Detection and Correction of Cycle Slip in Triple-Frequency GNSS Positioning

High precision positioning requires correct carrier phase observation. However, signal block will cause the discontinuity of the carrier phase named as cycle slip, which will severely depress the positioning efficiency and accuracy. Triple-frequency global navigation satellite system measurements bring benefit to the detection and repair of cycle slip. We propose a modified method to detect cycle slip based on combinations of triple-frequency signals. Cycle slips on the three combinations with longer wavelengths and lower noises are determined by the geometry-free model. Then, original cycle slips on three carriers are determined uniquely by the linear equations. To deal with the insensitive cycle slips, an alternative combination is presented as a supplementary. However, the residual of the first-order time-differenced ionospheric error cannot be ignored in this step or will be mistaken as cycle slip if not eliminated. To remove this interference, the residual is compensated by pre-estimations calculated by previous wide-lane combination with no cycle slips have been detected. In the end, real triple-frequency GPS data provided by IGS is processed by this method. The results show that the proposed method can detect all cycle slips in real time even under high ionospheric activity.