JRC HAS products

The Galileo High Accuracy Service (HAS) is an open access service broadcasting Precise Point Positioning (PPP) corrections through the data component (E6-B) of the Galileo E6-B/C signal [2] and by internet [3]. The implementation of the Galileo HAS will be staggered in two main phases, indicated as Phase 1 and Phase 2. In Phase 1 (also referred to as Initial Service) precise orbit and clock corrections for Galileo I/NAV [1] and GPS LNAV [5] navigation messages and satellite biases are being transmitted. Phase 2 will provide the HAS Full Service where, in addition to the above corrections, atmospheric corrections, authentication and other features will also be broadcast. On the 24th of January 2023, Galileo started to offer the Galileo HAS Initial Service [4], an anticipation of further fundamental technological advancements in Galileo’s signals and infrastructures. HAS extends not only the consolidated Open Service (OS) capabilities by providing more precise Global Navigation Satellite Systems (GNSSs) satellite orbits, clock errors and biases but also the perimeter of the system support, providing reference algorithms, guidelines, and standards to be implemented by the users to achieve the service goals.

The exploitation of HAS corrections in combination with a Precise Point Positioning (PPP) algorithm will allow achieving, in nominal conditions, a horizontal position accuracy below 20 centimetres (95%) and a vertical position accuracy below 40 centimetres (95%) after convergence for any user defined within the Galileo HAS service area [4]. The Galileo HAS Reference User Algorithm (UA), indicated as HAS-UA in the following, is a real-time PPP algorithm that applies HAS corrections to generate a Position, Velocity and Time (PVT) solution and can be used to demonstrate the HAS Initial Service user performance. The HAS-UA is the HAS reference algorithm used by EU Agency for the Space Programme (EUSPA) to characterise the typical HAS user performance specified in the HAS Service Definition Document (SDD). It is worth underlining that alternative algorithms could also be adopted to meet the above performance (e.g. [6], [7], [8], [9], [10], [11], [12]).

The HAS UA is designed to offer a simple and flexible solution suitable for any user. Thanks to its adaptive tuning, the HAS-UA can be applied under both static and dynamic conditions. Updates to the HAS-UA are expected along the Galileo HAS evolution, for example with the implementation of HAS Phase 2 and the transmission of additional HAS corrections. Consequently, evolutions of the HAS UA should be also expected.

The scope of this contribution is to introduce the HAS-UA, to clarify its condition of use and to provide a description of it, including the algorithm assumptions and mathematical background, to facilitate the algorithm use and implementation and to provide the results of an extended verification campaign.

As main feature, the HAS-UA can work in either double frequency or triple frequency modes supporting both Galileo single and Galileo plus GPS dual constellation modes. The HAS-UA is composed of two main blocks, the Pre-Processing (PP) and the Navigation (NAV) estimation blocks.

 The PP block performs the HAS-UA input data pre-processing. This task includes the data quality check, cycle slip detection and the estimation of a single epoch PVT solution (with the application of HAS corrections), which is used for the initialization of the NAV estimation when needed, the determinatio