The reference architecture of the system, which is the subject of the preliminary design, is measured for the provision of L1 services (Stage 1) while being scalable to support the extension of service areas for the different service levels. This architecture includes:
• A network of Reference Navigation Stations (NRS) deployed in different locations to collect data from GPS and Galileo signals, with a geographical distribution adjusted to optimise satellite observations and signal spreading conditions. This network is scalable to support the incremental expansion of service areas.
• Two Mission Control Centres (MCCs) comprising Navigation Processing Systems (NPS) to compute SBAS corrections and associated integrity bounds, and Central Control Systems (CCS) for system monitoring and control
• At least two Navigation Broadcast Stations (NBS) to uplink the signal carrying SBAS messages to the navigation payload of the GEO satellite(s)
• A wide area network to provide data communications between the different subsystems
• A space segment consisting of GEO satellite(s)
The A-SBAS system is designed to integrate up to 3 GEO satellites, with the corresponding NBS. The system is also scalable to support the provision of DFMC services through the integration of additional dedicated NPS, without impacting the provision of L1 services.