# Sampling Rate Impact on Precise Point Positioning with a Low-Cost GNSS Receiver
## 2 Methodology
### PPP-GNSS Data Processing  
The new version (version 3) of the Canadian Spatial Reference System PPP service software (CSRS-PPP) was used to process the GNSS data in kinematic and static mode. The main novelty of CSRS-PPP version 3 is the implementation of PPP-AR algorithms [37], which are used to resolve ambiguities for data collected as of 1 January 2018. When a specific set of corrections is applied to the observations of the carrier phase and the parameters of the phase differences are estimated. The ambiguity parameters set up in the PPP filter have an integer nature. Therefore, using sophisticated algorithms, it is possible to identify these integers and restrict their values. When this additional information is added to the solution the accuracy improves. In version 3 of the CSRS-PPP online software the ambiguity resolution is performed on the backward run. This means that epochs are processed first in a chronological order to ensure that all information is available before resolving ambiguities. Then starting with the last successfully processed epoch, ambiguity resolution is attempted. This process is repeated for all epochs in reverse order, that is, from the last to the first epoch. After the backward run is complete, a final back substitution is performed to obtain the final values of all parameters of interest in the process: receiver clocks, tropospheric zenith delays and positions (in kinematic mode) [37].  
For the PPP-GNSS data processing, CSRS-PPP can use different types of orbits and clock products such as rapid, ultra rapid and IGS final. For the experiment, the IGS final orbits at 30 s by the International GNSS Service (IGS) were used. According to [21; 36; 39] the software interpolates at the same sampling rate of the submitted RINEX by using the clock corrections. In the same way, a positioning close to 1 h and 30 min is necessary for kinematic and static mode, respectively. Thus, it allows it to solve the ambiguity of the carrier phase [37]. In this sense, the convergence of the GNSS method is fixed when the accuracy does not present changes or the ambiguities are constant. Table 1 summarizes the options and models implemented in the processing the GNSS data.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Processing Mode** & **Static and Kinematic** \\ \hline GNSS System & GPS + GLONASS \\ \hline Observations & Code and phase \\ \hline Frequency & L\({}_{1}\), L\({}_{2}\) \\ \hline Precise satellite orbits & Precise (IGS final) \\ \hline Satellite product input & CLK-RINEX \\ \hline Product interpolation & YES \\ \hline Phase center corrections & IGS (ATX) \\ \hline Tropospheric model & [PERSON] (GPT) for hydrostatic delay; Hopf (GPT) for wet delay; GMF for mapping functions \\ \hline Ionospheric model & Iono-free (L\({}_{1}\) and L\({}_{2}\)) \\ \hline Elevation cut off (degrees) & 15 \\ \hline \multirow{2}{*}{Observation intervals (s)} & Low-cost & 0.1, 0.2, 1, 5, 15, 30. \\  & Geodetic & 0.2, 1, 5, 15, 30. \\ \hline \multirow{2}{*}{Duration of observations (h)} & Low-cost & 2 \\  & Geodetic & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of processing options used by CSRS-PPP.