2020年7月北斗星基增强系统（BDSBAS）建设完成，向中国及周边地区用户提供符合国际民航组织标准的单双频增强服务。针对BDSBAS在中国南方地区受电离层影响严重且GPS L5频点未满星座导致BDSBAS存在增强服务性能不均匀、完好性空洞等问题，本文进行机载多级完好性监测策略研究，提出一种使用BDSBAS、ARAIM和RAIM进行组合多级完好性监测的策略。精密进近阶段下，在双频BDSBAS可用时进行RAIM复检，双频BDSBAS不可用时逐级切换到V-ARAIM或单频BDSBAS补足完好性监测，航路和非精密阶段下，双频BDSBAS不可用时逐级切换到H-ARAIM、单频BDSBAS或RAIM补足完好性监测，最终提高完好性服务连续可用不降级能力。本文通过实地车载试验和机载试飞试验进行策略验证，正常环境下多级完好性监测策略可实现APV-I服务等级完好性监测。相较单一完好性监测，多级完好性监测策略可实现有效导航历元最多提高0.36%，用户导航完好性监测可用性提高6.84%，多级完好性监测算法可提供更连续稳定的完好性监测性能。本文的研究工作为北斗加入国际标准提供修订思路，为推动北斗在民航应用提供技术基础和数据储备。

Abstract: In July 2020, the construction of the BeiDou Satellite-Based Augmentation System (BDSBAS) was completed, providing single-frequency and dual-frequency augmentation services compliant with International Civil Aviation Organization (ICAO) standards to users in China and surrounding regions. Addressing issues such as uneven augmentation service performance and integrity holes caused by severe ionospheric effects in southern China and the incomplete GPS L5 constellation, this paper investigates an airborne multi-level integrity monitoring strategy. We propose a combined strategy integrating BDSBAS, Advanced Receiver Autonomous Integrity Monitoring (ARAIM), and Receiver Autonomous Integrity Monitoring (RAIM). For precision approaches, RAIM verification is conducted when dual-frequency BDSBAS is active; otherwise, the system falls back to V-ARAIM or single-frequency BDSBAS for integrity support. For en-route and non-precision phases, the unavailability of dual-frequency BDSBAS triggers a progressive switch to H-ARAIM, single-frequency BDSBAS, or RAIM. This strategy ultimately improves the continuity of integrity services and avoids performance degradation. This strategy was validated through field vehicle tests and airborne flight tests. Results show that under normal conditions, the multi-level integrity monitoring strategy can achieve APV-I service level integrity monitoring. Compared with single integrity monitoring methods, the proposed strategy increases the proportion of effective navigation epochs by up to 0.36% and improves user navigation integrity monitoring availability by 6.84%. The multi-level integrity monitoring algorithm provides more continuous and stable integrity monitoring performance. This study provides revision ideas for incorporating BeiDou into international standards, and offers a technical foundation as well as data support for promoting the application of BeiDou in civil aviation.