An improved cascading ambiguity resolution (CAR) method with Galileo multiple frequencies

Abstract

Modernised GPS will provide navigation signals in three frequency bands and Europe’s Galileo system will provide navigation signals in four. When more carrier-phase frequency bands are available, more frequency combinations with longer equivalent wavelengths can be formed. If carrier phase ambiguity can be resolved quickly, the carrier phase measurements are eventually converted to ‘pseudorange’ type measurements, but with much higher measurement precision. Cascade ambiguity resolution (CAR) and integer least squares (ILS) methods are widely used for multiple frequency ambiguity resolution. However, there is a weakness in the CAR method. When trying to fix ambiguities of one combination, only part of all available measurements is used in CAR and this is the reason why the success rate of CAR is lower than that of ILS. In this paper, we propose an algorithm to improve CAR for multiple frequency ambiguity resolution. Instead of directly using formed combination, original carrier phase measurements of E1, E5a, E5b and E6 are used in every step while solving for the ambiguities with different combinations. Based on simulated Galileo data, ambiguity resolution performance with the improved CAR method is investigated and compared with the ILS method. It has shown that the performance of the proposed method is better than the ILS method in terms of time required for ambiguity resolution and misfixed rate. Also, we have adapted this method for long baselines. The ambiguity resolution performances for baselines of different distances are investigated.