As the development of the global navigation satellite system (GNSS), the navigation satellite transmitting multi-frequency signals becomes a prevailing trend. Currently, the usual GNSS precise orbit determination (POD) strategy uses dual-frequency (DF) ionosphere-free (IF) linear combination to build up the observation equation. In the area of precise positioning, it has been validated that the third frequency can decrease the convergence time of ambiguity resolution and has a subtle improvement on the positioning accuracy. However, there is no report about the benefits of the third frequency on GNSS POD. Although the precision of dual-frequency POD can meet requirements for generating different types of products, an obvious advantage of multi-frequency observations is that more robust results can be derived. Besides, with the third frequency observations, the improvements of orbits and clocks need to be validated. Thus, a triple-frequency (TF) uncombined (UC) POD method of GNSS satellites is developed. The hardware delay of carrier phase is divided by time-invariant and -variant components. Then the UC observation model is given by re-parameterizing the unknown parameters. The datum of satellite clocks is aligned to IGS products. The step-by-step ambiguity fixing method, i.e. the extra-wide-lane, wide-lane and narrow-lane ambiguities being fixed in sequence, is deduced by using double-differenced ambiguities in a network. We select 74 ground stations and 12 GPS BLOCK IIF satellites to process POD with a length of 20 days. Results of TF-UC POD show that about 10% improvements on orbits and clocks are received compared to L1/L2 DF-IF POD. The time-variant characteristic of phase biases from satellites and stations at the third frequency is analyzed, which shows that the bias at the station has a slight influence on the derived products. These results imply that the precision of orbits and clocks can be improved with observations from the third frequency added.

随着全球导航卫星系统（GNSS）的发展，发射多频信号的导航卫星成为一种主流趋势。当前，常规的GNSS精确轨道确定（POD）策略使用双频（DF）无电离层（IF）线性组合来建立观测方程。在精确定位方面，已经证实第三频率可以减少歧义分辨率的收敛时间，并且在定位精度上有细微的提高。但是，没有关于第三频率对GNSS POD的好处的报道。尽管双频POD的精度可以满足生成不同类型产品的要求，但多频观测的明显优势是可以得出更可靠的结果。除了，在第三次频率观测中，需要验证轨道和时钟的改进。因此，开发了GNSS卫星的三频（TF）非组合（UC）POD方法。载波相位的硬件延迟除以时不变和时变分量。然后通过重新参数化未知参数来给出UC观测模型。卫星时钟的基准与IGS产品对齐。通过在网络中使用双差歧义来推导逐步歧义固定方法，即按顺序固定超宽歧义，宽狭义歧义和窄狭义歧义。我们选择了74个地面站和12个GPS BLOCK IIF卫星来处理时间为20天的POD。TF-UC POD的结果表明，与L1 / L2 DF-IF POD相比，在轨道和时钟上的接收率提高了约10％。分析了卫星和台站在第三频率处的相位偏置的时变特性，这表明台站的偏置对导出的乘积影响很小。这些结果表明，通过增加第三个频率的观测结果，可以提高轨道和时钟的精度。