INSIGHTi
National Academies of Sciences, Engineering,
and Medicine Report on Ligado Networks and
the Interference Debate
September 23, 2022
On April 19, 2020, the Federal Communications Commission (FCC) approved an application by Ligado
Networks, a U.S. telecommunications company, to deploy a terrestrial network within the United States
using specific segments of L-Band spectrum—spectrum typically used for satellite services. Federal
agencies including the Departments of Defense (DOD), Homeland Security, and Transportation and
several Members of the House and Senate Armed Services committees objected to the decision. They
contend “loud” signals from Ligado’s terrestrial transmitters will overpower the reception of “soft”
signals from Global Positioning System (GPS) satellites and other mobile satellite services (MSS),
potentially impacting DOD operations near Ligado transmitters in the United States. This was discussed
during a May 2020 Senate Armed Services Committee hearing. Some Members of Congress, GPS
experts, GPS device manufacturers, the aviation industry, weather organizations, and others also opposed
the decision due to interference concerns. The FCC asserts that its decision, which required Ligado to
mitigate interference, would enhance U.S. leadership in advanced wireless services and had support from
many Members of Congress and Trump Administration officials.
National Telecommunications and Information Administration (NTIA) Petitions
On May 22, 2020, NTIA filed one petition with the FCC on behalf of the executive branch to stay the
order and another petition to reconsider the decision. On January 19, 2021, the FCC declined to stay the
order.
Congress Mandates Review of FCC Decision
The William M. (Mac) Thornberry National Defense Authorization Act for Fiscal Year 2021 (P.L. 116-
283) required, among other things, that DOD enter into an agreement with the National Academies of
Sciences, Engineering, and Medicine (NASEM) to conduct an independent technical review of the FCC’s
decision and to assess its impact on DOD operations.
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NASEM Report
On September 9, 2022, NASEM released its report. NASEM found “most commercially produced general
navigation, timing, cellular, or certified aviation GPS receivers will not experience significant harmful
interference from Ligado emissions,” but also that “some high-precision receivers, used for applications
such as farming, geodesy, and surveying and sold before about 2012, can be vulnerable to significant
harmful interference.” It also found certain MSS receivers provided by Iridium Communications Inc. for
DOD and others would experience harmful interference, under certain conditions.
In P.L. 116-283, Congress directed NASEM to compare two approaches used by the FCC to evaluate
interference—one based on a signal-to-noise interference protection criterion and the other based on
device-by-device measurement of GPS position error—to determine if they effectively mitigate
interference risk. NASEM found neither approach effective. It concluded that interference evaluation is
complex, noting multiple non-quantifiable definitions of harmful interference; lack of consensus about
which definitions to use; and that interference varies by device type and use.
According to NASEM, neither evaluation approach provides an “engineerable, predictable standard that
new entrants can readily use to evaluate impact.” In the absence of definitive receiver standards, “a new
applicant for emissions in an adjacent channel will have great difficulty in determining the emitter power
levels and stand-off distances that will be guaranteed not to cause Harmful Interference to [existing] GPS
receivers. A GPS receiver designer will be unable to design a receiver that will be guaranteed to tolerate
unknown potential future allowed levels of adjacent-band power.” NASEM also found “all GPS receiver
manufacturers could field new designs that could coexist with the authorized Ligado signals and achieve
good performance even if their existing designs cannot.” NASEM recommends the FCC work with
industry to develop receiver standards and with NTIA to resolve spectrum issues, conduct joint studies
and testing, define receiver performance standards, and set adoption timelines.
Responses to NASEM Report
DOD, NTIA, and Ligado released separate statements indicating the report validated their previous
positions.
DOD issued a statement that NASEM’s findings supported its testing approach, confirmed Ligado
emissions could harmfully interfere with DOD’s high-precision GPS receivers and mobile satellite
services, and concluded that FCC mitigation measures were “impractical, cost prohibitive, and possibly
ineffective.” The NTIA issued a similar statement and suggested that the FCC reconsider its decision.
Ligado Networks noted that NASEM found most GPS receivers will not experience harmful interference.
It stated “a small percentage of very old and poorly designed GPS devices may require upgrading,” and
said it is ready to assist agencies with outdated devices. In a September 12, 2022, letter to the FCC,
Ligado announced it is not moving forward on its trial deployment in order to work with NTIA on the
issue.
Considerations for Congress
As demand for mobile data increases, so do the possibility of spectrum disputes, including between the
FCC and NTIA. Congress designated the FCC as the lead agency in allocating spectrum. Former FCC
Chairman Ajit Pai argued the FCC has “put the U.S. on a path to lead the world in wireless innovation for
many years to come.” Meanwhile, some FCC decisions have raised interference concerns for federal
agencies and NTIA, which manages federal spectrum use. Bills have been introduced in the 117th
Congress (H.R. 2501, S. 1472) that would require the agencies to coordinate on spectrum decisions,
which the FCC and NTIA have started to do under their new Spectrum Coordination Initiative.
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Another area of potential congressional interest may be FCC and NTIA efforts to improve receiver
performance. In April 2022, the FCC issued a Notice of Inquiry examining receiver performance for
nonfederal uses. The FCC typically focuses its rules on transmitters, but acknowledges receiver
performance also drives spectrum decisions. Some industry organizations oppose fixed federal standards,
saying flexibility fuels innovation. NTIA submitted comments on its efforts to improve receiver
performance to protect federal functions.
Adoption of receiver standards could improve certainty for new entrants and expand spectrum use. New
standards may require entities, including federal agencies, to replace older receivers with new, higher-
performing receivers, which may impose costs.
Congress may be interested in monitoring the National Spectrum Strategy, and whether NTIA and FCC
are working to build consensus on future spectrum needs and interference standards.
Author Information
Jill C. Gallagher
Analyst in Telecommunications Policy
Disclaimer
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