Fast LAMBDA-based ambiguity resolution combined with WARTK technique for Galileo data simulated using ESA's Galileo Signal Validation Facility

Abstract

This contribution addresses the effect of having a triple frequency Global Navigation Satellite System (GNSS) on ambiguity resolution of long baselines, i.e. baselines for which the differential ionospheric delays cannot be ignored. Although it is recognized that a combination of GNSS’s is more effective for integer ambiguity resolution –the key to highly accurate positioning– than the use of three frequencies, it is still of interest to investigate single GNSS triple-frequency ambiguity resolution, especially since it is expected that the quality of the code data of Galileo triplefrequency signals will be better than of current dual-frequency GPS. For this purpose we have simulated triple-frequency Galileo signals using ESA’s Galileo Signal Validation Facility for a Wide Area network of permanent stations and user stations receiving Wide Area RTK (WARTK)ionospheric corrections from this network. The three user stations are located at 100-400 km from the network’s master reference station. Applying the ionospheric corrections by means of simple ionosphere-weighted processing demonstrated that instantaneous LAMBDA-based ambiguity resolution is feasible for the 100-km user baseline. However, as a result –in this simple approach– of poorer ionospheric corrections for the longer baselines, the instantaneous success rates drop to close to 0%, even using triple-frequency data. Despite this, the availability of a third frequency is beneficial in reducing the mean ambiguity initialization time when more epochs are used; depending on the noise levels of the code data the times to first fix the ambiguities are in the order of 10-50 sec for the 400-km baseline, applying the WARTK ionospheric corrections.