Key Algorithm Of New China Astronomical Position System

Navigation is the summary of a kind of technique which is used to guide plane, ship, vehicle and individual to reach destination by specified route accurately and safely. At ancient times, people were navigated by means of sun, fixed stars, etc., while currently the common navigation systems are astronomic navigation, inertial navigation and radio navigation. Astronomic navigation is the earliest one people used, which has the default of low precision and constrained by natural condition, weather and time. Inertial navigation, emerged in 1940s, is widely used in guiding vehicles, ships and planes for its strong anti-jamming ability. Radio navigation makes use of wireless wave, which can be divided into land-based and space-based system according to the position of base point. Two typical land-based systems are LORAN and Omega, while typical space-based systems are GPS of USA and GLONASS of Russia. NCAPS is a novel satellite navigation system presented by scientists of CAS recently, which is based on the principle that the land control station transmits the navigation signals via communication satellites, other than special navigation satellites, to the NCAPS receivers, in which the received signals are processed to obtain its detailed positioning information. Compared with GPS and GLONASS, the reference base point of NCAPS is a virtual point, and the real base point is at the land-based control station. The greatest predominance of NCAPS lies in its low cost of development, operation and maintenance while relatively high positioning precision. In this paper, the principle of NCAPS is discussed in detail and its positioning equations are deduced. To solve these equations, in addition to traditional linear algorithms and LEAST SQUARES, a method using optimization algorithm is presented. Finally, fundamental principle of Kalman filter and its application in data processing of NCAPS are discussed.