Rigas T. Ioannides

Detection and mitigation of non-authentic GNSS signals: Preliminary sensitivity analysis of receiver tracking loops

A myriad of applications are based on the positioning and timing information provided by GNSS systems. Protecting the system against any kind of interference has been always on the focus of researchers and manufacturers. Unintentional and intentional interferences are two well known ways to mislead the results of GNSS receivers. However, it has been recently, with the mass-market production of Software Defined Radio (SDR) equipment and cheap hardware signal generators, when retransmission of delayed signal replicas or the generation of a modified version becomes even more feasible. For this reason, this paper attempts to perform an initial sensitivity assessment of the receiver tracking stage against this singular kind of disturbance. This analysis is critical for the development of appropriate techniques to detect and mitigate the effects of non-authentic signals reception.

Galileo signal authenticity verification using signal quality monitoring methods

Civilian GNSS signals are highly vulnerable to structural interference due to publicly known signal structure and lack of encryption. This type of interference includes counterfeit GNSS like signals that are designed to deceive target GNSS receivers without being detected. A synchronized structural interference signal can mislead the tracking process of a receiver which may lead to the generation of a fake position solution. This paper focuses on analyzing the effect of this category of interference on correlator outputs of a Galileo receiver. Several signal quality monitoring (SQM) metrics are then designed to detect an abnormally shaped or asymmetric Galileo correlation peaks that are distorted due to the interaction between authentic and counterfeit signals. The statistical properties of the proposed metrics are then analyzed and proper interference detection thresholds are calculated based on these properties. Results show the effectiveness of these metrics in various scenarios of overlapped structural interference added to authentic Galileo signals.

Software-Defined Radio LTE Positioning Receiver Towards Future Hybrid Localization Systems

The appropriate positioning characteristics and fast deployment of Long Term Evolution (LTE) systems makes this technology a promising candidate towards future satellite and terrestrial hybrid scenario. Nevertheless, further studies on the achievable LTE positioning capabilities are still necessary for commercial or realistic network deployments. This paper describes a tool that provides standalone localization in LTE networks. The tool is a software-defined radio (SDR) receiver working at the LTE physical layer, performing acquisition, tracking and positioning. The SDR LTE positioning receiver is validated in a static scenario, showing position errors below three meters in the absence of multipath for a signal bandwidth of 1.08 MHz.

Signal-Level Integrity Monitoring Metric for Robust GNSS receivers

This paper deals with the problem of detecting distortions on the received signals of Global Navigation Satellite Systems (GNSS) that may degrade the measurements accuracy and compromise the overall receiver operation. Amongst others, multipath and spoofing are two of the most concerning threats for the robustness of GNSS receivers. These two phenomena have similar effects on the received signal, which can be exploited with the aim of developing a common defence mechanism. The detection process presented herein uses the fact that, in the presence of signal anomalies, the correlation function at the receiver side becomes distorted and loses its symmetry. An assessment on how severe is the effect of this distortion is presented herein. Besides, the proposed scheme is validated with the analysis of real signals simulated with an advanced hardware simulator.

An approach to discriminate GNSS spoofing from multipath fading

GNSS signals are vulnerable to various types of interference including jamming and spoofing attacks. Spoofing signals are designed to deceive target GNSS receivers without being detected by conventional receiver quality monitoring metrics. This paper focuses on detecting an overlapped spoofing attack where the correlation peaks of the authentic and spoofing signals interact during the attack. Several spoofing detection and signal quality monitoring (SQM) metrics are introduced. This paper proposes a spoofing detection architecture utilizing combination of different metrics to detect spoofing signals and distinguish them from multipath signals. Experimental results show that the pre-despreading spoofing detection metrics such as variance analysis are not sensitive to multipath propagation and can be used in conjunction with post-despreading methods to correctly detect spoofing signals. Several test scenarios based on different spoofing and multipath cases are performed to demonstrate the effectiveness of the proposed architecture to correctly detect spoofing attack ands distinguish them from multipath.

Sequential test for signal-level integrity monitoring in GNSS receivers

This paper addresses the problem of integrity monitoring in global navigation satellite system (GNSS) receivers. A new technique is proposed to quickly detect the presence of corrupted measurements caused by either multipath or spoofing threats. To do so, the symmetry of the correlation curve is permanently monitored, and a CUSUM-based sequential test is applied later on. Numerical results are provided to validate the technique and show its effectiveness.

Frequency-domain code replica detection for a GNSS receiver

This paper addresses the problem of detecting the presence of spreading signal replica in GNSS receivers, a problem that is often related to the presence of non-authentic GNSS signals. In order to carry out the detection process, a super-resolution frequency-domain technique is proposed based on the well-known Pisarenko harmonic decomposition, which allows us to circumvent many of the problems encountered by non-parametric spectral methods in the presence of short data records. The proposed technique allows to detect the presence of signal replicas while at the same time, it provides an estimate of its frequencies which can be used for frequency tracking purposes in integrity monitoring applications. The performance of the proposed technique has been tested with real GNSS signals from a hardware simulator, confirming the capability of this technique to detect real-life code replicas, even when they are just a few Hz apart.

An autonomous GNSS anti-spoofing technique

In recent years, the problem of Position, Navigation and Timing (PNT) resiliency has received significant attention due to an increasing awareness on threats and the vulnerability of the current GNSS signals. Several proposed solutions make uses of cryptography to protect against spoofing. A limitation of cryptographic techniques is that they introduce a communication and processing computation overhead and may impact the performance in terms of availability and continuity for GNSS users. This paper introduces autonomous non cryptographic antispoofing mechanisms, that exploit semi-codeless receiver techniques to detect spoofing for signals with a component making use of spreading code encryption.