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SPECIAL REPORT: GPS/GNSS
Momentum Builds to Fend Off GNSS

Jamming, Spoofing

By Nitin Dahad

he vulnerability of the Global Positioning System (GPS) is GNSS disruptions prompted the U.S. Department of Transporta-
widely acknowledged. Radio-frequency interference caused tion’s Maritime Administration to issue a warning last year about GPS
by jamming and spoofing is used to degrade a vital synchroni- interference. Its message to the industry stressed the need for using
T zation system providing positioning, navigation, and timing alternative PNT systems. Fearing complacency, the agency highlighted
(PNT) information for critical national infrastructure. interference sources, including multipath propagation, atmospheric
Much of this RF interference emanates from electronic devices, conditions, and GNSS segment issues such as erroneous data uploads.
radio antennas, or modems that are strong enough to drown out the In addition, multiple occurrences of loss of GPS signal during flights
relatively weak signals to Global Navigation Satellite System (GNSS) in Norway in 2017 and 2018 were reportedly attributed to jamming
receivers. That vulnerability creates a tempting target for bad actors. from nearby Russia. In fact, European aviation agency Eurocontrol
“The baddies are always coming up with more and more threats, reported earlier this year that there had been a 2,000% rise in GNSS
so we have to come up with ways to analyze and address them,” said interference incidents since 2018. The report also stressed that RFI
Rod Bryant, senior director of technology for positioning at wireless jamming is disproportionate: While the majority of RFI hotspots are in
specialist u-blox. conflict zones, they also affect civil aviation at distances of up to
Those defenses range from navigation message authentication and 300 km, reflecting jammer overkill.
signal encryption for the European Galileo system to anti-spoofing In another scenario, jammers were used to conceal the location of
frameworks for GPS using similar message authentication schemes. stolen luxury cars and fully loaded shipping containers. The U.S.
Before exploring those and other resiliency approaches, it’s useful Federal Bureau of Investigation issued a bulletin on the illegal
to get some perspective on the rising threats to GNSS and examine the operation in 2014, according to Guy Buesnel, a specialist in GNSS vul-
effects of GPS interference over the last several years. nerabilities at Spirent Communications.
Buesnel cited government efforts to raise awareness of GNSS vulner-
JAMMING AND SPOOFING abilities. For example, one report estimates the economic impact to the
Jamming a GPS signal requires little more than generating an RF U.K. of a complete loss of GNSS at £5.2 billion over a five-day period.
signal strong enough to drown out GNSS transmissions. Typically, Those and parallel U.S. efforts have prompted measures to boost the
a small transmitter sends radio signals in the same frequency band as a resilience of GNSS systems. “Accuracy is important, but it is important
GPS device. The resulting interference jams reception on GPS devices. to guarantee trust in the system, and we need reliability and availabil-
Because GPS jammers do not discriminate, they often inflict col- ity,” said Septentrio’s van Hees. “For example, can you receive signals
lateral damage. GPS-dependent air traffic control, search and rescue under adverse conditions?”
operations, the electric grid, and mobile-phone services are all vulnera- Trust requires such steps as signal fingerprinting to distinguish
ble to GPS jamming fallout. spoofers from a satellite signal. For instance, signal strength and timing
While jammers simply block GNSS signals, making accurate posi- from a spoofer may be a giveaway, especially because the satellite
tioning difficult or impossible, GPS spoofing involves the deliberate transmission will have a lower signal strength. Signal encryption is
transmission of signals similar to GPS but with incorrect information. By another option, including a framework called open-service navigation
replicating GNSS signals, a spoofer can fool a receiver into
thinking that it’s elsewhere in time or physical location.
Spoofing creates all kinds of havoc. For example, it
can be used to hijack autonomous vehicles and send
them on alternative routes. Spoofing can alter the routes
recorded by vehicle monitors or break the geofences used
to guard operational areas. It also poses a risk to critical
infrastructure, including power, telecommunication, and
transportation systems.
“Jamming involves making so much noise that the
[satellite signal] disappears,” said Jan van Hees, business
development and marketing director for GNSS receiver
maker Septentrio. “Spoofing is like a phishing attack on
the signal.”

GPS INTERFERENCE ON THE RISE
The U.S. Coast Guard has tracked a growing number of
high-profile incidents involving GPS interference. For
example, the loss of GPS reception in Israeli ports in 2019
left GPS-guided autonomous cranes inoperable — collat-
eral damage from the Syrian civil war. In 2016, more than
20 ships off the Crimean Peninsula were thought to be
the victim of a GPS spoofing attack that shifted the ships’
positions on electronic chart displays to land. The Chimera specification for spoof-proofing GPS (Source: Logan Scott Consulting)

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