An Improved Ambiguity Resolution of Three Carriers in Precise Point Positioning

Precise point positioning (PPP) is of great importance in fields requiring coordinates with high accuracy, such as geophysics, meteorology, and geodesy. Compared with relative positioning restricted by the length of baseline, PPP using a single receiver is more flexible. Carrier phase observations with much higher precision than pseudorange measurements are used in the positioning process of PPP. However, accurate estimation of integer ambiguity associated with carrier phase observations is a prerequisite. Then the integrity of the phase observable can be completed as a range measurement with high precision. With triple-frequency signals of global navigation satellite system (GNSS) available, combinations of original observations with longer wavelengths and lower noises are preferable. In this paper, we propose an improved ambiguity resolution (AR) method based on the traditional bootstrapping method to make it suitable for PPP and increase the precision of AR and positioning. Virtual ambiguities of extra-wide-lane, wide-lane, and modified narrow-lane combinations are resolved first for their relatively better characteristics. Furthermore, extra pseudoranges are included to decrease the ionospheric delay which cannot be ignored as it is in relative positioning. Then, original ambiguities on the three frequencies can be recovered from the combined ambiguities using three linear equations which are independent to each other. Finally, the performance of the improved method is tested with real GPS navigation data on three frequencies which is provided by the international GNSS service. Compared with the traditional bootstrapping method, it shows that the ambiguity residuals of the improved method have decreased which indicates more accurate estimation. The precision of the positioning results has increased accordingly.