Implications of the FCC-Approved Ligado Network for the Department of Defense

INSIGHTi

Implications of the FCC-Approved Ligado
Network for the Department of Defense
Updated November 1, 2023
On April 20, 2020, the Federal Communications Commission (FCC) unanimously approved an
application by Ligado Networks LLC (Ligado) to “deploy a low-power [9.8 decibel watts (dBW)]
terrestrial nationwide network in the 1526-1536 MHz, 1627.5-1637.5 MHz, and 1646.5-1656.5 MHz
bands [of the electromagnetic spectrum] that will primarily support Internet of Things (IoT) services.”
The U.S. military and other national security organizations traditionally use these frequency bands for
satellite operations. (For an in-depth discussion of the electromagnetic spectrum, see CRS Report
R46564, Overview of Department of Defense Use of the Electromagnetic Spectrum.) DOD, along with
agencies represented by the National Telecommunications and Information Agency (NTIA), opposed this
decision. That opposition related to the prospect that Ligado’s proposed network could interfere with
signals from satellites to Global Positioning System (GPS) receivers and from other satellite
communications providers. DOD notes that GPS is “widely and heavily integrated throughout [the
department]” (e.g., in precision weapons; air, land, and sea navigation; communications and network
synchronization) and is “critical to the lethality of the department’s forces.”
Congress, in Section 1663 of the William M. (Mac) Thornberry FY2021 National Defense Authorization
Act (P.L. 116-283), directed the Secretary of Defense to seek an independent technical assessment of the
FCC’s Ligado authorization order (FCC 20-48) from the National Academies of Sciences, Engineering,
and Medicine (NASEM). This assessment was to evaluate the potential for harmful interference to GPS
receivers and other mobile satellite services; to review potential methods for mitigating harmful
interference with DOD GPS devices or with devices “relating to or with the potential to affect the
operations and activities of the Department”; and to provide associated recommendations to DOD.
NASEM released this study on September 9, 2022.
DOD Concerns and Previous Studies on GPS Interference
In both its formal response to FCC 20-48 and its May 6, 2020, testimony before the Senate Armed
Services Committee (SASC), DOD cited two studies that shaped its belief that the Ligado network
“would cause unacceptable operational impacts and adversely affect the military potential of GPS”: a
2018 Department of Transportation (DOT) study and a 2016 classified study conducted by the U.S. Air
Force. Based on the DOT study findings for certified aviation, Ligado submitted an amended application
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to the FCC, reducing its proposed power levels. Per the FCC ruling, Ligado also agreed to maintain a 23-
MHz guard-band of unused spectrum designed to separate its transmissions from GPS, thus attempting to
mitigate potential interference.
DOD and the FCC disagreed, however, about the definition of and method of determining “harmful
interference” to GPS. While the FCC used a “performance-based” standard in assessing and approving
the Ligado network, DOD used the International Telecommunication Union standard of a 1 decibel
increase in noise within the respective GPS frequency range.
FY2021 NDAA-Mandated NASEM Study on Potential GPS Interference
The FY2021 NDAA-mandated NASEM study on potential GPS interference first assessed these
competing methods of determining “harmful interference” and determined that neither “[provides] an
engineerable, predictable standard that new entrants can readily use to evaluate impact.” Furthermore, the
study concluded that, while DOD’s method is “the more comprehensive and informative” of the two, it
may represent an “overly conservative” approach to the protection of GPS devices. NASEM then
examined the potential for harmful interference to GPS receivers and found that most commercially
produced GPS receivers—with the exception of some high-performance receivers—“will not experience
significant harmful interference from Ligado emissions as authorized by the FCC.” In contrast, NASEM
concluded that Iridium satellite systems, which provide mobile satellite services for the U.S. military,
“will experience harmful interference on their downlink [1617.775-1626.5 MHz] ... while those Iridium
terminals are within a significant range of a Ligado emitter—up to 732 meters.” This conclusion
“assumes a single user; the situation will be both more likely and more severe as the spatial density of the
users increases.” A classified annex contains additional details about NASEM’s assessment of the impact
of Ligado emissions on DOD systems. Finally, the NASEM study reviewed “the feasibility, practicality,
and effectiveness of [FCC 20-48’s] proposed mitigation measures” (e.g., “enacting exclusion zones for
Ligado emitters”; “enabling a ‘kill switch’ mechanism for Ligado to turn off emitters in some geographic
locations”). NASEM concluded that, in some cases, these measures “may not be practical at operationally
relevant time scales or at reasonable cost.” Congress may consider the circumstances in which such
measures may be effective.
DOD, NTIA, and Ligado Response
On September 29, 2022, DOD stated, “[the NASEM study] conclusions are consistent with DOD’s
longstanding view that Ligado’s system will interfere with critical GPS receivers and that it is impractical
to mitigate the impact of that interference.” NTIA similarly stated that “Ligado’s terrestrial operations
would cause harmful interference to GPS devices and that a number of the FCC’s mitigations would be
practically unworkable,” while Ligado stated that the NASEM study confirmed a previous FCC finding
that only “a small percentage of very old and poorly designed GPS devices may require upgrading.” On
September 12, 2022, Ligado notified the FCC that it planned to pause a trial deployment of its network, as
Ligado works with NTIA “to resolve in a fair and reasonable manner issues relating to the government’s
ongoing use of Ligado’s terrestrial spectrum.” On October 12, 2023, Ligado filed a complaint in the U.S.
Court of Federal Claims, stating the U.S. government and federal agencies have unlawfully prevented
Ligado from using its spectrum. The complaint further alleges that “[DOD] has taken Ligado’s spectrum
for the agency’s own purposes, operating previously undisclosed systems that use or depend on Ligado’s
spectrum without compensating Ligado.”
Potential Issues for Congress
Congress has passed additional legislation related to FCC 20-48 (see “Legislative Activity” in the
appendix of CRS Report R46564, Overview of Department of Defense Use of the Electromagnetic
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Spectrum) and has continued to express interest in the order’s implementation. For example, on August
17, 2022, eight Senators, including Senators Reed and Inhofe (the chairman and ranking member,
respectively, of the Senate Armed Services Committee), sent a letter to the FCC requesting that the FCC
stay and reconsider FCC 20-48. The letter notes that the Senators “remain gravely concerned that the
Ligado Order fails to adequately protect adjacent band operations—including those related to GPS and
satellite communications—from harmful interference impacting countless military and commercial
activities.”
As Congress continues to evaluate federal agency concerns regarding FCC 20-48, including DOD
concerns related to military operations, it may consider the conclusions of the NASEM study. For
example, Congress may consider NASEM’s proposals for “ways to mitigate further controversies,”
including the implementation of receiver standards or the development of “common receiver assumptions,
which could provide a common point of departure for analytic efforts.” Congress could also consider
whether or not to require greater interagency coordination to ensure that the executive branch
appropriately evaluates and accounts for commercial and national security interests—as well as the rights
of both current and future users—within spectrum allocation processes.


Author Information

Kelley M. Sayler

Specialist in Advanced Technology and Global Security




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