## 3 Data and Processing Strategy  
We first assessed the proposed method using 66 stations with identical hardware configurations from the Crustal Movement Observation Network of China [26]. All these stations are equipped with the same receiver (Trimble NetR8, Sunnyvale, California, USA) and antenna (TRM59800.00 SCIS, Sunnyvale, California, USA) types. Therefore, after neglecting the unit variations, we can assume that these receivers have comparable code IFB, and GLONASS PPP-IAR can thus be performed without considering IFCB corrections. This allows a control-group experiment to assess the proposed IFCB estimation strategy. Three weeks (covering days of year (DOY) 1-21 in 2013) of data collected at sampling interval 30 s were processed. 26 stations were used as base stations to generate the UPD products and the remaining 40 stations were used as rover stations to perform PPP-IAR. Figure 1 shows the distribution of these stations. We also selected 18 base stations with the same hardware configuration to generate UPDs, and 28 rover stations with diverse hardware configurations to assess the performance of the proposed method. Both the base and rover stations are located in France. All base stations are equipped with Trimble NetR5 receivers, whereas the rover stations have Trimble, Leica and TPS receivers plus a variety of antennas, domes, and firmware versions. Detailed information about the base and rover stations is given in Table 1. The distribution of the stations is shown in Figure 2. Data covering DOY 1-21 in 2013 with sampling interval 30 s were processed. The proposed strategy was implemented in Positioning and Navigation Data Analyst (PANDA) software [33], developed at Wuhan University, to process GPS + GLONASS data. The absolute phase center correction, phase wind-up effects, and station displacement models proposed by \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{1}{c}{**Manufacturer**} & **Receiver** & **Antenna** & **Dome** & **Firmware** & **Number** \\ \hline Base & Trimble & NET85 & TRM55971.00 & NONE & 4.41 & 18 \\ \hline \multirow{7}{*}{Rover} & \multirow{7}{*}{Trimble (Sunnyvale, California, USA)} & \multirow{7}{*}{NET8} & \multirow{7}{*}{TRM55971.00} & \multirow{7}{*}{NONE} & 4.19 & 1 \\  & & & & 4.48 & 3 \\  & & & & 4.42 & 3 \\ \cline{1-1}  & & & & 4.48 & 1 \\ \cline{1-1}  & & & & 4.61 & 1 \\ \cline{1-1}  & & & & 4.60 & 2 \\ \cline{1-1}  & & & & 4.60 & 1 \\ \hline \multirow{7}{*}{Rover} & \multirow{7}{*}{Leica (Heerbrugg, Switzerland)} & GR10 & LEIAS10 & NONE & 1.10 & 2 \\  & & LEIAR25 & LEIT & 2.00/4.007 & 1 \\ \cline{1-1}  & & & & 2.00/4.007 & 1 \\ \cline{1-1}  & & & & 7.8 & 1 \\ \cline{1-1}  & & & & 7.8 & 1 \\ \cline{1-1}  & & & & 7.5 & 4 \\ \cline{1-1}  & & & LEIAT504 GG & LEIS & 2.62 & 1 \\ \cline{1-1}  & & & & LEIAT504 GG & LEIS & 5.10 & 1 \\ \hline \multirow{2}{*}{TTS (Tokyo, Japan)} & \multirow{2}{*}{NETG3} & \multirow{2}{*}{TPSCR.G3} & \multirow{2}{*}{TPSH} & 4.0 & 3 \\  & & & & 3.4 & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Detailed information about hardware configuration for 18 base stations and 29 rover stations. Figure 1: Distribution of homogeneous stations used in China. Figure 2: Distribution of 18 base stations and 29 rover stations used in France. IERS conventions 2003 were applied. The a priori tropospheric zenith delays were calculated with the Saastamoinen model [34] and mapped into the slant ones with the global mapping function [35]. Eclipsing GPS and GLONASS satellites were deleted to avoid the effect of poorly modeled satellite attitudes. The final GPS/GLONASS orbit and clock products from the European Space Agency/European Space Operations Centre IGS analysis center [36] were fixed in both the UPD estimation and PPP-IAR. A priori precisions of 1 and 0.01 m were used for the IF code and carrier phase observations respectively. A cutoff angle of 7\({}^{\circ}\) was set for the GPS and GLONASS, and an elevation-dependent weighting strategy was used to weight measurements.