Inside GNSS Media & Research

MAR-APR 2018

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Page 26 of 67 M A R C H / A P R I L 2 0 1 8 Inside GNSS 27 GNSS SOLUTIONS is the path in inertial space (ignoring the Earth's orbit around the sun for simplicity). e problem, however, is that because orbits are parameterized in an ECEF frame, the computed position of the satellite will still be directly above the user. is leads to a situation where the true signal path and the computed signal path differ. Unless accounted for, this difference will manifest as a ranging error in the receiver's position engine, which computes the difference of the measured and predicted signal paths (i.e., ranges). e magnitude of the position error depends on the num- ber and distribution of satellites, as well as user latitude. As an example, in Cal- gary, Canada, ignoring Earth rotation results in a shi in the estimated user position of about 20 meters, primarily FIGURE 1 Example of a user located directly below a geostationary satellite, as viewed looking down on the north pole. The diagram assumes that this is the situation at the time of signal transmission. Diagram is not to scale. FIGURE 2 Example of a user directly below a geostationary satellite at time of signal transmission and signal reception. Since the signal travels from the satellite's position at time of transmission and arrives at the user's position at the time of reception, the actual distance traveled (blue line) is longer than the instantaneous separation of the two bodies. Diagram is not to scale. Assured PNT for platform navigation is critical for mission success. Our NavHub™ GNSS navigation system delivers high-assurance military positioning, navigation and timing (PNT) via our patented sensor fusion technology. The system can use a GPS Selective Availability Anti-Spoofing Module (SAASM), M-Code, multi- constellation GNSS and non-GNSS-based augmentation sources to provide scalable, assured PNT – regardless of the operating environment. © 2018 Rockwell Collins. All rights reserved. Photo courtesy of Oshkosh Defense, LLC.

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