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Commission establishes model to predict DTV signal strength

The FCC adopted a Report and Order and Further Notice of Proposed Rulemaking Nov. 22 establishing a rule laying out a point-to-point predictive model for determining whether an over-the-air DTV signal can be received with federally mandated signal intensity at a given location.

The rule, which covers reception of full-power, low-power, Class A and translator stations, was the second of two actions taken by the commission in late November to ensure compliance with requirements in the Satellite Television Extension and Localism Act of 2010 (STELA) related to determining whether a DTV signal can be received at a specific location. The other Report and Order dealt with actual measurement of DTV signal strength in the field.

As directed by Congress in STELA, the model established by the commission for predicting DTV signal strength is based on the Individual Location Longley-Rice (ILLR) model, established in CS Docket No. 98-201 and recommended to Congress. Congress also directed the commission to refine the predictive model as more data became available.

With the Report and Order and Further Notice of Proposed Rulemaking, the commission adopted an ILLR model that “incorporates parameters and features appropriate for prediction of the signal strengths of digital television signals” and a procedure for “continued refinement” of the model, the commission said.

One important parameter, and an area of disagreement between broadcasters and satellite TV operators filing comments in the proceeding, was whether the commission should include indoor antennas in its predictive model. Broadcast filers argued against including them, while satellite TV operators sought their inclusion in the model.

The commission chose an approach based on the use of an outdoor antenna 20ft above the ground for one-story structures and 30ft above for taller structures. In choosing this approach, the commission wrote, “The STELA specifies use of the digital television signal strength standard in Section 73.622(e)(1) of the rules as the threshold metric against which predictions are to be compared to make determinations of ‘served’ and ‘unserved.’ It is important and necessary that the signal strengths predicted by the model can be meaningfully compared to that standard.”

However, the commission said it was “aware and concerned” that using outdoor reception as a component of the model could result “in instances where a consumer who either cannot use an outdoor antenna or cannot receive service using an outdoor antenna and is not able to receive a station’s service with an indoor antenna will be found ineligible for satellite delivery of a distant network signal.” This concern is mitigated by the fact that DISH Network delivers local-into-local service in all 210 DMAs and DIRECTV offers the same service in all but 60 markets, it said.

Another area of disagreement between broadcast filers and satellite operators relates to how to treat time and location variability. TV signal strength varies by location and time due to factors affecting signal propagation at a given distance from a transmitter.

For the ILLR DTV model, the commission chose to use 50 percent as a location variability factor and 90 percent as the time factor. DIRECTV and DISH argued in comments that the predictive model should use 99 percent as the time variability factor. While acknowledging that viewers want to receive their DTV signals all of the time, the reality of terrestrial broadcast signal propagation make nearly 100 percent availability of signals “unrealistic.”

(The new STELA digital ILLR model and its specifications are available in OET Bulletin No. 73 in Appendix A.)

Phil Kurz is a contributing editor to TV Tech. He has written about TV and video technology for more than 30 years and served as editor of three leading industry magazines. He earned a Bachelor of Journalism and a Master’s Degree in Journalism from the University of Missouri-Columbia School of Journalism.