R-Mode Baltic – World-Wide first R-Mode Test Bed using MF and VHF transmissions

Abstract

Position, Navigation, and Timing (PNT) is part of the critical infrastructure necessary for the safety and efficiency of vessel movements, especially in congested areas. Global Navigation Satellite Systems (GNSS) have become the primary PNT source for maritime operations. Unfortunately, GNSS is vulnerable to jamming and interference, intentional or not, which can lead to the loss or, even worse, to incorrect PNT information. Furthermore, system errors could be identified in the past. Thus, additional supporting and complementary systems are required to provide resilient PNT. One candidate system, which could provide alternative positioning and timing information, is known as R-Mode, or ranging mode. The idea of R-Mode is based on the transmission of a ranging signal or a ranging message via marine radio beacons, which operate in the medium frequency (MF) band, or from Very High Frequency (VHF) shore networks using the VHF Data Exchange System (VDES). Over the last years a number of studies were performed which demonstrated the feasibility of R-Mode. In addition, first static tests validated the theoretical findings and showed the potential of R-Mode as a future contingency or backup system to GNSS. Within the European Union co-financed projects “R-Mode Baltic” and “R-Mode Baltic 2” (2017-2021) the world-wide first operational and transnational R-Mode test bed was implemented, which utilises already existing maritime radio beacons as well as new VDES base stations. This test bed enables on-board dynamic positioning in a large area located in the southwest Baltic Sea between Germany, Sweden, Poland and Denmark. This paper details that the existing maritime radio infrastructure of the southern Baltic Sea already fulfils the precondition for a successful implementation of a combined MF and VDES R-Mode system. The concept for the test bed was based on coverage prediction and accuracy estimation studies for MF and VDES R-Mode in the Baltic Sea. Further, the paper describes the implementation and operation of eight MF maritime radio beacons with R-Mode capabilities and the preparation of four VDES R-Mode sites. In addition, the paper provides detailed results from dynamic positioning campaigns, an overview about the results of a cost benefit analysis and a summary of ongoing standardisation activities related to R-Mode.