Abstract
An increasing number of researchers have conducted in-depth research on the advantages of low-cost single-frequency (SF) receivers, which can effectively use ionospheric information when compared to dual-frequency ionospheric-free combination. However, SF observations are bound to increase the unknown parameters and prolong the convergence time. It is desirable if the convergence time can be reduced by external information constraints, for example atmospheric constraints, which include ionosphere- or troposphere constraints. In this study, ionospheric delay constraints, tropospheric delay constraints, and their dual constraints were considered. Additionally, a total of 18,720 test experiments were performed. First, the nearest-neighbor extrapolation (NENE), bilinear- (BILI), bicubic- (BICU), and Junkins weighted-interpolation (JUNK) method of Global Ionospheric Map (GIM) grid products were analyzed. The statistically verified BILI in the percentage of convergence time, average convergence time, and computation time consumption of them shows a good advantage. Next, the influences of global troposphere- and ionosphere-constrained on the convergence time of SF Precise Point Positioning (PPP) were analyzed. It is verified that the ionosphere-constrained (TIC2) has significant influence on the convergence time in the horizontal and vertical components, while the troposphere-constrained (TIC1) has better effect on the convergence time in the vertical components within some thresholds. Of course, the dual constraint (TIC3) has the shortest average convergence time, which is at least 46.5% shorter in static mode and 5.4% in kinematic mode than standard SF PPP (TIC0).
Highlights
The concept and technology of Precise Point Positioning (PPP) were first proposed and implemented for the Global Positioning System (GPS) by the American Jet Propulsion Laboratory (JPL) in the late 1990s [1].PPP has attracted significant interest over the intervening years due to its high accuracy without needing a specific reference station, providing correctional information, simple operations, and cost effectiveness due to reductions in labor and equipment costs
Zhang et al [31] studied real-time Global Ionospheric Map (GIM) and its application in SF positioning, Aggrey and Bisnath [32] studied the effect of atmospheric-constrained on the convergence time of dual- and triple-frequency PPP, and Gao et al [33] applied the Inertial Navigation System (INS) to the ionosphere-constrained PPP to overcome the drawbacks that accompany unexpected and unavoidable substandard observation environments
According to the tropospheric delay product published by IGS, a virtual observation is used in the observation equation, and a troposphere-constrained SF GPS PPP is constructed
Summary
The concept and technology of Precise Point Positioning (PPP) were first proposed and implemented for the Global Positioning System (GPS) by the American Jet Propulsion Laboratory (JPL) in the late 1990s [1]. Shi et al proposed an improved method in which the deterministic representation is further refined by a stochastic process for each satellite with an empirical model for its power density [10] The results of this method show that the singleand dual-frequency PPP exhibited enhanced convergence time, and the positioning accuracy of SF data is only improved by 25% [11]. Zhang et al [31] studied real-time GIM and its application in SF positioning, Aggrey and Bisnath [32] studied the effect of atmospheric-constrained on the convergence time of dual- and triple-frequency PPP, and Gao et al [33] applied the Inertial Navigation System (INS) to the ionosphere-constrained PPP to overcome the drawbacks that accompany unexpected and unavoidable substandard observation environments. We will study ionospheric delay and tropospheric delay prediction models to provide virtual atmospheric delay observations for real-time PPP and provide a priori information for the constraint processing
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