Micaela Troglia Gamba

Statistical test applied to detect distortions of GNSS signals

The extremely low power of Global Navigation Satellite System (GNSS) signals makes them vulnerable to disturbances and interference from external sources. These induce distortions on the correlation function that reflect upon a degraded pseudoranges measurement and poor positioning accuracy. On the other hand, the wide spread use of GNSS receivers in critical applications demands for improved performance in terms of positioning accuracy and integrity. This paper proposes a new algorithm based on the statistical testing of post-correlation measurements to detect signal distortions and to prevent degradations in the receiver positioning performance. The application of statistical tests to GNSS is not yet deeply investigated, but some recent works already show good performance when Goodness of Fit (GoF) tests are applied to raw signal samples to detect interference. The paper presents a quality monitoring algorithm, based on the application of a statistical testing, known as sign test, applied to the post correlation stage of a GNSS receiver. Promising results are obtained to detect distortions in the correlation shape, for two different harsh environments, i.e., with the presence of interference sources and under a spoofing attack. The main advantages of the proposed method are the low complexity, the indipendence from the type of disturbance and the possibility of its application to any GNSS modulation.

N-FUELS and SOPRANO: Educational tools for simulation, analysis and processing of satellite navigation signals

In recent years, research activities in the field of Satellite Navigation have boosted worldwide. At the same time, it has become evident that few educational opportunities in the field were available for students and there was a need to develop dedicated tools for hands-on sessions. To partially answer this need, the NavSAS Group has developed N-FUELS and SOPRANO. N-FUELS, a MATLAB®-based signal simulator, allows students to understand the physical layer of the Global Navigation Satellite Systems (GNSS) signals and to learn how to manipulate them via software. SOPRANO, a collection of ANSI C language routines, implements the whole chain of GNSS signal elaboration in post-processing and enables testing and validation of new GNSS signal processing algorithms and architectures. Both tools are used in post-graduate courses at Politecnico di Torino with a high degree of internationalization, which opens interesting points of discussion concerning the introduction of novel educational tools able to meet the demand and the learning styles of students with different educational backgrounds and cultures.

Hypothesis testing methods to detect spoofing attacks: a test against the TEXBAT datasets

The hazardous effects of spoofing attacks on the global navigation satellite system (GNSS) receiver are well known. Technologies and algorithms to increase the awareness of GNSS receivers against such attacks become more important and necessary. We present the validation of two statistical spoofing detection methods, namely the Chi-square goodness of fit (GoF) test and the Sign test applied to pairwise correlator differences, for each satellite tracked by the receiver. The test bench for the algorithms, both implemented in a software receiver, is the public database produced by the University of Texas at Austin, which reproduces various representative cases of spoofing attacks (the so-called TEXBAT). The algorithms show a very promising capability of detecting the attack, in particular when an aggregate decision is taken based on a joint detection upon all the tracked satellites. Furthermore, the GoF test appears also reliable in dynamic conditions and in case of a huge power advantage of the spoofing signal. The response of the receiver to the attacks confirms the spoofing signal represents an “extraneous agent” which, before taking control of the receiver, can be recognized by properly combined strategies of signal quality monitoring.

Prototyping a GNSS-Based Passive Radar for UAVs: An Instrument to Classify the Water Content Feature of Lands.

Global Navigation Satellite Systems (GNSS) broadcast signals for positioning and navigation, which can be also employed for remote sensing applications. Indeed, the satellites of any GNSS can be seen as synchronized sources of electromagnetic radiation, and specific processing of the signals reflected back from the ground can be used to estimate the geophysical properties of the Earth’s surface. Several experiments have successfully demonstrated GNSS-reflectometry (GNSS-R), whereas new applications are continuously emerging and are presently under development, either from static or dynamic platforms. GNSS-R can be implemented at a low cost, primarily if small devices are mounted on-board unmanned aerial vehicles (UAVs), which today can be equipped with several types of sensors for environmental monitoring. So far, many instruments for GNSS-R have followed the GNSS bistatic radar architecture and consisted of custom GNSS receivers, often requiring a personal computer and bulky systems to store large amounts of data. This paper presents the development of a GNSS-based sensor for UAVs and small manned aircraft, used to classify lands according to their soil water content. The paper provides details on the design of the major hardware and software components, as well as the description of the results obtained through field tests.

Performance assessment of an ARM-based dual-constellation GNSS software receiver

In modern communications, the flexibility is a key point in the implementation of receivers because it eases the development of new products and the introduction of new features in already existing ones. In the silicon-based products the extra-cost associated to the introduction of a new functionality is mainly due to the development process rather than the extra silicon and components. On the other hand, full reconfigurability can be obtained far cheaply through a software based implementation: the well-known Software-Defined-Radio (SDR) approach. Global Navigation Satellite Systems (GNSS) receivers make no exception to this fact, and, in the last years, several examples of software GNSS receivers have been published in the literature. In this paper, the development of a new real-time dual-constellation GPS+Galileo SDR receiver on a low cost ARM-based embedded platform is described. The impact of implementation and optimization choices on the achieved performance is evaluated and compared to other two PC-based SDR receivers.

Post-correlation signal analysis to detect spoofing attacks in GNSS receivers

Due to the low level of the received power and to the known signal structure, Global Navigation Satellite Systems (GNSS) civil signals might be vulnerable to different sources of interference. Among them, the spoofing attacks are considered ones of the most deceptive, since their scope is controlling the output of the victim receiver. This paper presents a set of live experiments that validate the performance of a spoofing detection method, based on the Chi-square Goodness of Fit (GoF) test and applied post-correlation. Results are promising and show the GoF test capability to successfully warn the user in case of a spoofing attack.

Light weight GNSS-based passive radar for remote sensing UAV applications

Nowadays, Unmanned Aerial Vehicles (UAVs) platform are widely employed in a broad range of applications: from environmental monitoring and precise agriculture to humanitarian localization and rescue and prevention of events such as floods, fires, landslides. On the other hand, Global Navigation Satellite System Reflectometry (GNSS-R) is an emerging technique which allows to monitor Earths surface parameters. Recently, this technique has been applied to soil moisture monitoring. In this paper, a prototype of a GNSS-based passive radar, able to exploit GNSS reflected signals from ground for soil moisture monitoring applications is presented. The prototype is able to handle signals coming from three antennas: one up-looking Right-Hand (RH) Circular Polarized antenna, for the direct signal from satellite, and two down-looking antennas, one RH and the other Left-Hand (LH) Circular Polarized, to measure the signals coming after reflection from ground. It is made of low-cost hardware and it is small and lightweight in order to be mounted on board an aircraft or a UAV. It basically serves as data grabber: the collected data are stored to memory for off-line processing. The design and development of the prototype is illustrated and early results of an in-field test campaign are also presented.