Survey on Signal Processing for GNSS under Ionospheric Scintillation: Detection, Monitoring, and Mitigation

Ionospheric scintillation is the physical phenomena affecting radio waves coming from the space through the ionosphere. Such disturbance is caused by ionospheric electron density irregularities and is a major threat in Global Navigation Satellite Systems (GNSS). From a signal processing perspective, scintillation is one of the most challenging propagation scenarios, particularly affecting high-precision GNSS receivers and safety critical applications where accuracy, availability, continuity and integrity are mandatory. Under scintillation, GNSS signals are affected by amplitude and phase variations, which mainly compromise the synchronization stage of the receiver. To counteract these effects, one must resort to advanced signal processing techniques such as adaptive/robust methods, machine learning or parameter estimation. This contribution reviews the signal processing landscape in GNSS receivers, with emphasis on different detection, monitoring and mitigation problems. New results using real data are provided to support the discussion. To conclude, future perspectives of interest to the GNSS community are discussed

Analysis and Detection of Outliers in GNSS Measurements by Means of Machine Learning Algorithms

L'abstract è presente nell'allegato / the abstract is in the attachmen

Predicting Swarm Equatorial Plasma Bubbles via Machine Learning and Shapley Values

In this study we present AI Prediction of Equatorial Plasma Bubbles (APE), a machine learning model that can accurately predict the Ionospheric Bubble Index (IBI) on the Swarm spacecraft. IBI is a correlation (R2) between perturbations in plasma density and the magnetic field, whose source can be Equatorial Plasma Bubbles (EPBs). EPBs have been studied for a number of years, but their day-to-day variability has made predicting them a considerable challenge. We build an ensemble machine learning model to predict IBI. We use data from 2014 to 2022 at a resolution of 1s, and transform it from a time-series into a 6-dimensional space with a corresponding EPB R2 (0–1) acting as the label. APE performs well across all metrics, exhibiting a skill, association and root mean squared error score of 0.96, 0.98 and 0.08 respectively. The model performs best post-sunset, in the American/Atlantic sector, around the equinoxes, and when solar activity is high. This is promising because EPBs are most likely to occur during these periods. Shapley values reveal that F10.7 is the most important feature in driving the predictions, whereas latitude is the least. The analysis also examines the relationship between the features, which reveals new insights into EPB climatology. Finally, the selection of the features means that APE could be expanded to forecasting EPBs following additional investigations into their onset

Classification of Sources of Ionospheric Scintillation in High Latitudes through Machine Learning

The performance of Global Navigation Satellite Systems (GNSS) can be highly impacted by the interaction of the radio communication signal with ionized particles in the upper layers of the atmosphere (ionosphere). Depending on the shape of the cloud of particles, which is the irregularity, and its speed, the signal can be distorted gravely by intense oscillating signatures called scintillations. Those irregularities and their structures are only understood in-depth for particular events and case studies. In this study, we want to make use of the years of data available for high-rate high magnetic latitude GPS data. To gain a deeper insight into scintillations from multiple sources, we are investigating different machine learning approaches to classify and categorize scintillation events and draw conclusions about physical background processes. For the geomagnetic storm on the 9th of March 2012, we applied a hierarchical clustering analysis on high rate data in phase and power to categorize the temporal scintillation signatures according to their geomagnetic source region. We can distinguish manually selected events from stations inside the polar cap vs those from the auroral oval. From the geomagnetic background data, we are finding input features that will add the most efficiency to our model to detect the scintillation signatures caused by different irregularities and extract those candidate events. Based on this evolving database of events we expect to estimate the importance of the major sources of scintillation in each of the source regions and have a starting point for future studies with CNN and wavelet analysis

Securing Autonomous Vehicles Against GPS Spoofing Attacks: A Deep Learning Approach

With the rapid advancement of technology and multimedia systems, ensuring security has become a critical concern. Connected and Autonomous Vehicles (CAVs) are vulnerable to various hacking techniques, including jamming and spoofing. Global Positioning System (GPS) location spoofing poses a significant threat to CAVs, compromising their security and potentially endangering pedestrians and drivers. To address this issue, this research proposes a novel methodology that uses deep learning (DL) algorithms, such as Convolutional Neural Networks (CNN), and machine learning (ML) algorithms, such as Support Vector Machine (SVM), to protect CAVs from GPS location spoofing attacks. The proposed solution is validated using real-time simulations in the CARLA simulator, and extensive analysis of different learning algorithms is conducted to identify the most suitable approach across three distinct trajectories. Training and testing data include GPS coordinates, spoofed coordinates, and localization algorithm values. The proposed machine learning algorithm achieved 99% and 96% accuracy for the best and worst case scenarios, respectively. In case of deep learning, it achieved as high as 99% for best and 82% for the worst case scenario

Reconfigurable Antenna Systems: Platform implementation and low-power matters

Antennas are a necessary and often critical component of all wireless systems, of which they share the ever-increasing complexity and the challenges of present and emerging trends. 5G, massive low-orbit satellite architectures (e.g. OneWeb), industry 4.0, Internet of Things (IoT), satcom on-the-move, Advanced Driver Assistance Systems (ADAS) and Autonomous Vehicles, all call for highly flexible systems, and antenna reconfigurability is an enabling part of these advances. The terminal segment is particularly crucial in this sense, encompassing both very compact antennas or low-profile antennas, all with various adaptability/reconfigurability requirements. This thesis work has dealt with hardware implementation issues of Radio Frequency (RF) antenna reconfigurability, and in particular with low-power General Purpose Platforms (GPP); the work has encompassed Software Defined Radio (SDR) implementation, as well as embedded low-power platforms (in particular on STM32 Nucleo family of micro-controller). The hardware-software platform work has been complemented with design and fabrication of reconfigurable antennas in standard technology, and the resulting systems tested. The selected antenna technology was antenna array with continuously steerable beam, controlled by voltage-driven phase shifting circuits. Applications included notably Wireless Sensor Network (WSN) deployed in the Italian scientific mission in Antarctica, in a traffic-monitoring case study (EU H2020 project), and into an innovative Global Navigation Satellite Systems (GNSS) antenna concept (patent application submitted). The SDR implementation focused on a low-cost and low-power Software-defined radio open-source platform with IEEE 802.11 a/g/p wireless communication capability. In a second embodiment, the flexibility of the SDR paradigm has been traded off to avoid the power consumption associated to the relevant operating system. Application field of reconfigurable antenna is, however, not limited to a better management of the energy consumption. The analysis has also been extended to satellites positioning application. A novel beamforming method has presented demonstrating improvements in the quality of signals received from satellites. Regarding those who deal with positioning algorithms, this advancement help improving precision on the estimated position