# Evaluation of Ionospheric Delay Effects on Multi-GNSS Positioning Performance
## 5 Conclusions  
To fully evaluate the ionospheric delay effects on multi-GNSS positioning performances, multi-GNSS positioning models for single (b1, b2 and b3) and dual-frequency (b1/b2 and b1/b3) GNSS signals were assessed by different ionosphere processing schemes. The positioning models were extended to SPP or PPP processing with observations from single-, dual-, triple- and quad-constellations. Static datasets collected at ten stations over thirty consecutive days were utilized to evaluate the impact on positioning performance with ionospheric delay models. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Type**} & \multirow{2}{*}{**Schemes**} & \multicolumn{3}{c}{**b1/b2**} & \multicolumn{3}{c}{**b1/b3**} \\ \cline{3-8}  & & **N** & **E** & **U** & **N** & **E** & **U** \\ \hline G & IF & 0.905 & 1.613 & 3.147 & - & - & - \\ G & UC & 0.907 & 1.609 & 3.135 & - & - & - \\ G & BIM-cons & 0.878 & 1.595 & 3.162 & - & - & - \\ G & NTCM-cons & 0.905 & 1.587 & 3.159 & - & - & - \\ G & GIM-cons & 0.898 & 1.597 & 3.148 & - & - & - \\ C & IF & 1.435 & 2.490 & 5.679 & 1.560 & 2.954 & 5.886 \\ C & UC & 1.440 & 2.526 & 5.726 & 1.572 & 2.956 & 5.968 \\ C & BIM-cons & 1.360 & 2.374 & 5.535 & 1.390 & 2.464 & 5.828 \\ C & NTCM-cons & 1.387 & 2.309 & 5.488 & 1.398 & 2.444 & 5.692 \\ C & GIM-cons & 1.377 & 2.269 & 5.466 & 1.340 & 2.438 & 5.507 \\ R & IF & 0.917 & 1.873 & 3.303 & - & - & - \\ R & UC & 0.917 & 1.873 & 3.302 & - & - & - \\ R & BIM-cons & 0.944 & 1.875 & 3.472 & - & - & - \\ R & NTCM-cons & 0.944 & 1.889 & 3.434 & - & - & - \\ R & GIM-cons & 0.924 & 1.878 & 3.428 & - & - & - \\ E & IF & 1.028 & 1.809 & 3.566 & 1.109 & 2.099 & 3.364 \\ E & UC & 1.025 & 1.813 & 3.560 & 1.080 & 2.089 & 3.357 \\ E & BIM-cons & 1.040 & 1.805 & 3.486 & 1.066 & 1.918 & 3.306 \\ E & NTCM-cons & 1.030 & 1.771 & 3.404 & 1.097 & 1.847 & 3.318 \\ E & GIM-cons & 1.039 & 1.742 & 3.111 & 1.038 & 1.799 & 3.308 \\ GC & IF & 0.886 & 1.710 & 3.066 & 1.427 & 2.789 & 5.405 \\ GC & UC & 0.892 & 1.708 & 3.056 & 1.425 & 2.774 & 5.393 \\ GC & BIM-cons & 0.870 & 1.581 & 2.946 & 1.330 & 2.367 & 5.426 \\ GC & NTCM-cons & 0.889 & 1.563 & 2.957 & 1.355 & 2.353 & 5.238 \\ GC & GIM-cons & 0.827 & 1.529 & 2.922 & 1.293 & 2.307 & 5.007 \\ GR & IF & 0.811 & 1.525 & 2.903 & - & - & - \\ GR & UC & 0.807 & 1.523 & 2.907 & - & - & - \\ GR & BIM-cons & 0.790 & 1.496 & 2.874 & - & - & - \\ GR & NTCM-cons & 0.817 & 1.487 & 2.757 & - & - & - \\ GR & GIM-cons & 0.771 & 1.372 & 2.718 & - & - & - \\ GE & IF & 0.871 & 1.776 & 3.107 & 1.053 & 2.030 & 3.362 \\ GE & UC & 0.864 & 1.778 & 3.092 & 1.054 & 1.997 & 3.355 \\ GE & BIM-cons & 0.853 & 1.607 & 2.920 & 1.071 & 1.914 & 3.445 \\ GE & NTCM-cons & 0.854 & 1.604 & 2.884 & 1.077 & 1.826 & 3.275 \\ GE & GIM-cons & 0.834 & 1.587 & 2.868 & 0.994 & 1.771 & 3.247 \\ GCR & IF & 0.794 & 1.513 & 2.886 & - & - & - \\ GCR & UC & 0.787 & 1.511 & 2.884 & - & - & - \\ GCR & BIM-cons & 0.782 & 1.428 & 2.818 & - & - & - \\ GCR & NTCM-cons & 0.795 & 1.408 & 2.742 & - & - & - \\ GCR & GIM-cons & 0.755 & 1.305 & 2.701 & - & - & - \\ GCRE & IF & 0.777 & 1.426 & 2.702 & - & - & - \\ GCRE & UC & 0.760 & 1.393 & 2.695 & - & - & - \\ GCRE & BIM-cons & 0.774 & 1.345 & 2.476 & - & - & - \\ GCRE & NTCM-cons & 0.778 & 1.324 & 2.366 & - & - & - \\ GCRE & GIM-cons & 0.676 & 1.286 & 2.347 & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 7: RMS of dual-frequency PPP with IF approach, UC approach, and BIM-, NTCM- and GIM-constrained approaches (unit: cm). Comparative analysis showed that the positioning accuracy of single-frequency SPP with the external ionospheric model correction can obtain meter-level accuracy, and the vertical error is relatively larger than the horizontal components. For single-frequency SPP, the GIM correction solution achieves the best accuracy and the accuracy of SPP with NTCM correction is better than the solution with the BIM correction in the E and U components. The multi-GNSS single-frequency PPP results indicate that the GRAPHIC and UC approaches have the same performance levels.