WASHINGTON — The House Armed Services Committee fired the latest salvo in a growing dispute over the Federal Communications Commission’s approval of a 5G network that could interfere with GPS.

In a May 7 letter committee leaders asked FCC commissioners to reconsider their approval of Ligado’s proposal to use portions of the L-band spectrum for a 5G cellular network and argued that the order disregards federal law.

The letter from Committee Chairman Adam Smith (D-Wash.) and Ranking Member Mac Thornberry (R-Texas) says the FCC order did not comply with Section 1698 of the National Defense Authorization Act for Fiscal Year 2017 which prevents the commission from approving commercial terrestrial operations in certain portions of the L band spectrum until 90 days after the commission resolves concerns of harmful interference to GPS devices.

“We urge the commission to reconsider and impose additional mitigation steps to address the concerns of these users,” said the letter, which was endorsed by 20 lawmakers.

The letter was sent hours after the Senate Armed Services Committee wrapped up a hearing where DoD officials testified that they provided extensive data to the FCC proving that Ligado’s terrestrial network would cause interference both for civilian and military users of GPS.

HASC leaders said in the letter they plan to hold a classified hearing to review DoD’s testing reports and discuss the results with the FCC.

“It is essential that the commissioners understand the full implications when making a decision of this magnitude,” says the letter.

The Ligado dustup has become a microcosm of the larger debate over government and private use of spectrum as the United States worries it is falling behind in the global 5G technology race.

“Our committee is actively seeking solutions that will facilitate and direct DoD to share as much spectrum as possible for commercial use, but the nation faces threats that will require DoD to continue to use parts of the spectrum needed for 5G,” the HASC said. “We must be able to develop solutions that provide for the defense of the nation, and unleash the economic potential of 5G.” But they warned that national security concerns have to be taken into account.

The HASC asked each of the five FCC commissioners to provide by May 14 copies of the legal analysis that led them to their decision. It also asks the commissioners to confirm that they each received a briefing from DoD on the classified test data contained in the Department of Transportation Adjacent Band Compatibility Assessment from April 2018.

One of the sticking points is the 23 MHz “guard band” the FCC required as a buffer between Ligado’s network and GPS. DoD officials told the SASC on May 6 that the guard band won’t prevent interference with GPS signals. They insisted that they were completely surprised and caught off-guard by the FCC’s order.

An FCC spokesperson said in statement May 7 that many “untrue statements” were made at the hearing.

“The Department of Defense and every executive branch agency that is part of the Inter-department Radio Advisory Committee was given our draft decision last autumn, so the assertion that they were blindsided by it this April is preposterous.”

The metric used by the Department of Defense to measure harmful interference “does not, in fact, measure harmful interference,” the spokesperson said. “The testing on which they are relying took place at dramatically higher power levels than the FCC approved.”

The FCC made a unanimous, bipartisan decision “based on sound engineering principles,” the spokesperson said. “We stand by that decision 100% and will not be dissuaded by baseless fear mongering.”

Sandra Erwin writes about military space programs, policy, technology and the industry that supports this sector. She has covered the military, the Pentagon, Congress and the defense industry for nearly two decades as editor of NDIA’s National Defense...