Abstract
Time to first fix (TTFF) is one of the crucial indicators to evaluate the performance of a GPS receiver. In this paper, an orbit prediction algorithm to reduce the TTFF of GPS receivers without a network connection is presented. Satellite orbit is predicted by numerically integrating the satellite’s equation of motion. Satellite’s initial position and velocity value, as well as the Earth’s polar motion parameters, used in prediction correspond to the locally collected previous broadcast ephemeris. As the solar radiation pressure (SRP) is one of the most critical factors causing orbit prediction error, an empirical SRP model with two parameters that change with the movement of satellite and Earth is also described. The presented algorithm is verified by GPS satellites using the initial conditions divided from three groups of broadcast ephemeris data. Simulation results show that, with the SRP model described in this paper the satellite’s position error limited to 30 meters within 7 days prediction.
Highlights
Start navigation immediately is expected for people once their GPS receivers are turned on
Due to the time needed for the reception of the ephemeris data is the main reason for long Time to first fix (TTFF), one method to reduce it is to provide satellite position information by orbit prediction
Simulation results show that the orbit prediction algorithm proposed in this paper can provide a trusted satellite position and significantly reduce the TTFF of a GPS receiver
Summary
Start navigation immediately is expected for people once their GPS receivers are turned on It typically needs about 30 seconds for the receiver to provide the first position information even in an ideal receiving environment, during to the three first sub-frames which contain ephemeris data takes 18 seconds to transmit and the satellite sends it once every 30 seconds. Due to the time needed for the reception of the ephemeris data is the main reason for long TTFF, one method to reduce it is to provide satellite position information by orbit prediction. Simulation results show that the orbit prediction algorithm proposed in this paper can provide a trusted satellite position and significantly reduce the TTFF of a GPS receiver
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