Phil Kurz /
11.20.2008
Originally featured on BroadcastEngineering.com
FCC adopts distributed transmission systems rules

The FCC adopted rules Nov. 3 authorizing broadcasters to use distributed transmission systems (DTS) when appropriate to provide optimum DTV signal coverage for viewers in their service areas.

The rules, published in a report and order released to the public Nov. 7, enable broadcasters to use a network of DTS transmitters and antennas to continue providing over-the-air coverage to existing analog viewers as well as provide a signal for viewers in areas where off-air reception has been difficult. The rules also prohibit using DTS to cherry pick viewers in certain geographical areas with coverage and exclude others.

The commission’s action put in place technical and licensing rules that allow DTV stations to use a network of DTS transmitters in place of a single transmitter facility. According to the commission, a DTS network has the potential to use spectrum more efficiently and improve customer service. To that end, the commission held out the hope that use of DTS might solve service loss issues, such as those encountered during the early DTV transition in Wilmington, NC. Specifically, the FCC cited loss of coverage of some analog viewers of WECT (Ch. 6) living outside the station’s digital service area.

The commission based its rules on a “comparable area approach” by which a DTS network is set up to cover an area comparable to that which it would be licensed to cover with a single transmitter. The FCC rejected using an “expanded area approach” that would have allowed a DTS network to cover an area comparable to a broadcaster’s designated market area (DMA) as defined by Nielsen Media Research.

As part of the rules, the FCC also published a table of distances for broadcasters setting up a DTS network to ensure that its coverage is limited to their comparable service areas. The distances defined in the table specify “circles within which DTS coverage contours must be contained,” the rules said. In most cases, these circles equal or exceed the coverage stations will deliver following the DTV transition. The rules provide for broadcasters to file waivers to address circumstances similar to those encountered in Wilmington, NC. “Notwithstanding our Table of Distances, on a case-by-case basis, we will permit a station to use DTS if doing so will enable it to continue to serve its existing analog viewers within its analog Grade B contour who would otherwise lose service as a result of its transition,” the rules said.

The DTS rules specify that the same Part 73 licensing and technical rules that cover DTV single transmitter stations will apply to DTS stations. The DTS rules apply the Part 73 DTV effective radiated power (ERP), antenna height above average terrain (antenna HAAT) and emission mask rules as are applied to single transmitter stations.

A DTS system relies on tight synchronization of all transmitters in the network to avoid reception interference. In writing its new DTS rules, the commission specifically avoided requiring DTS transmitters to comply with a specific synchronization standard. It only required that the synchronization system employed “is effective in minimizing interference within the system” and provides viewers in the covered areas with service consistent with its rules.

The fact that the rules come about three months before the nation’s transition to digital television transmission in February 2009 was acknowledge by commissioners Michael Copps and Robert McDowell. McDowell noted that “even those licensees who are interested in it (DTS) are unlikely to be able to construct DTS facilities before February 17.”

Copps lamented the missed opportunity to implement DTS prior to the transition. “Had we identified these coverage issues earlier, we could have approved DTS months ago and given broadcasters enough time to build out before the transition,” he said. “Now that generally will not be possible.”


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