The IEC 61108-7 standard focuses on the minimum performance of shipborne receivers using Satellites Based Augmentation System (SBAS) L1 signals to be compliant to the performances within IMO Resolution A.1046(27). Apart from the minimum performance requirements, the standard specifies testing methods and a full set of scenarios with their pass/fail criteria. To verify the feasibility of the tests defined in the standard, a comprehensive test campaign has been carried out in a joint effort by European Satellite Services Provider (ESSP) and the European Commission Joint Research Centre (JRC), under the coordination of the European Union Agency for the Space Programme (EUSPA). This paper presents an assessment of the validity and appropriateness of the test scenarios and minimum performance requirements specified in the future IEC-61108-7 standard. To perform the campaign, dedicated setups have been designed and implemented at the JRC and at ESSP laboratories, where live and simulated GPS+SBAS signals have been used. For the analysis, all the Test Cases (TCs) described in the standard were implemented and two commercial devices were tested. From the results, it emerged that all the TCs were properly designed and implemented, therefore confirming the feasibility of the tests defined in IEC 61108-7.

Spoofing attacks pose a threat to drones that can lead to their crash or takeover. As a countermeasure, the European Space Agency has implemented the Timed Efficient Loss-tolerant Authentication (TESLA) broadcast protocol in the Galileo Open Service Navigation Message Authentication (OSNMA) to detect such events. This study explores the application of TESLA in detecting spoofing attacks targeted at drone swarms that rely on positioning systems utilizing ultra-wideband (UWB) technology. The results of our experiments reaffirm that UWB-based positioning systems are not automatically invulnerable from spoofing attacks and that cryptographic methods such as TESLA are required to provide a layer of protection against spoofing attacks to detect them effectively.

Galileo Open Service Navigation Message Authentication (OSNMA) has been transmitted stably over the last years and is expected to be declared operationally in the next months. While the protocol is very flexible, most of the parameters, such as key and tag sizes and cryptographic functions, have been already fixed in view of the operational declaration. However, some degree of flexibility remains in the tag and cross-authentication sequence. The cross-authentication sequence defines the satellites “cross-authenticated” by an authenticating Galileo satellite and is one of the main properties of the OSNMA protocol. It allows authenticating nearby Galileo satellites for higher redundancy against losses, authenticating data from satellites not connected to ground and therefore not transmitting OSNMA, and authenticating GPS or other data in the future. It has a significant impact on OSNMA performance: if the sequence is too long, many cross-authenticated satellites will not be seen by the users, limiting the optimal use of the OSNMA bandwidth, and with major impact in TBA (Time Between Authentications) and Time To First Authenticated Fix (TTFAF). If the sequence is too short, several non-connected but visible satellites may remain unauthenticated, also degrading performance. This paper presents an analysis with real SIS data from different cross-authentication sequences transmitted by Galileo over the last months, involving different tag distribution and number of cross-authenticated satellites including open-sky static, dynamic and urban environments. The work will show the degradation with suboptimal cross-authentication sequences and identifies current bottlenecks, proposing some recommendations for future sequences.

One year after Galileo High Accuracy Service (HAS) Initial Service declaration by the European Commission, this article present Galileo HAS accuracy and convergence comparative performance assessment between two different user algorithm configurations: static and dynamic. The assessment was conducted with two Galileo HAS User Terminal in parallel fed by the same antenna installation to obtain accuracy and convergence for the same period of time. The Galileo HAS User Terminal is a portable and autonomous device powered by a triple-frequency Galileo and GPS receiver and calculates a single (Galileo) or multi-constellation (Galileo + GPS) Galileo HAS using the Performance Characterization User Algorithm developed for the European Union Agency for the Space Programme (EUSPA). The performance assessment is completed with additional analysis in post-processing using a Precise Point Positioning (PPP) engine implementing the same algorithm than the User Terminal fed with International GNSS Service (IGS) stations observables and HAS Internet Data Distribution (IDD) corrections. The analysis is enhanced with an additional postprocessing analysis using the same IGS stations and CNES corrections.

Results for static conditions, assuming zero velocity in the Kalman filter, deliver accuracy performance at decimeter level 68% both horizontal and vertical. Results with the dynamic configuration, with a Kalman filter adaptable to changes in user velocity and fit for dynamic applications, indicate slightly over one decimeter 68% both horizontal and vertical. This article also compares both static and dynamic results vs. the Galileo HAS Service Definition Document (SDD) Appendix E typical positioning accuracy performance and presents the convergence time, or time to first precise fix, against positioning horizontal and vertical thresholds.

The purpose of this paper is to analyze the reaction of a real-time hardware multicorrelator GNSS receiver in realistic environments. In particular, we investigate how the GNSS signal correlations are distorted in two vehicular scenarios. The scenarios were recorded with a multi-frequency bit grabber and playback in the laboratory. The test campaigns were performed driving in two contrasting propagation environments. Rotterdam downtown was chosen to assess the multipath in challenging urban conditions while Nieuw-Vennep was selected as an open-sky/rural environment. The objective is to characterize the multipath of the received signal using a high-end GNSS receiver able to store 41 correlator outputs. The multipath error is estimated by comparing a local reference of the correlation function, which is estimated by using a GNSS simulator in the absence of GNSS disturbances, to the correlations estimated by the GNSS receiver in the vehicular scenarios. Two methods are considered. The first one consists in computing the error between the reference correlation function and the estimated ones. We evaluate the impact of the multipath on the temporal domain. The second one is based on estimating the multipath by implementing a Non-linear Least Squares estimator. The estimator provides reliable information about the power of the direct and reflected signals. We analyze the differences and similarities between both scenarios for several satellites having different elevations.

Advanced Receiver Autonomous Integrity Monitoring (ARAIM) is being developed to extend RAIM to multiple constellations and dual frequency, with the goal of providing first an increased coverage of horizontal guidance, and later, worldwide coverage of vertical guidance for aircraft operations.
To date, lots of effort is dedicated to assist the relevant standardization groups in consolidating the ARAIM concept for the development of future aviation standards. Those contributions focus on the specific aspects of algorithm processing and performance using real or simulated static user grid data.
However, significant differences in the quality of measurements made by a ground receiver compared to an avionics receiver may arise due to the operational constraints such as space weather (troposphere and/or ionosphere), multipath, satellite outages, and cycle slips.
The objective of our work is to present the results of H-ARAIM (Horizontal-ARAIM) reference algorithm using GPS and GALILEO dual-frequency flight data. Performances are analysed for typical arrival and approach manoeuvres with respect to positioning accuracy and integrity for RNP (Required Navigation Performance) operations, examining in detail the algorithm computational load during dynamics of the aircraft. More than 100 approaches and up to 18 hours of flight data have been post-processed using the EUROCONTROL PEGASUS tool.
Our work aims to provide an improved understanding of algorithm sensitivity to aircraft manoeuvres. We will show in detail the algorithm parameters setting used to compute horizontal position error and integrity bound for both Fault Detection and Fault Detection and Exclusion. Comprehensive integrity and accuracy performance will be discussed together with algorithm computational load with respect estimated airborne biases such as multipath, ionosphere delay and signal outages due to dynamics of aircraft.

This research investigates the positioning performance of the L-band Digital Aeronautical Communications System (LDACS) and presents a system architecture based on carrier-smoothed ground-to-air pseudoranges (PR) along with clock corrections derived from Asymmetric Two-Way Time and Frequency Transfer (A-TWTFT) filters. The objective is to achieve required positioning accuracy and integrity for aviation operations, addressing the complexities associated with utilizing a terrestrial communications system for Complementary Positioning, Navigation, and Timing (CPNT). Through error covariance analysis, the study assesses the steady-state value, convergence time and bounding performances of the filters. The positioning performance highlights the benefits provided by the proposed architecture.

As a result of developments in hardware and software technologies, the raw GNSS data can now be collected on different platforms, like smartphones, tablet computers and handheld receivers. In this study, the static and kinematic positioning performance of the Garmin GPSMAP 66sr handheld GNSS receiver has been tested. For the static test, GNSS data was collected for 24 hours on September 18-19, 2023. The collected daily dataset was divided into shorter sessions of 1, 2, 4 and 12 hours to assess the performance of the Garmin receiver as a function of occupation time. The whole and subgroup data were processed with the relative method by Topcon MAGNET Office software. Three continuously operating reference stations, i.e., ISTA, PALA and YALI, were used as reference control points to form a very short, short and relatively long baseline of about 45 meters, 5 km and 73 km, respectively. The coordinates obtained from each of the three different baseline solutions were compared with the known coordinates.

For a realistic kinematic test, the data was collected by walking for approximately 1 hour in a stadium on campus on July 29, 2023, using the Garmin and geodetic-grade GNSS receivers that connected to the same measurement pole. The collected data from both receivers was processed with the relative method, and the calculated Garmin coordinates were compared with those calculated by the geodetic receiver.

The whole and subgroup static and kinematic data of the Garmin receiver were processed again with the Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP) online service and the obtained PPP solutions were compared with the known coordinates.

The overall results show that the Garmin GPSMAP 66sr handheld receiver provides accuracy in the decimeter-to-centimeter range using the relative method when integer uncertainties were correctly resolved and, in the meter-to-centimeter range using the PPP technique.

Satellite positioning, navigation and timing applications have become an integral part of our daily lives, resulting in a growing demand for standard and high-precision location services. High-precision GNSS solutions have been around for several years. They primarily serve the surveying, construction and agricultural industries with decimeter to centimeter positioning accuracy in real-time based on GNSS signal measurements and correction data. More recently, the Galileo High Accuracy Service (HAS) was declared operational and is expected to benefit various markets and applications, such as maritime transport, drones, autonomous driving and precision agriculture, among others.

A GNSS performance analysis and monitoring system is being developed in the DLR Galileo Competence Center. Various parameters are monitored to characterize the performance of the four satellite navigation systems. For example, code-based positioning solutions are estimated at various stations locations around the globe.

The Galileo HAS will also be integrated into this system. This contribution discusses the system development aspect for the integration of the HAS service. Performance parameters for all GNSS are then presented with a focus on the new Galileo HAS service. The data management aspect of this analysis, i.e. storage, management and retrieval of data is based on a relational database, open-source software and in-house developed software tools.

The HAS message content is analyzed for key performance indicators and other descriptive statistics. Furthermore, the positioning results at different IGS station locations will be presented in order to characterize and eventually monitor the positioning performance of this new Galileo service.

Galileo ACAS is an assisted mode of Commercial Authentication Service (CAS) designed to enhance robustness against malicious attacks like spoofing. It operates by providing information to about some fragments of the unknown PRN codes in the E6-C signal. Unlike other approaches, ACAS uniquely employs TESLA keys provided by OSNMA in the E1-B signal for decryption, avoiding the need for key storage in potentially compromised receivers.

The encrypted fragments are made available to the receivers before the broadcast of the E6-C signal, along with their broadcast time. However, if the receiver lacks an accurate time reference, searching for these fragments, which typically last for milliseconds with periodicity that could extend to several seconds, can become impractical. In such cases, the probability of detection would be severely diminished due to the excessively large search space that ensues.

In the nominal operating mode for ACAS, this issue is resolved by obtaining initial estimates for the code phase delay and Doppler frequency from the E1-B signal. These estimates are then used to narrow down the search space for the E6-C signal. However, the alignment between the two signals is not perfect, particularly due to the intrinsic inter-frequency biases they exhibit.

To mitigate this issue, we can leverage auxiliary signals like E6-B, processed by HAS-compatible receivers. This is a logical choice as E6-B shares the same carrier frequency as E6-C. This could help in obtaining more precise estimates of the location of the encrypted fragments and improving the probability of detection, resulting in enhanced robustness for the ACAS authentication process.

This paper presents a comparison of uncertainties associated to the use of the E1-B and E6-B signals, based on real data samples obtained with an ACAS evaluation SDR-based platform. The results show the benefits of including E6-B in ACAS processing, with minimal implementation cost.