WASHINGTON — The chairman of the Federal Communications Commission defended the use of spectrum for 5G wireless services while a key senator called for a hearing on potential interference such services could have with space-based weather observations.

At a hearing of the Senate Commerce Committee June 12, FCC Chairman Ajit Pai dismissed claims that 5G services operating at the 24 gigahertz band could interfere with weather observations and thus degrade the accuracy of forecasts, saying studies that made those claims were flawed.

“Over the last two and a half years we have patiently waited for a validated study to suggest that our proposed limit is inappropriate. We’ve never gotten such a validated study,” he said on one of several occasions during the two-and-a-half-hour hearing when the subject came up.

He said the commission did receive a study that made such claims. Once the FCC’s staff obtained the source code for the modeling that estimated the potential interference, “the assumptions that clearly underlaid were so flawed as to make the study, in our view at least, meaningless.”

Pai’s comments were the latest salvo that has pitted the FCC against the Department of Commerce and NASA regarding use of the 24 gigahertz band for 5G services. Commerce, which is the parent department of the National Oceanic and Atmospheric Administration, and NASA have argued that allowing use of that band for 5G services could create interference with satellite observations of water vapor used in weather forecasting.

Asked about potential interference at the hearing by Sen. John Thune (R-S.D.), former chairman of the committee, Pai referred to “one of our federal partners” who offered that study but only in the last month provided the source code. “In our view, the assumptions that undergird that study are fundamentally flawed,” he said. That included not taking into account that 5G services will use beam-forming technologies rather than wider broadcasts to limit potential interference.

“We believe, ultimately, that we can have the best of both worlds. We can allocate the 24 gigahertz band for 5G and we can protect those very important passive weather sensors and other functionalities that other agencies and other parts of the government work on,” he said.

He also said that the debate could affect planning for the upcoming World Radiocommunication Conference this fall. “If the Department of Commerce’s position were to prevail, not only would this spectrum be unusable for 5G domestically, but we would also put at risk the U.S. position at the upcoming international conference in October,” he said. That would affect the use of the band worldwide. “This is not a road we want to go down.”

“I’m personally frustrated,” he said at one point. “The Department of Commerce has been blocking our efforts at every single turn.”

The two other Republican commissioners at the hearing, Brendan Carr and Michael O’Rielly, agreed with Pai when polled by the committee’s chairman, Sen. Roger Wicker (R-Miss.) about whether 5G services at 24 gigahertz posed any interference issues. The FCC’s two Democratic commissioners, Jessica Rosenworcel and Geoffrey Starks, were more noncommittal, instead arguing that the interagency dispute could disrupt ongoing auctions of spectrum.

“We have to resolve issues like this before we go to auction,” Rosenworcel told Wicker. “I have not been in the meetings where we have gotten to the bottom of just what threshold for out-of-band emissions should apply, but I share your disappointment that we are in this position right now. I don’t think it’s fair and I don’t think it’s right.”

Earlier in the hearing, Sen. Maria Cantwell (D-Wash.), ranking member of the committee, brought up the interference issue. “Peer-reviewed science research has concluded that, without key vapor data that could vanish due to actions on where spectrum has been allocated, this could impact our weather forecasting,” she said in her opening remarks.

Cantwell also discussed the potential 24 gigahertz interference issue during a May 14 hearing of the committee’s space subcommittee, asking NASA Administrator Jim Bridenstine and Kevin O’Connell, director of the Office of Space Commerce, about interference. Bridenstine and Commerce Secretary Wilbur Ross had previously warned about interference in a letter to the FCC in February.

“The 24 gigahertz band is critically important for our ability to characterize the amount of water vapor in the atmosphere,” Bridenstine said. “There is a risk that, if we do not have access to that spectrum, that our weather forecasting could be degraded. We are working right now with the FCC to work through a solution.”

“Whenever we have these spectrum auctions of any kind, we really need to be very careful,” said O’Connell, who echoed Bridenstine’s worries about a “deep reduction in the quality of our Earth observations for weather prediction.”

At the June 12 hearing, Cantwell said that Sen. Wicker had agreed to hold a separate hearing by the Senate Commerce Committee on the issue “in the near future.”

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...