Proposed DTS approach is ‘impractical,’ costly, says NAB/MSTV in FCC filing

A proposal from the wireless industry’s CTIA trade group and the Consumer Electronics Association to transition broadcasters from their big-stick, high-power transmitters to multiple, low-power synchronized transmitters and antennas in a distributed transmission system (DTS) received two thumbs down in reply comments filed with the FCC last week by the NAB and the Association for Maximum Service Television.

The CEA and CTIA offered the proposal as a way to free up contiguous spectrum that could be used to meet their forecasted future demand for wireless broadband service. Currently, a special FCC task force is working to create a National Broadband Plan due in Congress next month.

However, the MSTV and NAB said in reply comments filed Jan. 27 that transitioning from today’s DTV transmission infrastructure to one based on DTS single-frequency network transmitters would create service loss to viewers resulting from coverage gaps and interference.

As envisioned by the CTIA and CEA, DTS offers a way to free up between 100MHz and 180MHz of contiguous spectrum by reducing the co- and adjacent-channel DTV space needed to prevent over-the-air TV transmission interference. However, requiring local broadcasters to transition to a distributed transmission system would be infeasible, costly and create service coverage gaps and interference, the NAB/MSTV filing said.

While building a case against the DTS proposal, the broadcast groups did commend CTIA/CEA for recognizing that consumer investment in DTV should be protected, stating that broadcasters’ 6MHz channel allotment should be preserved and acknowledging that broadcasters should not bear the cost of any transition to reallocate spectrum for the wireless industry.

Still, NAB and MSTV found the core of the CEA/CTIA proposal unacceptable. “Replacing the current system with DTS would trigger heavy service losses to the American public,” the filing said. Explaining to the commission that the 8-VSB modulation method chosen for DTV service in the United States was selected for its “ability to efficiently cover large service areas,” the filing quoted the CEA/CTIA proposal, which acknowledged it “was not designed with an SFN (single-frequency network) architecture in mind.”

Theoretically, “a carefully engineered (DTS) system” with properly synchronized signals transmitted using the correct amplitude relative to one another could reduce interference, the filing said. However, real-world signal variations and tower siting problems would make an ideal DTS implementation unattainable. “DTS cannot be implemented to ‘cellularize’ DTV nationwide,” but rather is appropriate to fill in coverage gaps created by unique terrain, buildings and other circumstances, the filing said.

The CTIA/CEA proposal also dramatically underestimated the cost of implementing local DTS infrastructures on a national basis, the filing said. The DTS proposal puts the cost at between $1.37 billion to $1.83 billion. However, CTIA/CEA failed to take into account the fact that there are multiple stations in each broadcast market, each of which would require multiple transmitters, encoders and other equipment. A more realistic estimate taking all local broadcasters into account pegs the price tag for implementing DTS at between $11.7billion and $15.7 billion.

The NAB/MSTV filing also endorsed a call from the Department of Justice for greater use of secondary markets in spectrum and a National Telecommunications Information Administration request for a spectrum inventory analysis in submissions to the commission.

The broadcast groups said the agencies’ assumption that a shortage of spectrum will impede increased broadband competition was "particularly problematic."