Realization and Validation of GLONASS Triple-Frequency PPP Ambiguity Resolution with New CDMA L3 Signals

Integer ambiguity resolution considerable improves the performance of precise point positioning (PPP). With the popularity of multi-frequency observations, multi-frequency PPP ambiguity resolution (PPP-AR) for GPS, BDS and Galileo has been well studied, whereas there is a lack of research on GLONASS triple-frequency PPP-AR. Fortunately, GLONASS currently transmits CDMA signals on the third frequency of two GLONASS-K and four GLONASS-M + satellites, making it possible to investigate the triple-frequency PPP-AR. To fully exploit GLONASS triple-frequency observation, this study proposes a CDMA + FMDA combined multi-frequency PPP-AR model with the careful consideration of GLONASS phase inter-frequency clock bias (IFCB) errors. The characteristics of GLONASS IFCBs and EWL UPDs are also well investigated. To verify our proposed model, tracking data of 14 stations is used to estimate uncalibrated phase delay (UPD) and another 6 stations are selected as users to perform PPP-AR. A time- and satellite-dependent IFCB of about 0.2 0.5 m is identified for GLONASS-M + triple-frequency observations. After the removal of the IFCB, the EWL, WL and NL UPDs of GLONASS satellites show remarkable stabilities at several hours. About 99.9