Ships can be led astray with fake GPS signals. If signals for navigation of vessels are jammed or spoofed, positional and other critical data, such as course and speed, can be affected. Researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have tested new receiver systems and methods for suppressing interference in a three-day measurement campaign. These systems will allow the detection of future jamming and spoofing attempts. Their effect on on-board sensors can thus be drastically reduced, which in turn contributes to shipping safety.
From the laboratory to the sea
The DLR researchers first examined the suitability of measures for interference suppression under real conditions in the Baltic Sea. A team led by the DLR Institute of Communications and Navigation spent three days in the high seas. During the campaign, it was possible to demonstrate the effect of different interference and decoy methods on maritime receivers and systems and to what extent they are affected. "In addition, using these measurements we wanted to find ways of further improving the systems in terms of their immunity," explains Stefan Gewies, the DLR project manager for the measurement campaign.
The on-board systems
Today, modern shipping mainly uses satellite navigation systems such as GPS (Global Positioning System) or – in the future, also Galileo and Beidou – to navigate. The position, speed and time data supplied by receivers are required for key systems on board: The Electronic Chart Display and Information System (ECDIS), for example, show the position of the vessel on an electronic chart and the Automatic Identification System (AIS) transmits the ship's position and navigational data to other maritime transport users.
Jamming and spoofing
In the case of interference or decoy attempts such as jamming or spoofing, the reception of the signal is deliberately disrupted or corrupted. During so-called spoofing, in which fake signals are transmitted from a source other than the satellite to deceive the recipient and therefore affect the navigation, jammers superimpose the satellite signal with an interference signal that can lead to failure of the satellite-based navigation on board.
Successfully suppressing jamming
At the beginning of the DLR measurement campaign in the Baltic Sea, jammers produced artificial interference signals. For this, the scientists used the frequency on which the United States GPS (and the European Galileo satellite system also transmit their signals. Depending on the nature of the interference signal used, the standard on-board equipment on all ships involved failed one by one, which was often communicated to the operating crew by a haunting acoustic warning signal.
To suppress the interference signals, the scientists use the GALANT system, an antenna system developed at the Institute for Communications and Navigation. The characteristics of the GALANT antenna enable the interfering signals to be spatially hidden and at the same time improve the reception of the desired signals. The effect of jamming can thus be drastically reduced. "Specifically, this means that even with an interference power that is up to six orders of magnitude greater than the GPS user signal, the receiver systems of the participating vessels still provide correct position information," explains DLR researcher Stefan Gewies.
Spoofers can cause collisions
In a spoofing scenario, the received GPS signals were sent from a 'decoy ship' via an antenna to a second vessel. Because of this, the true position and direction of the second ship deviated considerably from the values reported by the 'GPS compass'. Sometimes, the on board instrumentation even indicated the position of the 'decoy ship' as supposedly being its own position. The scientists aboard the second vessel did not even notice a system failure – the deceptive spoofing attack was not registered by the ship's systems as such. "Spoofing therefore represents a danger for maritime users that should not be underestimated," notes Gewies and adds: "A manipulation such as this one going unnoticed represents a big threat because the technical systems on board can incorrectly assess the risk of collision." In the spoofing scenario, the DLR GALANT system could reliably identify the deviation from the expected direction of the satellite broadcast signal and detect the spoofer in real time.
During the measurement campaign, the GALANT system was, for the first time, coupled with another system developed at the Institute. The so-called PNT (Processing, Navigation and Timing) unit is a processing unit for navigation signals in the maritime sector. By combining data from various sensors, it provides navigation-related parameters such as position, course, speed and location with high reliability, continuity and robustness. It enables the assessment of errors in the position, navigation and time information of the satellite signals. The PNT unit is able to provide position and navigation solutions even when satellite reception is lost. PNT coupled with GALANT provided a consistently accurate graphical representation of the vessel on the electronic chart during the tests.
Remote sensing for rescuing people
The DLR scientists also put another system to the test: the Automatic Identification System, AIS. People in distress can transmit emergency messages by radio using the AIS rescue transmitter, known as SARTs (Search and Rescue Transmitter). AIS-SARTs are equipped with a built-in GPS and can share a person's position with other ships that are within receiving range and are also equipped with an AIS unit. During the measurement campaign in the Baltic Sea, various AIS-SARTs were used on 'drift dummies' – small floating platforms to simulate the drifting behaviour of a person in the water. During the jamming and spoofing scenarios, the DLR sresearchers investigated the effects of interference scenarios on the devices.
To detect the positional error of the AIS, the researchers compared its information with remote sensing data. A programme developed by DLR at the Earth Observation Center (EOC) merges TerraSAR-X radar satellite data with the information received from the AIS. From this, the position of the vessel can be determined directly from the satellite image and independently of the GPS. The deviation between the AIS data and the satellite data for ship detection could then be directly compared by the scientists. For the ship BALTIC TAUCHER II, for example, a deviation of about 300 metres was found at the time that the satellite image was acquired.
The measurement campaign
The measurement campaign took place in June 2016 in a special jamming test area in the Baltic Sea. In this small area, frequented by only a few ships, the manipulation of navigation systems and appropriate countermeasures can be tested. At times, up to four ships took part in the tests. The measurements were carried out by DLR in cooperation with the German Federal Maritime Police, the German Maritime Search and Rescue Service, the Federal Network Agency and the company Baltic Taucher. In addition to the DLR Institute of Communications and Navigation Center, the DLR Earth Observation Center (EOC) and the DLR Institute of Space Systems were also involved in the measurements.