# PPP and PPP-AR Kinematic Post-Processed Performance of GPS-Only, Galileo-Only and Multi-GNSS
## 1 Introduction  
The precise point positioning method (PPP) [1] is a well-known and widely used method for positioning using zero-difference observations. This method is used for calculating the coordinates of a station without the need of a reference station nearby as a control station. It has been used in numerous scientific applications; namely general static positioning [2] for local or global networks, kinematic positioning [3], time transfer [4], etc. The PPP accuracy reaches the highest levels once the carrier phase ambiguities are resolved--the so-called PPP-AR (PPP with ambiguity resolution) or less frequently integer PPP (IPPP). The French Space Agency, Centre National d'Etudes Spatiales (CNES) and the Collecte Localisation Satellites company (CLS Group) Analysis Centre (AC) of the International GNSS Service (IGS) use an undifferenced ambiguity resolution solution for GPS [5] and Galileo [6]. Such a method can be applied also for the determination of precise orbits and integer recovery clocks (IRC). In order to apply this method for PPP and PPP-AR for GPS and Galileo, satellite orbits and IRC products as well as satellite biases have to be consistent. In our study they are takenfrom the CNES-CLS AC. There are two conditions for this method: for PPP or PPP-AR, orbit and clock products have to be consistent and of the best quality; for PPP-AR IRCs and associated methods, biases need to be available for the products used. For the first condition, any precise orbit like the ones made available by the International GNSS Service (IGS) or Analysis Centers (ACs) in the frame of the Multi GNSS pilot project (MGEX) [7] can be used. For the second we can use the products delivered routinely by the CNES-CLS AC for GPS [8] and Galileo [6].  
So far there are already publications giving the possibilities of Galileo positioning [9] or studying the performance the benefit of using multi-GNSS measurements in PPP [7,8]. In a previous study [6] we presented the zero-differences approach used to compute IRC products for Galileo and GPS. Recently we presented the positioning capabilities of Galileo-only solutions [10]. In this article we examine the performance and precision of PPP and PPP-AR in a comparison of Galileo-only, GPS-only and GPS + Galileo AR solutions.  
This study is done using the GPS and the incomplete Galileo constellation. As of 2019, the Galileo constellation comprises 26 satellites in total (4 In-Orbit Validation (IOV) and 22 Full Operational Capability (FOC)). Two of the FOC satellites are in eccentric orbits, one IOV is not available and one FOC is not usable. The total number of usable satellites is 22: 3 IOV and 21 FOC satellites [11]. The full constellation is only 4 satellites away and it is scheduled for 2020 [12]. The following hypothesis is examined and verified: if GPS and Galileo measurements are of the same quality, then the simultaneous use of the two systems will give better accuracy than when using each system separately. If the two systems are compatible, then the number of measurements is nearly double than in a single-system solution, and the number of parameters (apart from biases for the different frequencies used) is the same.  
This publication is organized in the following sections. Firstly, the undifferenced ambiguity resolution and PPP-AR processing is briefly presented. Section 3 is devoted to the experiments, the processing and the results. Finally, in Section 4, some conclusions are given together with suggestions for further work and perspectives.