FCC Explains Methodology on Interference in Incentive Auction
The FCC offered advice to industry on two highly technical parts of the incentive TV auction Friday, with workshops on the methodology for “feasibility checks” for whether channels can move during the repacking part of the auction and on interservice interference prediction. The feasibility checking methodologies for the FCC’s incentive TV auction are “built on the substantial work we have done on the repacking process, including the development of the TVStudy software and development and release of repacking data,” said Gary Epstein, head of the FCC’s Incentive Auction Task Force, who opened the workshops. “These are technical but crucial parts of the incentive auction,” he said. “We're exploring this important concept as a way of making the reverse auction work efficiently while meeting key statutory requirements of the spectrum act.”
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The interservice interference methodology is equally important, Epstein said, as it “is an alternative to other approaches proposed by stakeholders, including a fixed pre-defined geographic separation between TV and wireless services.”
"The feasibility checking will ensure that there exists at least one feasible channel assignment for stations that are going to remain on the air,” said Brett Tarnutzer, assistant chief of the Wireless Bureau. “The question we're asking [is] whether a given set of TV stations could be assigned a channel in a particular band such that none of the interference constraints … are violated.”
The FCC’s decision would be based on three key inputs -- a question file listing the stations the FCC is trying to assess the feasibility of, a domain file listing the channels a station can be assigned and an interference file, Tarnutzer said. “These are fed into a feasibility checker and the result is one of three answers,” he said. “Yes, there exists at least one way that you could assign channels to this set of stations that you don’t violate any constraints, no, there’s no way to assign them each a channel … or that it couldn’t find a definitive yes or no answer within the time allotted.”
Predictions for interservice interference are focused on trying to determine what the separation between broadcast and wireless signals should be, and how they'll affect spectrum in surrounding markets, said Office of Engineering and Technology Chief Julius Knapp.
To use spectrum efficiently while protecting signals, the OET model presented at the workshop used a “more granular” method of analysis, taking a detailed look at each station’s transmission characteristics and the surrounding terrain using the same TVstudy software, said OET Associate Policy Chief Matthew Hussey. Though the system creates “quite a bit of data,” the benefits derived from the “more precise methodology” outweigh the complexity it adds to the process, he said. Using TVstudy to calculate both TV-to-TV interference and interservice interference is “complementary,” he said.
Since it’s very difficult to prevent 100 percent of interference, the OET model suggests placing “unavoidable interference” in the spectrum used for uplink, which would leave the downlink band clear nationwide and promote interoperability, said OET Technical Analysis Branch Chief Bob Weller.
"This data could allow us to map the impact of TV station assignment on wireless operations when determining what’s offered in forward auction,” said Tarnutzer. “This is just the first step in the prevention of interservice interference in the auction.”