# Design and Performance Analysis of BDS-3 Integrity Concept
## 2 BDS Integrity Concept
### Integrity Definition  
Due to the high requirements for safety and reliability, the concept of navigation integrity first appeared in the field of civil aviation. In order to be approved for the application in the field of civil aviation, GNSSs need to carry out and complete their standard research and formulation work under the ICAO framework, and promise ICAO all necessary service performance indicators, including integrity. According to the definition in the ICAO international standards and recommended practices (SARPs), integrity indicates the system's ability to detect faults and issue alerts. In order to make more detailed and accurate assessments, the integrity probability is further subdivided into the \"satellite service failure probability\" (denoted as \(\mathrm{P_{sat}}\)) and the \"constellation service failure probability\" (denoted as \(\mathrm{P_{const}}\)). Among them, the \"satellite service failure\" refers to the condition where the user range error (URE) of any single satellite exceeds the broadcast not-to-exceed (NTE) tolerance but the alarm cannot be achieved within the promised time. This type of failure will only affect itself and no other satellites. The \"constellation service failure\" refers to the condition where the UREs of more than two satellites exceed the corresponding NTEs at the same time, and the alarm cannot be achieved within the promised time. Once this type of failure appears, it means that some kind of common fault has occurred in the system. ICAO allows the GNSS to develop its customized integrity technical content. See Table 1 for the integrity risk probability indicator of each GNSS in ICAO SARPs [19; 21]. It can be seen from Table 1 that the integrity functions of each GNSS are quite different. GPS has global ground monitoring and injection capabilities, so once the service is abnormal, the system can send an alert in real time. Specifically, there are several alarm approaches for GPS, including using the health status indicator in the message, setting the satellite pseudo random number (PRN) code to \"37\", or broadcasting non-standard PRN \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Items** & **GPS** & **GNLOASS** & **Galileo** & **BDS** \\ \hline \multirow{4}{*}{\(\mathrm{P_{sat}}\)} & Error Tolerance & URE \textgreater{} 4.42 \(\times\) IAURA & URE \textgreater{} 70 m & URE \textgreater{} 4.17 \(\times\) URA & URE \textgreater{} 4.42 \(\times\) SISA for BIC and B2a \\ \cline{2-6}  & Time-to-Alert (TTA) & 10 s & 10 s & Not applicable & 60 s for ground monitoring and alarming; 6 s/300 s for satellite and alarming \\ \cline{2-6}  & Probability & \(\leq\)10\({}^{-5}\) & \(\leq\)10\({}^{-4}\) & \(\leq\)3 \(\times\) 10\({}^{-5}\) & \(\leq\)10\({}^{-5}\) \\ \hline \multirow{4}{*}{\(\mathrm{P_{const}}\)} & Error Tolerance & URE \textgreater{} 4.42 \(\times\) IAURA & URE \textgreater{} 70 m & URE \textgreater{} 4.17 \(\times\) URA & URE \textgreater{} 4.42 \(\times\) SISA for BIC and B2a \\ \cline{2-6}  & Time-to-Alert (TTA) & 10 s & 10 s & Not applicable & 300 s for ground monitoring and alarming; 6 s for satellite monitoring and alarming \\ \cline{1-1} \cline{2-6}  & Probability & 10\({}^{-8}\) & 10\({}^{-4}\) & \(\leq\)2 \(\times\) 10\({}^{-5}\) & \(\leq\)6 \(\times\) 10\({}^{-5}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: GNSS integrity performance in ICAO SARPs. codes. GLONASS indicates the operating status of the system to users through the health status indicator in the message. Galileo provides users with integrity information through the HS, DVS, SISA, and other parameters in the message; in addition, when the issue of data (IOD) of the message exceeds four hours, it also indicates that the system message is in an unhealthy state. BDS-3 is designed with two methods of ground integrity monitoring and satellite autonomous integrity monitoring (SAIM).