Introduction of the Double-Differenced Ambiguity Resolution into Precise Point Positioning

Abstract

According to the advantages of the precise point positioning (PPP) and the double-differenced (DD) model based algorithm, a new method for the integration of DD integer ambiguity resolution into PPP is presented. This method uses the undifferenced ambiguity estimated with PPP computation and the DD ambiguity generated from the DD model based algorithm to realize the PPP ambiguity fixing. In the presented method, the selection of the undifferenced ambiguity bases on the ratio test of the DD ambiguity and the ratio values based weight is used in PPP processing. This ensures the quality of the used undifferenced ambiguity. To validate the presented method, two experiments are implemented using the ten days (11 to 20 August 2014) data from local and regional reference stations and the moved two receivers. The results of the presented strategy show that improvements are achieved in all three coordinate components. The 1-h, 2-h, and 4-h PPP results indicate that the mean relative improvements were about 19%, 18%, and 15% for north, east, and up components. These results also show that prominent improvements of 29%, 31%, and 25% for north, east, and up components were obtained when the ratio values based weight was used. The application of the presented method in the displacement monitoring was implemented with the experiment and it showed that the PPP estimation computed with the presented strategy benefits local or regional displacement monitoring and improves the detecting ability for displacement.

Single-Frequency Precise Point Positioning Using Regional Dual-Frequency Observations

“…Thus, the precise ionosphere delay at the user can be interpolated using the inverse distance weighted method after the ionosphere delay at the reference epoch of k and the accumulated epoch-differenced ionosphere delay computed with geometry-free phase observation are obtained. The inverse distance weighted method [ 6 ] is calculated by the following: where g is the total number of reference stations; is the interpolated precise ionosphere delay at single-frequency user of u ; is the weight; is the distance between the dual- and single-frequency user stations.…”

“…When the precise ionosphere delay at the user is obtained, the single-frequency user can carry out the PPP computation. Equation (1) shows that the ambiguity of the L1 observation absorbs the satellite FCB so that it cannot be fixed to an integer value, and the ambiguity fixing method is not suitable for implementation [ 6 ]. The ambiguity fixing is beneficial to improve the positioning accuracy and shorten convergence time.…”

“…To improve the positioning accuracy of the SF-PPP, its ambiguity needs to be fixed by introducing the DD ambiguity into it. The satellite-differenced (SD) L1 observation of the satellites a and b at user is written as in [ 6 ]: where and are satellite clock errors in meters. Equation (10) shows that the SD algorithm cancels the receiver FCB.…”

“…In regards to the relative positioning of the SF receiver, two receivers at least are needed, and the relative positioning results are easily affected by the displacement of the localized infrastructure. Therefore, the ability of displacement detection by relative positioning is limited [ 6 ]. Different from the relative positioning, the service of the correction information for the ionosphere delay, which is estimated using the GNSS geometry-free combination, is needed for single-frequency and single-receiver-based absolute positioning.…”

“…The PPP-enabled ambiguity resolution has been studied and implemented [ 6 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ], and these studies focus on the recovering of the integer characteristic. In Li et al [ 6 ] and Odijk et al [ 29 ], the double-differenced ambiguity was introduced in PPP ambiguity processing to improve the positioning accuracy of PPP and promote the detecting ability of the PPP in displacement monitoring. This method avoids the estimation of the FCB, and the PPP ambiguity fixing was realized based on the introduced SD ambiguity from reference stations and the double-differenced ambiguity fixing.…”