## 3 Integrity Monitoring Method of Space-Ground Integration
### Simulation Results and Sensitivity Analysis
#### 3.4.3 Discussion  
This paper provides an initial proposal for the development of the next-generation BeiDou integrity monitoring system. In this proposal, BeiDou integrity performance can be improved with advanced SAIM (A-SAIM) and an SBAS with LEO (L-SBAS). The proposed A-SAIM technique is an upgraded evolution of traditional SAIM approaches. It extends from single-satellite autonomous integrity monitoring to multi-satellite joint integrity monitoring. It provides comprehensive integrity monitoring capabilities against signal anomalies, large and small clock anomalies, and ephemeris anomalies. Additionally, the proposed A-SAIM technique is designed to include intelligent prediction capabilities against the anomalies above.  
In addition to A-SAIM, GNSS integrity performance can be significantly benefited from LEO constellations. For one thing, LEO satellites can serve as space monitoring stations so as to enhance the integrity monitoring capability for GNSS satellite faults and constellation faults. Compared to ground monitoring stations, LEO satellites have global coverage and have longer tracking arcs for GNSS satellites. In another application, LEO satellites can act as navigation satellites that transmit navigation signals to users. This will increase the number of visible satellites at the user end, thereby having the potential to  
Figure 21: Global coverage rate comparison under Category I precision approach (CAT-I).  
Figure 20: Global average horizontal protection level comparison.  
reduce protection levels. However, the performance of this approach is heavily influenced by the LEO satellite fault probability and the LEO constellation fault probability.  
To maximize the benefits from LEO constellations for enhancing BeiDou integrity performance, it is crucial to improve the reliability of LEO satellites under cost and resource constraints. In terms of hardware design, components and materials with radiation resistance should be selected, and critical parts should utilize triple-mode designs to improve single-event upset resilience. In manufacturing and testing validation, it is important to strengthen process and quality control during production to conduct various environmental tests to eliminate early failures and to validate performance under on-orbit working conditions. Regarding operation and maintenance, it is essential to develop an autonomous health management system through simulated telemetry and digital telemetry to monitor satellite conditions on orbit, promptly addressing anomalies to shorten fault duration and avoid permanent failure.  
Finally, it is worth mentioning that the A-SAIM technique is necessary for the next-generation BeiDou system, even if the LEO constellation can provide integrity monitoring capabilities against satellite faults. The reasons are three-fold. First, the reliability of LEO satellites may not be sufficient because of low-cost hardware and limited resources. Second, A-SAIM can fulfill integrity monitoring for signal anomalies and clock anomalies more accurately and more quickly based on the onboard hardware. In contrast, this task is challenging for both LEO-based space monitoring stations and ground monitoring stations. Third, the altitude of LEO satellites is low, making it difficult to provide integrity services to high-orbit users (e.g., spacecraft).