What is GPS Spoofing?

GPS (GNSS) spoofing is a cyberattack in which malicious actors broadcast counterfeit satellite signals that overpower genuine satellite signals at a receiver’s antenna, causing the receiver to calculate a completely false position, velocity, or time. Unlike jamming — which simply disrupts GNSS — spoofing is more dangerous because the receiver continues to operate normally, unaware that its reported position is fabricated. This sophisticated form of interference has evolved from a niche concern into a growing threat affecting GNSS-reliant systems across aviation, autonomy, defence, and logistics sectors.

How GPS Spoofing Works

A GNSS spoofer mimics genuine satellite signals by broadcasting fake signals on the same frequencies (typically L1 GPS, ~1575.42 MHz) at higher power than the legitimate satellite signals. The attack typically follows a sequence:

1. Signal capture: The spoofer initially matches the receiver’s current tracking state — transmitting signals consistent with its current position fix.
2. Gradual takeover: The spoofer slowly shifts the fake signals to steer the receiver’s calculated position away from its true location — often without triggering any receiver alarm, since the transition appears gradual.
3. Full control: Once the receiver is tracking only the fake signals, the spoofer can guide it to any desired false position, velocity, or time.

The most sophisticated attacks use multiple coordinated transmitters to simulate realistic satellite geometry and Doppler shifts, making them nearly indistinguishable from genuine signals at the receiver level.

Types of Spoofing Attacks

• Signal Replay: Captures legitimate signals and re-broadcasts them with a delay.
• Progressive Attacks: A subtle method starting with a single spoofed satellite (often one not yet visible to the vehicle) to slowly drift the receiver’s position.
• Ephemeris Manipulation: Broadcasting false satellite orbital data (ephemerides) to force positioning engines to discard legitimate solutions.

Who Uses GPS Spoofing?

GPS spoofing was once the domain of nation-states with sophisticated equipment. It has since become more accessible, with documented real-world cases including:

• Military/electronic warfare: Countries use GPS spoofing defensively to protect sensitive locations (airports, military bases) by causing approaching drones or missiles to navigate off-course.
• Maritime spoofing: Ships near conflict zones (Black Sea, Persian Gulf, Strait of Hormuz) have reported mass spoofing events where vessels’ AIS positions appeared on land — often hundreds of kilometres from their actual location.
• Drone evasion: Criminals use portable spoofers to confuse drone geofencing systems to enable flight in restricted airspace.
• Financial fraud: Some financial markets use GPS timing for trade timestamping; spoofing could theoretically manipulate these timestamps.

Spoofing vs. Jamming

Jamming broadcasts radio-frequency noise on GNSS frequencies, blocking the receiver from tracking legitimate signals. The receiver knows something is wrong — it simply loses its fix. Spoofing is more insidious: the receiver maintains a fix, but the position is false. Without spoofing detection, an operator has no indication anything is wrong.

For safety-critical applications (autonomous vehicles, aviation, maritime), undetected spoofing is potentially catastrophic — a vehicle navigating to a false position could cause collisions, equipment damage, or loss of life.

How to Detect and Mitigate GNSS Spoofing

Modern receivers use internal monitors to identify inconsistencies in the radio frequency (RF) environment:

• Autocorrelation Monitoring (ACM): This identifies signal distortion. In a spoofing attack, the interaction between the authentic and counterfeit signals creates a non-planar or “deformed” correlation peak.
• False Lock Detection: Detection systems monitor signal characteristics to identify “mimic” signals. This typically requires a carrier-to-noise density ratio (C/N0) equal to or greater than 40 dB/Hz for a flag to be raised.
• Early Frequency Ramp Identification: Identifies unnatural, sudden shifts in signal frequency that do not align with standard satellite orbital physics or vehicle motion.
• Tracking Duration Requirements: To prevent a system from trusting a malicious signal immediately, satellites must be consistently tracked for at least 5 seconds before they are used in a position fix.

How Skylark Defends Against Spoofing

Skylark Precise Positioning Service defends against spoofing through a combination of secure infrastructure, advanced server-side anomaly detection, and continuous monitoring of validated satellite data. By cross-referencing incoming signals against trusted reference stations, the system can identify discrepancies that indicate a malicious broadcast.

A core component of this defense is the Spoofed Queue mechanism. When the system detects suspicious signal characteristics, it moves the affected satellites into a dedicated “quarantine” queue for a configurable timeout period (typically 300 seconds by default). This prevents the potentially compromised data from influencing the navigation solution while the system continues to monitor the signal for legitimacy.

The system also utilizes a constellation-wide safeguarding protocol. If the number of compromised satellites from a single constellation exceeds a specific threshold (usually 5 satellites) the entire constellation is flagged as spoofed. This triggers immediate alarms and prompts the receiver to stop using that constellation entirely to maintain the integrity of the positioning fix.

Beyond these queueing protocols, Swift employs a multi-layered defense strategy. This includes the use of authenticated ephemeris to verify satellite orbital data and the Starling Positioning Engine, which uses sensor fusion to compare GNSS data against other vehicle sensors. By combining multi-constellation protection with these proprietary features, the system ensures a high level of resilience against both simple and sophisticated spoofing attempts.

Read our article to learn more: How Skylark Precise Positioning Service Defends Against GNSS Spoofing.

As GNSS systems become increasingly critical for autonomous vehicles, defence, and critical infrastructure, developing robust spoofing detection and mitigation capabilities remains essential for maintaining system integrity and safety.