BDS-3 currently has 28 operational satellites in orbit, of which 27 IGSO/MEO satellites provide open services on five frequencies simultaneously. In particular, the linear combinations of the BDS-3 B1C/B1I/B2a signals have significant benefits in reducing the influence of ionospheric delay error as well as improving ambiguity estimation and positioning accuracy. The presented optimal ionosphere-free combination (242, 218, − 345) and ionosphere-reduced combination (2, 2, − 3) can improve the measurement accuracy by about 20% compared to the BDS-3 B1C/B2a or GPS L1/L5 dual-frequency combination. The ionosphere-reduced combination (2, 2, − 3) with a wavelength of 10.9 cm is almost immune to the ionospheric delay error and has a smaller noise amplification factor compared to the existing dual-frequency combinations. Therefore, its combined ambiguities can be fixed directly even in the case of a long baseline, which can simplify the traditional precise positioning process based on the ionosphere-free combination. The numerical results of BDS-3 real data show that the triple-frequency ionosphere-free or ionosphere-reduced combinations can improve the single-point positioning accuracy by 16–20% and the phase differential positioning accuracy by 7–9%, respectively. The ambiguity resolution of the ionosphere-reduced combination (2, 2, − 3) is achieved with a fixing rate of 88.4% over long baseline up to 1600 km. The presented ionosphere-free and ionosphere-reduced combinations are also very promising to be applied in current PPP applications to simplify the ambiguity fixing process as well as improve positioning accuracy and shorten convergence time.

中文翻译：

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BDS-3 B1C / B1I / B2a三频信号对精确定位和歧义度分辨率的好处

BDS-3目前有28颗在轨运行卫星，其中27颗IGSO / MEO卫星同时在五个频率上提供开放服务。特别地，BDS-3 B1C / B1I / B2a信号的线性组合在减少电离层延迟误差的影响以及改善歧义估计和定位精度方面具有显着优势。与BDS-3 B1C / B2a或GPS L1 /相比，提出的最佳无电离层组合（242、218，-345）和减少电离层组合（2、2，-3）可以将测量精度提高约20％。 L5双频组合。与现有的双频组合相比，波长为10.9 cm的电离层缩减组合（2，2，-3）几乎不受电离层延迟误差的影响，并且噪声放大系数较小。因此，即使在基线较长的情况下，其组合模糊度也可以直接固定，这可以简化基于无电离层组合的传统精确定位过程。BDS-3真实数据的数值结果表明，无三点电离层或电离层减少的组合可以分别将单点定位精度提高16–20％，将相位差定位精度提高7–9％。减少电离层的组合（2、2，-3）的歧义分辨率可在长达1600 km的长基线上达到88.4％的固定率。提出的无电离层和减少电离层的组合也非常有希望用于当前的PPP应用中，以简化歧义固定过程，提高定位精度并缩短收敛时间。