Although the FCC recently gave the green light to Ligado Networks’ application to deploy a low-power terrestrial network in the L-Band, the years-long debate is not over yet, with legislators raising concerns as Pentagon officials continued to warn of harmful interference with civil and military GPS systems.
The House Armed Services Committee (HASC) on Thursday sent a letter to FCC commissioners expressing “deep concern” with the agency’s unanimous April 19 decision and urged additional mitigation steps to address interference issues flagged by the national security community.
“The national security community was unanimous in the judgement that approval of the use of certain portions of the L band spectrum could pose an unacceptable risk to the use of the Global Positioning System (GPS) in the United States,” the letter states. “In addition, other federal and nonfederal users of this spectrum have raised serious concerns, including satellite communications providers and airlines."
The HASC asked commissioners to respond to questions including the legal analysis for their decision and whether each received a briefing on classified Department of Defense test data that accompanied the Department of Transportation’s 2018 Adjacent Band Compatibility Testing.
This comes after Pentagon officials on Wednesday testified before the Senate Armed Services Committee about national security impacts from Ligado’s planned network, which is meant to support 5G and IoT services.
FCC commissioners and Ligado representatives were not invited to the hearing, but Ligado sent a letter to the Senate committee leaders, pointing to extensive testing and consultation with federal agencies, and GPS device manufacturers over the years to develop its proposal and ensure the network can protect GPS users.
“The FCC’s decision was delivered after four years of consideration, carefully and meticulously analyzes the extensive record, all of the testing in the record, the DoD’s position, national and international standards on protecting GPS, and all available evidence, and it concluded on a bipartisan and unanimous basis that the Ligado spectrum proposal will not affect GPS devices.”
The letter, signed by Ligado Chairman Ivan Seidenberg and CEO Doug Smith, also cited “stringent conditions” imposed by the FCC order to protect GPS. Those include a 23-megahertz guard band to protect GPS users; limiting base stations to low power levels of 9.8 dBW (a more than 99% reduction from the 32 dBW Ligado proposed in its 2015 application); coordination and advanced deployment notification requirements; and expectations that Ligado will bear the burden of replacing or repairing any affected U.S. government receivers.
At the senate hearing, however, Department of Defense Chief Information Officer Dana Deasy said (PDF) the conditions “fall short in many critical respects.” The 23 MHz guardband wouldn’t protect many varieties of GPS receivers since they’re designed to tolerate interference from space systems in adjacent spectrum but would be overpowered by the proposed terrestrial system, according to Deasy. Coordination and replacement conditions are also unfeasible, he said, noting both the scale and the classified nature of military GPS use.
“There are millions of GPS receivers in use by federal agencies, industry and general consumers that are mobile,” Deasy said. “Given the massive scale, there is no way to protect those mobile operations.”
“The inability of Ligado to meet these stringent conditions in order to protect GPS is why the FCC should have rejected the Ligado proposal, based on the extent that no practical solution or mitigation is available that would permit Ligado to operate without high likelihood of widespread interference,” Deasy said. “The bottom line is that 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.”
In contrast, Ligado stressed that after four years and what amounted to thousands of hours of testing, results showed the network wouldn’t be an issue for GPS devices.
“In its Order, the FCC concluded that GPS devices are absolutely entitled to the very highest level of protection in the spectrum that belongs to GPS and that the Ligado proposal gives them that protection,” the Ligado letter stated. “From the study conducted by the DOT, the study conducted by NASCTN, and every other study, the record is, and has for years been, unambiguous and crystal clear: no GPS device will experience any issue whatsoever—even the smallest change in the background noise level (1 dB)—when operating in the band allocated to GPS.”
It added that throughout the FCC proceeding, the DoD “never filed any technical information or analysis, and at no point did DoD provide information expressing specific technical concerns to the FCC. That remains true to this day.”
The HASC asked if that assertion was independently confirmed by the FCC commissioners through the classified DoD briefings, saying it’s “essential that the commissioners understand the full implications when making a decision of this magnitude.”
The HASC wants FCC commissioners to reply within seven days.