Performance Assessment on Expanding SBAS Service Areas of GAGAN and MSAS to Singapore Region

摘要

In past decade, the GPS plays an important role in many navigation applications. In some cases, the GPS is the only device providing navigation service. For safety-of-life user, GPS alone cannot provide the stringent performance in accuracy, integrity and availability. As a result, several SBAS (Satellite Based Augmentation System) systems have been developed to provide corrections and assistances to GPS users. The notably SBAS systems are U.S. WAAS (Wide Area Augmentation System), Europe EGNOS (European Geostationary Navigation Overlay Service) and Japanese MSAS (Multi-functional Satellite Augmentation System), In addition, India and Russia have engaged in the deployment and development of SBAS system, named GAGAN (GPS Aided Geo Augmented Navigation) and SDCM (System of Differential Correction and Monitoring). Also, other regions in the world currently proceed feasibility studies on SBAS. For instance, SACCSA (The Augmentation Solution for the Caribbean, Central America and South America) project in Latin-America, ASAS (African Satellite Augmentation System) in Africa and Malaysian SBAS. SBAS broadcast the correction for ionosphere delay and satellite clock. By using these corrections, the user position accuracy can improve to several meters or better. In Singapore, Changi airport is one of busiest airport in the world, and it handled more than fifty million passengers in 2012. Additionally, Singapore is located in the equatorial region so that the ionosphere activities are dramatic. Currently, there is no SBAS service in the Singapore region. The objective of this paper is to propose a fusion scheme to exploit the correction and integrity monitoring messages from nearby two SBAS systems, GAGAN and MSAS and then provide a reliable correction for GPS users. Singapore is not located in the service volume of either GAGAN or MSAS. Because of the lack of SBAS monitoring stations, the navigation quality in Singapore region cannot be assured through either GAGAN or MSAS. The messages from both SBAS systems can be still received. Therefore, it is desired to investigate how messages from GAGAN and MSAS can be utilized to enhance the performance for GPS user. Then, its goal is to ensure a smooth transition and assured navigation performance in this region. In the paper, both GAGAN and MSAS messages are firstly received and analyzed for the assessment of the signal quality. And then, a comparison with the requirements at different phases of flight is made. A synergistic integration of the messages from by GAGAN and MSAS in Singapore is developed to pave a way for the future regional augmentation system implementation. An extrapolation scheme is proposed to expand the coverage of ionospheric delay correction messages from GAGAN and MSAS. All proposed fusion and extrapolation schemes are assessed by using real data to evaluate performance. The result shows that our approach has reliable performance compared to a surveying-grade receiver.