Phasor Measurement Units (PMUs) have been instrumental in building a reliable and robust Power System. Recent blackouts have increased the importance of PMUs and PMUs from various manufacturers are being installed in the in large quantities in the North American Grid. The interoperability and accuracy of these PMUs is important to obtain full benefit of the wide area monitoring systems. With the large number of installed PMUs it has become necessary to validate their performance and understand the limitations of each model. A test system was built by NIST in cooperation with NASPI to test for compliance to the existing IEEE C37.118 standard. This thesis presents the development of a Steady State Test System at Virginia Tech based on the NIST Steady State Testing system. The various issues that were faced during the process of development are discussed and the methodology implemented for solving these problems is described. This thesis also presents the additional benefits derived from the results obtained when different PMUs were tested using the Virginia Tech PMU Steady State Test System. / Master of Science

The testing of unmanned vehicles presents a need for an independent device capable of accurately collecting position and orientation data. While commercial-off-the-shelf components could be pieced together to sense and record this information, this is an expensive, large, and heavy solution, not suitable for small or aerial vehicles. The micro wireless instrumented payload, or μWIP, was designed precisely for this purpose. The μWIP includes a GPS receiver, 3-axis accelerometer, 3-axis gyroscope, and 3-axis magnetometer which are used to measure an unmanned vehicle's position and orientation. The device also uses a secure digital card for data storage, and an 802.11b module to provide wireless connectivity. Additionally, the μWIP contains a on-board battery and the circuitry required to charge it. Firmware for the ARM7 processor was written to allow sensor calibration and data transmission, and a user interface was designed to run on a personal computer. The finished design is a tiny 3''x5''x1'', and weighs a mere 0.8 pounds including battery and antennas. It is capable of continuously streaming accurate GPS and inertial data over an 802.11b wireless network for over 5 hours. Having a bill of materials cost just over $600, the μWIP is also more cost effective than any alternative solutions. This thesis details the hardware and software design of the μWIP, as well as the initial testing, calibration, and evaluation of the device. / Master of Science

Massive GPS navigation services are used by billions of people in their daily lives. GPS spoofing is quite a challenging problem nowadays. Existing Anti-GPS spoofing systems primarily focus on expensive equipment and complicated algorithms, which are not practical and deployable for most of the users. In this thesis, we explore the feasibility of a simple text-based system design for Anti-GPS spoofing. The goal is to use the lower cost and make the system more effective and robust for general spoofing attack detection. Our key idea is to only use the textual information from the physical world and build a real-time system to detect GPS spoofing. To demonstrate the feasibility, we first design image processing modules to collect sufficient textual information in panoramic images. Then, we simulate real-world spoofing attacks from two cities to build our training and testing datasets. We utilize LSTM to build a binary classifier which is the key for our Anti-GPS spoofing system. Finally, we evaluate the system performance by simulating driving tests. We prove that our system can achieve more than 98% detection accuracy when the ratio of attacked points in a driving route is more than 50%. Our system has a promising performance for general spoofing attack strategies and it proves the feasibility of using textual information for the spoofing attack detection. / Master of Science / Nowadays, people are used to using GPS navigation services in their daily lives. However, GPS can be easily spoofed and the wrong GPS information will mislead victims to an unknown place. There are some existing methods that can defend GPS spoofing attacks, but all of them have significant shortcomings. Our goal is to design a novel system, which is cheap, effective, and robust, to detect general GPS spoofing attacks in real-time. In this thesis, we propose a complete system design and evaluations for performance. Our system only uses textual information from the real physical world and virtual maps. To get more accurate textual information, we use state of the art techniques for image processing and text recognition. We also use a neural network to help with detection. By testing with datasets in two cities, we confirm the promising performance of our system for general GPS spoofing attack strategies. We believe that textual information can be further developed in the Anti-GPS spoofing systems.

Advancements in Global Positioning System (GPS) technology now make GPS data collection for transportation studies and other transportation applications a reality. Base map for the application can be obtained by importing the road centerline map into GIS software like AutoCAD Map, or Arc/Info or MapixTM. However, such kinds of Road Centerline maps are not available for all places. Therefore, it may be necessary to collect the data using GPS units. This thesis details the use of GPS technology to produce route maps that can be used to predict arrival time of a bus. This application is particularly useful in rural areas, since the bus headway in a rural area is generally larger than that in an urban area. The information is normally communicated through various interfaces such as internet, cable TV, etc., based on the GPS bus location data. The objective of this thesis is to develop an operational procedure to obtain the digitized route map of any desired interval or link length and to examine the accuracy of the digitized map. The operational procedure involved data collection, data processing, algorithm development and coding to produce the digitized route maps. An algorithm was developed produce the digitized route map from the base map of the route, coded in MATLAB, and can be used to digitize the base map into any desired interval of distance. The accuracy comparison is made to determine the consistency between the digitized route map and the base map. / Master of Science

Position in the environment is essential in any autonomous system. As increased accuracy is required, the costs escalate accordingly. This paper presents a simple way to systematically integrate sensory data to provide a drivable and accurate position solution at a low cost. The data fusion is handled by a Kalman filter tracking five states and an undetermined number of asynchronous measurements. This implementation allows the user to define additional adjustments to improve the overall behavior of the filter. The filter is tested using a suite of inexpensive sensors and then compared to a differential GPS position. The output of the filter is indeed a drivable solution that tracks the reference position remarkably well. This approach takes advantage of the short-term accuracy of odometry measurements and the long-term fix of a GPS unit. A maximum error of two meters of deviation from the reference is shown for a complex path over two minutes and 100 meters long. / Master of Science

Global Navigation Satellite Systems (GNSS) for vehicle navigation and timing are widely relied upon by many users in a variety of different sectors such as transit, financial, military, and many others. There are a number of ways for an agent to purposefully degrade a GNSS user's navigation performance. One such attack is a spoofing attack where the agent transmits signals with the same signal structure as GNSS signals, but they are modified to produce an incorrect navigation solution. Resiliency to these attacks is important for GNSS navigation. Two methods for GNSS resiliency are explored in this dissertation. The first method uses a Controlled Reception Pattern Antenna and receiver in order to obtain direction of arrival estimates of all visible signals and their computed pseudoranges. Two contributions were produced for this method. The first contribution is an optimization of a DoA cost metric that use DoA estimates along with known GNSS ephemerides to distinguish authentic signals from spoofed signals. The second contribution of this work is a combined DoA/pseudorange cost metric to improve the classification of authentic signals from spoofed signals as well as improve its robustness to multi-transmitter spoofing attacks. The second method uses a method known as Chimera, which involves authenticating the civilian L1C GPS signal using a digital signature in the navigation message and punctures in the spreading code. This method can be used to distinguish authentic and spoofed signals, however, a delay between the time the signal is tracked by the receiver and the time when it can be determined authentic is inherent in Chimera and degrades navigation performance. This delay can range from 2 seconds to 3 minutes. Four additional contributions have been made in support of Chimera. The first Chimera contribution is the design and evaluation of a navigation system for Chimera using a tightly coupled GPS/INS extended SRIF that accounts for the Chimera authentication delays. The second Chimera contribution is an investigation into staggering of the authentication times of the GPS satellites in order to improve navigation results. The third Chimera contribution is the development of a RMS or maximum steady-state position error metric to compare the accuracy achieved by different authentication group designs when used in conjunction with the previously discussed filter from the first Chimera contribution. The fourth Chimera contribution investigates different authentication group designs to find groups that will produce low value metrics. These investigations included local authentication group optimization, synthesizing a global design using local designs, and the effects of time and IMU grade. Each of these contributions has a significant impact on improving either the resilience of a GPS receiver to spoofing or the navigation accuracy of a GPS receiver that is inherently resilient to spoofing. / Doctor of Philosophy / Global Positioning System (GPS) navigation and timing plays a pivotal role in a variety of different sectors such as transit, financial, military, and many others. There have been instances where a signal is purposefully generated to look similar to a GPS signal in order to mislead a GPS user of their true position, velocity, and timing. This type of attack is known as a spoofing attack. This dissertation discusses two methods to identify these spoofed signals so that they are not used to disrupt nominal navigation and timing. The first method uses multiple GPS antennas to determine the direction of all visible signals. This dissertation provides an algorithm to distinguish the authentic GPS signals from the spoofed signals using the determined signal directions. The second method is for the GPS satellites to watermark the GPS signal they transmit, using modern encryption techniques, to be able to authenticate incoming signals. This method, however, produces a delay between when the signal is received by a GPS user and when it can be deemed authentic. This delay is a problem for navigation. This dissertation develops techniques for dealing with this delay by incorporating an Inertial Measurement Unit (IMU). This dissertation also proposes the idea to stagger the time that the digital signature, which is needed for signal verification, is sent from different GPS satellites. Lastly, this dissertation investigates how different staggered groupings of GPS satellites improve navigation performance and provides a metric for quantifying the navigation performance of different groupings. Overall, the dissertation's contributions to the first method improve the resilience of a receiver to spoofing attacks while the contributions to the second method improve navigation performance of an inherently resilient method.

We aim at expanding the horizon of existing research on cyberattacks against the time-syncrhonized devices such as PMUs and PDCs, along with corresponding countermeasures. We develop a PMU-PDC cybersecurity testbed at Virginia Tech Power and Energy Center (PEC) lab. The testbed is able to simulate real-world GPS-spoofing attack (GSA) and false data injection attack (FDIA) scenarios. Moreover, the testbed can incorporates cyberattack detection algorithm in pseudo real-time. After that, we propose three stealthy attack scenarios that exploit the vulnerabilities of time-synchronization for both PMU and PDC. The next part of this dissertation is the enhancement of Hankel-matrix based bad data detection model. The existing general Hankel-matrix based bad data detection model provide satisfactory performance. However, it fails in differentiating GPS-spoofing attack from FDIA. We propose an enhanced phase angle Hankel-matrix model that can conclusively identify GPS-spoofing attack. Furthermore, we reduce the computational burden for Hankel-matrix based bad data and cyberattack detection models. Finally, we verify the effectiveness of our enhanced Hankel-matrix model for proposed stealthy attack scenarios. / Doctor of Philosophy / Modern power systems incorporate numerous smart metering devices and communication channels to provide better resiliency against hazardous situations. One such metering device is Phasor Measurement Device (PMU), what provides GPS time-synchronized measurements to the system operator. The time-synchronized measurements are critical in ensuring the cyber and physical security of grids. However, like other smart devices, PMUs are susceptible to conventional cyberattacks. In addition to conventional cyberattacks, PMUs are also vulnerable to attacks against its time-synchronization. In this work, we dig deep into the realm of cyberattacks against time-synchronization of PMUs. We propose novel stealthy attacks against PMU time synchronization. Furthermore, we enhance existing attack detection model to conclusively identify such stealthy attacks and implemented the model in cybersecurity testbed that we developed at Virginia Tech.

Afin d’obtenir un positionnement GPS de précision centimétrique, il est important de bien modéliser les erreurs telles que les délais ionosphérique et troposphérique ainsi que les erreurs d’horloge et d’éphémérides. Pour une solution de précision centimétrique utilisant des mesures de phase, il est également important d’être en mesure de détecter et de corriger les sauts de cycle, car ceux-ci introduisent des biais artificiels dans la solution, qui peuvent entraîner des erreurs dans l’estimation des coordonnées. Les sauts de cycle sont causés par la perte de réception des signaux occasionnée par des obstructions entre les satellites et l’antenne. Que ce soit pour un positionnement temporel relatif GPS qui n’utilise qu’un seul récepteur (aucune station de référence) ou en mode relatif conventionnel ou le PPP (Precise Point Positioning), les sauts de cycle obligent l’utilisateur à recommencer la période d’initialisation lorsqu’il reste moins de 4 satellites non obstrués. Le but de ce projet est d’évaluer l’apport d’une méthode pour détecter et corriger les sauts de cycle dans une solution GPS mono-fréquence en utilisant des mesures complémentaires provenant d’un gyro-accéléromètre. Le modèle utilisé lors des tests est le AHRS400CC-100 de la compagnie CrossBow. Avec cette méthode, il est possible de comparer, pour chaque satellite, la différence d’ ambigüités, calculée à partir des observations GPS et celle prédite à partir de la position calculée avec les mesures du gyro-accéléromètre. Dans le cadre de ce projet, plusieurs étapes ont dû être réalisées. La première étape était de valider la précision des observations du AHRS400CC-100, puis de quantifier pour chacun de ses capteurs, la marche aléatoire et l’instabilité du biais. Ensuite, d’exploiter les mesures du gyro-accéléromètre afin de calculer une solution de navigation, et d’identifier les limites de précision de l’instrument en mode statique et cinématique. La dernière étape était de combiner la solution de navigation du gyro-accéléromètre à celle du GPS pour évaluer pendant combien de temps le gyro-accéléromètre maintient un positionnement avec suffisamment de précision pour détecter et corriger un saut de cycle. Les résultats ont démontré que des sauts de cycle pourraient être détectés et corrigés instantanément après une coupure du signal GPS d’une durée de 10 secondes pour un positionnement statique et pouvant atteindre 5 secondes en mode cinématique dans des conditions idéales sinon 1 à 2 secondes. Pour augmenter l’efficacité de l’application de détection et de correction de sauts de cycle, l’implémentation d’un filtre de Kalman pour effectuer la fusion des observations GPS et du gyro-accéléromètre pourrait être réalisée dans le cadre de travaux futurs. / In order to achieve centimetre precision using GPS, one must use the carrier phase measurements. It is also important to minimise the impact of the many errors that affect GPS measurements: ionosphere and tropospheric delays, orbit and clocks errors. Another essential part of a precise GPS measurement, is the detection and correction of cycle slips. These slips, caused by the interruption of the GPS signal, introduce artificial biases in the measurement that result in erroneous coordinate estimates. For different GPS solution such as Real Time Kinematic (RTK), Time Relative positioning (TRP) or Precise Point positioning (PPP), to correct cycle slips, the user must restart the initialisation process. In this research, a method to detect and correct cycle slip in monofrequence GPS solution is explored. This methode uses inertial data provided by an attitude and heading reference system (AHRS). The model that is used here is Crossbow’s AHRS400CC-100. With this method, it is possible to compare, for each observed satellite, the ambiguity difference between the ambiguity values calculated from GPS observations and those predicted by the navigation solution calculated from the AHRS observations. It is effective to integrate AHRS to GPS. An AHRS can potentially be used for cycle slip detection and fixing. Using the AHRS measurements, one can achieve centimetre level precision for short periods of time. This method of positioning can be used during GPS signal loss to maintain the navigation solution. Once the GPS signal is retrieved, it is possible to compare the ambiguity difference between satellite line of view vector of each satellite calculated using GPS observations and satellite line of view vector calculated from the last AHRS position GPS observations. For this research project, the initial task was to validate the precision of the AHRS400CC-100 observations, and to quantify random walk error and bias instability for each of the instruments sensors using static data sets. The next task was to use the AHRS measurements to calculate a navigation solution and to identify the instruments limitations of position precision using static and kinematic data. The last task was to combine AHRS and GPS observations, to obtain an integrated navigation solution. Once the solution implemented, simulated data gaps were added to the data set in order to evaluate the maximum duration of GPS data loss after which it is possible to detect and correct GPS cycle slips using the autonomous AHRS navigation solution. According to the results of the experiments using the method proposed in this paper, AHRS positioning appears to maintain adequate precision for cycle slip detection and fixing for up to 10 seconds for static positioning and up to 5 seconds for kinematic positioning in ideal conditions.

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2007-2008. / Le positionnement ponctuel de précision (PPP) par satellites GPS requiert encore une longue période d’observations pour atteindre une précision centimétrique, car la résolution des ambiguïtés de phase en mode absolu est contrainte par la présence d’erreurs non modélisées et de biais de phase au récepteur et aux satellites. Afin de mieux comprendre le contexte lié à la résolution des ambiguïtés de phase dans le PPP, un bilan d’erreurs affectant les observations de phase a d’abord été effectué pour évaluer les possibilités de fixer les ambiguïtés à l’entier adéquat. Puis, une approche utilisant un simulateur de signaux GPS a été proposée pour le calibrage des biais de phase d’un récepteur GPS, mais les biais estimés subissent, entre autres, l’influence des biais de code non modélisés et des effets thermiques du récepteur. Finalement, des modifications ont été apportées à la méthodologie actuelle du calibrage des biais de phase des satellites afin d’améliorer la cohérence des biais estimés avec le mod`ele fonctionnel du PPP. Des erreurs non modélisées se propagent toutefois dans les résultats obtenus et, à cet effet, des pistes d’améliorations sont suggérées. Le calibrage des biais de phase est certainement un élément essentiel à l’obtention instantanée d’une précision centimétrique en mode absolu. / GPS Precise Point Positioning (PPP) still requires long observation sessions in order to achieve cm-level accuracy because ambiguity resolution in point positioning is affected by unmodeled errors and by the presence of receiver and satellite phase biases. In order to gain a better understanding of ambiguity resolution in PPP, an error budget has been made to assess the possibilities of accurate ambiguity fixing. Then, an approach using a GPS simulator has been proposed to calibrate receiver phase biases, and the results show evidence of unmodeled code biases and thermal effects in the receiver. Finally, modifications to the actual calibration methods of satellite phase biases have been suggested to improve compatibility with PPP’s functional model. Residual errors still affect the estimated values and suggestions are made to improve the proposed methodology. The calibration of phase biases is an important issue in achieving instantaneous cm-level point positioning.

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California / The real time acquisition and monitoring of the aircraft trajectory parameters is essential for the safety of the flight tests campaigns held by most of the tests centers. Nowadays the us age of an airborne GPS receiver as the main sensor for these parameters has become the preferred solution for the Flight Tests Instrumentation (FTI) systems. The main problem arises when it is required a high accuracy for these measurements (e.g. air data calibration) where the solution is achieved through differential GPS techniques. The integration of this solution requires the acquisition and the correlation of the pseudorange and phase measurements for all GPS satellites in view observed by both base and rover GPS receivers. To avoid the usage of an additional uplink for the GPS differential corrections (i.e. from the base receiver to the rover), it was developed a novel solution where the GPS observables acquired by the rover receiver are merged into the FTI PCM data stream and processed in the Telemetry ground station by a Real Time GPS Navigation (GNAV) tool together with the GPS observables acquired by the base receiver. The GNAV development is divided into several phases where the accuracy for the trajectory parameters and the complexity of the solution increases. The prototype system was built and evaluated against the post-mission Ashtech PNAV® tool and the initial tests results show a satisfactory performance for the GNAV. The tests profiles are fully compliant with the Federal Aviation Administration (FAA) Advisory Circular (AC) 25-7A.