"GNSS jamming works by producing a Radio Frequency (RF) signal strong enough to overpower the relatively weak transmissions made by GNSS satellites."
GNSS jamming may sound like a complex topic, but it’s a lot simpler than you might think. It doesn't matter what type of application GNSS is used for. The fact is that GNSS signals can be jammed quite easily and without the use of complex or expensive technology.
Still, more advanced GNSS interference tactics are used by both civilians and the military, so we walk through the basics below.
What is GNSS Jamming?
GNSS signals can be jammed with GNSS jammers like Personal Protection Devices (PPD), many of which are available on the web and relatively easy to purchase despite being illegal in the United States.
GNSS jammers can be as simple in structure as the common 'cigarette lighter' jammers that can be plugged into car charger ports, or as complex as those with rechargeable batteries and dozens of antennas (hedgehog jammers) that help push out stronger interference signals. Jammers can range significantly in price, with some of the most basic costing as low as $30.
Every type of jammer has its own specific signal characteristics, which can be used by GNSS jamming detection services to identify the jammer or help locate the signal source.
GNSS jamming can happen unintentionally, and increasingly so as technology continues to evolve, but it also happens intentionally, and many use these jammers for both harmless and nefarious purposes.
How Does GNSS Jamming Work?
GNSS jamming works by producing a Radio Frequency (RF) signal strong enough to overpower the relatively weak transmissions made by GNSS satellites.
Part of the reason that GNSS signals are weak is that they are sent from orbit, around 20,000 km above the Earth’s surface. Since the GNSS signals must travel so far before reaching a GNSS receiver, they weaken over the distance, making them vulnerable to both GNSS jamming and GNSS spoofing (described here).
GNSS jamming is commonly a deliberate act, and more people are beginning to use GNSS jammers to circumvent everyday tracking applications at jobs and for personal reasons. Many use GNSS jammers to do things like prevent tracking of a vehicle, ship, aircraft, or smartphone device, but there are numerous applications for GNSS jamming.
GNSS satellites typically send signals in one or more of three different Radio Frequency (RF) bands. Those are L1, L2, and L5. Most GNSS satellites operate solely in the L1 and L2 bands, but newer satellites are being built that operate in the L5 band.
Since the signals from GNSS satellites are so weak, a very small amount of RF interference in the L-band the signal is being sent can severely disrupt elements of a GNSS system. These elements include things like velocity, timing, and position data. When disrupted or jammed, inadequate global positioning and navigation can quickly ensue.
While different risks exist for different GNSS applications, GNSS jamming can cause physical harm and even significant economic losses.
GNSS Jamming Detection from Earth
GNSS interference takes numerous forms. Chirps, tones, pulses, and matched-code interference are all forms of GNSS interference. To stop a GNSS attack, we must develop situational awareness by understanding how GNSS jamming emitters work and how they can be eliminated.
A study published by the Journal of the Institute of Navigation discussed how a network of ground-based receivers could geolocate and track chirp-style and matched-code jamming signals. However, terrestrial-based networks are fixed to a single location, so only emitters in the immediate vicinity can be identified and tracked.
While a network of ground receivers is one way to identify a GNSS jamming signal, the following can also signal a GNSS attack.
Signal Strength
Valid GNSS signals fall far below a normal background noise level, so interference is likely present if energy is detected in the L-bands where the signals are being broadcasted.
The strength of signals transmitted by GNSS satellites do not vary at the GNSS receiver due to the distance the signal travels, but signals from a jamming device are very strong relative to normal GNSS signals. Consequently, a sudden increase in signal strength could mean that a jamming signal began transmitting nearby.
Loss of GNSS Function
If a GNSS jamming signal is strong enough or within the appropriate range, the GNSS receiver or device will stop functioning altogether. This indicator is more obvious than others, but can be a clear indicator of jamming.
GNSS Jamming Detection from Space
While GNSS interference detection from the ground is typically done with a stationary network and can only locate jamming signals in the immediate vicinity, GNSS jamming detection from Low Earth Orbit (LEO) is a proven asset for the detection, classification, and geolocation of GNSS interference.
Since satellites are orbiting the Earth and can sometimes be moved or arranged to satisfy the application at hand, identifying and tracking GNSS jamming signals from space is a much more reliable method than ground identification.
In fact, jamming emitter geolocation from space offers near-global coverage and a continuous and frequent refresh rate, presenting a wide-scale picture of ground-based GNSS interference.
Further, LEO satellites are nearly 20,000 km from the planet's surface, so they are far enough from ground interference sources to track legitimate GNSS signals. Ultimately, this allows LEO constellations to provide unprecedented interference geolocation.
A few companies currently offer jamming emitter geolocation services from space, namely Spire Global and Hawkeye360.
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