Guo Fei, Li Xin, Liu Wanke
School of Geodesy and Geomatics, Wuhan University, Wuhan 430079, China.
Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, Wuhan 430079, China.
Sensors (Basel). 2016 Jun 18;16(6):909. doi: 10.3390/s16060909.
The BeiDou satellite-induced code biases have been confirmed to be orbit type-, frequency-, and elevation-dependent. Such code-phase divergences (code bias variations) severely affect absolute precise applications which use code measurements. To reduce their adverse effects, an improved correction model is proposed in this paper. Different from the model proposed by Wanninger and Beer (2015), more datasets (a time span of almost two years) were used to produce the correction values. More importantly, the stochastic information, i.e., the precision indexes, were given together with correction values in the improved model. However, only correction values were given while the precision indexes were completely missing in the traditional model. With the improved correction model, users may have a better understanding of their corrections, especially the uncertainty of corrections. Thus, it is helpful for refining the stochastic model of code observations. Validation tests in precise point positioning (PPP) reveal that a proper stochastic model is critical. The actual precision of the corrected code observations can be reflected in a more objective manner if the stochastic model of the corrections is taken into account. As a consequence, PPP solutions with the improved model outperforms the traditional one in terms of positioning accuracy, as well as convergence speed. In addition, the Melbourne-Wübbena (MW) combination which serves for ambiguity fixing were verified as well. The uncorrected MW values show strong systematic variations with an amplitude of half a wide-lane cycle, which prevents precise ambiguity determination and successful ambiguity resolution. After application of the code bias correction models, the systematic variations can be greatly removed, and the resulting wide lane ambiguities are more likely to be fixed. Moreover, the code residuals show more reasonable distributions after code bias corrections with either the traditional or the improved model.
北斗卫星诱导码偏差已被证实与轨道类型、频率和仰角有关。这种码相位偏差（码偏差变化）严重影响使用码测量的绝对精密应用。为了减少其不利影响，本文提出了一种改进的校正模型。与Wanninger和Beer（2015）提出的模型不同，本文使用了更多数据集（近两年的时间跨度）来生成校正值。更重要的是，在改进模型中，随机信息即精度指标与校正值一起给出。然而，传统模型只给出了校正值，而精度指标则完全缺失。使用改进的校正模型，用户可以更好地理解他们的校正，特别是校正的不确定性。因此，这有助于完善码观测的随机模型。精密单点定位（PPP）中的验证测试表明，合适的随机模型至关重要。如果考虑校正的随机模型，可以更客观地反映校正后码观测的实际精度。因此，使用改进模型的PPP解在定位精度和收敛速度方面均优于传统模型。此外，还对用于模糊度固定的墨尔本-伍本纳（MW）组合进行了验证。未校正的MW值显示出强烈的系统变化，幅度为半个宽巷周期，这妨碍了精确的模糊度确定和成功的模糊度解算。应用码偏差校正模型后，系统变化可以大大消除，由此产生的宽巷模糊度更有可能被固定。此外，使用传统模型或改进模型进行码偏差校正后，码残差显示出更合理的分布。
