Tropospheric error correction in assisted GPS signals

Abstract

Though standalone cell phone technology is sufficient to navigate, presently, in the developed and the under developed countries of the world, almost every cell phone has a Global Positioning System (GPS) receiver embedded in it. This combined system is called as assisted GPS. There are various issues to be dealt critically while using such systems. For instance, cellular networks and GPS signals encounter various types of errors in which tropospheric error is one. This paper focusses on the estimation of tropospheric error and its correction in cell phone signals as well as GPS signals. In order to estimate the tropospheric delay, four different tropospheric error correction models are implemented. Two models, namely Hopfield model and European Geo-stationary Navigation Overlay Service (EGNOS) model are implemented for GPS signals and other two models, namely Radio Technical Commission for Aeronautics (RTCA) and Locata Tropospheric (LTC) model are implemented for cellular signals. The results indicate that in case of GPS signals, as the altitude increases, tropospheric delay (TD) gradually decreases. The maximum TD is observed at the surface of earth for Hopfield model (13 m) as well as for EGNOS model (13.2 m). In case of cellular signals, TD increases as the altitude increases since the base stations are on the ground. At an altitude of 14 km, TD is observed for RTCA model as 9.08 m and for LTC model, it is 11.41 m.