Spectrum Interference Issues: Ligado, the L-Band, and GPS

Spectrum Interference Issues: Ligado, the L-Band, and GPS

May 28, 2020
Spectrum Interference Issues: Ligado, the L-Band, and GPS
On April 20, 2020, the Federal Communications
conditions, with advisement from the Interdepartment
Commission (FCC) unanimously approved a controversial
Radio Advisory Committee.
application by Ligado Networks, a U.S. satellite
Guided by these international and domestic agreements and
communications company, to deploy a terrestrial
requirements, the FCC has designated segments of the L-
nationwide network using L-Band radio spectrum. Ligado’s
Band for specific uses to avoid interference (see Figure 1).
stated intent is to offer a combined satellite and terrestrial
The lower portion (1525-1559 MHz) is used for space-to-
communications network that will enable other
Earth satellite downlink communications and the upper
telecommunications carriers to deploy 5G services and
portion (1610-1660.5 MHz) for Earth-to-space satellite
provide wireless internet to support industrial networks.
uplink communications. The segment in between (1559-
The Ligado case has triggered debate within the federal
1610 MHz) is designated for civilian GPS signals.
government about priorities for use of the radio spectrum
Figure 1. L-Band
and the framework in which spectrum decisions are made.
Federal agencies including the Departments of Defense
(DOD), Homeland Security, and Transportation and many
members of the Armed Services committees in both Houses

of Congress object to the FCC’s decision. They argue that
Source: Adapted by CRS from Richard N. Clarke, Are Popular
“loud” signals from Ligado’s high-power terrestrial
Wireless Services Like Wi-Fi and GPS Becoming the Pirate Radio of the 21st
transmitters will overpower “soft” signals from Global
Century?, June 28, 2016, https://papers.ssrn.com/sol3/papers.cfm?
Positioning System (GPS) satellites operated by DOD,
abstract_id=2847792.
potentially disrupting military operations. GPS device
Notes: Numbers show frequency ranges of each segment in MHz.
manufacturers, the aviation industry, public safety agencies,
Interference may occur when high-power signals
and others that rely on GPS oppose the FCC’s decision,
transmitted in one band disrupt signals in a nearby band due
citing potential interference with billions of GPS-reliant
to out-of-band emissions (OOBE). Interference may also
devices and systems. Several Members of Congress, the
occur when receivers tuned to one band inadvertently
Secretary of State, and the Attorney General have supported
receive signals from a nearby band, known as out-of-band
the FCC decision, asserting that it could accelerate
reception (OOBR). To prevent interference, satellite
domestic 5G deployments and increase the competitiveness
operators can create guard bands (narrow bands of unused
of U.S.-based manufacturers of 5G equipment.
frequency), reduce the power levels from terrestrial
The L-Band
transmitters to limit OOBE, or adjust or upgrade GPS
Ligado’s proposed network would use the L-Band, the
equipment to limit OOBR.
segment of the radio spectrum in the 1-2 gigahertz (GHz)
Background on the Ligado Proposal
frequency range, a portion of which (1525 MHz-1660.5
In 2003, the FCC adopted rules allowing satellite
MHz) is allocated for satellite use. L-Band radio waves
companies operating in the L-Band to deploy Ancillary
travel long distances and penetrate clouds, fog, and
Terrestrial Component (ATC) stations—terrestrial
vegetation, making them useful for satellite
infrastructure to fill satellite coverage gaps. Providers were
communications and position, navigation, and timing
required to offer integrated (satellite/terrestrial) services
services, such as GPS, that provide precise geolocation and
using dual-mode devices. The rules were intended to
timing information to enabled devices. L-Band users
increase the efficiency of spectrum use, reduce service
include private satellite communications operators, space
costs, increase operational capacity, enhance public safety
agencies in various countries, DOD, the Federal Aviation
communications, and strengthen domestic competition.
Administration (FAA), the National Oceanic and
Atmospheric Administration, and private
In 2004, the FCC authorized a company called Mobile
telecommunication service providers, among others.
Satellite Ventures to operate ATC stations to supplement its
satellite services. Other L-Band users objected, citing
Use of the L-Band is coordinated globally by the
interference concerns, and the company did not build a
International Telecommunications Union (ITU), as
terrestrial network. In 2009, after making an agreement
specified in its Radio Regulations. North American use of
with another satellite company to gain access to a larger,
the L-Band is coordinated by satellite operators, pursuant to
contiguous segment of spectrum and negotiating more
a 1996 international agreement—the Mexico City
flexible interference standards related to ATC stations,
Memorandum of Understanding (MOU). Domestically, the
Mobile Satellite’s parent company, SkyTerra, requested that
FCC manages commercial use of the L-Band through
the FCC waive its ATC rules and grant it authority to
licensing, and the National Telecommunications and
substitute the more flexible technical requirements. GPS
Information Administration (NTIA) manages federal
service providers and users, including government agencies,
agency use, assigning frequencies and setting terms and
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Spectrum Interference Issues: Ligado, the L-Band, and GPS
objected, citing the potential for interference between ATC
NTIA dated March 23, 2020, strongly opposed the
stations and GPS receivers. The objectors argued that U.S.
application, citing 10 U.S.C. §2281, which states that the
law and FCC regulations placed the burden on SkyTerra to
Secretary of Defense “may not agree to any restriction on
mitigate interference. Both sides submitted test results to
the GPS proposed by the head of a department or agency of
the FCC to support their claims. In March 2010 the FCC
the United States outside DOD that would adversely affect
granted the waiver, citing public interest.
the military potential of GPS.”
In 2010, SkyTerra was incorporated into a new firm,
Some carriers say the proposed network would provide
LightSquared, which proposed to deploy a nationwide
access to spectrum to expand 5G services, while others note
satellite/terrestrial 4G network to carry mobile phone and
that the band has not been designated for 5G use globally
broadband traffic. NTIA, on behalf of several federal
and no current equipment or device can operate in the band.
agencies and GPS users and equipment manufacturers,
FCC Draft Order and Reaction to Draft Order
objected, claiming the terrestrial base stations would
“overload” GPS receiver
On April 16, 2020, the FCC released a draft order to
s and interfere with GPS services.
In January 2011, the FCC approved LightSquared’s request
approve Ligado’s application. Secretary of State Mike
Pompeo urged approval, saying quick action by the FCC is
on the condition that it address GPS interference concerns.
“vital to our national security and will help ensure that the
LightSquared modified its proposal and submitted technical
United States is the global leader in advanced
reports to the FCC purporting to show that interference
technologies.” Attorney General William Barr stated that
could be mitigated. GPS trade groups, interagency technical
FCC approval “is essential if we are to keep our economic
bodies, and federal agencies submitted technical reports
and technological leadership and avoid forfeiting it to
purporting to show continued potential for interference. The
Communist China.”
FCC withdrew approval in February 2012. Three months
later, LightSquared declared bankruptcy.
FCC Decision on Ligado and Reactions
The company emerged from bankruptcy in 2015 and was
On April 20, 2020, the FCC unanimously approved
Ligado’s application
subsequently renamed Ligado Networks. After
, with conditions. Ligado agreed to (1)
reconfiguring its use of its L-Band frequencies, in May
deploy a low-power terrestrial nationwide network in bands
2018 Ligado modified its proposal and sought FCC
farther away from the GPS band; (2) mitigate interference
approval to deploy a terrestrial network using bands farther
by reducing power levels at its base stations to 99.3% less
away from GPS (see Figure 2). It stated that it had resolved
than proposed in its 2015 application; (3) create a guard
differences with GPS operators and users and the FAA.
band greater than 20 MHz between its terrestrial service
and the GPS band, and guard bands between its terrestrial
Figure 2. 2018 Ligado Proposal
service and other users; and (4) report base stations’
locations and mitigate any reports of interference.
Several Members of Congress praised the FCC decision,
asserting that Ligado’s project will lead to more efficient
use of spectrum, expand broadband use, and enable 5G
innovation. Conversely, many members of the House and
Senate Armed Services Committees expressed their

opposition, citing national security concerns. The Senate
Source: “Impact of Ligado’s Proposal on SATCOM, Aviation and
committee held a hearing on May 6, 2020, and sent a letter
Weather Data Users (Coalition Deck),” September 2019,
to the FCC opposing the project, signed by 32 Senators. On
https://ecfsapi.fcc.gov/file/10906015584180/Coalition%20Deck%
May 22, 2020, the NTIA filed a petition with the FCC to
20for%20Sept.%204%202019%20FCC%20meetings.pdf.
stay the order, and a separate petition to reconsider.
Notes: The proposal includes multiple guard bands (yel ow). It
Considerations for Congress
eliminates the previously proposed use of the 1545-1555 MHz band
As demand for mobile data increases, and new data-
to create a wider guard band between its downlink operations and
intensive uses emerge, such as autonomous vehicles, the
GPS. GSO = Geostationary Orbit; MSS = Mobile Satel ite Service;
potential for disputes over the allocation, management, and
AWS-3 = Advanced Wireless Services (mobile communications).
use of spectrum is likely to increase. This includes disputes
Viewpoints on the 2018 Ligado Proposal
between federal agencies such as the FCC and the NTIA.
Commenters were divided on the Ligado proposal. Some
Congress can potentially examine current federal processes
telecommunication carriers, infrastructure equipment
for setting spectrum priorities, balancing competing user
providers, advanced technology firms, and consumer
needs, and resolving spectrum disputes. Options for
advocacy organizations supported the proposal, saying it
Congress could include a 2004 recommendation by the
would make more spectrum available for innovative
Government Accountability Office that a neutral arbiter,
technologies and advanced 5G services.
such as an office within the White House or the National
Academies of Sciences, Engineering, and Medicine, should
GPS service providers, equipment makers, and GPS users
provide objective review of technical reports and resolve
objected, citing OOBR concerns. Several federal agencies
disputes between competing users and uses.
objected to Ligado’s proposal. In December 2019, NTIA
wrote to the FCC on behalf of the Executive Branch
Jill C. Gallagher, Analyst in Telecommunications Policy
recommending it reject the proposal. In March 2020, the
Alyssa K. King, Analyst in Transportation Policy
U.S. Air Force sent NTIA a memorandum signed by 12
Clare Y. Cho, Analyst in Industrial Organization and
federal agencies, describing potential impacts to military
Business
operations if GPS systems are disrupted. A DOD letter to
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Spectrum Interference Issues: Ligado, the L-Band, and GPS

IF11558

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