Is it realistic to think the nation’s television transmission infrastructure could successfully be transitioned from the traditional approach that relies on a high-power transmitter, tall tower and big antenna to something akin to a cell phone network?
According to the inventor of the technology used to synchronize multiple transmitters in a single frequency network (SFN) for ATSC digital television transmission and one of the industry’s leading authorities on distributed transmission systems (DTS), the answer is probably not, especially when the concept moves from the theoretical into the real world.
“I think technically it could be made to work,” says Merrill Weiss, president of Merrill Weiss Group, an electronic media consultancy. “But economically, it is not doable with the way things are priced these days.”
The reason such a radical redirection of the nation’s TV broadcast infrastructure is even on the table is the FCC’s Congressional mandate to develop a National Broadband Plan and the wireless industry’s assertion that it needs at least 800MHz of spectrum to meet future demand for wireless broadband Internet service.
In theory, a DTS broadcast architecture relying on low-power transmitters would allow channels to be packed much closer together than they are today and thus free up spectrum for wireless Internet service.
The NAB and Association for Maximum Service Television have called the idea “impractical.”
Among the problems with this approach is whether or not broadcasters can get access to the tower sites that would be needed and what to do about dead reception zones between markets that would be necessary to prevent adjacent market interference, says Weiss.
“The only way a single frequency network works is when each transmitter is transmitting identical data,” he says. However, stations sharing the same channel assignment in adjacent markets would not be transmitting the same bits. Thus, they would either create interference in areas where their markets adjoin, or they would be forced to create a reception dead zone.
“If we assume that the interference zone is double the radius of the service area, if you have transmitters providing service to a five-mile radius, then you are going to have a gap between markets of at least five miles where you can’t provide service because of the interference between markets.”
That approach could work for isolated markets, but in regions of the country with adjacent markets such as Boston and Providence, RI, or Baltimore and Washington, D.C., the tightly spectrum-packed DTS approach becomes “problematic,” adds Weiss.
Another question mark is whether such a radical redesign of TV transmission infrastructure would even free up enough spectrum to make taking on the task worthwhile. “Look at how much spectrum you get back,” advises Weiss. “The best way is to put all TV broadcasters together side by side from channel 14 to channel 42 or 43 in the largest markets.”
When spectrum allocated to public safety and radio astronomy are taken into account, things get especially tight in larger markets. “There are 26 stations in the L.A. market,” he says. Assuming all stations were positioned at the low end of the current UHF band, the result would be recovery of only eight or nine channels, a total of 48MHz or 54MHz. Spectrum recovery in smaller markets could be more.
Weiss also describes the cost of implementing local DTS transmission nationwide as “horrendous,” particularly if stations don’t tap into the economies of scale of sharing DTS transmission sites. “Even if you do that, the economics don’t work for the most part,” he says. Tower rental and fiber interconnects between DTS transmission sites make the approach economically unfeasible.
There is one thing, however, that could make DTS attractive, says Weiss. “If broadcasters move in large numbers to DTS, it will be because of mobile and handheld service,” he says.
