Impact of Changing Grid Spacing of Ionospheric Corrections on the Performance of the Wide-Area Differential GPS

Abstract

Ionospheric delay is recently recognized as a major error source for satellite navigation systems. The wide-area differential GPS systems broadcast ionospheric correction information to suppress ranging error due to ionosphere. For example, US WAAS and Japanese MSAS broadcast ionospheric corrections for grid points located at every five by five degrees of geographic latitude and longitude. The performance of these systems depends on activity of ionosphere.

In fact the ionosphere has the significant activities in low magnetic latitude regions including southwestern Japan. In order to mitigate ranging error caused by active ionosphere and thus to improve the performance of the wide-area differential GPS systems, it is said that one possible way is enhancement of the spatial density of the ionospheric corrections. The author investigated the effect of the density of ionospheric corrections through generating the wide-area differential correction information regarding various ionospheric grid spacing. The corrections were applied to measurements at user locations to analyze user positioning accuracy. The results demonstrate changing grid spacing of the ionospheric correction information might not be effective to improve user positioning accuracy unless applying additional monitor stations or further modification of the correction algorithms.