Reliable GPS position on an unreliable hardware

International audienceThis work address the fault tolerance topic in the GPS context. Starting from a noiseless GPS receiver, redundant mechanisms can be added to design a more resilient GPS receiver in the presence of errors due to process, voltage and temperature (PVT) variations. These mechanisms are based on different layer of abstraction to guarantee a mutual trade-off of system performance (quality of the position given by the GPS receiver), hardware reliability and implementation complexity. An Application-specific integrated circuit (ASIC) will be designed with two versions of the GPS receiver: the standard version, and a complex version where fault tolerant techniques are added to make the GPS receiver more tolerant to errors

Signal processing techniques for GNSS anti-spoofing algorithms

The Global Navigation Satellite Systems (GNSS) usage is growing at a very high rate, and more applications are relying on GNSS for correct functioning. With the introduction of new GNSSs, like the European Galileo and the Chinese Beidou, in addition to the existing ones, the United States Global Positioning System (GPS) and the Russian GLONASS, the applications, accuracy of the position and usage of the signals are increasing by the day. Given that GNSS signals are received with very low power, they are prone to interference events that may reduce the usage or decrease the accuracy. From these interference, the spoofing attack is the one that has drawn major concerns in the GNSS community. A spoofing attack consist on the transmission of GNSS-like signals, with the goal of taking control of the receiver and make it compute an erroneous position and time solution. In the thesis, we focus on the design and validation of different signal processing techniques, that aim at detection and mitigation of the spoofing attack effects. These are standalone techniques, working at the receiver’s level and providing discrimination of spoofing events without the need of external hardware or communication links. Four different techniques are explored, each of them with its unique sets of advantages and disadvantages, and a unique approach to spoofing detection. For these techniques, a spoofing detection algorithm is designed and implemented, and its capabilities are validated by means of a set of datasets containing spoofing signals. The thesis focuses on two different aspects of the techniques, divided as per detection and mitigation capabilities. Both detection techniques are complementary, their joint use is explored and experimental results are shown that demonstrate the advantages. In addition, each mitigation technique is analyzed separately as they require specialized receiver architecture in order to achieve spoofing detection and mitigation. These techniques are able to decrease the effects of the spoofing attacks, to the point of removing the spoofing signal from the receiver and compute navigation solutions that are not controlled by the spoofer and lead in more accurate end results. The main contributions of this thesis are: the description of a multidimensional ratio metric test for distinction between spoofing and multipath effects; the introduction of a cross-check between automatic gain control measurements and the carrier to noise density ratio, for distinction between spoofing attacks and other interference events; the description of a novel signal processing method for detection and mitigation of spoofing effects, based on the use of linear regression algorithms; and the description of a spoofing detection algorithm based on a feedback tracking architecture

Demo: Localisation in a faulty digital GPS receiver

The increase in integration density and the requirement of low power supplies to reduce energy consumption can make circuits more and more sensitive to hardware errors. The loss of robustness increases with process/voltage and temperature (PVT) variations. This demo presents a platform used first to implement a noiseless GPS receiver algorithm. Redundant mechanisms can be added, then, to the design to make the GPS receiver more resilient against upset errors due low supply voltage. The platform can be used, so, to evaluate the performance and the complexity of the proposed mechanisms

Performance assessment of a low-complexity autoregressive Kalman filter for GNSS carrier tracking using real scintillation time series

Altres ajuts: Acord transformatiu CRUE-CSICIonospheric scintillation is one of the most challenging sources of errors in global navigation satellite systems (GNSS). It is an effect of space weather that introduces rapid amplitude and phase fluctuations to transionospheric signals and, as a result, it severely degrades the tracking performance of receivers, particularly carrier tracking. It can occur anywhere on the earth during intense solar activity, but the problem aggravates in equatorial and high-latitude regions, thus posing serious concerns to the widespread deployment of GNSS in those areas. One of the most promising approaches to address this problem is the use of Kalman filter-based techniques at the carrier tracking level, incorporating some a priori knowledge about the statistics of the scintillation to be dealt with. These techniques aim at dissociating the carrier phase dynamics of interest from phase scintillation by modeling the latter through some correlated Gaussian function, such as the case of autoregressive processes. However, besides the fact that the optimality of these techniques is still to be reached, their applicability for dealing with scintillation in real-world environments also remains to be confirmed. We carry out an extensive analysis and experimentation campaign on the suitability of these techniques by processing real data captures of scintillation at low and high latitudes. We first evaluate how well phase scintillation can be modeled through an autoregressive process. Then, we propose a novel adaptive, low-complexity autoregressive Kalman filter intended to facilitate the implementation of the approach in practice. Last, we provide an analysis of the operational region of the proposed technique and the limits at which a performance gain over conventional tracking architectures is obtained. The results validate the excellence of the proposed approach for GNSS carrier tracking under scintillation conditions

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

Advanced Integration of GNSS and External Sensors for Autonomous Mobility Applications

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

Snapshot Estimation Algorithms for GNSS Mass-Market Receivers

This thesis resumes the PhD program carried out in the signal processing, satellite positioning and telecommunication fields, within the Navigation, Signal Analysis and Simulation (NavSAS) group, Department of Electronics and Telecommunications (DET) of Politecnico di Torino, in the period going from January 2012 to December 2014. The main topic of the PhD activity is represented by Global Navigation Satellite System (GNSS) receivers core technologies. In particular, it deals with the design, development, test and performance assessment of innovative architectures, techniques, and algorithms for Global Positioning System (GPS) and Galileo receivers, both professional high performance and commercial mass-market. GPS, and in general GNSSs are radio-communication infrastructures, aimed to enable a generic user to compute Position, Velocity and Time (PVT). The signals transmitted by a constellation of satellites are processed by an electronic device, performing trilateration with respect to the satellites, taken as reference points. At least 4 satellites are required to be in Line of Sight (LOS) with the receiver, so as to obtain 4 different signals and to solve the 4 navigation unknowns: latitude, longitude, height and time. Since their first appearance, in the early seventies, GNSS chipsets and devices are gaining a fundamental role in most applications of everyday life, and their global market continues to grow rapidly. In 25 years, GNSS receivers became extremely used worldwide, not only for positioning and navigation purposes, but also for time synchronization, thus spanning an unlimited range of applications, from commercial to scientific, from military to recreational. GNSS mass-market receivers are extremely widespread, produced in very high volume—hundreds of millions just for smartphones and tablets—and sold at a limited price. This variety of applications and possibilities represents the main reason of the continuous growth of the GNSS field: in fact, new systems are emerging beside GPS, such as GLONASS, currently operational and in expansion, Galileo and Beidou. With the latest trends of multi-constellation receivers, the positioning accuracy can greatly improve, as well as its robustness, availability, reliability, but at the expense of a greater complexity and power consumption

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

Authentication and Integrity Protection at Data and Physical layer for Critical Infrastructures

This thesis examines the authentication and the data integrity services in two prominent emerging contexts such as Global Navigation Satellite Systems (GNSS) and the Internet of Things (IoT), analyzing various techniques proposed in the literature and proposing novel methods. GNSS, among which Global Positioning System (GPS) is the most widely used, provide affordable access to accurate positioning and timing with global coverage. There are several motivations to attack GNSS: from personal privacy reasons, to disrupting critical infrastructures for terrorist purposes. The generation and transmission of spoofing signals either for research purpose or for actually mounting attacks has become easier in recent years with the increase of the computational power and with the availability on the market of Software Defined Radios (SDRs), general purpose radio devices that can be programmed to both receive and transmit RF signals. In this thesis a security analysis of the main currently proposed data and signal level authentication mechanisms for GNSS is performed. A novel GNSS data level authentication scheme, SigAm, that combines the security of asymmetric cryptographic primitives with the performance of hash functions or symmetric key cryptographic primitives is proposed. Moreover, a generalization of GNSS signal layer security code estimation attacks and defenses is provided, improving their performance, and an autonomous anti-spoofing technique that exploits semi-codeless tracking techniques is introduced. Finally, physical layer authentication techniques for IoT are discussed, providing a trade-off between the performance of the authentication protocol and energy expenditure of the authentication process

Impact of GNSS singular events on the integrity of airport navigation systems

GNSSs are currently used in civil aviation to provide aircraft with position and velocity estimates from en-route to precision approach operations. Extending the use of GNSS to the guidance function during airport surface operations and under zero-visibility conditions remains a challenge. Indeed, during these operations, GNSS measurements may be affected by GNSS singular events, such as multipath or ionosphere anomalies. GNSS singular events may lead to unacceptable position errors in terms of accuracy and integrity for the zero-visibility guidance function. Current GNSS integrity monitoring systems are not designed to totally account for the GNSS singular event effects. The development of GNSS integrity monitoring systems designed to properly protect users from the singular event effects is essential to use GNSS for the guidance function under zero-visibility conditions. GNSS measurement error and integrity failure models are key inputs in the design of GNSS integrity monitoring systems. In this thesis, work has been mainly focused on the development of GNSS multipath measurement errors, on the assessment of the multipath impact on the GNSS-based position error, and on the development of GNSS multipath integrity failure models. For this matter, the dual frequency GPSL1C+GPSL5 and GalileoE1+GalileoE5a multipath pseudo- range error model adapted to airport navigation has been firstly proposed. Next, the impact of multipath on the GNSS-based position error has been assessed. To do so, a double constellation GPS+Galileo/IRS tight coupling algorithm based on a linearized Kalman filter has been selected. The theoretical and quantitative analysis of the impact of the GNSS multipath ranging errors on the horizontal position bias and on the covariance matrix of the horizontal position error have been proposed. Finally, a GNSS multipath integrity failure model has been proposed. The model describes the signature of the GNSS single multipath ranging failures, the factors influencing the signature as well as the occurrence model of these failures and their conditions of occurrence