## 2 Simulation Setup and Estimation
### Estimated SRP Parameters  
SRP is the largest non-gravitational force disturbing the orbits of MEO and GSO satellites [33; 34; 35]. To include an SRP error in the procedure, we used the box-wing (BW) model from [26] when generating the orbits for the simulation. For the GNSS solutions, we used empirical SRP parameters in the least-squares adjustment. No BW parameters were estimated. ECOM2 [36], with a total of nine SRP parameters, was selected as the basic empirical SRP model. The model was defined in the DYB coordinate system: D points from the satellite to the Sun, Y is the direction along the solar panels and B completes the right-handed orthogonal system. The ECOM2 (Equation (1)) SRP parameters were estimated as constant as well as periodic sine and cosine terms, including a once per revolution term in B as well as two and four times per revolution terms in D. \(\Delta\)u is the argument of latitude with respect to the Sun. In the further context, the constant parameters had a subscript 0. A subscript s was used for the sine parameter and a c for the cosine parameter. The per revolution term was numbered following the corresponding directions: D, Y or B. As discussed in [16], it is possible to estimate up to 13 SRP parameters in a POD process when using measurements of two or more different observation techniques. The L-band-only measurement scenario could not benefit from estimating more than nine SRP parameters. Therefore, for the results shown in this work, we used ECOM2 (Equation (1)) for scenarios only using the L-band. \[ \begin{split}&\text{D}=\text{D}_{0}+\text{D}_{2\text{c}}\cos(2 \Delta\text{u})+\text{D}_{2\text{s}}\sin(2\Delta\text{u})+\text{D}_{4\text{c}} \cos(4\Delta\text{u})+\text{D}_{4\text{s}}\sin(4\Delta\text{u}),\\ &\text{Y}=\text{Y}_{0},\\ &\text{B}=\text{B}_{0}+\text{B}_{1\text{c}}\cos(\Delta\text{u})+ \text{B}_{1\text{s}}\sin(\Delta\text{u}),\end{split}  \tag{1}\] \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Estimated Parameters** & **L-Band** & **OTWL** & **OISL** \\ \hline Station specific tropospheric & & & \\ zenith delays & Yes, every two hours. & No. & - \\ \hline Ground station coordinates & No. & No. & - \\ \hline Satellite initial state vectors and solar radiation & Yes. & Yes. & Yes. \\ pressure parameters & & & \\ \hline Phase ambiguities (float) & Yes. & - & - \\ \hline Epoch-wise satellite and ground & Yes. & Yes. & Yes. \\ station clock parameters & One clock for each satellite and each ground station. & & \\ \hline \hline \end{tabular}
\begin{tabular}{c c} \hline \hline  & & Yes. \\ Daily range and clock synchronization biases & No. & One transmitter and one receiver bias per entity, each for OTWL and OISL \\  & & (also in scenarios with L-band+OTWL+OISL). \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Estimated parameters with respect to each observation technique. For scenarios using combinations of measurement techniques, we used an extended SRP model containing more than nine parameters. While the estimated parameters for D and Y stay the same, we extended further, per the revolution terms, for B. First, we extended the ECOM2 by the B\({}_{3}\) parameter (sine and cosine (Equation (2)). \[\text{B}=\text{B}_{0}+\text{B}_{\text{1c}}\,\cos(\Delta\text{u})+\text{B}_{\text {1s}}\,\sin(\Delta\text{u})+\text{B}_{\text{3c}}\,\cos(3\Delta\text{u})+\text{B} _{\text{3s}}\,\sin(3\Delta\text{u}), \tag{2}\]  
Second, we extended Equation (2) by the B\({}_{5}\) parameters (sine and cosine (Equation (3)). Again, the D and Y parameters are identical to ECOM2 (see Equation (1)) when using this SRP modeling. \[\text{B}=\text{B}_{0}+\text{B}_{\text{1c}}\,\cos(\Delta\text{u})+\text{B}_{ \text{1s}}\,\sin(\Delta\text{u})+\text{B}_{\text{3c}}\,\cos(3\Delta\text{u})+ \text{B}_{\text{3s}}\,\sin(3\Delta\text{u})+\text{B}_{\text{5c}}\,\cos(5\Delta \text{u})+\text{B}_{\text{5s}}\,\sin(5\Delta\text{u}), \tag{3}\]  
For each simulation scenario, we used the SRP modeling that is the best in the solution.