Computation of satellite clock–ephemeris corrections using a priori knowledge for satellite-based augmentation system

Abstract

The dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) should be able to provide a vertical protection level in the range of 10---12 m, which is sufficient to support Category I precision approach operations. Because of the limited data rate of the SBAS signal and the need to augment 91 satellites simultaneously, DFMC SBAS does not broadcast equivalent terms for fast pseudorange corrections in legacy L1-only SBAS. An analysis of the wide area augmentation system (WAAS) suggests that the range error after applying long-term satellite error corrections, known as satellite clock---ephemeris (SCE) corrections in DFMC SBAS, is not accurate enough for Category I operations. Thus, it is necessary to improve the accuracy of these SCE corrections. With the construction of DFMC SBAS, there is an opportunity to upgrade the SCE correction algorithm. Based on the fact that the Global Navigation Satellite System SCE parameter-fitting error constitutes the majority of the SCE error, we propose a method of computing the SCE corrections by combining a priori knowledge of the SCE parameter-fitting error with real-time measurements. A comparison of the user range error after applying WAAS SCE corrections and fast corrections indicates that the proposed method extends the period when a satellite is augmented by 22.9 % and reduces the root mean square error by 27 %.