Real-Time GPS Orbit and Clock Corrections Using IGS Ultra-Rapid Precise Orbit Products

Mireia Carvajal-Librado*, Won-Seok Han, Kwan-Dong Park

The International GNSS Service (IGS) delivers real-time orbit and clock corrections for the Global Navigation Satellite System (GNSS) through its Real-Time Service (RTS), supporting precise positioning applications worldwide. In this paper, is presented a novel methodology for RTS corrections of GPS orbit and clock errors utilizing ultra-rapid precise orbit products from Crustal Dynamics Data Information System (CDDIS). This system, developed in MATLAB, automates the retrieval of SP3 ultra-rapid solutions and broadcast ephemerides on an hourly basis. The methodology uses the predicted segment of SP3 ultra-rapid solutions to identify and rectify discrepancies through detailed comparison with broadcast ephemerides. The correction process involves the retrieval of the latest SP3 and ephemerides files, performing precise interpolation, and applying Phase Center Offset (PCO) corrections. By calculating the discrepancies in satellite positions and clock biases, the system generates real-time correction files with refined orbit and clock adjustments for real-time applications, which are uploaded hourly. These corrections have a similar approach to the Galileo High Accuracy Service (HAS), involving the determination of satellite positions and velocities, calculating error vectors, and transforming these into corrections using rotation matrices and interpolation techniques. Preliminary results show the system’s capability to provide real-time corrections. The system's ability to provide real-time corrections offers valuable contributions to satellite navigation and positioning, offering new insights and capabilities for both practical applications and theoretical research in satellite-based navigation systems. Keywords: GPS, RTS correction, real-time, precise orbit determination