The FCC-Approved Ligado Network and
Potential Technical Issues for DOD Use of
GPS
June 1, 2020
On April 20, 2020, the Federal Communications Commission (FCC) unanimously authorized 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.”
These frequency bands are traditionally used for satellite operations. The Department of Defense (DOD)
opposed this decision—along with the Departments of Homeland Security, Transportation, the Interior,
and Justice; the Federal Aviation Administration; and others—due to concerns that Ligado’s proposed
network could interfere with signals from satellites to Global Positioning System (GPS) receivers.
Congress may consider the FCC’s decision, as well as DOD and other federal agency concerns about the
decision, as it conducts oversight of the FCC. Congress may also consider broader issues related to fifth
generation (5G) mobile technologies, such as the allocation of spectrum among competing users and the
impact of spectrum decisions on national security and GPS modernization.
How GPS Works
GPS consists of a constellation of at least 24 satellites in six orbital planes to provide global coverage,
ground-based receivers, and user equipment such as smartphones. The satellites are positioned
approximately 12,500 miles above the Earth’s surface, in what is termed Medium Earth Orbit (MEO).
Because of the distance the radio waves have to travel from MEO to GPS receivers on Earth, the satellite
signals arriving to the earth’s surface are extremely weak—approximately negative 160 dBW (see Figure
1). GPS satellites broadcast two primary signals, which are used for position, navigation, and timing: L1,
an unencrypted course acquisition signal (broadcast around 1575 MHz), and L2, also known as P(Y)
code—the encrypted signal used by the military for improved accuracy (broadcast around 1227 MHz). L2
in turn enables advanced military capabilities like precision-guided munitions. Other military applications
using GPS include navigation systems, communications encryption, and command and control platforms,
such as blue force tracker, which monitors the location of friendly forces. Due to the complexity of L2
encryption, military GPS equipment must first acquire an L1 signal to identify its relative position before
acquiring an L2 signal.
