Global Positioning Satellite System Navigation Accuracy with Updated Ephemerides

摘要

The Global Positioning System is composed of three segments: the Master Control Station (MCS), the space segment with 21 satellites at semi-synchronous altitude, and the user segment which consists of any number of receivers that can process four satellite transmissions for a navigation solution. The MCS performs many vital functions such as creating and uploading each satellite ephemeris. If the MCS were unable to perform these functions, the system accuracy would degrade gracefully over two weeks. After two weeks with no uploaded ephemerides, the satellites would begin broadcasting empty messages which could be used to form pseudorange measurements, although no ephemeris would be available. By using old ephemerides from other sources and current pseudoranges, updated ephemerides could be formed and used to navigate. GPS system tests, provided ephemerides and raw pseudoranges from the constellation of seven test satellites for this evaluation of navigation accuracy using old broadcast ephemerides and current pseudoranges. The resulting navigation accuracy appears to be comparable to normal system accuracy, though there are numerous variables affecting the accuracy. Theses. (jhd)