## 5 Experiments and Performance Evaluation
### WADGPS Performance Analysis  
This paper first used four NSTB reference stations to validate the implementation of the WADGPS system, and three of them are used as the WADGPS RSs and one acts as the WADGPS user. The RSs distribution is shown in Figure 14. The blue RSs are used as the WADGPS RSs, and the yellow RS is used as the WADGPS user. Three-day data is used in this process and they are dated from 2008/12/13 to 2008/12/15. Because the locations of these NSTB RSs are precisely known, we could use them to perform the positioning performance analysis. Figure 15 shows the positioning error distributions in both east and north directions when the WADGPS user applies the WADGPS messages generated by the implemented WADGPS MS with three NSTB RSs. The vertical positioning error distribution is shown in Figure 16. In these figures, the blue dashed line indicates the 95% error bounds on the positioning errors. To show the benefits of using the WADGPS corrections, comparisons of two positioning methods are summarized in Tables 2 and 3. The GPS positioning performance with the WADGPS corrections outperforms the stand alone GPS positioning performance. As a result, the positioning accuracy is improved by the implementation of WADGPS. Furthermore, this paper uses the same three-day data to verify the integrity of the WADGPS MS algorithms, and Figure 17 shows that the HPL values successfully bound the horizontal positioning errors. Figure 18 uses Stanford Chart to validate the LNAV performance of this WADGPS system. As shown in this figure, this WADGPS implementation could provide the LNAV service with no HMI for entire three days period (_i.e._, availability \(>\) 99.999%). The number of satellites used in the solutions is shown in Figure 19. Thus, the WADGPS system implemented in this work is validated. Figure 13: The WADGPS reference stations status window. Figure 14: The NSTB reference stations distribution. Figure 15: (a) The positioning error distribution and 95% error bound in east direction using NSTB data. (b) The positioning error distribution and 95% error bound in north direction using NSTB data. \begin{table}
\begin{tabular}{|c|c|c|} \hline
**Mean** & **Stand alone GPS** & **WADGPS** \\ \hline
**East (m)** & \(-\)0.506 & 0.090 \\
**North (m)** & 0.436 & \(-\)0.085 \\
**Vertical (m)** & 15.707 & \(-\)7.968 \\ \hline \end{tabular}
\end{table} 
Table 2: Mean of the positioning error (NSTB). Figure 16: The vertical positioning error and 95% error bound using NSTB data. Figure 17: The HPL and horizontal positioning error (NSTB). \begin{table}
\begin{tabular}{|c|c|c|} \hline
**95\% error bound** & \multirow{2}{*}{**Stand alone GPS**} & \multirow{2}{*}{**WADGPS**} \\ \cline{1-1}
**(two-sigma)** & & \\ \hline
**Horizontal (m)** & 7.10 & 3.55 \\
**Vertical (m)** & 16.10 & 8.10 \\ \hline \end{tabular}
\end{table} 
Table 3: Accuracy of the positioning performance (NSTB). Next, this work uses the e-GPS observation stations operated by Taiwan MOI to evaluate the LNAV performance of the WADGPS implementation. The e-GPS observation stations distribution is shown in Figure 20, and their locations are listed in Table 4. In order to evaluate the performance change due to the number of RSs, this paper uses two kinds of WADGPS RSs constellations in Taipei  
Figure 19: The number of satellites used in positioning solutions (NSTB). Figure 18: The LNAV (NPA) performance of the implemented WADGPS with NSTB data. FIR. One uses three RSs (_i.e._, RS 1, RS 2 and RS 3) and the other uses four RSs (_i.e._, RSs 1-4). The RS 5 is used as the WADGPS user in the experiments. Five-day data is used in the experiments and they are dated from 2009/10/01 to 2009/10/05. For the WADGPS system with three RSs in Taipei FIR, Figure 21 shows the positioning error distributions in both east and north directions, and Figure 22 shows the vertical positioning errors distribution.