The Galileo High Accuracy Service (HAS): A Pioneer Free-of-Charge Global Precise Positioning Service

Galileo HAS (High Accuracy Service) is a PPP (Precise Point Positioning) service offered by Galileo. Galileo is the first global navigation satellite system (GNSS) to provide such a service free of charge, H24 operated, enabling decimeter level accuracy performance and of global scope. The precise corrections provided by the Galileo HAS allow users to reduce the error associated with the orbit and clocks provided through the Galileo Open Service broadcast navigation messages and the GPS Standard Positioning Service navigation data. These corrections, together with the biases provided by the service and when processed by an appropriate user algorithm, enable the computation of a high accuracy positioning solution in real-time. The HAS Initial Service, declared by the current Galileo infrastructure in January 2023, enables the provision of the so-called HAS Service Level 1 (SL1) globally and with a committed performance over an almost global service area (certain areas not characterized). Even if the performances do not reach the HAS Full Service targets yet, the Galileo HAS initial service provides decimeter level typical accuracy performance, still leaving room for classic commercial applications and innovation at user level for usages requiring the most stringent performance (e.g. centimeter level accuracies, position authentication and/or integrity). It should be highlighted that, unlike other PPP services which typically rely on denser reference stations networks, the Galileo HAS Initial Service only exploits GNSS measurements from 15 Galileo Sensor Stations (GSS). The full description of the HAS Initial Service, including performance levels and coverage, is provided in the HAS service definition document (SDD) [1]. In the future, the Galileo HAS Full Service will provide an improved version of the global SL1 and a new regional SL2, covering Europe and with a shorter convergence time thanks to ionospheric corrections. The paper addresses the Galileo HAS implementation status in detail, including a thorough presentation of the Galileo HAS Initial Service.