Significance of instrumental biases and dilution of precision in the context of GAGAN

Abstract

The positional accuracy of the GPS Aided GEO Augmented Navigation (GAGAN) system is basically dependent on ranging errors and the satellite constellation geometry. This paper focuses on enhancing the performance of the system through the estimation of instrumental biases and augmentation of GAGAN using pseudolites (pseudo-satellites). The line-of-sight ionospheric measurements derived from the Global Positioning System (GPS) observables are corrupted by the instrumental biases present in both the GPS satellites and the receivers. The instrumental bias and Total Electron Content (TEC) results (Hyderabad GAGAN station (78.47°E, 17.45°N)) obtained using the Kalman filter technique are presented in this paper. It is found that the estimated biases are almost stable during the observation period and show close proximity with other reported values in the open literature. For some strategic applications further augmentation of GAGAN with pseudolites is necessary. Five configurations comprising GPS/geostationary satellites and pseudolites are considered for optimizing the Dilution of Precision (DOP). It is found that the pseudolite-system with properly located pseudolites can augment GAGAN and improves the positional accuracy of the user.