Abstract
Along with the rapid development of GNSS, not only BeiDou, but also Galileo, and the newly launched GPS satellites can provide signals on three frequencies at present. To fully take advantage of the multi-frequency multi-system GNSS observations on precise point positioning (PPP) technology, this study aims to implement the triple-frequency ambiguity resolution (AR) for GPS, Galileo, and BeiDou-2 combined PPP using the raw observation model. The processing of inter-frequency clock bias (IFCB) estimation and correction in the context of triple-frequency PPP AR has been addressed, with which the triple-frequency uncalibrated phase delay (UPD) estimation is realized for real GPS observations for the first time. In addition, the GPS extra-wide-line UPD quality is significantly improved with the IFCB correction. Because of not being contaminated by the IFCB, the raw UPD estimation method is directly employed for Galileo which currently has 24 satellites in operation. An interesting phenomenon is found that all Galileo satellites except E24 have a zero extra-wide-lane UPD value. With the multi-GNSS observations provided by MGEX covering 15 days, the positioning solutions of GPS + Galileo + BeiDou triple-frequency PPP AR have been conducted and analyzed. The triple-frequency kinematic GNSS PPP AR can achieve an averaged 3D positioning error of 2.2 cm, and an averaged convergence time of 10.8 min. The average convergence time can be reduced by triple-frequency GNSS PPP AR by 15.6% compared with dual-frequency GNSS PPP AR, respectively. However, the additional third frequency has only a marginal contribution to positioning accuracy after convergence.
Highlights
Precise point positioning (PPP) is an absolute positioning technique which has advantages in terms of high computational efficiency and low cost (Malys and Jensen 1990; Zumberge et al 1997; Kouba and Héroux 2001)
We first formulate the observation equations and stochastic model for PPP based on raw measurements, address the methods applied to inter-frequency clock bias (IFCB) and triple-frequency uncalibrated phase delay (UPD) estimation, and the modified strategy for reference satellite selection in GPS triple-frequency PPP ambiguity resolution (AR)
With the IFCB, the triple-frequency UPD estimation was realized for the real GPS observation for the first time
Summary
Precise point positioning (PPP) is an absolute positioning technique which has advantages in terms of high computational efficiency and low cost (Malys and Jensen 1990; Zumberge et al 1997; Kouba and Héroux 2001). Since 2009, GPS has started to replace the old satellites with the new Block IIF, which are transmitting the third civil signal L5 (1176.45 MHz) in addition to the existing L1 (1575.42 MHz) and L2 (1227.60 MHz) signals. There are 12 Block IIF satellites in operation. As a latecomer navigation satellite system, BeiDou and Galileo are both the constellations of which all operating satellites transmit triple-frequency signals. BeiDou and Galileo are currently at the rapid deployment stage. The frequencies are 1561.098 MHz (B1), 1207.14 MHz (B2), and 1268.52 MHz (B3) for BeiDou-2 signals, while 1575.42 MHz (E1), 1176.45 MHz (E5a), and 1207.14 MHz (E5b) for Galileo signals.
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