# Construction Progress and Aviation Flight Test of BDSBAS
###### Abstract
Also, no intervals of loss of the continuity of operation of the EGNOS system were recorded. Japan's SBAS, named as MSAS (MTAST (Multi-functional Satellite) Satellite-Based Augmentation System), began operation in September 2007. After over 10 years' operation, the first two GEOs, named MTSAT-1R and MTSAT-2, respectively, have been decommissioned in 2015 and 2020 [15]. Since 2020, MSAS GEOs have been replaced by QZSS GEOs for SBAS service as a part of the QZSS program [16]. Due to the ionosphere condition of the low magnetic latitude of the service area, MSAS has provided horizontal navigation only for en-route to NPA (non-precision approach) operations since the beginning [17]. However, recently research for vertical guidance has been conducted with the assumption of 13 domestic ground monitor stations for MSAS in 2020 and later. This upgrade of MSAS will provide LPV operation at the most airports in Japan and LPV-200 at some major airports [18]. India's GAGAN (GPS Aided GEO Augmentation Navigation) was certified in two steps: on 30 December 2013 for RNP 0.1 operations, and on 21 April 2015 for APV-I operations [19; 20]. In order to meet the set object of APV-I over the India land mass, GAGAN has developed an appropriate region-specific ionosphere model, which makes it the first SBAS in the world to be certified for APV-I operation in the equatorial region [21]. In aviation applications, the Indian government requires that the new aircraft purchased after 1 January 2019 be equipped with SBAS equipment, and encourages the retrofitting of the existing fleet by incentivizing airline operators [20; 22]. Russia's SDCM and GLONASS are integrated constructions to provide users with GLONASS-based services. Currently, the SDCM testing work has been completed, and the system is at the initial stage of certification. According to the plan, SDCM will use three Luch-5M GEOs to replace the original three GEOs from 2020, and add an additional Luch-5M GEO in 160\({}^{\circ}\) E orbit to jointly support SBAS L5. The four core GNSS constellations are all considerations for the SDCM DFMC service, and the expected positioning accuracy is up to 0.5 m [23]. South Korea government has also developed its own SBAS, named the Korea Augmentation Satellite System (KASS), with the goal of providing APV-I operation as early as from year 2022 [24]. Since 2020, KASS has begun to provide initial open service. The assessed availability performance of the initial service is more than 99%, and the assessed positioning accuracy in the horizontal and vertical directions is 0.92 m (95%) and 1.61 m (95%), respectively [25]. Currently, KASS is in the system certification stage. According to the plan, operation certification will be started simultaneously in 2021 [26]. At present, all of the SBASs in service are single-frequency (SF) SBAS which augments GPS L1 C/A. Due to the impact of ionospheric anomalies, SF SBAS service performance has not met the requirements of Category I precision approach (CAT-I). Only WAAS and EGNOS have reached LPV-200. To reduce the impact of ionospheric anomalies on service performance and enhance the service performance by using multi-GNSSs which can improve the geometric layout of constellations, the International Civil Aviation Organization (ICAO) DFMC SBAS SARPs (DS2) working group has developed the draft of Dual-Frequency Multi-Constellation (DFMC) SBAS international standards. The ICAO Air Navigation Commission (ANC) has forwarded the draft of DFMC SBAS SARPs to States parties and relevant international organizations for comments. As one of the components and service types of BDS-3, BDSBAS is of great significance to improving the navigation integrity of aviation users in China and surrounding areas [27]. As early as 2012, China began to carry out system design and formulate development plans. In 2015, it began to actively participate in the joint research and formulation of SBAS international standards and conduct surveys and site selection of monitoring stations [28].