科研之友
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摘要
To validate the new system design and the new technology of the third-generation BDS (BeiDou-3), five non-GEO experimental satellites were launched during 2015 and 2016. In addition to the B1I and B3I signals that have been emitted by BeiDou-2, three newly designed civil signals (B1C, B2a, and B2b) were first transmitted by these satellites and are planned to be partly applied to the official BeiDou-3 satellites. In this study, the signature of elevation-dependent systematic biases in code measurements, which are commonly observed from BeiDou-2 satellites, was investigated for the three new civil signals based on observations collected using different types of receivers at different locations. Our results show that the RMS of multipath combination residuals of the new civil signal B1C was statistically larger than those of B2a and B2b signals. This indicates that B1C tends to be more seriously affected by multipath effects than B2a and B2b. Furthermore, the station elevation-dependent and satellite nadir- and azimuth-dependent multipath signatures were analyzed in detail. The results show that elevation-dependent variations in code measurements of B1I and B3I signals still exist for BeiDou-2 satellites, including the latest IGSO-6 (C13) launched in 2016. Based on different receivers which are equipped with all-in-view antennas, these types of code biases seem to be absent in the legacy B1C, B2a, and B2b frequency bands for BeiDou-3 in-orbit validation satellites. However, benefited from multipath-free conditions, results from a 40-m dish antenna reveal that the satellite-induced code pseudorange variations still exist in the bands of B1C, B2a, and B2b of BeiDou-3 in-orbit validation satellites, although their variation ranges are only at a level of approximately 0.1 m.
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