# Research on the Impact of BDS-2/3 Receiver ISB on LEO Satellite POD
## 3 POD Strategy
### POD Model  
Table 1 expresses the measurement models, dynamic models and estimated parameters used in this study. ### POD Model  
Table 1 expresses the measurement models, dynamic models and estimated parameters used in this study. ### POD Model  
Table 1 expresses the measurement models, dynamic models and estimated parameters used in this study. \begin{table}
\begin{tabular}{c c} \hline
**Measurement Model** & **Models/Parameters** \\ \hline Observations & IF code measurements (1 m priori sigma), \\  & IF phase measurements (1 cm priori sigma) \\ \hline GNSS precise products & GFZ multi-GNSS rapid products \\ \hline Ionospheric delay & first-order delay eliminated, high orders neglected \\ \hline GNSS phase center offset (PCO) & igs14\_2086.4 tx \\ \hline GNSS phase center variation (PCV) & Neglected \\ \hline Tianping-1B PCO & Nominal value [26] \\ \hline Tianping-1B PCV & Neglected \\ \hline LEO attitude & Nominal model [26] \\ \hline Smallest elevation angle & 8\({}^{\circ}\) \\ \hline Time span/interval & 30 h, 10 s \\ \hline
**Dynamics** & **Models/Parameters** \\ \hline Earth gravity model & EIGEN\_GL04C, 120 \(\times\) 120 [48] \\ \hline N-body disturbance & DE421 [49] \\ \hline Relativistic effect & IERS 2010 [50] \\ \hline Earth orientation parameter & IERS 2010 [50] \\ \hline Ocean tide & FES 2004, 10 \(\times\) 10 [51] \\ \hline Solid earth and pole tide & IERS 2010 [50] \\ \hline Solar radiation pressure & Cannonball model [52] \\ \hline Atmospheric drag & JB2008 [53] \\ \hline Empirical force & Piecewise periodic estimation of sin and cos coefficients in along and cross directions and not in radial direction \\ \hline
**Estimated parameters** & **Parameters** \\ \hline Tianping-1B initial state & Position and velocity at initial state \\ \hline Receiver clock error & One value estimated per GNSS and per epoch \\ \hline Ambiguities & One value per GNSS satellite per arc \\ \hline Solar radiation pressure coefficients & One value per POD arc \\ \hline Atmospheric drag coefficients & 1 per 1.5 h \\ \hline Empirical force coefficients & 1 per 3.0 h \\ \hline \end{tabular}
\end{table} 
Table 1: Measurement model, dynamic model and estimated parameters. Figure 1: BDS and GPS satellite orbit accuracy. In this paper, the IF code and phase measurements are processed to solve the Tianping-1B orbit solutions with GFZ multi-GNSS rapid products. The a priori noise errors are 1 m for the IF code measurements and 1 cm for the IF phase measurements. The IF measurements eliminate the first-order ionospheric delay and neglect the higher-order delay. The GNSS antenna PCO (phase center offset) is from the igs14_2086.atx, and the Tianping-1B receiver antenna PCO is set to the nominal value (\(-\)0.087, 0.018, \(-\)0.23211) m [26]. The antenna PCVs of GNSS and receiver are neglected. The nominal attitude of Tianping-1B is a stable zero-yaw attitude mode (refer to [26]). The smallest elevation angle is set to 8\({}^{\circ}\). The time span of POD arc is set to 30 h, and the interval of measurements is 10 s.  
The dynamic models are adopted in the POD experiments, such as earth gravity of the 120 \(\times\) 120 EIGEN_GL04C, N-body disturbance of DE421, relativistic effect, ocean tide of 10 \(\times\) 10 FES 2004, solid earth and pole tide, solar radiation pressure of the Cannonball model, atmospheric drag of JB2008 and empirical forces. The least squares algorithm is adopted to solve the unknown variable, such as the satellite initial state, the clock errors, ambiguity parameters and dynamic parameters. The clock errors are estimated per GNSS per epoch. The ambiguity parameter is set to one estimated value per arc per GNSS satellite without cycle slip. The coefficient of the Cannonball model is estimated by one parameter per POD arc. The coefficients of the JB2008 atmospheric drag model are estimated as one parameter per 1.5, and the sin and cos coefficients of the empirical force are estimated as one parameter per 3h in the along and cross directions.