The GPS modernization and the European Galileo system will provide signals in three and four frequency bands. When more carrier-phase 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. The Cascade Ambiguity Resolution (CAR) method and Integer Least Squares (ILS) are two methods which are widely used for ambiguity resolution with multiple frequencies. In this paper, we propose an improved CAR method for multiple frequency ambiguity resolution. Instead of directly using combination measurements in mathematical model like CAR method, original carrier phase measurements are used. Also, we have established a uniformed model for both short and long baseline ambiguity resolution. Based on simulated data and optimal combinations, ambiguity resolution performance with the improved CAR is investigated and compared with ILS method. It has shown that the performance of the new method is better than ILS method in terms of time required for ambiguity resolution and mis-fixing rate. The results demonstrate that it is possible to resolve ambiguity every epoch if the measurement noise is less than 6 mm.
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