Accounting for Galileo–GPS inter-system biases in precise satellite positioning

Abstract

Availability of two overlapping frequencies L1/E1 and L5/E5a of the signals transmitted by GPS and Galileo systems offers the possibility of tightly combining observations from both systems in a single observational model. A tightly combined observational model assumes a single reference satellite for all observations from both Galileo and GPS systems. However, when inter-system double-differenced observations are created, receiver intersystem bias is introduced. This study presents the results and the methodology for estimation and accounting for phase and code GPS-Galileo inter-system bias in precise relative positioning. The research investigates the size and temporal stability of the estimated bias for different receiver pairs as well as examines the influence of accounting for the inter-system bias on the user position solution. The obtained numerical results are based on four experiments carried out at different locations and time periods using both real and simulated GNSS data.

Inter-System Differencing between GPS and BDS for Medium-Baseline RTK Positioning

“…Odijk and Teunissen [13,15] found that the code and phase DISBs between two systems could be cancelled out for baselines with receiver pairs of the same manufacturer. Paziewski and Wielgosz [14] also reached the same conclusion. For receivers of different manufacturers, although DISBs cannot be eliminated, their stability in time has been proven, and thus can be calibrated in advance.…”

“…Some recent contributions indicated that a priori calibration of DISBs led to better AR and positioning performance [11,[13][14][15]35]. Indeed, between GPS L1-Galileo E1 and other cases with overlapping frequencies, the fractional phase DISB can be easily obtained from fixed integer ambiguities.…”

“…For receivers of different manufacturers, although DISBs cannot be eliminated, their stability in time has been proven, and thus can be calibrated in advance. Using these characteristics, the obvious improvement of ambiguity resolution (AR) and positioning with calibrated DISBs for short and long baseline RTK have been verified, the details of which can be seen in [11,[13][14][15][16]. For the real-time estimation of DISBs and application for AR, Tian et al [12] proposed a particle filter-based method to estimate GPS L1-Galileo E1 phase DISBs based on the fact that the accuracy of a given DISB value can be qualified by the related fixing ratio.…”

“…For the code DISB, it can be easily parameterized or corrected with a priori calibration due to the simplicity of the pseudorange equation. For the phase DISBs, if the a priori phase ISB information is precisely known, the inter-system DD ambiguities can also be fixed to integers for the overlapping frequencies between two systems (e.g., GPS L1 and Galileo E1) [11,13,14]. Odijk and Teunissen [13,15] found that the code and phase DISBs between two systems could be cancelled out for baselines with receiver pairs of the same manufacturer.…”

Positioning and applications

“…The most recent precise positioning model is developed to be applied in multi-GNSS relative positioning . On the other hand this approach forces additional modelling of hardware biases which are introduced in tightly combined multi-GNSS model (Paziewski and Wielgosz, 2015).…”