Beatrice Motella

Detection of spoofed GPS signals at code and carrier tracking level

Due to the large amount of different new applications based on GNSS systems, the issue of interference monitoring is becoming an increasing concern in the satellite navigation community. Threats for GNSS can be classified as unintentional interference, jamming and spoofing. Among them, spoofing is more deceitful because the target receiver might not be able to detect the attack and consequently generate misleading position solutions. Different kind of spoofing attacks can be implemented depending on their complexity. The paper analyzes what is known as intermediate spoofing attack, by means of a spoofer device developed at the Navigation Signal Analysis and Simulation (NavSAS) laboratory. The work focuses on the spoofing detection, performed by implementing proper signal quality monitoring techniques at code and carrier tracking level.

Method for Assessing the Interference Impact on GNSS Receivers

The definition of new families of curves named interference error envelope (IEE) and interference running average (IRA) is presented. Such tools are able to assess the impact of RF interference on different GNSS receivers, taking into account the features of the in-band interference source. In fact the actual impact on the final performance is strictly related to the specific receiver architectures. Continuous wave (CW) and wide band (WB) interference signals are considered in order to assess by means of IEE and IRA the robustness of new modulations based on the multiplexed binary offset carrier (MBOC) scheme for several receiver configurations, by varying the discriminator spacing, type, and the front-end filter bandwidth. Interference robustness is evaluated and compared with those of the well-known binary phase shift keying (BPSK) and binary offset carrier BOC(1,1) modulations. Simulation and theoretical results are validated by means of laboratory tests, proving the reliability of IEE curves for interference impact assessment.

Performance assessment of low cost GPS receivers under civilian spoofing attacks

Services based on Global Navigation Satellite Systems (GNSS) are currently in use in many critical networked infrastructures and crucial applications. Within the described scenario, the importance for the GNSS community of investigating the effects of spoofing attacks, together with anti-spoofing techniques, appears essential. This paper describes the results of preliminary tests performed in lab on low cost GNSS receivers under spoofing attack. Such tests have been performed at the Istituto Superiore Mario Boella (ISMB) research institute and at the European Commission Joint Research Centre (EC-JRC) with the final goal of identifying effective countermeasures to increase receivers robustness.

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.

Methods of goodness of fit for GNSS interference detection

The number of applications based on Global Navigation Satellite System (GNSS) technology is constantly increasing; consequently, the requirements related to signal quality are becoming more and more important. This paper exploits results of the decision theory, aiming at investigating the performance of the goodness of fit test when applied to interference detection in GNSS receivers. It proposes two versions of a signal quality monitoring algorithm: one working exclusively precorrelation, the other providing postcorrelation information as well.

Validation of a signal quality monitoring technique over a set of spoofed scenarios

Since the early years of the operational capability of the Global Positioning Systems for civil purposes, the security aspects related to the use of the signals have always been a reason of concern. Nevretheless, jamming and spoofing of signals have always been seen as hard to implement due to the requires advanced skills for the design and the high cost of the equipment needed. Nowadays, with the advances in technology have brought to the attention that such threats to GNSS receivers are indeed more feasible. This paper deals, then with a low-complexity signal processing algorithm, named in literature a Signal Quality Monitoring Technique, testing its capabilities in realistic spoofed scenarios. Such a technique is based on the measurements of the correlation function peak quality as well as on the joint use of a pair of extra-correlators in order to detect vestigial signal presence. The work presented in this paper aims at validating the performance of the technique as an anti-spoofing method. The assessment was performed using a set of scenarios, named Texas Spoofing Test Battery (TEXBAT), which is provided by the Radionavigation Laboratory of the University of Texas at Austin.

A Method to Assess Robustness of GPS C/A Code in Presence of CW Interferences

Navigation/positioning platforms integrated with wireless communication systems are being used in a rapidly growing number of new applications. The mutual benefits they can obtain from each other are intrinsically related to the interoperability level and to a properly designed coexistence. In this paper a new family of curves, called Interference Error Envelope (IEE), is used to assess the impact of possible interference due to other systems (e.g., communications) transmitting in close bandwidths to Global Navigation Satellite System (GNSS) signals. The focus is on the analysis of the GPS C/A code robustness against Continuous Wave (CW) interference.

GNSS interference detector based on Chi-square Goodness-of-fit test

Interference is an actual problem for Global Navigation Satellite System (GNSS) receivers. Despite a wide amount of research works available in literature, the growing risk represented by portable jamming devices indicates that interfering signals are still a concern for GNSS-based services. The design of simple detection methods, possibly applicable to all types of interference, remains an open challenge for receiver designers. In this paper we introduce a method based on the statistical characteristics of the received signal, able to provide early warnings in case of interference. The method is based on the Chi-square Goodness-of-Fit test and can be applied to all types of interfering signals with moderate complexity. First tests on simulated and real signals demonstrated promising detection perfomance, even with low power interference hard to detect with conventional algorithms in frequency and time domain.

On the interference mitigation based on ADC parameters tuning

The function of the front-end of a global navigation satellite system (GNSS) receiver can be roughly described as the provision of received signal samples at intermediate frequency (IF) to the base band section. Due to the low power of the received signal, several phenomena might threat the correct operation of the front-end, and consequently degrade the performance of the acquisition and tracking stages. Among them, the interference from external electromagnetic sources is one of the most dangerous, due to the variety of candidates each with different features, that might affect the GNSS signals. This paper aims at presenting an analysis of the different blocks of the receiver chain in terms of performance degradation, due to the presence of wide-band interference. In particular the focus will be on the assessment of the impact of the tuning of the parameters of the analog to digital converter (ADC) on the receiver robustness to interfering sources.

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.