The design of a solution for the authentication of both navigation data bits and spreading code chips, referred to as SNAP and suitable for the evolution of the Galileo E1 OS signal, is presented in the paper. Though the technique is innovative and able to achieve predefined authentication performance, it exploits the structure of the legacy Galileo signal and the characteristics of the OS NMA. A detailed overview of the open choices for the design of signal components dedicated to authentication is provided, together with an analysis of signal parameters definition. A possible implementation option of the SNAP solution is also presented.

GNSS links may require increased data rates to accommodate future features and needs (e.g. precise positioning, authentication, reduction of TTFFD). A particular form of $M$-ary orthogonal modulation designed for DSSS systems, the CCSK modulation, has been proposed for this purpose. This modulation inherently allows noncoherent processing at receiver side and has the potential to improve the energy efficiency of the data link with respect to classical DSSS/BPSK signals. In this article, $q$-ary ($q\in \lbrace 2,M\rbrace$) LDPC-based channel coding for $M$-ary CCSK is analyzed, both in terms of robustness and computational complexity. $(q=M)$-ary LDPC-coded CCSK is compared to a bit-interleaved binary LDPC-coded CCSK strategy. Though both solutions provide very reliable links for practical decoding algorithms, it is shown that adequately-designed bit-interleaved binary LDPC-coded CCSK signals can offer the additional flexibility inherent to BICM while remaining competitive from the point of view of both error rate performance and computational complexity. The latter can be adjusted through the use of incomplete iterative demapping schedules. The optimization of this performance/complexity trade-off is discussed.

There is an increasing demand for navigation capability for space vehicles. The exploitation of the so-called Space Service Volume (SSV), and hence the extension of the Global Navigation Satellite System (GNSS) from terrestrial to space users, is currently considered a fundamental step. Knowledge of the constellation antenna pattern, including the side lobe signals, is the main input for assessing the expected GNSS signal availability and navigation performance, especially for high orbits. The best way to define and share this information with the final GNSS user is still an open question. This paper proposes a novel methodology for the definition of a high-fidelity and easy-to-use statistical model to represent GNSS constellation antenna patterns. The reconstruction procedure, based on antenna characterization techniques and statistical learning, is presented here through its successful implementation for the “Galileo Reference Antenna Pattern (GRAP)” model, which has been proposed as the reference model for the Galileo programme. The GRAP represents the expected Equivalent Isotropic Radiated Power (EIRP) variation for the Galileo FOC satellites, and it is obtained by processing the measurements retrieved during the characterization campaign performed on the Galileo FOC antennas. The mathematical background of the model is analyzed in depth in order to better assess the GRAP with respect to different objectives such as improved resolution, smoothness and proper representation of the antenna pattern statistical distribution. The analysis confirms the enhanced GRAP properties and envisages the possibility of extending the approach to other GNSSs. The discussion is complemented by a preliminary use case characterization of the Galileo performance in SSV. The accessibility, a novel indicator, is defined in order to represent in a quick and compact manner, the expected Galileo SSV quality for different altitudes and target mission requirements. The SSV characterization is performed to demonstrate how simply and effectively the GRAP model can be inserted into user analysis. The work creates the basis for an improved capability for assessing Galileo-based navigation in SSV according to the current knowledge of the antenna pattern.

Global Navigation Satellite Systems (GNSSs) provide free services such as the Galileo High-Accuracy Service (HAS) to enhance navigation precision. The Joint Research Centre (JRC) developed a monitoring system for HAS corrections from Galileo signals and the internet, comparing them with Multi-GNSS Experiment (MGEX) products. HAS is also exploited to compute daily position and timing solutions of IGS stations and JRC receivers. Performance is evaluated by analyzing HAS ephemeris errors and positioning accuracy considering single- and dual-constellation modes. Signal-in-space and Internet data distribution HAS corrections, their streams, and the derived experimental HAS products are stored at the JRC and made available for research.