Ionospheric Delay Estimation for Improving the Global Positioning System Position Accuracy

Abstract

The ionospheric delay is one of the largest sources of error that affects the Global Positioning System (GPS) positioning accuracy. By combining simultaneous measurements of signals at two different frequencies the effect can be minimized due to the dispersive nature of the ionosphere. But it remains a problem for single-frequency GPS receiver users. GPS signal propagation speed in the ionosphere is characterized by its refractive index. The phase and group refractive indexes are derived to calculate the ionospheric effect on the GPS signal measurement. Several electron density models such as Bent and IRI are available for the study of electron density profiles at different altitudes of the ionosphere. Klobuchar model is the only model available for estimating the ionospheric time delay for single frequency GPS users. The Klobuchar model is a simple-computational model with an ideal description for the ionosphere’s average behaviour. In dual frequency receivers, ionospheric delay can be estimated precisely by taking the advantage of the dispersive nature of the ionosphere. The delay is estimated by measuring the difference in arrival times of the two GPS frequencies. In this paper Total Electron Content (TEC) values are presented for a typical day using phase and code measurements of a dual frequency GPS receiver located at Hyderabad, India and using the Klobuchar model also. The results are analyzed and presented.