Mass-Market Receiver for Static Positioning: Tests and Statistical Analyses

Nowadays, there are several low cost GPS receivers able to provide both pseudorange and carrier phase measurements in the L1band, that allow to have good realtime performances in outdoor condition. The present paper describes a set of dedicated tests in order to evaluate the positioning accuracy in static conditions. The quality of the pseudorange and the carrier phase measurements let hope for interesting results. The use of such kind of receiver could be extended to a large number of professional applications, like engineering fields: survey, georeferencing, monitoring, cadastral mapping and cadastral road. In this work, the receivers performance is verified considering a single frequency solution trying to fix the phase ambiguity, when possible. Different solutions are defined: code, float and fix solutions. In order to solve the phase ambiguities different methods are considered. Each test performed is statistically analyzed, highlighting the effects of different factors on precision and accurac

A Testbed for Developing and Evaluating GNSS Signal Authentication Techniques

An experimental testbed has been created for developing and evaluating Global Navigation Satellite System (GNSS) signal authentication techniques. The testbed advances the state of the art in GNSS signal authentication by subjecting candidate techniques to the strongest publicly-acknowledged GNSS spoofing attacks. The testbed consists of a real-time phase-coherent GNSS signal simulator that acts as spoofer, a real-time softwaredefined GNSS receiver that plays the role of defender, and post-processing versions of both the spoofer and defender. Two recently-proposed authentication techniques are analytically and experimentally evaluated: (1) a defense based on anomalous received power in a GNSS band, and (2) a cryptographic defense against estimation-and-replay-type spoofing attacks. The evaluation reveals weaknesses in both techniques; nonetheless, both significantly complicate a successful GNSS spoofing attackAerospace Engineering and Engineering Mechanic

The Texas Spoofing Test Battery: Toward a Standard for Evaluating GPS Signal Authentication Techniques

A battery of recorded spoofing scenarios has been compiled for evaluating civil Global Positioning System (GPS) signal authentication techniques. The battery can be considered the data component of an evolving standard meant to define the notion of spoof resistance for commercial GPS receivers. The setup used to record the scenarios is described. A detailed description of each scenario reveals readily detectable anomalies that spoofing detectors could target to improve GPS securityAerospace Engineering and Engineering Mechanic

Analysis of Satellite Timing and Navigation Receiver Pseudorange Biases due to Spreading Code Puncturing and Phase Optimized Constant Envelope Transmission

There is a desire for future GPS satellites to be software-defined to enable greater operational flexibility and adapt to a variety of current and future threats. This includes implementing new modulation techniques such as phase optimized constant envelope transmission (POCET) and asymmetric signal authentication methods such as chips message robust authentication (Chimera). Any new GPS signal transmitted must be backwards compatible with the millions of receivers already in use. This thesis shows a variety of tests performed to demonstrate the effects of Chimera and POCET-enabled signals. It is shown through actual radio frequency signal generation, testing the response of current-generation high accuracy commercial off-the-shelf GPS receivers to these signals, that both Chimera and POCET, as implemented in a GPS signal constellation, are backwards compatible

Ionospheric scintillation effects on GPS measurements and algorithms to improve positioning solution accuracy

2017 Summer.Includes bibliographical references.The ionosphere is an important cause of disturbances on GNSS signals, especially in high latitudes and equatorial areas. Previous studies indicate that while ionospheric scintillation may cause abrupt, random fluctuations in carrier phase measurements, its impact on pseudorange is less serious. Since modern GNSS receivers, especially those for high precision applications, use carrier phase-smoothed pseudoranges to improve accuracy of position solutions, there exists the need to have a better understanding of the scintillation effects on carrier phase measurements and developing means to mitigate scintillation induced errors in navigation solutions. In this thesis, scintillation impacts are demonstrated on carrier phase and pseudorange measurements using real scintillation data collected at high latitudes and equatorial areas, and the effect on positioning is investigated and mitigated. To obtain a more insightful and quantitative understanding of the impact, the data was used to generate position solutions using standard navigation processing algorithms. The results clearly indicate that sudden carrier phase discontinuities during strong scintillation lead to the degradation of carrier-smoothed pseudorange accuracy and consequently, results in large position errors. During strong scintillation with no carrier phase discontinuities, comparatively smaller position errors are found due to phase fluctuations that cause small changes in the range measurements. Based on this analysis, we give examples of several approaches to mitigate these problems, and use these approaches to present adaptive positioning techniques to mitigate scintillation induced position errors. One algorithm simply replaces the carrier-smoothed pseudorange with the unsmoothed pseudorange for satellites that are affected by outages on the carrier phase measurements, or if strong scintillation is detected. Another adaptive algorithm uses the GDOP to determine if a scintillating satellite can be completely removed from the navigation processing to improve positioning accuracy. Results show that the algorithms that substitute the unsmoothed pseudorange increase errors by 24.5% as compared to a conventional technique that repairs cycle slips, which indicates that it is still best to use the carrier-smoothed pseudoranges as long as there are no discontinuities. Results from the adaptive technique based on the analysis of the GDOP show a reduction of maximum errors on average by 13% on all of the data sets when comparing to a conventional algorithm. It was also found that a new carrier-smoothing technique can reduce maximum errors by 7.9% on average. Alternative approaches for future improvements are also discussed

Investigation on the Actual Robustness of GNSS-based Timing Distribution Under Meaconing and Spoofing Interferences

Long-term stability and accurate time synchronization are at the core of timing network facilities in several critical infrastructures, such as in telecommunication networks. In these applications, timing signals disciplined by Global Navigation Satellite Systems (GNSS) receivers, i.e., One Pulse-per-Second (1-PPS), complement Primary Reference Time Clocks (PRTCs) by compensating for long-term drifts of their embedded atomic clocks. However, GNSS receivers may expose timing distribution networks to Radio Frequency (RF) vulnerabilities being the cause of possible degraded or disrupted synchronization among the nodes. This paper presents a test methodology assessing the resilience of new GNSS timing receivers to different classes of intentional RF interferences. The analysis of the results compares the effects of practicable spoofing and meaconing attacks on the 1-PPS generated by three Commercial off-the-shelf (COTS) GNSS timing receivers, currently employed in timing applications. On one hand, the results emphasised the robustness of State-of-the-Art (SoA) mitigation technologies compared to previous generations’ devices. On the other hand, the vulnerability of SoA receivers to meaconing attacks highlights the limits of such mitigation solutions that may turn to severe effects on telecommunication networks’ performance

Modeling and Simulating GNSS Signal Structures and Receivers

In this thesis an end-to-end simulation was implemented encompassing the important effects from the user segments point of view. The modeling and implementation aimed to take all the relevant features into account that have a direct and significant impact on the performance of a GNSS receiver. In particular, emphasis was on the effects that are hard to formulate and treat theoretically, such as non-linearities, stochastic processes and the highly complex boundary conditions generated by the interaction of the signal with the environment. The three most important parts of the model development are the signal model, the signal propagation model and the receiver model. The signal model is an extension of the well-known signal modeling used to describe GPS signals. The present model was extended to include any sort of signal structure The most important part of the signal propagation model is essentially a ray-tracing algorithm together with the application of the Fresnel equations. This is a 3-D exact specular ray-tracing, which was derived and implemented during the work accompanying this thesis. Beside the signal model the receiver model constitutes a major part of this work. Essentially, it is a dynamic modeling of the tracking process (DLL and PLL). As the model is based on continuous calculus it was a challenge to incorporate the effects of the noise processes. However, this was solved by using the Îto calculus to extend the ordinary differential equations to stochastic differential equations. The implementation was verified by comparing the results to known theoretical expressions and an indirect experimental verification was performed in the sense that some of the theoretical formulas have been compared with experimental data.In dieser Artbeit wurde ein end-to-end Simulator entwickelt, der die wichtigsten Effekte aus der Sicht des Empfängernutzers berücksichtigt. Bei der Modellierung und der Implementierung wurde versucht die Faktoren zu berücksichtigen, die einen wesentlichen Einfluss auf die Performance eines GNSS Empfängers haben. Die drei wichtigsten Modellkomponenten sind das Signalmodell, das Signalausbreitungsmodell und das Empfängermodell. Das Signalmodell ist eine Verallgemeinerung des bekannten Signalmodells, das für die Modellierung von GPS C/A-code Signalen verwendet wird. Dieses Modell wurde für beliebige Signalstrukturen erweitert. Der Kern des Signalausbreitungsmodells ist ein Ray-tracing Algorithmus zusammen mit der Anwendung der Fresnel Gleichungen. Dabei handelt es sich um ein exaktes, dreidimensionales Ray-tracing Modell, das während der Arbeit entwickelt und implementiert wurde. Das Empfängermodell stellt ebenfalls einen wichtigen Teil der Arbeit dar. Im Wesentlichen werden die Regelkreise (DLL und PLL) als dynamischer Prozess modelliert. Das Modell basiert auf einem kontinuierlichen Ansatz, was die Einbindung von Rauschprozessen erschwerte. Durch die Interpretation der gewöhnlichen Differentialgleichungen als stochastiche Differentialgleichungen und Verwendung des Îto Kalküls konnten verrauschte Signale berücksichtigt werden. Die Implementierung wurde durch den Vergleich bekannter theoretischer Ergebnisse verifiziert. Da die meisten theoretischen Ausdrücke schon mit Experimenten verglichen worden sind, kann dies als indirekter Vergleich mit Experimenten gesehen werden

Control of position sensor input to Ecdis on high speed craft

Project thesis submitted in part fulfilment of the requirements for the degree of Master of Science in Position and Navigation Technology at The University of NottinghamBy 2018 all larger ships are to be equipped with Electronic Chart Display and Information System (ECDIS). The paradigm shift from paper charts to electronic charts has been a technological leap for mariners, and the Integrated Navigation Systems (INS) are getting more and more complex. This leads to new challenges for the navigators of today. Global Navigation Satellite Systems (GNSS) such as GPS are the primary position sensor input for ECDIS, and it has since its early beginning in the middle of the 1990s been very reliable. National and worldwide statistics show that there has been a slight increase in navigational accidents since the introduction of ECDIS, but the reasons for this is not clear. In the literature review it is laid down that position sensors have its potential fault, and GNSS and its augmentation systems is described to better understand its advantageous and limitations. Control of ECDIS with position control methods are explored, and divided into two methods of control: Visual- and Conventional methods. Through field work, simulator tests and interviews the findings are clear. The navigators of today rely too much upon their primary position sensor which normally is a GNSS such as GPS. A questionnaire reveals that the navigators have insufficient deeper system knowledge of the navigation aids in use. This can lead to a potentially serious accident with loss of lives and large environmental damage. To achieve safe navigation it is important to continuously conduct control of primary position sensor input to ECDIS with a secondary position sensor by visual- and/or conventional control methods. The advantages and limitations with the different methods of control are discussed. Position sensors such as GNSS can fail, and navigators of today and tomorrow need to monitor the position sensor input to ECDIS with other means than GNSS

Behaviour of large scale structures of the electron content as a key parameterfor range errors in GNSS applications

The Total Electron Content (TEC) of the ionosphere is a key parameter for describing the ionospheric state. This paper deals with the large scale behaviour of TEC under low and high solar activity conditions. Large scale structures of the plasma density are formed by fundamental ionospheric processes mainly driven by solar radiation input, neutral winds and electric fields. The monitoring of large scale structures contributes to a comprehensive understanding of these coupling mechanisms which are rather complex particularly under perturbed geomagnetic conditions. The paper addresses techniques to monitor TEC with sufficient accuracy of a few TEC units (1016m-2) to measure large scale structures over Europe and over the polar areas. The availability of GPS data from global GPS receiver networks as e.g., those from the International GPS Service (IGS) is dense enough to generate TEC maps on a continuous base. A model assisted technique is briefly described for mapping TEC over the European and polar areas. A statistical estimation of horizontal TEC gradients reveals large scale gradients of up to about 6 TECU/1000 km under high solar activity conditions at an occurrence probability level of about 1%. Occasionally, during severe ionospheric storms this value may increase by a factor of 10 or even more. A close correlation of large scale gradients and the geomagnetic activity has been found giving the chance to forecast TEC gradient amplitudes by using predicted geomagnetic indices. Since TEC is proportional to first-order range errors in Global Satellite Navigation Systems (GNSS) such as the US GPS and the Russian GLONASS the study of the behaviour of this parameter has a practical meaning in GNSS based navigation and positioning. The paper addresses the close relationship between TEC and ranging errors in GNSS. Having in view Galileo, the planned Europe’s own global satellite navigation system, some aspects related to the mitigation of ionospheric propagation errors within the European Geostationary Navigation Overlay System (EGNOS) are discussed. Since EGNOS will augment the two above mentioned satellite navigation systems and make them suitable for safety critical applications such as flying aircraft or navigating ships through narrow channels the ionospheric propagation errors have to be mitigated as much as possible