Inside Galileo HAS: A new era of free high-precision GNSS

Image: ESA

Developed by the European Union, Galileo is an independent, global, satellite-based navigation system that provides a range of services. Among its most significant advancements is the Galileo High Accuracy Service (HAS), which aims to offer free, high-precision positioning to users worldwide. This article explores Galileo HAS, covering its history, architecture, implementation phases, performance, limitations, and future prospects. 

What is the Galileo High Accuracy Service? 

Galileo HAS is a precision augmentation service leveraging precise point positioning (PPP) to provide corrections to GNSS signals, aiming at a positioning accuracy of less than 20 cm horizontally and 40 cm vertically. Unlike the traditional real-time kinematic (RTK) method, which depends on local reference stations, HAS delivers corrections globally via Galileo satellites using the E6-B signal, as well as over the Internet. The service provides corrections for measurements on multiple frequencies across both Galileo and GPS constellations, enhancing real-time positioning performance. 

The concept of a high-accuracy service for Galileo was driven by growing demand for decimeter-level accuracy in applications such as precision agriculture and autonomous vehicles. Initially envisioned as a paid service under the Galileo Commercial Service, feasibility studies in 2014 confirmed its potential. In 2018, the European Commission decided to offer HAS free of charge. 

In the Galileo HAS specifications, two Service Levels are defined. Service Level 1 with global availability and the enhanced Service Level 2 for the European Coverage Area. The Galileo HAS roadmap consists of three phases: Phase 0 (testing and experimentation), Phase 1 (Initial Service), and Phase 2 (Full Service). After extensive internal testing, Phase 1 was officially launched in January 2023, marking a significant milestone in Galileo’s evolution as a leading GNSS provider. Phase 2 is currently in development and expected to launch in the near future. 

Technical Components 

Galileo HAS is designed with several key components that enable its high-precision capabilities. One of the most critical aspects involves orbit and clock corrections. These corrections compensate for inaccuracies in satellite orbital positions and clock errors, which are major sources of positioning errors in standard GNSS. Another essential element of HAS is the provision of signal bias corrections to enable precise carrier phase ambiguity resolution, which in turn greatly improves positioning accuracy. In the current Initial Service (Phase 1), Service Level 1 provides only code bias corrections, along with orbit and clock corrections. In Phase 2, Service Level 1 will be upgraded to include both code and phase bias corrections, while Service Level 2 will further add atmospheric (ionospheric and tropospheric) corrections for the European Coverage Area. 

Capable GNSS receivers decode the high-accuracy corrections broadcast on the E6-B channel for Galileo (E1, E5a, E5b, E5, AltBOC, E6) and GPS (L1, L2, L5) signals and apply them via algorithms to enhance positioning solutions. This refines raw measurements to reduce errors, providing decimeter-level accuracy for use in fields rangiranging from ecological surveys to city infrastructure management and routine mapping tasks. 

In addition to satellite broadcasts, the corrections are also made available over the Internet via the NTRIP protocol, providing an alternative access method for users with network connectivity. Notably, receiving HAS corrections via NTRIP eliminates the need for a receiver with E6-B capability, but the receiver still needs to implement the PPP algorithm to process the corrections. 

Architecture 

The Galileo HAS relies on the robust infrastructure already established within the Galileo system. At the foundation of this network are the Galileo Sensor Stations (GSS), a global network of 15 monitoring stations (according to the latest updates). These stations play a vital role by continuously collecting GNSS measurements, which serve as the raw data needed to generate precise corrections. The collected data are then processed by the High Accuracy Data Generator (HADG). This system analyzes the GSS input and produces high-precision corrections for both Galileo and GPS signals. Once the corrections are prepared, they are transferred to Uplink Stations (ULS), which transmit the correction data to the Galileo satellites for distribution via Signal-in-Space, or to an NTRIP caster for distribution over the Internet. In the case of Signal-in-Space distribution, the Galileo satellites themselves serve as the delivery mechanism to users worldwide, broadcasting the corrections globally via the E6-B signal. 

Galileo HAS Roadmap 

The HAS is being rolled out in three phases, ensuring progressive development and refinement: 

Phase 0 (2020–2022): Internal Testing 

• Focused on validating the feasibility of broadcasting HAS corrections via the E6-B signal. 
• Tests involved internal and external stakeholders, with feedback used to refine the service. 

Phase 1 (January 2023–Present): Initial Service 

• Declared operational on January 24, 2023, Phase 1 provides Service Level 1 with global coverage, though with reduced performance compared with the enhanced Service Level 1 expected in Full Service (Phase 2). 
• Current corrections include orbits, clocks, and code biases. 
• The service area excludes certain regions (e.g., parts of the Pacific and Australia) because of infrastructure limitations. 
• Convergence time is specified as <300 seconds (Service Level 1) or <100 second (Service Level 2), with horizontal accuracy <20 cm and vertical accuracy <40 cm under optimal conditions. Currently, accuracy <20 cm may be achieved with a convergence time up to 60 minutes, owing to the lack of phase bias and atmospheric corrections. 

Phase 2 (Future): Full Operational Capability 

• Will provide full Service Level 1 performance globally with horizontal accuracy <20 cm and vertical accuracy <40 cm, adding phase bias corrections for faster convergence <300 seconds. 
• Will introduce Service Level 2 for regional coverage in Europe with horizontal accuracy <20 cm and vertical accuracy <40 cm, adding phase bias and atmospheric corrections for faster convergence (<100 seconds). 
• Will include data authentication and enhanced infrastructure for improved reliability and coverage. 

Challenges and Limitations 

The current capabilities of Galileo HAS are constrained by several limitations, which are expected to diminish as the system evolves. Global coverage is not yet fully established, with parts of the Pacific region and Australia remaining outside the service area. While users can receive HAS corrections anywhere in the world, the official performance specifications apply only within the service boundaries. However, even within the service area, achieving the specified accuracy presently requires long convergence times, limiting applicability in scenarios that demand rapid solutions. Convergence time is expected to decrease significantly in Phase 2, when phase bias and atmospheric corrections are introduced. 

As of 2025, relatively few commercial receivers support HAS corrections via E6-B, with availability concentrated in professional and industrial receivers. The lack of integration into mass-market devices limits broader adoption, reflecting both the technology’s ongoing development and the additional hardware complexity required to receive HAS corrections. 

Finally, while decimeter-level corrections are sufficient for a wide range of applications, many professional domains, such as surveying, demand cm-level accuracy. Even at Full Service, HAS will not provide this level of precision, meaning that certain fields will continue to rely on RTK. However, considering that most RTK vendors require a paid subscription or charge per hour, HAS can still provide great value to surveyors and other professionals through its use in preliminary work or applications where cm-level accuracy is not critical, offering decent accuracy free of charge. 

The Road Ahead 

The Galileo constellation was recently reinforced with satellites 31 and 32, which became operational in January 2025, while the ground segment underwent major upgrades in 2024. Despite these improvements, Phase 1 (Initial Service) remains the only operational HAS capability. As of September 2025, Phase 2 remains in active development. In January 2025, it was announced that the European Union Agency for the Space Programme (EUSPA) awarded GMV a 45-month, €12 million contract to develop an enhanced HADG that will support enhanced Service Level 1 globally and Service Level 2 for Europe. The contract’s duration provides an indication of the anticipated timeline for completion. 

An inquiry regarding the timeline for Galileo HAS Service Level 2 (Phase 2) was submitted to the European GNSS Service Centre (GSC) Helpdesk. Their reply stated that the schedule is not available at this time and will be announced through GSC channels once released. 

Wider adoption is anticipated as more GNSS receivers capable of receiving and decoding the E6-B signal to process HAS corrections become available, enabling sectors such as autonomous transportation, fleet management, and smart agriculture to capitalize on improved performance. Adoption is also expected to accelerate when Galileo HAS reaches Full Operational Capability with the launch of Phase 2, which will reduce convergence times and broaden the system’s applicability. 

Ultimately, Galileo HAS is positioned to become a cornerstone of high-accuracy GNSS, democratizing access to professional-grade precision.