# Precise Orbit Determination for GNSS Maneuvering Satellite with the Constraint of a Predicted Clock
## 3 Experiment Analysis
### Algorithm Validation with Normal Data
It is noticed that the orbit differences of the unconstrained solution increase slightly with the processing time in all directions. \begin{table}
\begin{tabular}{c c} \hline
**Item** & **Applied Models** \\ \hline Geopotential & EGM 2008 model (12 \(\times\) 12) \\ \hline M-body gravity & Sun, Moon and planets \\ \hline Tidal forces & Solid Earth, pole, ocean tide \\  & IERS conventions 2010 [32] \\ \hline Solar Radiation Pressure & Reduced CODE 5-parameter with no initial value \\ \hline Relativistic effects & IERS conventions 2010 \\ \hline Basic observables & \begin{tabular}{c} Un-differenced ionosphere-free combinations of code \\ and phase observations on GPS L1/L2, BDS B1/B2 \\ \end{tabular} \\ \hline Processing interval & 30 s \\ \hline Cutoff elevation & 7\({}^{\circ}\) \\ \hline Weighting & \(p=\begin{cases}1,&e>30^{\circ}\\ \sin^{2}e,&e\leq 30^{\circ}\end{cases}\) \\ \hline Satellite antenna PCO and PCV & \
\begin{tabular}{c}igs08.atx \\ \end{tabular} \\ \hline Receiver antenna PCO and PCV &
\begin{tabular}{c} GPS: isg08.atx \\ BDS: using the same as GPS \\ \end{tabular} \\ \hline Phase wind-up & Corrected [33] \\ \hline Tropospheric delay & [PERSON] model (1972) + random-walk process \\ \hline Satellite clock & Estimated as white noise \\ \hline Receiver clock & Estimated as white noise \\ \hline Earth rotation parameters (ERP) & Estimated with tight constraint \\ \hline Inter-system biases & Estimated as constant parameters \\ \hline Ambiguity & Fixed for GPS/BDS (IGSO, MEO) separately \\ \hline \end{tabular}
\end{table} 
Table 1: Dynamic models and observation models used in the GPS/BDS POD processing. It might because that more cycle slips will occur with the progress of POD processing and the ambiguity parameters consequently increase with processing time, which worsens the estimation of satellite positions. Though significantly reduced, the orbit differences of clock-constrained solutions exhibit more apparent growth rate in the radial direction, which can be attributed to precision degradation of the predicted satellite clocks with processing time. \begin{table}
\begin{tabular}{c c c c c} \hline
**Satellite PRN** & **Orbit Type** & **HDOP** & **RDOP** & **Number of Stations** \\ \hline C01 & & 3.53 & 71.07 & 41 \\ C02 & & 3.96 & 70.84 & 28 \\ C03 & GEO & 3.81 & 66.28 & 39 \\ C04 & & 4.28 & 64.56 & 34 \\ C05 & & 3.84 & 69.66 & 34 \\ \hline C06 & & 3.05 & 54.78 & 39 \\ C07 & & 3.38 & 52.72 & 41 \\ C08 & IGSO & 3.31 & 50.68 & 39 \\ C09 & & 3.51 & 73.90 & 35 \\ C10 & & 3.18 & 45.69 & 41 \\ C13 & & 3.79 & 66.60 & 33 \\ \hline C11 & & 3.19 & 28.40 & 29 \\ C12 & & 3.46 & 36.68 & 16 \\ C14 & MEO & 2.42 & 27.10 & 39 \\ G01 & & 2.29 & 25.29 & 38 \\ G02 & & 2.37 & 21.28 & 37 \\ \hline \end{tabular}
\end{table} 
Table 2: Orbital dilution of precision (DOPs) for BDS and GPS satellites at 22:00:00, DOY 124, 2017. GEO—geostationary orbit; IGSO—inclined geosynchronous orbit; MEO—Median Earth orbit. Figure 4: RMS of GPS and BDS orbit differences in the radial, cross-track and along-track directions of the clock-constrained and traditional RPPP POD solutions with respect to the dynamic POD solution.