## 4 Results  
### Satellite and the Acquisition of Data  
The time range of the experimental data collection is 11:02 to 18:00 on 7 March 2022 (Beijing time). Data processing and analysis shall be carried out within the time range when the satellite elevation meets the requirements. Our selected satellite elevation mainly ranges from 30\({}^{\circ}\) to 70\({}^{\circ}\), and the satellite elevation can be calculated from the satellite's broadcast ephemeris. The duration of raw IF data used for the data processing shall be greater than 1 h to ensure the effectiveness of the analysis results. When selecting the period, we try to ensure that the elevation of the selected satellite is within a certain similar range, so as to reduce the impact of satellite elevation when analyzing the ranging accuracy alone under a specific PRN. At the same time, considering the slow processing speed of SDR and the huge storage space required for data results, we basically choose an interval of 1 to 3 h for further processing, which not only ensures that the satellite elevation conditions are met, but also ensure the processing process is not too long. As the structure of the ranging code broadcasted from a satellite system is similar under a frequency point, the ranging performance of the system can be reflected by processing at least one set of satellite data, and the conclusion is not affected by the number of satellites and satellite orbit type. Therefore, only limited satellite data have been processed and analyzed in our research. The signals from satellites with PRN 37 (MEO) and PRN 39 (IGSO) were used for the ranging accuracy analysis of B2a. The satellite with PRN 37 is an MEO satellite. Its satellite elevation has a large variation range, so we can also collect and process its data for a long time to study the relationship between ranging accuracy and the satellite elevation. When processing B1C frequency points, we use satellite PRN 39 for data processing, which is consistent with the selection of B2a satellites. This is an IGSO satellite, which can ensure a high satellite elevation and a long time in the observation period. At the same time, thanks to the good interoperability and compatibility of BDS-3, the B2a is consistent with the center frequency of GPS LSC. Therefore, we use the same raw IF signal to analyze the ranging accuracy of LSC PRN 4 for comparison with the BDS-3. GPS PRN 4 satellite is also an MEO satellite, which has a large range of elevation changes. We can use this satellite to compare the ranging performance of the GPS L5 with that of the BDS-3 frequency point of B2a and B1C. In the experiment, the zero-baseline experimental environment can only ensure that all conditions are consistent before the signal is connected to each channel of the IF signal recorder. There are four channels and two crystal oscillators in our recorder. Two of the channels share one crystal oscillator and a frequency point, while four channels share a clock. So, the bias between the channels at the same frequency point is small. In our work, the path difference between two channels at the same frequency point are calculated to investigate the accuracy of the ranging code. Therefore, in the data processing, we ignore the system error of the receiver and consider the hardware delay equal in each signal channel. We calculate the code signal path differences directly after mapping the waveform figure as Figure 3. By analyzing the solutions in Table 2, we find that there is no bias for the two channels at the frequency of 1176.45 MHz, while there is a 26 cm bias for the two channels at the frequency of 1575.42 MHz. When signals of all channels are processed by the GNSS-SDR according to Figure 4, the coherence integration time is set as 10 ms to enhance the signal-to-noise ratio. After processing 10 ms data, the complete waveform data can be obtained, and the code signal path differences can be calculated by the differences between the extreme values of the waveform.