By Javier Benedicto
Head, Galileo Programme department,
European Space Agency

Javier Benedicto, left, accept the 2018 GPS World Satellites Leadership Award on behalf of Giuliano Gatti of the European Space Agency, from Phil Froom of Rockwell Collins. (Photo: Melanie Beus)

Since the Galileo initial services declaration in December 2016, the Galileo Program has been providing global PNT and search-and-rescue services for users worldwide. The European GNSS Agency (GSA) just issued its GNSS 2019 Market Report in October, providing a complete overview of the current status and trends of the GNSS worldwide market with focus on European GNSS (Galileo and EGNOS) applications and services.

In parallel with service provision, the Galileo Program is undertaking extensive infrastructure development and deployment activities to reach Full Operational Capability (FOC), incorporating new service capabilities, but above all aiming at increasing the robustness and resilience of the system infrastructure, operations and service provision.

Galileo’s signal-in-space quality has steadily improved over the past few years, reaching in 2019 a best signal-in-space error (SISE) of about 0.25 meters (95%, global average; Figure 1). This has been achieved through a combination of several factors, including the increased number of operational satellites, enhanced versions of the Ground Mission Segment, and higher uplink rate of the navigation message (lower age of data). This performance is well within Galileo’s initial service accuracy commitments, as defined in the public Open Service – Service Definition Document (OS SDD).

Figure 1. Long-term historical SISE plot over a 30-day sliding window, constellation averaged. (Image: ESA)

Figures 2 and 3 (see page 40) show Galileo’s timing performance as broadcast UTC offset and GGTO accuracy. The evaluation was performed with calibrated GPS/Galileo timing receivers operated in UTC(k) laboratory (PTB, INRIM). Again, the initial timing service commitments have been fully met.

Figure 2. Galileo Broadcast UTC offset accuracy performance. (Image: ESA)

Figure 3. Galileo GGTO offset accuracy performance. (Image: ESA)

Probably the most significant discriminator of Galileo compared to other GNSS is its capability to broadcast multi-frequency (E1, E6, E5) signal components on all operational satellites. The position performance of a dual-frequency user receiver on-ground is shown in Figure 4. This measurement from June 2019 demonstrates a Galileo position accuracy well below 2 m (95%).

Figure 4. Galileo position accuracy performance, dual-frequency, June 2019. (Image: ESA)

With the aim of further improving the Open Service (OS) performance, three newly introduced I/NAV message improvements on Galileo E1-B are under implementation, namely FEC2 Reed-Solomon Clock and Ephemeris (CED), Reduced CED, and Secondary Synchronization Pattern (SSP). Galileo Open Service (OS) users will benefit from improved robustness in terms of navigation data retrieval in challenging environments, in addition to facilitating a reduced time to first fix. Those I/NAV improvements on Galileo E1-B are backwards compatible with previously released OS SIS ICDs.

In addition, Galileo infrastructure is currently being upgraded to provide means for OS authentication. The protocol proposed uses the E1B External Data Broadcast Service (EDBS) to provide authentication data to the user. The OS Navigation Message Authentication (NMA) is based on an adaptation of the Timed Efficient Stream Loss-tolerant Authentication (TESLA) protocol.

Beyond the OS, the Galileo system has been designed to allow for the dissemination of value-added data, such as high accuracy and authentication, in the E6B signal component. The component has been designed to broadcast the Galileo High Accuracy Service based on the provision of accurate satellite data (clocks, orbits and biases) and atmospheric data (mainly ionospheric corrections) to enable multi-frequency multi-constellation PPP with correction data transmitted through an open format in the Galileo E6B signal.

The introduction in early 2020 of the automatic acknowledgment of the SAR/Galileo Return Link Message (RLM) as part of the Cospas-Sarsat system will enable space assets to be used for search and rescue — persons in distress will get swift acknowledgement that their alert has been detected and located. The Return Link is the means to interact with a SAR beacon, improving the effectiveness of SAR operations. Extensive testing has demonstrated that the median latency for the reception of a return link message on the ground is 14.2 seconds, while 99% of messages are received within 57 seconds, after the request for the RLM transmission is delivered to Galileo (from Cospas-Sarsat to the RLSP). At the same time, the measured rate of reception was 100%, considering line-of-sight availability, thanks to the very robust Galileo navigation data link. This performance has been demonstrated to be…