Abstract
In the precise point positioning-ambiguity resolution (PPP-AR) method, the wide-lane (WL) and narrow-lane (NL) uncalibrated phase delays (UPDs) are instrumental in resolving the WL and NL ambiguities, respectively, ultimately achieving PPP-AR. In the traditional UPD estimation algorithms, the ionosphere-free (IF) ambiguity is typically employed for estimating NL ambiguities and isolating NL UPDs. However, in the PPP algorithm, IF ambiguities are treated as constant parameters, which necessitates the separation of time-varying UPD products from these constants. This approach inherently results in that the NL UPDs for each satellite being significantly influenced by the cumulative observation data from prior epochs, which might even be from a long time ago. To get the true variation characteristics of the NL UPDs, this paper proposes a real-time NL UPD estimation method based on a sliding time window. Specifically, when the reference station performs PPP calculation with the aim of UPDs estimation, the estimation method based on a sliding time window is adopted. The reliability of this new approach has been thoroughly scrutinized through rigorous experimental comparisons. The findings demonstrate that, compared to NL UPDs calculated using the traditional method, the NL UPDs estimated using the proposed method more accurately reflect the true values of UPDs in the current epoch. Furthermore, the successful fixing rate, the average Time-To-First-Fix (TTFF), and correct fixing rate of PPP-AR results have significantly improved when employing the proposed method.