## 2 Experimental Settings  
A sensor car shown in Figure 1 provided by Virtual Vehicle Research GmbH (Graz, Austria) was equipped by the study consortium members with three Septentrio Mosaic-X5 GNSS receivers in different configurations and an iMAR iNAT-FSLG-01 inertial measurement system (IMU) with gyro compassing capability (high-end fiber-optic gyroscope) and an integrated GNSS receiver (Novatel OEM/29-2.01). All GNSS receivers were connected to the same antenna using an active one-by-four antenna splitter. The used antenna model was a NavXperience 3G+C multi-band GNSS antenna. The architecture of this setup is shown in Figure 2. The test vehicle was equipped with the DataSpeed drive-by-wire kit ([[https://www.dataspeedinc.com/](https://www.dataspeedinc.com/)]([https://www.dataspeedinc.com/](https://www.dataspeedinc.com/)), accessed on 15 May 2023), which enables access to most CAN data as well as the control actuators for ADAS/AD system-development purposes. The vehicle was also equipped with additional sensors, which could be modified depending on the measurement or the use-case requirements. The GNSS receivers were connected to the so-called car PC (industrial PC installed in the vehicle) for power supply and data monitoring. The car PC was powered over an inverter belonging to the vehicle's DataSpeed drive-by-wire kit. The connection between the PC and the X5 receivers was achieved via USB and ethernet (cf. Figure 2). A control laptop was also connected via ethernet. All three Mosaic-X5 receivers received the GNSS signals via the same antenna and operated in the RTK mode using the incoming RTCM messages via 4G mobile internet. To guarantee that all receivers are receiving identical RTCM data with the same latency, Septentrio Data Link software was used to act as an RTCM splitter, acting as an NTRIP client to receive correction data in the form of virtual reference station data and forward the data to all receivers via a TCP stream. GNSS receivers operating in theh RTK mode can either output RTK fixed solutions, where the carrier phase ambiguities could be solved (estimated as an integer value), which provides the best positioning accuracy, or RTK float solutions, where the carrier phase ambiguities could be estimated as float values only, resulting typically in less accurate position information. When the receiver could not compute RTK positions, it fell back to so-called Single Point Positioning (SPP), where only data from the satellites were used in the PVT computation. The resulting positions were saved together with relevant information such as the type of solution attained, the quality of the solution, the satellites that were used for the position estimation, and so forth. The data were stored using the SBF protocol with a sampling rate of 10 Hz. The Mosaic-X5 receivers are one of the first mass-market receivers natively supporting Galileo OSNMA. For the performance analysis, one receiver was configured to use all GPS L1/L2 + Galileo E1/E5a satellite signals (called _OSNMA off_) for the PVT solution. The second receiver was configured in the OSNMA loose configuration. According to Septentrio, this means using all GPS signals and Galileo signals from satellites with authenticated navigation messages or unknown status. The third receiver was configured to use no GPS signals and only authenticated Galileo signals (called _OSNMA strict_). The reason for not using either Glonass or Beidou is that in the final stage, the Galileo OSNMA service will support Galileo and GPS, and hence, the OSNMA loose configuration should give an estimate of the final performance of Galileo OSNMA. The Galileo navigation data were recorded including I/NAV messages containing the OSNMA-related data bits. The measurement data from the FOG-based EGSNS/IMU iMAR iNAT FSLG-01 system were post-processed to serve as a highly accurate reference solution for data analysis. Therefore, the IMU data rate was recorded at 500 Hz and the GNSS data at 1 Hz.