Improvement of Differential GPS Performance Using Range Measurements Between Satellites

Abstract

In global positioning system (GPS), inter-satellite link information enables communication between satellites, and inter-satellite range (ISR) represents the distance between satellites used for satellite maintenance. We propose a method to improve position accuracy using distance measurements between satellites, such as ISR. However, ISR information has not been made available to users until now. Therefore, we define distance measurements with inter-satellite ephemeris distance (ISED), which uses satellite coordinates calculated by GPS broadcast ephemeris rather than ISR, and propose a method to improve the position accuracy. ISED accuracy is solely determined by GPS broadcast ephemeris accuracy. GPS ephemeris has recently recorded greater accuracy; therefore, ISED can serve as an additional measurement for user navigation solution. When ISED serves as an additional measurement, the observation matrix is extended, resulting in a reduction in dilution of precision (DOP). Therefore, user accuracy is improved by applying ISED owing to the reduction in DOP. Additionally, the analysis results by applying real experimental data show that DOP, with an extended observation matrix, is more effective in the vertical than the horizontal part. Moreover, the differential GPS (DGPS) shows better performance than the standalone GPS when ISED is applied. The analysis results of applying real data to the method using the proposed ISED showed that vertical position errors were conspicuously decreased compared with horizontal position errors, and the performance was excellent for the DGPS. The proposed method is expected to be highly applicable in aircraft takeoff and landing, where the vertical sector is critical.