The Impact of Interference on GNSS Receiver Observables – A Running Digital Sum Based Simple Jammer Detector

A GNSS-based navigation system relies on externally received information via a space-based Radio Frequency (RF) link. This poses susceptibility to RF Interference (RFI) and may initiate failure states ranging from degraded navigation accuracy to a complete signal loss condition. To guarantee the integrity of the received GNSS signal, the receiver should either be able to function in the presence of RFI without generating misleading information (i.e., offering a navigation solution within an accuracy limit), or the receiver must detect RFI so that some other means could be used as a countermeasure in order to ensure robust and accurate navigation. Therefore, it is of utmost importance to identify an interference occurrence and not to confuse it with other signal conditions, for example, indoor or deep urban canyon, both of which have somewhat similar impact on the navigation performance. Hence, in this paper, the objective is to investigate the effect of interference on different GNSS receiver observables in two different environments: i. an interference scenario with an inexpensive car jammer, and ii. an outdoor-indoor scenario without any intentional interference. The investigated observables include the Automatic Gain Control (AGC) measurements, the digitized IF (Intermediate Frequency) signal levels, the Delay Locked Loop and the Phase Locked Loop discriminator variances, and the Carrier-to-noise density ratio (C/N0) measurements. The behavioral pattern of these receiver observables is perceived in these two different scenarios in order to comprehend which of those observables would be able to separate an interference situation from an indoor scenario, since in both the cases, the resulting positioning accuracy and/or availability are affected somewhat similarly. A new Running Digital Sum (RDS) -based interference detection method is also proposed herein that can be used as an alternate to AGC-based interference detection. It is shown in this paper that it is not at all wise to consider certain receiver observables for interference detection (i.e., C/N0); rather it is beneficial to utilize certain specific observables, such as the RDS of raw digitized signal levels or the AGC-based observables that can uniquely identify a critical malicious interference occurrence

Jamming of GPS & GLONASS signals - a study of GPS performance in maritime environments under jamming conditions, and benefits of applying GLONASS in Northern areas under such conditions

Project thesis submitted in part fulfilment of the requirements for the degree of Master of Science in Positioning and Navigation Technology, The University of Nottingham.Growing dependence on Global Navigation Satellite System (GNSS), especially GPS, for positioning and navigation at sea has raised a concern about the potential risks of signal interference. Technology for jamming is easily available, and in recent years there have been many cases of intentional jamming. As GPS is the principal means of position fixing used by the Norwegian Navy, important questions to find answers to is how vulnerable the GPS and the Electronic Chart Display and Information System (ECDIS) are to a jamming attack, and further whether employing the Glonass satellite system in addition to GPS will provide better performance regarding robustness and redundancy when receivers are exposed to jamming. By having a Coast Guard Vessel operating inshore the Norwegian fjords as case, this research aims to explore these issues and it does so by asking the following research questions: - Will employing Glonass in addition to GPS provide better performance in Northern areas when the systems are exposed to GNSS jammers? - How is the ability of the existing GPS system on board a Norwegian Coastguard Vessel to provide a reliable position when there is a jamming threat, and how will the ECDIS system on board handle an eventually loss of GPS position? The study consists of two jamming tests: A static test where focus is to analyze and compare the GPS and Glonass system and a dynamic test where the GPS and ECDIS system on board is analyzed when exposed to jamming. The results from the static test showed that the jammer has effect on large distances, and that the different receivers used react differently when exposed to jamming. Further, the carrier-to-noise ratios for Glonass are less affected by the jammer, and the receiver is able to track Glonass satellites with lower carrier-to-noise ratios than GPS satellites. We have seen that utilizing Glonass satellites in addition to GPS satellites in the receiver contribute to a later loss of position fix and an earlier calculation of new position under difficult jamming conditions. The dynamic test showed that the marine grade GPS receiver is easy to jam. A weak jamming signal caused the GPS receivers to give misleading information without any warning from itself or the ECDIS system. The ECDIS system provided an adequate DR positioning, but there are issues that need to be resolved for better functionality. As Glonass signals has shown to be more resistant to jamming than GPS signals, applying the Glonass system in addition to GPS might provide benefits with regards to reliability and redundancy, especially for maritime navigation in Northern areas where the Glonass satellites also have higher elevation and better coverage than GPS

Detection and Classification of {GNSS} Jammers Using Convolutional Neural Networks

Global Navigation Satellite Systems (GNSSs) have been established as one of the most significant infrastructures in today's world and play an important role in many critical applications. It is known that the power of the GNSS signals at the receivers' antenna is extremely weak and the transmitted signals are vulnerable to interference, which can cause degraded positioning and timing accuracy or even a complete lack of position availability. Thus, it is essential for GNSS applications to detect interference and further recognize the types of it for the mitigation in GNSS receivers to guarantee reliable solutions. In this paper, the focus is on the automatic detection and classi-fication of chirp signals, known as one of the most common and disruptive interfering signals. The classifier is a Convolutional Neural Networks (CNN) based on multi-layer neural networks that operate on the representation of the signals in transformed domains, Wigner- Ville and Short Time Fourier transforms. The representation of signals is fed to a CNN algorithm to classify the different shapes of chirp signals. The proposed method is performed in two case-study scenarios: the monitoring and classification by a terrestrial interference monitor and from a Low-Earth-Orbit (LEO) satellite. The experimental results demonstrate that the CNN model has a classification accuracy of 93 % and can be a suitable approach to classify different shapes of chirp signals

On the Use of an Ultra-Tight Integration for Robust Navigation in Jammed Scenarios

Peer reviewe

Robustness, Security and Privacy in Location-Based Services for Future IoT : A Survey

Internet of Things (IoT) connects sensing devices to the Internet for the purpose of exchanging information. Location information is one of the most crucial pieces of information required to achieve intelligent and context-aware IoT systems. Recently, positioning and localization functions have been realized in a large amount of IoT systems. However, security and privacy threats related to positioning in IoT have not been sufficiently addressed so far. In this paper, we survey solutions for improving the robustness, security, and privacy of location-based services in IoT systems. First, we provide an in-depth evaluation of the threats and solutions related to both global navigation satellite system (GNSS) and non-GNSS-based solutions. Second, we describe certain cryptographic solutions for security and privacy of positioning and location-based services in IoT. Finally, we discuss the state-of-the-art of policy regulations regarding security of positioning solutions and legal instruments to location data privacy in detail. This survey paper addresses a broad range of security and privacy aspects in IoT-based positioning and localization from both technical and legal points of view and aims to give insight and recommendations for future IoT systems providing more robust, secure, and privacy-preserving location-based services.Peer reviewe

Satellite-Based Communications Security: A Survey of Threats, Solutions, and Research Challenges

Satellite-based Communication systems are gaining renewed momentum in Industry and Academia, thanks to innovative services introduced by leading tech companies and the promising impact they can deliver towards the global connectivity objective tackled by early 6G initiatives. On the one hand, the emergence of new manufacturing processes and radio technologies promises to reduce service costs while guaranteeing outstanding communication latency, available bandwidth, flexibility, and coverage range. On the other hand, cybersecurity techniques and solutions applied in SATCOM links should be updated to reflect the substantial advancements in attacker capabilities characterizing the last two decades. However, business urgency and opportunities are leading operators towards challenging system trade-offs, resulting in an increased attack surface and a general relaxation of the available security services. In this paper, we tackle the cited problems and present a comprehensive survey on the link-layer security threats, solutions, and challenges faced when deploying and operating SATCOM systems.Specifically, we classify the literature on security for SATCOM systems into two main branches, i.e., physical-layer security and cryptography schemes.Then, we further identify specific research domains for each of the identified branches, focusing on dedicated security issues, including, e.g., physical-layer confidentiality, anti-jamming schemes, anti-spoofing strategies, and quantum-based key distribution schemes. For each of the above domains, we highlight the most essential techniques, peculiarities, advantages, disadvantages, lessons learned, and future directions.Finally, we also identify emerging research topics whose additional investigation by Academia and Industry could further attract researchers and investors, ultimately unleashing the full potential behind ubiquitous satellite communications.Comment: 72 page

Interference Mitigation and Localization Based on Time-Frequency Analysis for Navigation Satellite Systems

Interference Mitigation and Localization Based on Time-Frequency Analysis for Navigation Satellite SystemsNowadays, the operation of global navigation satellite systems (GNSS) is imperative across a multitude of applications worldwide. The increasing reliance on accurate positioning and timing information has made more serious than ever the consequences of possible service outages in the satellite navigation systems. Among others, interference is regarded as the primary threat to their operation. Due the recent proliferation of portable interferers, notably jammers, it has now become common for GNSS receivers to endure simultaneous attacks from multiple sources of interference, which are likely spatially distributed and transmit different modulations. To the best knowledge of the author, the present dissertation is the first publication to investigate the use of the S-transform (ST) to devise countermeasures to interference. The original contributions in this context are mainly: • the formulation of a complexity-scalable ST implementable in real time as a bank of filters; • a method for characterizing and localizing multiple in-car jammers through interference snapshots that are collected by separate receivers and analysed with a clever use of the ST; • a preliminary assessment of novel methods for mitigating generic interference at the receiver end by means the ST and more computationally efficient variants of the transform. Besides GNSSs, the countermeasures to interference proposed are equivalently applicable to protect any direct-sequence spread spectrum (DS-SS) communication

On the Threat of Systematic Jamming of GNSS

This paper presents a study of the threat of malicious interference to GNSS and examines the special case where the jamming device is incrementally more sophisticated than a typical always-on interference source. The concept of a systematic jamming attack is considered, where the interference signal is intentionally synchronized with the GNSS signals, with the intention of causing maximum disruption with the minimum power expenditure. Various attack methodologies are examined for the case of a civilian L1 receiver. It is shown that, depending on the attack strategy, the target signal and the target receiver, data-recovery, navigation and timing can be denied to a user with some tens of decibels less average power than a traditional jamming attack. It is further shown that some attacks may be capable to effectively deny some receiver functionality in a subtle manner such that presence of the malicious interference goes undetected. Key signal and receiver features that expose a vulnerability are identified and some means of improving receiver robustness are provided

A New Differential Positioning Method using Modulation Correlation of Signals of Opportunity

Global Navigation Satellite Systems (GNSS) have become the positioning systems of choice for many applications. However, GNSS signals are susceptible to obstruction, interference and jamming. Therefore, to maximize robustness and integrity, it is necessary to employ a dissimilar positioning technology that can operate independently and back-up GNSS. One such technology exploits 'signals of opportunity' - signals that are designed for purposes other than navigation.This paper presents a system that uses amplitude modulation (AM) radio broadcasts in the medium frequency (MF) band. At these frequencies, the predominant ground-wave propagation mode offers better coverage in remote areas and over sea than is achievable with higher frequency signals.The system is differential and operates by correlating modulation information between the reference and user receivers. A system of this form mitigates the deterioration in and around buildings encountered in prior systems and can provide absolute position using fewer signals than a system using only carrier phase.The system presented in this paper uses generalized cross correlation to obtain time difference of arrival measurements that are subsequently used for position determination. Preliminary results indicate the system provides a robust position solution. Moreover, the system offers the potential to be combined with carrier phase measurements to achieve enhanced performance, while the modulation correlation technique is readily extendable to other types of signal

GNSS Related Threats to Power Grid Applications

As power grid environments are moving towards the smart grid vision of the future, the traditional schemes for power grid protection and control are making way for new applications. The advancements in this field have made the requirements for power grid’s time synchronization accuracy and precision considerably more demanding. So far, the signals provided by Global Navigation Satellite Systems have generally addressed the need for highly accurate and stable reference time in power grid applications. These signals however are highly susceptible to tampering as they are being transmitted. Since electrical power transmission and distribution are critical functions for any modern society, the risks and impacts affiliated with satellite-based time synchronization in power grids ought to be examined. This thesis aims to address the matter. The objective is to examine how Global Navigation Satellite Systems are utilized in the power grids, how different attacks would potentially be carried out by employing interference and disturbance to GNSS signals and receivers and how the potential threats can be mitigated. A major part of the research is done through literature review, and the core concepts and different implementations of Global Navigation Satellite Systems are firstly introduced. The literature review also involves the introduction of different power grid components and subsystems, that utilize Global Positioning System for time synchronization. Threat modeling techniques traditionally practiced in software development are applied to power grid components and subsystems to gain insight about the possible threats and their impacts. The threats recognized through this process are evaluated and potential techniques for mitigating the most notable threats are presented.Sähköverkot ovat siirtymässä kohti tulevaisuuden älykkäitä sähköverkkoja ja perinteiset sähköverkon suojaus- ja ohjausmenetelmät tekevät tilaa uusille sovelluksille. Alan kehitys on tehnyt aikasynkronoinnin tarkkuusvaatimuksista huomattavasti aikaisempaa vaativampia. Tarkka aikareferenssi sähköverkoissa on tähän saakka saavutettu satelliittinavigointijärjestelmien tarjoamien signaalien avulla. Nämä signaalit ovat kuitenkin erittäin alttiita erilaisille hyökkäyksille. Sähkönjakelujärjestelmät ovat kriittinen osa nykyaikaista yhteiskuntaa ja riskejä sekä seuraamuksia, jotka liittyvät satelliittipohjaisten aikasynkronointimenetelmien hyödyntämiseen sähköverkoissa, tulisi tarkastella. Tämä tutkielma pyrkii vastaamaan tähän tarpeeseen. Päämääränä on selvittää, miten satelliittinavigointijärjestelmiä hyödynnetään sähköverkoissa, kuinka erilaisia hyökkäyksiä voidaan toteuttaa satelliittisignaaleja häiritsemällä ja satelliittisignaalivastaanottimia harhauttamalla ja kuinka näiden muodostamia uhkia voidaan lieventää. Valtaosa tästä tutkimuksesta on toteutettu kirjallisuuskatselmoinnin pohjalta. Työ kattaa satelliittinavigointijärjestelmien perusteet ja esittelee erilaisia tapoja, kuinka satelliittisignaaleja hyödynnetään sähköverkoissa erityisesti aikasynkronoinnin näkökulmasta. Työssä hyödynnettiin perinteisesti ohjelmistokehityksessä käytettyjä uhkamallinnusmenetelmiä mahdollisten uhkien ja seurausten analysointiin. Lopputuloksena esitellään riskiarviot uhkamallinnuksen pohjalta tunnistetuista uhkista, sekä esitellään erilaisia menettelytapoja uhkien lieventämiseksi