# Estimating BDS-3 Satellite Differential Code Biases with the Single-Frequency Uncombined PPP Model
## 4 Experimental Results and Analysis
### Satellite DCBs Estimated by SF Data from Single Station
It is important to note that the station names displayed on the horizontal axis of  
Figure 4: The RMS values of the satellite DCB estimates on six selected days. Figure 5 are arranged in descending order from north to south based on the latitude value of each station. To be precise, the first six stations, namely THU2 to GAMG, are situated at latitudes higher than 30\({}^{\circ}\) N, while the last nine stations, namely YAR2 to MAW1, are located at latitudes lower than 30\({}^{\circ}\) S. The remaining stations fall within the latitude range of 30\({}^{\circ}\) N to 30\({}^{\circ}\) S.  
The observed discrepancies in the accuracy of estimated satellite DCBs across different stations, despite utilizing the same estimation method, are evident from the results. Notably, the estimated satellite DCBs display significantly more fluctuations in the low latitude regions. In addition, there are several stations that frequently demonstrate RMS values exceeding 3 ns, particularly those situated within the latitude range of 25\({}^{\circ}\) N to 25\({}^{\circ}\) S. These stations include MKA, PTGG, GUAM, IASC, SEGY, SOLO, DARW, and TONG. This pattern of higher RMS values at these low-latitude stations indicates lower accuracy in the estimated satellite DCBs. The RMS values at low-latitude stations display a significant range of variation, spanning from 1.31 ns to 6.81 ns. This wide range emphasizes the relatively lower reliability of satellite DCB estimates at low-latitude stations. However, it is important to note that on specific days, such as DOY 88 for NNOR and CZTG, and DOY 61 for LCK3, the RMS values of the satellite DCB estimates exceeded 2 ns even at mid- and high-latitude stations. Overall, the RMS values at mid- and high-latitude stations remained below 2 ns, indicating a higher level of accuracy compared to the estimates at low-latitude stations. Based on the repeatability of RMS values across different days, Figure 4 illustrates that, among the mid- and high-latitude stations, there is a higher level of consistency in RMS values for stations located in the Northern Hemisphere, as opposed to those in the Southern Hemisphere. Specifically, the RMS values of stations in the Northern Hemisphere remain around 1 ns, whereas the RMS values of stations in the Southern Hemisphere display a wider range. This feature suggests that the accuracy of the satellite DCB estimates is relatively more stable and consistent in the Northern Hemisphere. Conversely, in the Southern Hemisphere, there may be more variability in the accuracy of the estimates. This phenomenon indicates that ionospheric irregularities are more pronounced in the Southern Hemisphere compared to the Northern Hemisphere. In general, the RMS value of satellite DCB estimates using SF data from a single station is expected to be better than 1 ns, particularly in the Northern Hemisphere. From this perspective, SF receivers are comparable to DF receivers for satellite DCBs estimation. However, ionospheric variability can introduce additional challenges and complexities in ionospheric modeling, potentially leading to increased variability in the accuracy of satellite DCB estimates in the Southern Hemisphere. Figure 5: The RMS values of the satellite DCB estimates for all stations over 30 days.