## 6 Experimental Verification and Analysis
### Analysis of Inter-Satellite Link Budget  
Based on the BDS-3 topological characteristics, we proceed to analyze the link budget. Table 7 presents the key parameter values for the BDS-3 ISL link budget.  
The system noise temperature \(T_{s}\) noise power spectral density \(N_{0}\), noise power \(N\), required normalized signal-to-noise ratio \(\left(E_{b}/N_{0}\right)_{req}\), and required carrier-to-noise ratio \(\left(C/N_{0}\right)_{req}\) can be calculated using Equations (15), (16), (18) and (19). The computed parameter values are presented in Table 8.  
To meet the system's BER requirements while minimizing the demand for CCFD self-interference cancellation, the transmission power for BeilDou ISL signals was analyzed to determine the optimal power level. This experiment evaluated a transmission power sequence of [25 W, 30 W, 35 W, 40 W, 45 W, 50 W]. Figure 13 illustrates the carrier-to-noise ratio at the receiver in the case of transmission power variations.  
The threshold value is set as the required carrier-to-noise ratio \(\left(\left(C/N_{0}\right)_{req}\right)\) calculated in Table 8, i.e., 61.31 dBHz. It can be seen that in the whole process of ISL measurement, to satisfy the received carrier-to-noise ratio is always greater than the required carrier-to-noise ratio, the transmit power of the signal is selected as the most appropriate 35 W, and the range of the satellite received carrier-to-noise ratio in this case is 61.6 dBHz--69.3 dBHz. When the link margin is 0, the minimum transmit power can be derived as 33.5223 W using  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Unit** \\ \hline \(f_{BDS\_ISL}\) & 23 & GHz \\ G\({}_{t\_BDS}\) & 35 & dBi \\ \(C_{r\_BDS}\) & 35 & dBi \\ \(L_{S\_BDS}\) & 2 & dB \\ \(L_{N\_BDS}\) & 2 & dB \\ \(L_{P\_BDS}\) & 1 & dB \\ \(L_{D\_BDS}\) & 0.3 & dB \\ \(\bar{B}_{f}\) & 20.46 & MHz \\ \(F\) & 4 & dB \\ \(T_{a}\) & 100 & K \\ \(T_{0}\) & 290 & K \\ \(R_{b\_ISL}\) & 100 & kbps \\ \(L_{M}\) & 3 & dB \\ \(P_{b}\) & \(10^{-7}\) & \(\backslash\) \\ \hline \hline \end{tabular}
\end{table}
Table 7: The key parameter values for the BDS-3 ISL link budget.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Unit** \\ \hline \(T_{s}\) & 964.51 & K \\ \(N_{0}\) & \(-198.76\) & \(\text{dBW}/\text{Hz}\) \\ \(N\) & \(-125.65\) & dBW \\ \(\left(E_{b}/N_{0}\right)_{req}\) & 11.31 & dB \\ \(\left(C/N_{0}\right)_{req}\) & 61.31 & dBHz \\ \hline \hline \end{tabular}
\end{table}
Table 8: The computed parameter values for the BDS-3 ISL link budget.  
Equation (21). Theoretically, any transmit power exceeding this value would satisfy the requirements for inter-satellite measurement and communication. In this study, a transmit power of 35 W is selected, resulting in a link margin of approximately 0.187 dB, which meets practical application scenarios.  
If the CCFD technology is introduced into the BDS-3 ISL communication and measurement system, it is necessary to ensure that the self-interference signal received at the satellite receiver can be suppressed below the receiver's noise floor, thereby avoiding any impact on normal inter-satellite communication and measurement. The self-interference signal is transmitted through the antenna and directly received by the receiving antenna. By comprehensively considering factors such as transmission circuit loss and polarization loss, the required self-interference suppression amount for the system can be calculated as follows:  
\[[C]=[P_{t\_BDS}]+[G_{t\_BDS}]-[L_{S\_BDS}]-[L_{P\_BDS}]-[N] \tag{49}\]  
where \(C\) is the required self-interference suppression amount. By incorporating the results calculated earlier, the system's self-interference suppression amount can be determined to be 174.6 dB. Section 2 of the paper has indicated that the current level of self-interference suppression can reach 180 dB; thus, introducing the CCFD technology into the BDS-3 ISL scenario is feasible.