Reliable Navigation Without Satellites: Alternatives and Complements to GNSS
Global Navigation Satellite Systems (GNSS) are a vital component of modern aviation. GNSS disruptions or outages can therefore significantly affect the safety and efficiency of air traffic. The research project PEAC – Performance Enhanced Alternatives and Complements to GNSS advanced ground-based alternatives and complements to GNSS to make airspace navigation more independent and resilient.
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Project duration: January 2022 to December 2024
Navigating Without GPS
Satellite systems such as GPS or Galileo can fail – whether due to technical faults or natural phenomena like solar storms. Such failures can have serious implications for aviation, as accurate positioning is essential for safe flight routes and efficient air traffic management. For this reason, PEAC (Performance Enhanced Alternatives and Complements to GNSS) further developed ground-based technologies such as the LDACS radio system, which operates independently of satellites and can be used for both data transmission and navigation. This provides an effective alternative to GNSS systems.
The LDACS(L-band Digital Aeronautical Communications System) is a digital communications system for aviation. It was developed to replace analogue radio systems and to provide a reliable, high-speed data link between aircraft and ground stations.
How Does Alternative Navigation Work Without GNSS?
While GNSS relies on signals from multiple satellites, alternative navigation methods (e.g. LDACS or Distance Measuring Equipment – DME) use ground-based transmitters to measure distances and determine an aircraft’s position. This principle is similar to traditional radio navigation systems but is significantly more accurate thanks to modern technologies. Additionally, the system can also be used for time synchronisation. The PEAC project developed methods to further improve the measurement accuracy and minimise interference caused by atmospheric effects or multipath propagation. The aim was to achieve a positioning accuracy of less than 40 metres for 95% of the time, and a time synchronisation deviation of no more than 50 ns, even under challenging conditions.
Enhanced Safety Through Alternative Navigation Systems
A key research focus of PEAC was assessing how the availability of an alternative navigation system would impact airspace safety. Particularly in the event of a GNSS outage, the question arises whether alternative systems can maintain the same safety level under identical traffic conditions. One of the project’s main goals was therefore the development of methods for the technical and operational evaluation of alternative navigation solutions in the aviation context.
As part of the project, the DLR Institute of Air Transport analysed the potential effects of different APNT systems on airspace safety. To this end, a comparison metric was developed based on the horizontal collision risk between aircraft, allowing for a comparative assessment of various systems. These analyses were based on real flight data, spatial performance profiles of the navigation systems, and simulations in which collision risks were calculated for different navigation scenarios.
The results highlight the potential of alternative navigation solutions to maintain collision-related safety levels in continental airspace even during GNSS outages.
The PEAC Project – Reliable Navigation in Aviation
Project duration: 1 January 2022 to 31 December 2024
Participating DLR institutes: DLR Institute of Communications and Navigation, DLR Institute of Air Transport
Further development of ground station networks and APNT technologies
Future work will focus on the design of ground station networks, the comparison of different APNT technologies, and the long-term assessment of their impact on airspace and new flight procedures.
