The short-term variability in receiver code biases (RCBs) has been identified as a prominent source of error leading to the degradation of precise point positioning (PPP) performance and ionospheric total electron content (TEC) estimation accuracy. To minimize the adverse impact of RCB variability, this study extends the modified PPP (MPPP) method from the GPS only dual-frequency (DF) model to multifrequency (MF) and multiconstellation cases. In the MF MPPP method, multi-GNSS (GPS, BDS and Galileo) dual-, triple- or even arbitrary-frequency observations can be jointly processed in a flexible and reliable way by taking the time-varying RCBs of all available signals into account. Benefiting from this, the between-epoch fluctuations experienced by RCBs for all constellations and frequencies can be detected and their adverse impacts on the ionospheric observables and ambiguity parameters are mitigated. Compared to the traditional MF PPP method, the retrieval accuracy of the multi-GNSS-based ionospheric observables using our proposed method can be improved by more than 74% in the presence of significant intraday RCB variations. The variation trends are not always consistent for RCBs in different frequency bands for different satellite systems. The dependence of multi-GNSS and MF RCB variations on the ambient temperature is also verified. The percentages of the stations analyzed with the absolute Pearson correlation coefficient (PCC) values above 0.8 for BDS are higher than those of GPS and Galileo, and the temperature dependence of RCB on the second frequency band is higher than those of the first frequency band for all the three constellations.

接收器代码偏差 (RCB) 的短期变化已被确定为导致精确单点定位 (PPP) 性能和电离层总电子含量 (TEC) 估计精度下降的重要误差源。为了最大限度地减少 RCB 变异的不利影响，本研究将改进的 PPP (MPPP) 方法从仅 GPS 双频 (DF) 模型扩展到多频 (MF) 和多星座情况。在MF MPPP方法中，通过考虑所有可用信号的时变RCB，可以灵活可靠地联合处理多GNSS（GPS、BDS和Galileo）双频、三频甚至任意频观测。受益于此，可以检测到所有星座和频率的 RCB 经历的历元波动，并减轻它们对电离层可观测值和模糊度参数的不利影响。与传统的MF PPP方法相比，在存在显着日内RCB变化的情况下，使用我们提出的方法基于多GNSS的电离层观测量的反演精度可以提高74%以上。不同卫星系统不同频段的RCB的变化趋势并不总是一致的。多 GNSS 和 MF RCB 变化对环境温度的依赖性也得到了验证。北斗系统分析的绝对皮尔逊相关系数（PCC）值大于0.8的台站比例高于GPS和伽利略系统，且RCB对第二频段的温度依赖性高于第一频段。所有三个星座。