Could 5G cause GPS problems?

Pushback is building against a Federal Communications Commission decision to let Ligado Networks use of spectrum adjacent to sensitive satellite-based Global Positioning Systems.

"This is a complex issue, but it boils down to risk," said Jim Inhofe, (R-Okla.), chairman of the Senate Armed Services Committee at a May 6 hearing. "We shouldn't risk GPS signals for the benefit of one company."

Ligado Networks is looking to deploy a low-power nationwide 5G network, a plan the FCC backed on April 20, after making the decision over the previous weekend, according to Inhofe.

"A few powerful people made a hasty decision over the weekend," Inhofe said. "Ligado waited until the whole world was distracted by the virus and in total secrecy on a weekend passed the most controversial licensing bill in the history of the FCC," he said.

“What I would want to do would be to get [the FCC decision] reversed,” said Inhofe later in the hearing.

The FCC decision gave conditional go-ahead to commercial wireless provider Ligado's plans to deploy a low-power terrestrial nationwide 5G network in the L-Band.

The approval alarmed the DOD, as well as many lawmakers and other stakeholders because the spectrum is directly adjacent to GPS bands.

In an April 22 column published in Defense News, Inhofe and other defense committee leaders from both parties said the FCC should withdraw its approval of Ligado's application and work with the National Telecommunications and Information Administration and the Defense and Transportation Departments on a more viable solution.

"There are too many unknowns and the risks are too great to allow the proposed Ligado system to proceed in light of the operational impact to GPS," said Deasy in his testimony. Military systems receivers are only a portion the GPS gear in military systems, which would confound replacement or remediating to accommodate Ligado's network.

During his testimony, Griffin said transmissions from Ligado's ground-based system would swamp and overwhelm satellite transmissions for GPS systems. "It would be like trying to hear the sound of leaves rustling over the noise of 100 jets taking off," he said.

"Ligado recognizes their system causes interference," said Deasy, which is why guard band and power reductions were part of the plan.

In giving Ligado the go-ahead, the FCC said the company had to protect GPS bands from interference, including requiring Ligado to have "significant" 23 Mhz guard-bands in its own spectrum to separate its transmissions from neighboring satellite GPS operations, as well as limiting the power levels to its base stations and respond to entities that had experienced interference.

"The FCC's protections are impractical. Guard-band and power reductions won't work," said Deasy. He said later that DOD officials have had a "good history" working on spectrum issues in which the military and commercial sectors have competing equities. The "typical give and take" between DOD and the FCC on the Ligado network, however, was non-existent. "We were caught off guard" when the FCC voted to approve it on that April weekend, he said.

Deasy said didn't see the FCC's decision on Ligado's network coming, because discussions long before it tended to show the agency knew that most federal agencies, including the Federal Aviation Administration, Department of Transportation and others, as well as U.S. airlines, opposed it.

Over the next few months, Deasy said DOD will embark on testing 5G capabilities to see how some applications, such as augmented virtual reality, smart bases and warehouses would work alongside commercial applications effectively. Dynamic spectrum sharing that better coordinates mid-band spectrum among commercial and defense networks, he said, is a better way forward for 5G services.

The FCC noted in announcing the approval of all five commissioners, that the Ligado plan had broad support from the likes of Secretary of State Mike Pompeo and Attorney General William Barr, to Sen. Mark Warner (D-Va.) Rep. Doris Matsui (D-Calif.). FCC Chairman Ajit Pai called the approval "another step forward for American leadership in 5G and advanced wireless services."

However, even some of the FCC's commissioners weren't completely convinced the plan won't interfere with GPS.

"This decision was an extremely close call," said FCC Commissioners Jessica Rosenworcel and Geoffrey Starks in a joint April 22 statement. "While many stakeholders now back the ancillary terrestrial service that is the subject of this order, others remain concerned about the potential for harmful interference."

Additionally, they said the decision exposed how disjointed federal spectrum management is, with the FCC moving one way, and the DOD another.

"As we move to the next generation of wireless service, it is imperative that we have an improved inter-agency system and a stronger whole-of-government approach to our 5G effort," they said.

During the hearing, several senators said they wanted to hear from the FCC and Ligado to balance out their understanding of the issue.

A version of this article first appeared on FCW, GCN's sibling publication.