Research and Scholarship (College of Engineering)

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    Evaluation of Orbit Errors and Measurement Corrections in Differential Navigation With LEO Satellites
    (Institute of Navigation, 2023-09) Saroufim, Joe; Hayek, Samer; Kassas, Zaher
    Ephemeris errors and measurement corrections in differential navigation with low Earth orbit (LEO) space vehicles (SVs) are analyzed. First, orbit errors are characterized for the non-differential case, showing the dependency of the range measurement errors on the receiver-to-SV geometry. The study is then extended to the differential case, where the maximum differential range error is found to occur when the baseline is normal to the projected measurement vector from one receiver onto the local navigation frame. A simulation study is presented to assess the differential navigation performance with 14 Starlink and 11 OneWeb LEO satellites. The framework fused differenced pseudorange measurements from a base and rover to LEO SVs with inertial measurement unit (IMU) measurements via an extended Kalman filter (EKF) in a tightly-coupled fashion to estimate the rover’s states. The simulation considered an aerial vehicle equipped with a tactical-grade IMU, an altimeter, a GNSS receiver, and a LEO receiver making pseudorange measurements to the LEO SVs. During 300 seconds of flight time, the vehicle traveled a distance of 28 km, the last 23 km of which were without GNSS, achieving a three-dimensional (3-D) position root mean squared error (RMSE) of 52 cm, compared to 12.5 m using the non-differential framework. Experimental results are presented, showing the potential of differential navigation in reducing ephemeris, clocks, and atmospheric errors. A ground vehicle traversed a distance of 540 m in 60 seconds, the last 492 m of which without GNSS signals, while making Doppler measurements to 2 Orbcomm and 1 Iridium LEO SVs, whose ephemerides were obtained from two-line element (TLE) files, propagated with simplified general perturbation 4 (SGP4) orbit propagator. The differential framework yielded a position RMSE of 7.13 m, compared to 41.29 m using non-differential measurements, and 87.74 m with GNSS-aided IMU.
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    A look at the stars: navigation with multi-constellation LEO satellite signals of opportunity
    (Autonomous Media, LLC, 2023-08) Kassas, Zaher; Kozhaya, Sharbel; Saroufim, Joe; Kanj, Haitham; Hayek, Samer
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    Protecting the skies: GNSS-less aircraft navigation with terrestrial cellular signals of opportunity
    (Institute of Navigation, 2022-09) Kassas, Zaher; Abdallah, Ali; Lee, Chiawei; Jurado, Juan; Wachtel, Steven; Duede, Jacob; Hoeffner, Zachary; Hulsey, Thomas; Quirarte, Rachel; Tay, RunXuan
    This paper shows how to protect our skies from harmful radio frequency interference (RFI) to global navigation satellite system (GNSS) signals, by offering terrestrial cellular signals of opportunity (SOPs) as a viable aircraft navigation system backup. An extensive flight campaign was conducted by the Autonomous Systems Perception, Intelligence, and Navigation (ASPIN) Laboratory in collaboration with the United States Air Force (USAF) to study the potential of cellular SOPs for high-altitude aircraft navigation. A multitude of flight trajectories and altitudes were exercised in the flight campaign in two different regions in Southern California, USA: (i) rural and (ii) semi-urban. Samples of the ambient downlink cellular SOPs were recorded, which were fed to ASPIN Laboratory's MATRIX (Multichannel Adaptive TRansceiver Information eXtractor) software-defined receiver (SDR), which produced carrier phase measurements from these samples. These measurements were fused with altimeter data via an extended Kalman filter (EKF) to estimate the aircraft's trajectory. This paper shows for the first time that at altitudes as high as about 11,000 ft above ground level (AGL), more than 100 cellular long-term evolution (LTE) eNodeBs can be reliable tracked, many of which were more than 100 km away, with carrier-to-noise ratio (C/N0) exceeding 40 dB-Hz. The paper shows pseudorange and Doppler tracking results from cellular eNodeBs along with the C/N0 and number of tracked eNodeBs over the two regions, while performing ascending, descending, and grid maneuvers. In addition, the paper shows navigation results in the semi-urban and rural regions, showing a position root mean-squared error of 9.86 m and 10.37, respectively, over trajectories of 42.23 km and 56.56 km, respectively, while exploiting an average of about 19 and 10 eNodeBs, respectively.