In GPS spoofing, the attacker places a radio transmitter near a target to interfere with GPS signals. He can prevent data from being received, or even transmit incorrect coordinates or time information.
This involves the generation and transmission of formally valid but incorrect position data. These jammers are also called pseudolites because they are usually operated on the ground and imitate the signal from satellites. Both civil and military receivers are affected.
The aim is not only to interfere with the reception of GPS signals but also to deceive GPS receivers in such a way that incorrect position data is the result. This results in messages from ghost ships or the jumping of positions.
The devices on the affected vessels, fed by their GPS receivers, send signals as if at full speed, while in reality the vessels are firmly docked in port. In addition, GPS signals fail completely. This can also result in mysterious fake maneuvers: The affected GPS receivers calculate that they are going in a counter-clockwise direction at a speed of about 50 km/h in a circle, while in reality, they are stationary.
For this purpose, spoofing involves transmitting on the same frequency as the GPS satellites and overlaying their signals. Either only the signal of one or several GPS satellites can be overlaid by the fakes at the same time.
Since the determination of the position with GPS is based on a very precise time measurement (runtime measurement), it is not trivial to generate both valid, incorrect, and plausible position data at the point of the GPS receiver to be influenced.
Remedies against GPS spoofing include direction sensitive receiving antennas, which receive the GPS signals only from the GPS satellites, i.e. from above, and strongly suppress interfering signals coming from pseudolites and from ground level.