frequency networks."

Tom Long, director of engineering for Long Communications' WHKY Hickory, N.C., received FCC approval for his DTS last May and plans to deploy the service in the fall. He hopes it will improve reception of the main signal, but his real goal is to lay down a ubiquitous mobile DTV signal.

"We think the technology is going to go handheld," he says. "We want to cover the entire Charlotte market on a single frequency and have 90 dB or more on most signal levels."

Long acknowledges that deploying DTS is "not the cheap way to go." A 47-mile microwave link cost $100,000 and brought the cost of a single DTS site to about $250,000, he says. That's why Long whittled back his original plan from four sites to two and also why he'd like some other Charlotte stations to join him in building and sharing a system.

"This is the way everybody will eventually have to go," he says. "If somebody wants to buy space on my microwave, I'll offer to lease space."

Because it is expensive and because mobile DTV can be initially deployed without it, DTS may continue to sit on the technological back burner for a little longer.

But it should finally have its day.

Says Jay Adrick, VP of broadcast technology at Harris: "When mobile comes along and there are receivers out there, there will be quite a few stations that end up deploying DTS."