## 5 Results
### Verification and Analysis of S-Band Test Data
Carrier+PNc means the proposed signal combination utilizing the carrier and the first-order clock component of the PN code ranging signal for frequency synchronization with about 2 MHz of effective bandwidth. The combination of the carrier and one DOR beacon signal, as processed traditionally, is denoted as Carrier+DOR\({}_{1}\). On the other hand, the combination of the clock component of the carrier and PN code ranging signal under the proposed method is represented as Carrier+PNc. Both methods are employed for frequency synchronization, respectively, to obtain the coarse time delay estimation, thereby resolving the integer ambiguity of the \(\pm\)DOR\({}_{1}\) signal cross-spectrum phase. The residual delays of the two situations and their bias are shown in the upper and lower half of Figure 8. It can be seen that the trends of the time delay obtained by the two signal combinations are consistent. The accuracy of the time delay obtained by the Carrier+DOR\({}_{1}\) combination is relatively higher than that of the Carrier+PNc combination. This is mainly due to the fact that the wider the effective synchronization bandwidth, the higher the accuracy of the time delay when the accuracy of the cross-spectrum phase is close. The residual delay bias obtained by the two combinations is relatively stable, peaking at approximately 2 ns, which results in a maximum bias of about 0.015 cycles (2\(\pi\)) and 0.08 cycles in the cross-spectrum phase when the bandwidth are about 7.5 MHz and 40 MHz, respectively. In other words, this time delay bias will not introduce the deviation of integer ambiguity resolution, and the time delay estimation results must be consistent with the traditional scheme. Furthermore, the estimation accuracy of the interferometry time delay using only the clock component of the pseudo-code ranging signal and carrier is analyzed when the DOR beacon signal is not modulated in the S-band. The time delay is resolved by two signal combinations, as depicted in Figure 9, where Carrier+DOR represents the carrier and two DOR beacon signals, and Carrier+PNc stands for the carrier and clock components of the PN code ranging signal; therefore, the corresponding bandwidth of the effective signals are 7.5 MHz and 2 MHz, respectively. We can find that the residual time delay trends obtained by the two signal combinations are consistent with those presented in Figure 8. Notably, the residual delay random error associated with the Carrier+PNc signal  
Figure 7: The comparison of the cross-phase of two different combinations of the downlink signal. combination is approximately one order of magnitude greater than that of Carrier+DOR, the discrepancy being due to the coupling effect between the bandwidth and cross-spectrum phase measurement accuracy. The deviation of the two time delay results is stable with an average value of about 0.56 ns. This may be caused by the nonlinear effect of S-band ionospheric delay, which can be corrected by differential calibration observation or ionospheric delay measurement equipment. Considering the comprehensive influence of tropospheric delay, station location error, S-band ionospheric delay, and other sub-ns level errors, there is a marginal loss in the random accuracy of time delay (about 0.56 ns for this test scenario). Even so, the S-band  
Figure 8: The residual delay estimation results of the two signal combinations (**upper** half) and their deviation (**lower** half). Figure 9: The delay estimation results of the two signal combinations (**upper** half) and their deviation (**lower** half). signal system can still detune the DOR beacon signal, and only utilize the pseudo-code ranging clock component to achieve the interference time delay measurement. Then, the downlink signal power can be saved or the detect distance can be enlarged. This is significant for lunar and deep space exploration, especially when the downlink signal power is tight.