Performance bounds for VDE-SAT R-Mode

There has been growing interest within the satellite navigation community in the possibility of delivering positioning and timing services from existing or emerging constellations of Low-Earth Orbit communication satellites. At the same time, the international maritime community has been investigating the potential use of communication signals transmitted from shore-based stations for positioning—a concept commonly referred to as ‘ranging mode’, or R-Mode. The driving force for these developments is the desire to reduce the reliance on traditional Global Navigation Satellite Systems (GNSS). One of the technologies being considered for use in R-Mode is the evolution of the Automatic Identification System (AIS) known as the Very High Frequency Data Exchange System (VDES). VDES has a terrestrial and a satellite component. The feasibility of using terrestrial VDES transmissions for ranging was studied in a previous publication by the authors. This paper builds on the previous study and extends its results to the satellite component of VDES. Statistical bounds on the ranging error are derived for all downlink waveforms currently being considered for use in satellite VDES and for several custom-designed transmission formats. The analysis supports the feasibility of using both the existing and custom waveforms in ranging applications and points to related trade-offs that will need to be considered in the design of satellite VDES R-Mode systems.