Session A3: Aviation, Aeronautics, and Uncrewed Aerial Applications 1

Uncovering Payload-Induced Signal Distortions: First Comprehensive Study Across the Galileo E1/E5a Constellation
Christoph Enneking, Steffen Thoelert, Florian C. Beck, Michael Meurer, German Aerospace Center (DLR)
Location: Holiday 6 (Second Floor)
Date/Time: Thursday, Sep. 11, 8:57 a.m.

Global Navigation Satellite Systems (GNSS) and their augmentations—such as Satellite-Based Augmentation Systems (SBAS), Ground-Based Augmentation Systems (GBAS) or Receiver Autonomous Integrity Monitoring (RAIM), positioning—are critical enablers of high-integrity applications across various domains. Several of these augmentations provide safety-of-life integrity and support the protection level requirements for precision approach and landing. The introduction of additional GNSS constellations and signals has created the potential for enhanced performance and accessibility to a broader user base. With the declaration of Full Operational Capability (FOC) for Galileo imminent, attention to the constellation’s signal quality and its implications for safety-critical users is more relevant than ever.
This study focuses on signal deformations in the Galileo E1 and E5a bands that originate from imperfections in the satellite payload, specifically analog impairments leading to frequency-dependent amplitude and phase distortions. These payload-induced distortions affect the achieved code phase measurements at the user side and, ultimately, the positioning, navigation, and timing (PNT) solution, whereas the resulting errors depend on receiver parameters and characteristics. It is the aim of the paper to assess these impairments for the complete fleet of Galileo satellites and to quantify their impact depending on aforementioned receiver parametrizations.
For this purpose, a large, high-gain dish antenna and two vector signal analyzers were employed to capture raw signal data with high dynamic range and temporal resolution. Substantial effort was invested in ensuring the quality and consistency of the measurement process. Contributions from the antenna system, feed, and analog components were carefully calibrated and removed. Additionally, ionospheric effects and Doppler shifts were corrected prior to the estimation of the analog distortions. This is the first study to characterize signal deformation effects across the entire operational Galileo constellation, extending beyond earlier work that covered only a limited number of satellites.
In a second step, the effect of these signal deformations on the receiver’s code tracking bias is investigated. The observed code biases vary systematically across the Galileo constellation. Except for a common mode bias that is typically absorbed, these biases are known to lead to biases of the PNT solution. While biases observed by a reference receiver can be broadcast to compensate for this effect in differential GNSS applications, even slight deviations of the specific user receiver from the reference (in terms of frequency response, bandwidth, correlator design etc.) can cause user-specific errors in code tracking and position estimation. Given the measured signal deformations, we determine differential code bias maps across a wide range of relevant correlator spacings and front-end bandwidths.
?Our findings underscore the importance of accounting for signal deformation effects in integrity-critical GNSS applications and contribute to the refinement of signal models for Galileo-based services. This work also lays the foundation for further research into anomalous deformation faults. For the appropriate threat model, optimal detection metrics can now be computed, contributing to the future development of more robust GNSS integrity monitoring systems.