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 called pseudolites because they usually operate on the ground and imitate satellites' signals. 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 so that incorrect position data results. This results in messages from ghost ships or jumping-off 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. 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. In reality, they are stationary.
For this purpose, spoofing involves transmitting on the same frequency as the GPS satellites and overlaying their signals. Either the fakes can overlay only the signal of one or several GPS satellites 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, e.g., from above. They strongly suppress interfering signals coming from pseudolites and ground level.