An Improved Multi-Satellite Method for Evaluating Real-Time BDS Satellite Clock Offset Products

Abstract

Two methods are widely used for evaluating the precision of satellite clock products, namely the single-satellite method (SSM) and the multi-satellite method (MSM). In the satellite clock product evaluation, an important issue is how to eliminate the timescale difference. The SSM selects a reference satellite to eliminate the timescale difference by between-satellite differencing, but its evaluation results are susceptible to the gross errors in the referenced satellite clock offsets. In the MSM, the timescale difference is first estimated and then removed. Unlike the GPS, the BeiDou Navigation Satellite System (BDS) consists of three types of satellites, namely geosynchronous earth orbit (GEO), inclined geosynchronous orbit (IGSO), and medium earth orbit (MEO) satellites. The three types of satellites have uneven orbital accuracy. In the generation of satellite clock products, the orbital errors are partly assimilated into the clock offsets. If neglecting the orbital accuracy difference of the three types of BeiDou satellites, the MSM will obtain biased estimates of the timescale difference and finally affect the clock product evaluation. In this study, an improved multi-satellite method (IMSM) is proposed for evaluating the real-time BDS clock products by removing the assimilated orbital errors of the three types of BDS satellites when estimating the timescale difference. Three real-time BDS clock products disseminated by three different International GNSS Service (IGS) analysis centers, namely CLK16, CLK20, and CLK93, over a period of two months are used to validate this method. The results indicate that the assimilated orbital errors have a significant impact on the estimation of the timescale difference. Subsequently, the IMSM is compared with the SSM in which the referenced satellite is rigorously chosen, and their RMS difference is only 0.08 ns, which suggests that the evaluation results obtained by the IMSM are accurate. Compared with the traditional MSM, the IMSM improves the RMS by 0.16, 0.11, and 0.07 ns for CLK16, CLK20, and CLK93, respectively. Finally, three real-time BDS clock products are evaluated using the proposed method, and results reveal a significant precision difference among them.

Research on BeiDou Satellite Positioning Algorithm Based on GPRS Technology

“…Since the RTK model constructed in Section 2.3 cannot eliminate the error and multipath error caused by the relativistic effect, a new method is presented in this section to measure the calculated pseudorange of the carrier phase [17].…”

“…Based on the concept of the composition, positioning algorithm, and positioning error of the BeiDou Satellite Navigation System, the ephemeris error, ionospheric error, and tropospheric error in the navigation system positioning are analyzed in-depth, to reduce the ephemeris error. A single-point positioning error compensation method based on a dual-frequency combined ionospheric deionization model for ionospheric errors and a high-precision regional fusion model for reducing tropospheric errors are presented [17]. ere is a certain error between the theoretical position of the satellite and the actual position in the actual situation, that is, the satellite orbit difference of the broadcast ephemeris (also known as the satellite orbit deviation).…”

Real-time prediction of the approximate non- homogeneous white exponential law BDS clock bias sequences: modelling and strategy

“…There are currently three kinds of BDS real-time clock bias products available. Among them, the clock bias product of broadcast ephemeris is a set of satellite clock parameters broadcasted by the system every hour, and users can make quadratic polynomial fitting according to the parameters to achieve clock bias prediction, with an accuracy of about 10 ns [10][11] . The ultra-rapid predicted clock bias product provided by the GNSS monitoring and assessment system (iGMAS) is updated every 6 hours, using observation data from the previous 24 hours (with an observation accuracy of about 0.5 ns) to predict the clock bias for the next 24 hours (with a prediction accuracy of about 2 ns to 6 ns), although it is more accurate than the broadcast ephemeris [12][13] , it still cannot meet the requirement of real-time decimeter-level positioning and high-precision timing.…”