What is Galileo High Accuracy Service?

The Galileo High Accuracy Service (HAS) is a free-of-cost satellite-based navigation system that provides various navigation services to users having Galileo-compatible receivers. Galileo is a Global Navigation Satellite System (GNSS) that was launched in 2016 by the European Space Agency (ESA). It is said to be the first satellite constellation to provide a Precise Point Positioning (PPP) by sending direct signals from space.

Galileo HAS provides two levels of service: Level 1 and Level 2. Level 1 provides global Precise Point Positioning (PPP) coverage with a horizontal accuracy of better than 25 cm, vertical accuracy of better than 40 cm and a convergence time of 300 s. Level 2 provides PPP coverage with atmospheric corrections for European countries only with a horizontal accuracy of better than 25 cm, vertical accuracy of better than 40 cm and a convergence time of 100 s. Both levels support frequency bands E1/E5b/E5a/E6 and E5 Galileo frequency bands and L1/L5/L2 frequency bands of GPS.

Galileo HAS’s internal testing has been ongoing since 2019 and has now entered High Accuracy (HA) testing and the experimentation stage. The delivery of initial services of Level 1 are expected to start sometime in 2022 and full service is expected in 2024. 

How does Galileo HAS Work?

Galileo HAS uses signals in the E6 band (1260-1300 MHz) and terrestrial links for communication. The main lobe of the signal along with most of the signal power in present in the 1273.75-1283.75 MHz bandwidth. E6 signals are modulated with a Binary Phase Shift Keying (BPSK) at a carrier frequency of 1278.75 MHz, which is used by all satellites and shared through a Code Division Multiple Access (CDMA) RF channel access.  

Figure 2

The Galileo HAS architecture involves various modules for achieving high accuracy corrections as shown in Figure 2. A High Accuracy Data Generator (HADG) module receives data from the Galileo Sensor Stations (GSS) and generates corrections for Galileo satellites and GPS. The High Accuracy (HA) data corrections are sent to the Galileo Core System module and the Core System compiles the information in one single message of 448 bps per connected satellite and uploads it to the Galileo satellites through the Uplink Stations (ULS). Galileo satellites then broadcast the HA data corrections through the Galileo E6-B signal component and through the terrestrial link, accessible to the users via the internet. The user-receivers implement PPP algorithms to apply HA data corrections to the navigation data received via the E1-B signal.

To reduce external interferences in HA data, Galileo HAS uses various protection layers. The first is data-level protection where it digitally signs the message for its authenticity. The second level is data encryption in which the data is replaced by an unpredictable bit-stream, generated through a secret key, making the signal indistinguishable from noise. Signals’ time of arrival is also considered for verification of authenticity.

Once fully operational, the Galileo HAS will provide benefits to a wide range of applications including:

1. Agriculture
   1. Guidance in large farm areas
   2. Farm-machinery positioning in large farm areas
   3. Site-specific data analysis applications
2. Railways
   1. Cold movement detections of trains for European train control systems (ETCS)
   2. Infrastructure survey
   3. Gauging survey
   4. Structural monitoring
3. Geomatics
   1. GIS/Mapping
   2. Hydrographic survey
   3. Offshore explorations
4. Aviation
   1. Drones: Positioning and Navigation System
   2. Airport: Integrated surface management systems
5. Maritime
   1. Port operations
   2. Riverbed and coastal seabed survey
   3. Dynamic positioning of vessels
6. Road
   1. Autonomous driving
   2. Reconnaissance in search and rescue operations
   3. Safety-critical applications