# Phase Center Corrections for BDS IGSO and MEO Satellites in IGb14 and IGSR3 Frame
## 4 Results and Validation
### Validation
#### 4.4.2 Coordinates  
A BDS-only precise point positioning (PPP) was performed using the three sets of daily orbit and clock parameters from the global network solutions determined in the last subsection. Furthermore, two sets of GPS-only PPP were also performed with the  
Figure 6: Influences of the three kinds of antenna models on orbit boundary disclosure for BDS satellites. The solution based on the isg14_2102.txt antenna model is represented as IGS. The BDS orbit solutions using new satellite antenna PCCs are represented as F14 as well as FR3. orbits and clocks determined within IGb14 and IGSR3 frame, respectively. The daily station coordinates, hourly constant tropospheric zenith pass delay, carrier phase ambiguities and epoch-wise receiver clocks were solved. Coordinatingly, three BDS-only (BDS-IGS, BDS-F14, and BDS-FR3), as well as two GPS-only solutions (GPS-F14 and GPS-FR3), were obtained. The seven-parameter Helmert transformations were carried out to compare the BDS-IGS, BDS-F14, and GPS-F14 PPP-derived coordinates with the IGS legacy daily final estimates in IGb14 frame, whereas the GPS-FR3 and BDS-FR3 solutions were compared to the initial combined coordinates of the third IGS reprocess, available at [[ftp://igs-rf.ign.fr/pub/repro3_tests/2008-2019/IGS1R03](ftp://igs-rf.ign.fr/pub/repro3_tests/2008-2019/IGS1R03) TST/]([ftp://igs-rf.ign.fr/pub/repro3_tests/2008-2019/IGS1R03](ftp://igs-rf.ign.fr/pub/repro3_tests/2008-2019/IGS1R03) TST/) (accessed on 30 December 2020), with Helmert transformations. The scale parameters obtained from the Helmert transformations gave the assessment of consistency of the GPS- and BDS-derived station heights with respect to IGb14 as well as IGSR3 frame. The scale bias between the GPS- and BDS-only PPP coordinates and the IGb14 and IGSR3 reference frame are shown in Figure 7.  
We clearly noticed a significant bias for BDS-IGS PPP solutions, whereas it was significantly reduced when applying BDS F14 PCC estimates. The mean scale parameter of the BDS-IGS and BDS-F14 solutions was \(+0.446\,\pm\,0.153\) ppb and \(+0.012\,\pm\,0.111\) ppb, respectively. It clearly demonstrated that the discrepancy between BDS-derived station heights with IGS recommended PCCs and IGS legacy solutions decreased when the new BDS satellite antenna corrections were introduced. For the GPS-F14 PPP solution, there was a bias up to \(-0.102\,\pm\,0.084\) ppb, close to the scale inconsistency between our software and the IGS antenna model. Previously, [PERSON] [14] estimated the PCCs for GPS with 31 days data from 145 ground stations and demonstrated that the averaging Z-PCO difference between the estimated and IGS recommended one was \(14.5\,\mathrm{mm}\), equivalent to \(-0.095\,\mathrm{ppb}\). Hence, we believe the scale inconsistency between PANDA and IGS antenna model is within a level of \(-0.1\,\mathrm{ppb}\), and is possibly caused by the data processing strategy used, as well as the minor inconsistency of error models in the software. Without a doubt, this inconsistency will be assimilated into the BDS PCO estimation. However, its impact is minor, compared to the agreement (about 4 cm) between the two GPS PCO solutions estimated by GFZ and Technische Universitat Munchen (TUM) [4], as well as the accuracy (a few cm) of the IGS antenna model [30]. Furthermore, the residuals of the BDS-derived station heights (after the  
Figure 7: Scale bias between the GPS- and BDS-only precise point positioning (PPP) coordinates and the IGb14 (**up**) and IGSR3 (**bottom**) reference frame. The GPS- and BDS-only solutions based on the igs14_2102_atx antenna model and GPS-only with igsR3_207.4x are represented as GPS-F14 as well as BDS-IGS, and GPS-FR3 respectively. The BDS-only solutions using new satellite antenna PCCs are represented as BDS-F14 as well as BDS-FR3. Helmert transformation) were slightly reduced from 9.65 to 8.62 mm for the BDS-IGS and BDS-F14 solutions.