Abstract
Global Positioning System (GPS) is a satellite-based navigation system that provides a three-dimensional user position (x,y,z), velocity and time anywhere on or above the earth surface. The satellite-based position accuracy is affected by several factors such as satellite clock error, propagation path delays and receiver noise due to which the GPS does not meet the requirements of critical navigation applications such as missile navigation and category I/II/III aircraft landings. This paper emphasizes on modelling the satellite clock error and orbital solution (satellite position) error considering the signal emission time. The transmission time sent by each satellite in broadcast ephemerides is not accurate. This has to be corrected in order to obtain correct satellite position and in turn a precise receiver position. Signal transmission time or broadcast time from satellite antenna phase center is computed at the receiver using several parameters such as signal reception time, propagation time, pseudorange observed and satellite clock error correction parameters. This corrected time of transmission and broadcast orbital parameters are used for estimation of the orbital solution. The estimated orbital solution was validated with the precise ephemerides which are estimated by Jet Propulsion Laboratory (JPL), USA. The errors are estimated for a typical day data collected on 11th March 2011 from dual frequency GPS receiver located at Department of Electronics and Communication Engineering, Andhra University College of Engineering, Visakhapatnam (17.73°N/83.319°E).
Highlights
Global Positioning System (GPS) has been widely used for precise positioning and navigation applications
The satellite clock errors and orbital solution errors are estimated and the analysis of the error which are supported by the relevant graphs and the tables are presented in this paper
The broadcast orbital solution error and satellite clock error are estimated using the data collected by the receiver from 02:00 hours to 02:39 hours with an epoch interval of 15 seconds
Summary
In addition to the propagation errors, the receiver position accuracy, availability, reliability and integrity of GPS navigation solution are affected by satellite clock errors and orbital solution errors. For precise navigation applications, satellite clock error needs to be corrected. This deviation is due to uncertainty in the gravitational model, limited accuracy of the orbit representations and inadequately modelled surface forces on the satellites like solar radiation pressure and atmospheric drag. The orbital solution errors are estimated by comparing the broadcast ephemerides with the precise ephemerides obtained by JPL, USA.
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