39C3: Navigation system "R-Mode" against the Baltic Jammer

Three researchers from the German Aerospace Center (DLR) presented the current status of the so-called Ranging Mode (R-Mode). The project is likely to gain importance in times of hybrid threats. It was presented at the 39th Chaos Communication Congress (39C3) in Hamburg on Saturday.

Niklas Hehenkamp, a research associate at DLR in Neustrelitz, opened the presentation with a comparison from Star Wars pop culture: He described the current situation in navigation as "The Phantom Menace" – the dark threat. He was referring to the increasing jamming and spoofing activities in the Baltic Sea, which have been ongoing for a good two years and particularly affect the area around the Russian oblasts of Kaliningrad and Gdansk.

These disturbances, which are of Russian origin according to the Federal Ministry of Defence and are often associated with the term "Baltic Jammer", demonstrate the dangerous dependence of modern infrastructure on global navigation satellite systems (GNSS) such as GPS or Galileo. As the hardware for such jamming maneuvers is now readily available, the risk for maritime and air traffic is increasing. "We need a backup system, as we are currently dependent on a single technology," warned Hehenkamp. The researchers' goal is a system that is cost-effective, easy to operate, and above all resistant to the type of jamming that currently disables GNSS signals.

Years ago, DLR experts, along with other EU scientists, began to consider satellite-independent solutions. Their goal: to secure the sovereignty of European navigation capabilities. R-Mode relies on a terrestrial basis and uses existing maritime infrastructure in the medium wave range, specifically IALA radio beacons.

Promising Results

Much has happened since the initial tests in 2014 and 2015. In cooperation with partners from Poland, Denmark, Norway, Sweden, Finland, and Estonia, the participants established a pre-operational test field in the Baltic Sea. To ensure the nanosecond-level synchronization required for satellite-independent navigation, DLR uses highly stable rubidium atomic clocks as a time reference and specialized signal modulators that feed the navigation signal into existing radio infrastructures.

The technical challenges are considerable. Hehenkamp explained that the propagation of signals in the medium wave range occurs directly as a ground wave along the Earth's surface, which requires precise modeling of ground conductivity. The team uses modern satellite remote sensing data for this purpose, incorporating factors such as soil moisture or seawater salinity. The researchers found existing material from the International Telecommunication Union (ITU) only as a non-machine-readable PDF that still listed Germany as divided into East and West.

The results for R-Mode deployment so far are promising. During the day, the system achieves an accuracy of about 12 meters with a probability of 95 percent. At night, this value deteriorates to about 63.7 meters due to atmospheric reflections, which is still considered sufficient for shipping. "We will find a solution to open up the system," promised Hehenkamp, also with a view to the future broader availability of the required basic data.

Test field with improved technology near Rügen

Lars, a second engineer from the DLR site in Neustrelitz, supplemented the description of the status quo with a comparison to other approaches such as the ESA project Celeste, which is based on ten satellites in low Earth orbit (LEO). While such LEO systems offer global coverage, the DLR researcher pointed out that their signals are still comparatively weak and thus remain susceptible to jamming. Furthermore, they require considerable resources. R-Mode, on the other hand, is designed as a civilian backup system that can also be operated independently by smaller countries. As the system uses existing medium wave and VHF technology in the UKW range, the range is about 300 kilometers, which can cover the entire Baltic Sea. The goal is clearly stated: "The system will be operational by the end of 2026."

A third pillar of development is the use of the VHF range, which Markus from the DLR site in Oberpfaffenhofen described. While conventional Automatic Identification System (AIS) is hardly an option for navigation due to high utilization, the new VDES (VHF Data Exchange System) with a bandwidth of 1000 kHz offers significantly more space. However, the bureaucratic hurdles are high here, as the allocation of frequencies for navigation purposes must be decided at the World Radiocommunication Conference (WRC). This meeting only takes place every three to four years.

Nevertheless, practical tests are in full swing. On Bavaria's Ammersee, the team is already successfully testing VDES-based navigation with the water rescue service, achieving an accuracy of about 10 meters. There have even been initial attempts in aviation. A DLR research motor glider flew over Hamburg, with a deviation of about 200 meters. DLR is currently setting up a semi-permanent test field south of Rügen. Three stations with commercial hardware will demonstrate there that R-Mode is ready for tough use in coastal areas. This brings closer a future where captains in the Baltic Sea will no longer have to stare helplessly at their jammed GPS displays as soon as electronic jammers become active nearby.

(emw)