## 4 Results
### Ranging Accuracy Analysis  
In this subsection, the ranging accuracies of BDS-3 B2a and B1C according to code signal path differences are analyzed. We processed the measurements from PRN 39 for B2a from 11:05 to 13:40 and PRN 39 for B1C from 12:00 to 13:15, while plotting the code signal path differences and the time distribution of satellite elevation. In addition, the center frequency of the GPS L5C frequency point is the same as that of BDS B2a. We processed its data from 11:05 to 13:09 for comparisons. The corresponding calculation results are shown  
Figure 7: Satellite elevation distribution of B2a PRN 37 satellite code signal path differences STD. the data composition, so they should be regarded as gross errors and discarded. In addition, the data observation duration of BIC is about 1 h shorter than that of B2a. This is because the data point processing results in the selected period of BIC are denser than those in other periods. The variation range of the satellite elevation data is similar to that of B2a, which can more intuitively reflect the distribution of code signal path differences. The observation duration meets the minimum 1 h requirement described in Section 4.1. In this way, the overall characteristics of BIC signal code signal path differences can be seen during this period of time, and the decline in the amount of data will not affect the main conclusions. It is worth noting that there is an obvious overall data deviation in the calculation results of B1C. Except for the BIC signal, the code signal path difference of other signals is between \(-0.5\) m and \(0.5\) m, which means that their ranging accuracy remains basically unchanged. However, compared with other analyzed frequency points, the calculation result of BIC has a very significant deviation from the theoretical value 0 m, and the whole calculation result shows an upward trend. To quantitatively describe this change, the overall code signal path differences RMS, mean value, and STD of each frequency point in the observation processing time can also be calculated. The corresponding processed figures and data results are given in Table 2.  
The RMS, STD, and mean value of satellite data in the whole period are calculated. It has been pointed out in Section 4.2 that there is only a weak negative correlation between satellite elevation and ranging accuracy when the satellite elevation is between \(30^{\circ}\) and \(90^{\circ}\) in our study. Therefore, the influence of satellite elevation can be ignored if the results of long-term observation are used. Moreover, the conclusion of ranging accuracy will not be affected by the number of satellites and processing time. It can be considered that the conclusions drawn from the satellites selected in this experiment are universal. Under the BDS B2a frequency point, the RMS values are 0.1526 m for PRN 37 and 0.1527 m for PRN 39, respectively. We note that BDS B2a covers two satellite orbit types, MEO and IGSO, and their data results are basically consistent. Therefore, the difference of satellite orbit types can be ignored, and it can be considered that the result of ranging accuracy is only related to the signal structure of different frequency point. Under the BDS B1C frequency point, our RMS value is 0.2674. We can note that the RMS value of BIC is lower than the RMS value of B2a. To enhance the comparison of data, we use the same raw IF data and processing method to calculate the code signal path differences of the GPS L5C band. The results show that the ranging accuracy of BDS-3 B2a and GPS L5C are roughly the same, and both of them are significantly better than the ranging accuracy of BIC. For the average value of code signal path differences, the calculation results of GPS L5C and BDS B2a are on the order of \(10^{-2}\) m, while the average value of the BIC signal is 0.1996 m, which is far from the theoretical value of zero. The experimental data also show that B2a and GPS L5C have similar ranging performances.