Browsing by Author "Gebre-Egziabher, Demoz"

Now showing 1 - 9 of 9
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    Analysis of GPS-based Real Time Attitude Determination System for ITS Application
    (Intelligent Transportation Systems Institute, Center for Transportation Studies, University of Minnesota, 2012-11) Gebre-Egziabher, Demoz; Lie, Fidelis Adhika Pradipta
    This work describes the development and testing of GPS-based attitude and heading determination system (AHRS) using single-frequency (L1) carrier phase differential GPS (CPDGPS). Vehicle's attitude can be uniquely determined from two non-collinear relative position vectors, known as the baseline vectors. The accuracy of the resulting attitude estimate depends on the accuracy of the baseline vector estimates and their respective magnitudes (length). The shorter the baseline, the higher the vector accuracy required to give the same attitude accuracy that can be obtained through longer baseline system. Issues such as ambiguity resolution and phase center variations are discussed. Test result shows that single-frequency CPDGPS is still a challenge, mainly caused by the integer ambiguity problem inherent to CPDGPS problem. A more feasible but less accurate method using a short baseline is also discussed. Phase center calibration remains a challenge for this attitude determination system.
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    Analysis of Single Frequency, Carrier Phase Based GPS Positioning Performance and Sensor Aiding Requirements
    (Intelligent Transportation Systems Institute, Center for Transportation Studies, University of Minnesota, 2013-01) Gebre-Egziabher, Demoz; Mokhtarzadeh, Hamid
    The work described in this report outlines the design and testing of a low-cost, single frequency, carrier phase positioning system. Furthermore, aiding sensor accuracy requirements are analyzed to improve the robustness of the carrier phase system after emerging from signal outages. The applications of interest are ones with safety-of-life implications such as driver assist systems.
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    Analysis of Unmanned Aerial Vehicles Concept of Operations in ITS Applications
    (Center for Transportation Studies, 2011-03) Gebre-Egziabher, Demoz; Xing, Zhiqiang
    The work described in this report is about developing a framework for the design of concept of operations (CONOP), which use small uninhabited aerial systems (SUAS) to support of intelligent transportation system (ITS) application of highway and transportation infrastructure monitoring. In these envisioned applications, these vehicles will be used for tasks such as remote collection of traffic data or inspection of roads and bridges. As such, a risk that has to be managed for these applications is that of vehicle-infrastructure collision. Various solutions to ensure safe separation between the unmanned aerial vehicle (UAV) and the object being inspected have been proposed. However, most, if not all, of these solutions rely on a multi-sensor approach, which combines digital maps of the infrastructure being inspected with an integrated GPS/Inertial navigator. While "turn key" solutions for such multi-sensor systems exist, the performance specifications provided by their manufactures does not provide sufficient information to allow precisely quantifying or bounding the collision risk. Furthermore, size, weight and power (or SWAP) constraints posed by these small aerial vehicles limits the use of redundant hardware and/or software as a risk mitigation strategy. The purpose of the work reported here was to develop a framework for the design of CONOPs, which take these SUAS limitations into account. The method outlined shows, in part, how these vehicle/infrastructure collision risks can be estimated or conservatively bounded.
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    Cell Phone Navigation
    (2015-02) Layh, Trevor; Larson, Jordan; Jackson, John; Agamawi, Yunus; Taylor, Brian; Gebre-Egziabher, Demoz; Krause, Joel; Gustafson, Jacob
    Cell Phone Navigation project funded by the U.S. Department of Homeland Security in Fall 2013 which tasked the UMN UAV Research Lab with proposing a backup navigation system within one year for SUAVs in GPS-denied environments. A cascaded Attitude Heading Reference System and Dead Reckoning system was designed which was capable of being aided by cell phone time-of-arrival information. This backup navigation system was integrated into a UltraStick 25e airframe equipped with the Goldy Flight Control System. Flight testing was conducted to characterize performance during short duration GPS outages. Longer duration GPS outages were simulated using Monte Carlo hardware-in-the-loop simulations. A full report on this work was created for DHS and is included in this project archive. Additionally, this research was presented and published for the Institute of Navigation International Technical Meeting, and those materials are also included in this project archive.
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    Evaluation of Low-Cost, Centimeter-Level Accuracy OEM GNSS Receivers
    (Minnesota Department of Transportation, 2018-02) Jackson, John; Saborio, Ricardo; Ghazanfar, Syed Anas; Gebre-Egziabher, Demoz; Davis, Brian
    This report discusses the results of a study to quantify the performance of low-cost, centimeter-level accurate Global Navigation Satellite Systems (GNSS) receivers that have appeared on the market in the last few years. Centimeter-level accuracy is achieved using a complex algorithm known as real-time kinematic (RTK) processing. It involves processing correction data from a ground network of GNSS receivers in addition to the signals transmitted by the GNSS satellites. This makes RTK-capable receivers costly (in excess of $10,000) and bulky, making them unsuitable for cost- and size-sensitive transportation applications (e.g., driver assist systems in vehicles). If inexpensive GNSS receivers capable of generating a position solution with centimeter accuracy were widely available, they would push the GNSS revolution in ground transportation even further as an enabler of safety enhancements such as ubiquitous lane-departure warning systems and enhanced stability-control systems. Recently manufacturers have been advertising the availability of low-cost (< $1,000) RTK-capable receivers. The work described in this report provides an independent performance assessment of these receivers relative to high-end (and costly) receivers in realistic settings encountered in transportation applications.
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    Observability and Performance Analysis of a Model-Free Synthetic Air Data Estimator
    (Journal of Aircraft, 2019) Sun, Kerry; Regan, Christopher D; Gebre-Egziabher, Demoz
    The performance, accuracy, and observability of a model-free angle of attack and angle of sideslip estimator are presented. The estimator does not require an aircraft dynamic model; rather, it only relies on measurements from a GPS receiver, an inertial measurement unit, and a pitot tube. The estimator is an inertial navigation system (INS)/GPS extended Kalman filter augmented with the states to account for wind and an additional measurement from a pitot tube. It is shown that the estimator is conditionally observable. Conditions (maneuvers) that enhance its observability are identified. A bound on the angle of attack and angle of sideslip estimate uncertainties is derived. The effect of INS/GPS, horizontal and vertical wind uncertainty on the accuracy of angle of attack and angle of sideslip estimate is assessed. Simulation and flight-test results of the method are presented. The results show that the 1−σ bound on a small, slow-flying unmanned aerial vehicle for angle of attack and sideslip angle estimates are about 5 and 3 deg, respectively.
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    RPV/UAV Surveillance for Transportation Management and Security
    (University of Minnesota Center for Transportation Studies, 2008-12) Gebre-Egziabher, Demoz
    This report describes the results of an investigation into some of the technical and operational issues associated with using Unmanned Aerial Systems (UAS) for the application of surveillance in support of transportation infrastructure management and security. As part of this investigation a low-cost, miniature, hand-launched aerial vehicle and supporting ground systems suitable for surveillance of highways and traffic infrastructure were developed. Except for the ground station software, this system was built from off-the-shelf components. The ground station software developed was used to enhance ground station operators' situational awareness and simultaneously allow analysis of the data transmitted from the aerial vehicle. In addition, a key system that was developed was an open-source Guidance, Navigation and Control (GNC) software suite for autonomous operation of small aerial vehicles. The culmination of this work was a series flight tests where the UAS developed was used as a tool to enhance situational awareness over a simulated traffic incident or emergency situation. The test consisted of defining a series of waypoints around the area of the simulated incident and launching the miniature aerial vehicle to autonomously fly from waypoint to waypoint.
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    Signal of Opportunity Time Difference of Arrival Estimation Using Adaptive Filtering Techniques
    (2017 IEEE Aerospace Conference, 2017) Runnels, Joel T.; Gebre-Egziabher, Demoz; Glesener, Lindsay
    EXACT and SOCRATES are a pair of CubeSats being developed to advance the TRL of a dual-use sensor. It can function either as x-ray detector used for characterization of high energy photons or as a sensor for measuring relative ranges between users in deep space operations. The ranging function of the sensor is described in this paper. After describing the measurements generated by the sensor, the algorithms that make use of this information to generate a position solution are presented. As a validation case study, data from the Japanese spacecraft Suzaku’s observation of the Crab Nebula Pulsar is used to estimate the spacecraft’s change in position along the line-of-sight to the pulsar, using this estimation scheme. Suzaku’s observations are suitable for this application because the spacecraft's Hard X-Ray Detector (HXD) is similar in effective surface area to the prototype X-Ray/gamma-ray detector currently under development for use onboard EXACTand SOCRATES. Thus, validation of this technique using data from Suzaku serves to verify the feasibility of this navigation technique onboard other spacecraft with detectors of similar size.
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    Two-Stage Batch Algorithm for Nonlinear Static Parameter Estimation
    (Journal of Guidance, Control, and Dynamics, 2020) Kerry, Sun; Gebre-Egziabher, Demoz
    A two-stage batch estimation algorithm for solving a class of nonlinear, static parameter estimation problems that appear in aerospace engineering applications is proposed. It is shown how these problems can be recast into a form suitable for the proposed two-stage estimation process. In the first stage, linear least squares is used to obtain a subset of the unknown parameters (set 1) and a residual sampling procedure is used for selecting initial values for the rest of the parameters (set 2). In the second stage, depending on the uniqueness of the local minimum, either only the parameters in the second set need to be re-estimated, or all the parameters will have to be re-estimated simultaneously, by a nonlinear constrained optimization. The estimates from the first stage are used as initial conditions for the second-stage optimizer. It is shown that this approach alleviates the sensitivity to initial conditions and minimizes the likelihood of converging to an incorrect local minimum of the nonlinear cost function. An error bound analysis is presented to show that the first stage can be solved in such a way that the total cost function will be driven to the optimal cost, and the difference has an upper bound. Two tutorial examples are used to show how to implement this estimator and compare its performance to other similar nonlinear estimators. Finally, the estimator is used on a 5-hole Pitot tube calibration problem using flight test data collected from a small unmanned aerial vehicle that cannot be easily solved with single-stage methods.