![]() ![]() ( 2020) proposed to rebroadcast the corrected parameters of the SBAS service via the Ground-Based Augmentation System (GBAS) to the aircraft. Moreover, Weng and Chen ( 2019) investigated the vertical integration of the SBAS service and a local monitoring station to reduce vertical protection levels (VPL). ![]() For instance, the improvements of the fast and long-term corrections for the Wide Area Augmentation System (WAAS) SBAS service were proposed by Chen et al. Although SBAS services do not support the APV-II and CAT-I categories (the precision approach (PA) model based on the ICAO standard), some augmented parameters have been investigated for improvements. ( 2017), and it supports the APV-I service. Next, the GPS aided Geo Augmented Navigation (GAGAN) SBAS system over Sri Lanka was assessed by Dammalage et al. The LPV-200 and APV-I services (RTCA 2006) have availabilities of about 92% and 70%, respectively. ( 2016), the Korea Augmentation Satellite System (KASS) was explored on the Korean peninsula and confirmed based on the two phase-of-flight categories. In the literature, most research works on the L1 SBAS focus on the assessment of SBAS availabilities and the improvement of augmented parameters. However, since DFMC SBAS is still under the standardization process by the International Civil Aviation Organization (ICAO) and is not expected to be available until November 2022, the L1 SBAS system is currently still of much interest. Currently, there are two generations of SBAS: (1) the L1 SBAS operating on L1 frequency (1575.42 MHz) alone (RTCA 2006) and (2) the dual-frequency multi-constellation (DFMC) SBAS operating on the L1 and L5 (1176.45 MHz) frequencies (ICAO 2018b). The augmented information for the SBAS-equipped GNSS receivers is broadcast by the SBAS geostationary satellites (European GSA 2020). Satellite-Based Augmentation System (SBAS) is crucial to improve services in aeronautical navigation based on Global Navigation Satellite System (GNSS). ![]() The GAGAN performances with the proposed method for the APV-I and LPV-200 categories are improved up to 57% and 53%, respectively, in comparison with the baseline method of the IGP correction. In addition, we perform a preliminary availability assessment of two critical phases of flights. More reductions in the positioning errors are found in September and December than other months. The analysis shows that using the estimated corrections, the positioning errors are reduced both on quiet days and locally disturbed days in 2019. Then the ionospheric corrections are obtained from the estimated local ionospheric delays. The local ionospheric delays are estimated based on the proposed method with the observed GPS and GAGAN data in Thailand. Hence, in this work, we propose a new method based on the geometry-free ionospheric delay estimation with a single frequency (L1) and a single reference station requirement. Although the Global Positioning System (GPS) aided Geo Augmented Navigation (GAGAN) SBAS is available, the performances are degraded due to the discrepancies of the ionospheric correction over Thailand and surrounding areas. L1 SBAS operates on the L1 frequency (1575.42 MHz) and is currently still of interest since all GNSS satellites and receivers do not fully support additional frequencies such as L5 (1176.45 MHz). Satellite-Based Augmentation System (SBAS) is essential to support aircraft navigation. ![]()
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