How jamming works
Satellite navigation signals are weak by the time they reach the ground. Schmidt and colleagues note that the power of GNSS signals measured at the Earth’s surface is below the noise floor, which makes them vulnerable to interference.
A jammer exploits this by transmitting radio energy in the same frequency band. EASA describes jamming as intentional radio frequency interference that prevents GNSS receivers from locking on to satellite signals, leaving navigation ineffective or degraded. Kazim, Darwich and Marais describe the same effect from the receiver’s side: jamming disturbs the GNSS band, degrading performance or blocking the receiver from acquiring satellites entirely.
Jamming is one kind of interference among several. GPS.gov lists radio emissions in nearby bands, intentional or unintentional jamming, and naturally occurring space weather as sources of GPS interference.
Jamming vs spoofing
EASA and GPS.gov discuss the two attacks together, but they do different things.
- Jamming denies service. The receiver loses its fix or its accuracy degrades, and in principle it can tell something is wrong.
- Spoofing deceives. The receiver gets a counterfeit signal and computes a wrong position or time, which may look normal.
That difference matters for apps. A jammed phone reports that it has no good fix or a poor one; a spoofed phone may report a confident, wrong answer. How GPS spoofing is detected covers the second case.
Where jamming happens
GPS.gov’s accuracy guidance lists radio interference or jamming among the far less common causes of a wrong position, behind everyday ones such as buildings, trees and indoor use. In some regions, though, it has grown. EASA reports a notable increase in GNSS jamming and spoofing since February 2022, particularly around conflict zones and in areas including the Mediterranean, the Black Sea, the Middle East, the Baltic Sea and the Arctic. It notes that interference can occur during any phase of flight and lead to re-routing or diversions.
Interference is now tracked at a global scale. GPS.gov describes a U.S. Space Force mission that publishes daily unclassified heat maps showing intentional interference with positioning, navigation and timing, including spoofing, around the world. EASA’s own analysis uses the position quality that aircraft broadcast over ADS-B, and looks for several aircraft reporting poor values in the same area.
Small, local jammers matter too. GPS.gov records a fine the FCC proposed in 2013 against an individual whose GPS jamming device, used on a highway outside Newark Airport, interfered with an aviation safety system in 2012.
Is GPS jamming legal?
In the United States, no. GPS.gov states that federal law prohibits the operation, marketing or sale of any jamming equipment that interferes with authorised radio communications, including GPS. There are no exemptions for use within a business, classroom, residence or vehicle, and it is also unlawful to advertise, sell, distribute or import jammers to consumers. Penalties can include substantial fines, seizure of the equipment and criminal sanctions including imprisonment. GPS.gov notes that local law enforcement has no independent authority to use jammers, with limited exceptions for federal agencies under applicable statutes.
Rules in other countries are set by their own regulators.
How jamming is detected
Receivers expose measurements that change when the band fills with noise. Kazim, Darwich and Marais study two observables from a commercial receiver: automatic gain control (AGC), the receiver’s automatic adjustment of its input amplification, and the carrier-to-noise density ratio (C/N0) of each satellite’s signal. They evaluate how a chirp jammer affects both on a GPS L1 receiver and how well each detects it.
EASA’s guidance for aircraft operators is to verify position using non-GNSS means and to report anomalies.
Designing for a lost fix
An app cannot stop a jammer, but it can avoid being surprised by one. Treat “no fix” and “poor accuracy” as normal states, show them honestly, and fall back to other sources of position where they exist; how phones find their location without GPS describes those sources. For anything that depends on location being right, such as access or payments, do not rely on one signal that a nearby transmitter can remove.