Abstract
The regional constellation of the BeiDou navigation satellite system (BDS) has been providing continuous positioning, navigation and timing services since 27 December 2012, covering China and the surrounding area. Real-time kinematic (RTK) positioning with combined BDS and GPS observations is feasible. Besides, all satellites of BDS can transmit triple-frequency signals. Using the advantages of multi-pseudorange and carrier observations from multi-systems and multi-frequencies is expected to be of much benefit for ambiguity resolution (AR). We propose an integrated AR strategy for medium baselines by using the combined GPS and BDS dual/triple-frequency observations. In the method, firstly the extra-wide-lane (EWL) ambiguities of triple-frequency system, i.e., BDS, are determined first. Then the dual-frequency WL ambiguities of BDS and GPS were resolved with the geometry-based model by using the BDS ambiguity-fixed EWL observations. After that, basic (i.e., L1/L2 or B1/B2) ambiguities of BDS and GPS are estimated together with the so-called ionosphere-constrained model, where the ambiguity-fixed WL observations are added to enhance the model strength. During both of the WL and basic AR, a partial ambiguity fixing (PAF) strategy is adopted to weaken the negative influence of new-rising or low-elevation satellites. Experiments were conducted and presented, in which the GPS/BDS dual/triple-frequency data were collected in Nanjing and Zhengzhou of China, with the baseline distance varying from about 28.6 to 51.9 km. The results indicate that, compared to the single triple-frequency BDS system, the combined system can significantly enhance the AR model strength, and thus improve AR performance for medium baselines with a 75.7% reduction of initialization time on average. Besides, more accurate and stable positioning results can also be derived by using the combined GPS/BDS system.
Highlights
Besides the Global Navigation Satellite Systems (GNSS) GPS and GLONASS which have already been operational for a longer time, the Galileo and BeiDou navigation satellite system (BDS) have recently become operational
He [23] tested with real BDS data and concluded that the geometry-free and ionospheric-free (GIF) method was influenced by the large noise amplification factor, and especially limited when multi-path errors exist in carrier phase observations
When using the least-squares ambiguity decorrelation adjustment (LAMBDA) method to search the WL integer ambiguities of BDS and GPS, we choose a stricter threshold of ratio, i.e., 3.0, to ensure the enough reliability, since the WL ambiguities are solved with single-epoch model
Summary
Besides the Global Navigation Satellite Systems (GNSS) GPS and GLONASS which have already been operational for a longer time, the Galileo and BeiDou navigation satellite system (BDS) have recently become operational. He [23] tested with real BDS data and concluded that the GIF method was influenced by the large noise amplification factor, and especially limited when multi-path errors exist in carrier phase observations. Using real BDS observations, Tang et al [24] compared the cascading rounding and integer least-square (ILS)-ased stepwise AR performance, and proposed a modified single-epoch stepwise AR which took the slant ionosphere effect of each satellite into consideration. Real data with baseline distances varying from about 28.6 to 51.9 km, which all contain GPS/BDS dual/triple-frequency observations, are used to test the AR performance of the proposed method. Real data with the baseline distance varying from about 28.6 to 51.9 km, which all contain GPS/BDS dual/triple-frequency observations, are processed in Section 4 (Experimental analysis) to test the performance of the proposed method.
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