Abstract
Different from GPS, GLONASS, GALILEO and BeiDou-3, it is confirmed that the code multipath bias (CMB), which originate from the satellite end and can be over 1 m, are commonly found in the code observations of BeiDou-2 (BDS) IGSO and MEO satellites. In order to mitigate their adverse effects on absolute precise applications which use the code measurements, we propose in this paper an improved correction model to estimate the CMB. Different from the traditional model which considering the correction values are orbit-type dependent (estimating two sets of values for IGSO and MEO, respectively) and modeling the CMB as a piecewise linear function with a elevation node separation of 10°, we estimate the corrections for each BDS IGSO + MEO satellite on one hand, and a denser elevation node separation of 5° is used to model the CMB variations on the other hand. Currently, the institutions such as IGS-MGEX operate over 120 stations which providing the daily BDS observations. These large amounts of data provide adequate support to refine the CMB estimation satellite by satellite in our improved model. One month BDS observations from MGEX are used for assessing the performance of the improved CMB model by means of precise point positioning (PPP). Experimental results show that for the satellites on the same orbit type, obvious differences can be found in the CMB at the same node and frequency. Results show that the new correction model can improve the wide-lane (WL) ambiguity usage rate for WL fractional cycle bias estimation, shorten the WL and narrow-lane (NL) time to first fix (TTFF) in PPP ambiguity resolution (AR) as well as improve the PPP positioning accuracy. With our improved correction model, the usage of WL ambiguity is increased from 94.1% to 96.0%, the WL and NL TTFF of PPP AR is shorten from 10.6 to 9.3 min, 67.9 to 63.3 min, respectively, compared with the traditional correction model. In addition, both the traditional and improved CMB model have a better performance in these aspects compared with the model which does not account for the CMB correction.
Highlights
The Chinese BeiDou navigation satellite system is an important constituent part of the Global Navigation Satellite Systems (GNSS)
The inclined geosynchronous orbit (IGSO) satellites are less impacted by the code multipath bias (CMB) than the medium-altitude Earth orbit (MEO) satellites especially at B3 and B2 frequency
These results demonstrated the existence of the CMB difference even for the satellites at the same orbit type
Summary
The Chinese BeiDou navigation satellite system (abbreviated as BDS or BeiDou) is an important constituent part of the Global Navigation Satellite Systems (GNSS). Different from GPS, GLONASS and GALILEO, BDS satellites run in medium-altitude Earth orbit (MEO), and in geostationary orbit (GEO) and inclined geosynchronous orbit (IGSO). BDS is the first satellite system which transmits triple-frequency signals on all satellites in operation. It has already launched a regional navigation service by the end of 2012. (at the beginning of 2018), a total of 14 BeiDou-2 satellites including five GEO, six IGSO, and three MEO satellites is in operation for public use, transmitting triple-frequency signals centered at B1 (1561.098 MHz), B2 (1207.14 MHz), and B3 (1268.52 MHz)
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