# BDS-3 Time Group Delay and Its Effect on Standard Point Positioning
## 3 Experimental Data and Processing Strategies
### Bds-3
Interestingly, we note that the noise in the dual-frequency positioning errors is greater than that in the single-frequency positioning errors. We surmise that this finding may be attributed to the fact that noise is magnified in the dual-frequency SPP scheme [10]. Figure 22 shows box-whisker diagrams of the distributions of the positioning errors in the tgd-corr and non-corr schemes for the six stations for the 41-day period. The outliers, first quartile, third quartile and inter-quartile range in the distribution in the figure are as stated before. There are three findings highlighted here. First, it is obvious in the figure that the number of outliers at each station is very small, which further proves that positioning using BDS is reliable. Second, unlike for BDS-2, the positioning errors for all stations are basically similar; thus, we can conclude that BDS-3 eliminated the regional limitation characteristics of BDS-2. Third, including the BRCH station, the medians and 75 th percentiles from the \"tgd-corr\" scheme at all stations is less than 10 m. For the \"non-corr\" scheme, the medians and 75 th percentiles are much larger than those from the \"tgd-corr\" scheme, which proves that the TGD parameters need to be corrected for BDS-2 positioning. Figure 18: Horizontal positioning error scatter plots of B1I/B3I SPP with and without TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the E component error and the N component error, respectively (unit: m). Figure 19: Vertical positioning error scatter plots of B1I/B3I SPP with and without TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the universal time (h) and the U component error, respectively (unit: m). Figure 20: Horizontal positioning error scatter plots of BIC/B2a SPP with and without TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the E component error and N component error, respectively (unit: m). Figure 21: Vertical positioning error scatter plots of B1C/B2a SPP with and without TGD correction for the six selected stations. In each plot, the horizontal and vertical axes indicate the universal time (h) and the U component error, respectively (unit: m). Figure 13:0 _Cont._  
To further quantify the positioning accuracy, we give the RMS values for the daily single- and dual-frequency positioning errors with and without TGD correction for the BRCH station, displayed in Figures 23 and 24. In the two figures, it is clearly shown that both the single- and dual-frequency positioning accuracy values with TGD correction are better than those without TGD correction. The positioning accuracy of BIC- and B2a-based BDS-3 SPP is similar to that of B1I- and B3I-based SPP. The above results can be further demonstrated in Figure 25, showing the improvement in the E, N and U components from the \"tgd-corr\" scheme compared to that from the \"non-corr\" scheme at different stations. First, we consider the single-frequency positioning accuracy. Taking the B1C signal as an example, the horizontal positioning accuracy with the \"tgd-corr\" scheme is more than 50% higher than that with the \"non-corr\" scheme, and the vertical positioning accuracy is improved by more than 25%. The B1I- and B2a-based SPP results at other stations show similar features to those of the B1C signal; we will not describe them in detail herein. Second, for the positioning accuracy of BIC/B2a- and B1I/B3I-based SPP, the horizontal positioning accuracy based on the \"tgd-corr\" scheme compared to the \"non-corr\" scheme improved in the range of 33.93% to 85.08%, and the vertical positioning accuracy was improved in the range of 30.12% to 59.19%. We also calculated the means of the RMSs at different frequencies and different schemes for 41 days at the six stations (Table 6). The empirical analysis of the obtained results yielded three conclusions.