Study And Implementation On GPS/BDS RAIM Forecast System

General aviation is an important part of civil aviation in our country.But compared with the commercial transport aircraft, its navigation services are inadequate hindering the development of general aviation. Using GNSS navigaiton, its advanced technology and good accuracy can accelerate the construction of general aviation. But the GNSS navigation process must meet integrity requirements. Integrity characterizes a navigation system ability to provide timely warning to users when there are some faults or the positioning error exceeds the limit, the system should not be used for navigation.At present, the commonly used method of integrity monitoring is RAIM. It is a kind of algorithm embedded in the receiver that can meet the needs of real-time monitoring of dynamic users without external interference. RAIM has been widely used with the advantages of low cost and quick response to system fault. But RAIM has a strict demand on quantity and geometrical position of visible satellites. The fault detection of RAIM requires at least five satellites in the visual field of receiver, while at least six to fault exclusion. If the above requirements are not met, then RAIM is unavailable. If that happens, airborne equipment could not guarantee the accuracy of GPS or BEIDOU positioning result. Then the aircraft safety will be seriously affected. To avoid the aircraft encountering in flight stage of unavailability of RAIM, The CAAC requires airlines to predict the RAIM availability of flight route and terminal before the plane takes off that can assist the airline dispatch personnel clearances.This thesis introduces the GPS, BEIDOU system architecture and respective space-time system, and calculation of satellite position followed by the introduction of the RAIM technology fault detection process.Meanwhile the causes of RAIM prediction and RAIM prediction method are described. Next the article from the functional requirements and performance requirements of the system gives the features and requirements of RAIM prediction system to be achieved.And on this basis, it conducts detailed design of the system. In this paper, considering the satellite number and geometry, GPS unavailable plan, almanac, it has RAIM prediction on all the country's airports, routes, regions and areas in Shaanxi Province by HPL method. The HPL value calculated will be compared with the HAL in deferent prediction level to obtain RAIM prediction results in different modes. At the same time, this paper developed a RAIM prediction information publishing platform, users can access a variety of RAIM prediction modes via the network. After testing, the system functionality and performance meet basic needs, but also on the problems of the system were analyzed. The author will improve the system in-depth study at a later time.The system will be applied in general aviation flight service stations, providing RAIM availability information of route,terminal,NPA as well as working area for the flight dispatch departments and regulatory authorities as a basis for manager to make and check flight plan.