## 2 Current Status of GNSS Integrity Service
### Current Status of Integrity Services of GPS, Galileo, and GLONASS
#### 2.2.2 SBAS Integrity Services  
Currently, there are multiple operational SBASs worldwide, and there are also some SBASs under construction. These SBASs include the Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay Service (EGNOS), the Multifunctional Satellite Augmentation System (MSAS), GPS-aided Geo-augmented navigation  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Constellation** & **Type** & **Accuracy Parameters** & **Health Indicators** \\ \hline \multirow{4}{*}{**GPS**} & \multirow{2}{*}{LNAV} & \multirow{2}{*}{User Range Accuracy (URA) (4 bits)} & Alert Flag (AF) (1 bit), SV Health (6 + 8 bits), Integrity Status Flag (ISF) (1 bit), and Anti-Spoof (A-S) Flag (1 bit) \\ \cline{2-3}  & & & \\ \cline{2-3}  & & & \\ \cline{2-3}  & & & \\ \hline \multirow{4}{*}{**Galileo**} & \multirow{2}{*}{F/NAV} & \multirow{2}{*}{Signal-in-Space Accuracy (SISA) (8 bits)} & E5a Signal Health Status (2 bits) and E5a Data Validity Status (1 bit) \\ \cline{2-3}  & & & \\ \cline{2-3}  & & & \\ \hline \multirow{2}{*}{**GLONASS**} & \multirow{2}{*}{CDMA} & Ephemeris (5 bits) and Clock Bias (5 bits) Accuracy Factors & Signal Health and Data Validity Attributes \\ \hline \hline \end{tabular}
\end{table}
Table 4: Integrity parameters in the broadcast ephemeris of the GPS, Galileo, and GLONASS.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Content** \\ \hline Correction parameters & Fast Corrections, Long-Term Satellite Error Corrections, Mixed Fast Corrections, and Ionospheric Delay Corrections \\ \hline \multirow{2}{*}{Accuracy parameters} & User Differential Range Error (UDRE), Grid Ionospheric Vertical Error (GIVE), and Clock Ephemeris Covariance Matrix Message \\ \hline Degradation parameters & Fast Correction Degradation Factor and Degradation Parameters \\ \hline \hline \end{tabular}
\end{table}
Table 3: Parameters in the BDSBAS message.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Constellation** & **SISRE Accuracy** & **Satellite Fault Rate** & **Constellation Fault Rate** & **Continuity Risk** & **Availability** \\ \hline \multirow{2}{*}{**GPS**} & 30 m (any satellite, global average, 99.94\%); & \(1\times 10^{-5}\)/h & \(1\times 10^{-8}\)/h & \(2\times 10^{-4}\)/h & 0.957 \\  & 30 m (any satellite, worst position, 99.79\%) & & \(3\times 10^{-5}\)/h & \(2\times 10^{-4}\)/h & / & 0.920 \\ \hline \multirow{2}{*}{**Galileo**} & 10 m (any satellite, global average, 99.9\%) & & \(3\times 10^{-5}\)/h & \(2\times 10^{-4}\)/h & / & 0.920 \\  & 20 m (any satellite, worst position, 99.9\%) & & & & \\ \hline \multirow{2}{*}{**GLONASS**} & 18 m (any satellite, global average, 99.37\%) & \(1\times 10^{-4}\)/h & \(1\times 10^{-4}\)/h & \(2\times 10^{-3}\)/h & 0.950 \\ \cline{2-3}  & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 5: Performance standards of GPS, Galileo, and GLONASS.  
(GAGAN), the System for Differential Corrections and Monitoring (SDCM), the Korean Augmentation Satellite System (KASS), the African Satellite-Based Augmentation System (ASECNA), and the Australia/New Zealand Satellite-Based Augmentation System (SPAN).  
The architectures of these SBASs are similar to that of the BDSBAS. They rely on a regional network of ground monitoring stations to perform integrity monitoring and generate the SBAS messages. The parameters in the SBAS messages include correction parameters, accuracy parameters, and degradation parameters. The SBAS messages are transmitted by GEO satellites. Tables 6 and 7 compare the integrity parameters in the SBAS message among the WAAS, EGNOS, and SDCM. Moreover, they show the certification status of these SBASs.