The snapshot Fault Detection (FD) algorithm of Advanced Receiver Autonomous Integrity Monitoring (ARAIM) necessitates the allocation of continuity and integrity risk requirements from the operational exposure time level to the single epoch level. Current studies primarily focus on finding a conservative Number of Effective Samples (NES) as a risk mapping factor. However, considering that the NES varies with the observation environment and the type of the fault mode, applying a fixed NES can constrain the performance of the algorithm. To address this issue, the continuity and integrity risks over the operational exposure time are analyzed and bounded based on all epochs within the exposure time. A more adaptable method for continuity and integrity budget allocation over the operational exposure time is presented, capable of monitoring the continuity and integrity risks over the recent operational exposure time in real time, and dynamically adjusting the allocation values based on the current observation environment. Simulation results demonstrate that, compared with the allocation method based on a fixed NES, ARAIM based on the proposed allocation method exhibits superior performance in terms of the availability. At an FD execution frequency equal to the required Time-To-Alert (TTA), the dual-constellation H-ARAIM provides 100% of the global coverage with 99.5% availability of the RNP 0.1 service, and the dual-constellation V-ARAIM provides 86.38% of the global coverage with 99.5% availability of the LPV-200 service.

Antenna Group Delay Variation (AGDV) is a hardware error source that affects the performance of Dual-Frequency Multi-Constellation (DFMC) Ground-based Augmentation System (GBAS), and these errors are difficult to distinguish from multipath errors. Currently, AGDV is usually modeled as a part of the multipath error, which is called the multipath-AGDV model. However, because of the inconsistency of AGDV and multipath when switching among different positioning modes of GBAS, and because the traditional model does not consider the impact of the azimuth on AGDV, using the traditional multipath-AGDV model will cause the protection levels to be inaccurately calculated. In this paper, azimuth-based modeling of AGDV is conducted by using anechoic chamber measurements. The biases and standard deviations of AGDV based on azimuths are analyzed and modeled, and the calculation method for the DFMC GBAS protection level is optimized. The results show that the azimuth-based AGDV model and protection level optimization algorithm can better avoid the error exceeding the protection level than the multipath-AGDV model. Compared with AGDV elevation model, the VPLs of the B1C signal are increased by 0.24 m and 0.06 m, and the VPLs of the B2a signal are reduced by 0.01 m and 0.16 m using the 100 s and 600 s DFree filtering positioning modes, respectively. The changes in the B1C and B2a protection levels reflect the changes in AGDV corresponding to the azimuth for the respective frequencies, further ensuring the integrity of airborne users, especially when they turn near the airport.

The L-band Digital Aeronautical Communications System (LDACS) is a broadband, high speed and secure communication technique. It is an essential component of the air-to-ground communication system in the framework of the Future Communication Infrastructure (FCI), and is the first integrated Communication, Navigation and Surveillance (CNS) authenticate by the International Civil Aviation Organization (ICAO). This study analyzes the development requirements for the aviation air-to-ground communication system. The status of the LDACS, including the presentation of the technique the ICAO standardization and the typical application scenarios are provided. Description of the key LDACS techniques is followed, which consist of the implement of broadband communication within limited spectrum resources, compatibility with the L-band open-sky signals, integration of navigation and communication, mobility management and multi-link access technology based on Aeronautical Telecommunication Network using Internet Protocol Suite (ATN/IPS), and the secure transmission of data. The status and challenges of the LDACS development in China is also provided.

Dual-Frequency Ground-Based Augmentation Systems (GBAS) can be affected by receiver Inter-Frequency Bias (IFB) when Ionosphere-Free (Ifree) smoothing is applied. In the framework of the proposed GBAS Approach Service Type F (GAST-F), the IFB in the Ifree smoothed pseudorange can be corrected. However, IFB residual uncertainty still exists, which may threaten the integrity of the system. This paper presents an improved algorithm for the airborne protection level considering the residual uncertainty of IFBs to protect the integrity of dual-frequency GBAS. The IFB residual uncertainty multiplied by a frequency factor is included in the Ifree protection level together with the uncertainty of other error sources. To verify the proposed protection level algorithm, we calculate the IFB residual uncertainties of ground reference receivers and user receiver based on BDS B1I and B3I dual-frequency observation data and carry out a test at the Dongying Airport GBAS station. The results show that the proposed Ifree protection level with IFB residual uncertainty is 1.48 times the current protection level on average. The probability of Misleading Information (MI) during the test is reduced from 3.2 × 10⁻⁴ to the required value. It is proven that the proposed protection level can significantly reduce the integrity risk brought by IFB residual uncertainty and protect the integrity of dual-frequency GBAS.