## 6 Experimental Verification and Analysis
### Analysis of Inter-Satellite Ranging Accuracy  
This section analyzed the accuracy of inter-satellite pseudo-code ranging. First, the experimental simulation condition for pseudo-code ranging is provided, with specific parameter values shown in Table 9. Due to the rapid variation in inter-satellite distances and the significant Doppler shift between satellites, directly acquiring and tracking received signals is challenging. Therefore, navigation ephemeris data are often utilized to assist in practical inter-satellite link measurements. Since the navigation ephemeris can provide satellite positional accuracy at the meter level and velocity calculation precision of 0.1 mm/s, for an inter-satellite carrier frequency of 23 GHz and a code rate of 10.23 MHz, the corresponding delay and Doppler uncertainty regions are confined within half a code chip and 1 Hz, respectively. This allows the system to bypass the acquisition phase and pro  
Figure 13: Carrier-to-noise ratio at the receiver in the case of transmission power variations. ceed directly to the tracking phase. In this experiment, the delay and Doppler uncertainty regions are set to 0.5 code chips and 1 Hz, respectively, meeting the practical requirements of inter-satellite measurements. To evaluate the performance enhancement of pseudo-code ranging in CCFD, this experiment developed a MATLAB-based digital simulation platform for inter-satellite measurement. The tracking subsystem implemented a carrier-aided code loop architecture to compensate for dynamic stress effects, featuring a non-coherent early-late power discriminator for code tracking and a dot product phase detector for carrier recovery. Considering the brief link establishment window characteristic of BDS-3 ISLs and the stringent temporal requirements for signal ranging, the experiment configured 1.5 s and 3 s as the ranging time thresholds for TDHD and CCFD systems, respectively. The reason for selecting 3 s as the measurement duration in CCFD is that the regime supports uninterrupted measurements in each time slot, so the total length of the time slot can be selected as the measurement duration. The experimental outcomes are presented in Figures 14 and 15, demonstrating the comparative performance between operational modes. Figure 14: Comparison of ranging accuracy between CCFD and TDHD modes at a carrier-to-noise ratio of 61.6 dBHz. \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **Description** & **Value** & **Unit** \\ \hline \(f_{code}\) & Pseudo-code rate & 10.23 & MHz \\ \(f_{BDS\_ISL}\) & Carrier frequency & 23 & GHz \\ \(f_{d}\) & Doppler shift uncertainty region & 1 & Hz \\ \(\tau_{d}\) & Code delay uncertainty region & 0.5 & chip \\ \(B_{L}\) & Noise band of the carrier loop & 25 & Hz \\ \(d\) & Correlation interval & 0.5 & \\ \(T_{coh}\) & Coherent integration time & 2 & ms \\ \(T_{non\_coh}\) & Non-coherent integration times & 3 & \\ \(G_{carrier}\) & Carrier loop gain & 0.01 & \\ \(G_{code}\) & Code loop gain & 0.01 & \\ \(C/N_{0}\) & Carrier-to-noise ratio & 61.6\(-\)69.3 & dBHz \\ \hline \end{tabular}
\end{table} 
Table 9: The key parameter values for the BDS-3 ISL pseudo-code ranging. According to the experimental simulation conditions, under the CCFD and TDHD schemes, selecting code loop equivalent noise bandwidths \(B_{n}\) of 2 Hz and 5 Hz, respectively, can achieve better ranging accuracy and convergence performance. Figures 14 and 15 present the simulation results of pseudo-code ranging accuracy under the two schemes at the maximum \(C/N_{0}\) of 69.3 dBHz and the minimum \(C/N_{0}\) of 61.6 dBHz, respectively. Analysis of the results indicates that the signal can achieve rapid convergence and stabilization within a short time under the simulated conditions. The last 20% of the time segment was selected for evaluating the ranging accuracy, and the results are summarized in Table 10.  
Analysis of the experimental results reveals that at a \(C/N_{0}\) of 61.6 dBHz, the 1\(\sigma\) ranging accuracy is 1.9 cm under the CCFD scheme and 3.9 cm under the TDHD scheme.