## 4 Simulation Results and Discussion
### Simulation 1  
In simulation 1, we detected three sets of point targets based on the B3I signals of four BDS satellites without considering clutter and noise. The point target information is expressed in Table 2, where the points were set with an interval of 30 m, and its geometric distribution was plotted in Figure 7. In particular, to better study the detection property, the RCS ratios of target 1, target 2, and target 3 were set to 2:5:15.  
Figure 6: The technical process of multiple GNSS-R signals and multiple-targets detection.  
To study the target peak resolution effectiveness of the sampling method at 33 m, Figures 8 and 9 show the RCS data distribution and one-dimensional range detection results with sampling at 33 m. In Figure 8, the circle line expresses the original RCS distribution of point target 3 under each satellite, and the star line represents the data with a sample at 33 m. In Figure 9, the curves are the detection peaks of point target 3 under each satellite, and its direction and length vary with the detection angle. Taking Figure 8 as a comparison, we found that the small peaks in the detection results of Figure 9 are in good agreement with the sampling data at 33 m in terms of amplitude and range point. The results can be utilized to estimate the RCS distribution of targets and verify target recognition.  
To research the Doppler and range information of detection by four satellites, the simulation shows the DDM results of three sets of point targets of the B3I signal from four satellites separately in Figure 10. Because the resolution of B3I is near 30 m, each set of point targets was detected as a few light points in the DDM, and according to the number of points set in each target, we identified that the highlights are target 3, target 2, and target 1, in order from the strongest to the weakest. Among the four detection results, the Doppler frequency of each target ranged from \(-1000\) to \(1900\) Hz for the high speed and different radiation angle of the satellites, but the difference in the Doppler value among targets was stable at approximately 400 Hz on account of the target points and receiver location. The motion of the receiver and the target determine the Doppler difference among targets. Moreover, the range and velocity information of the detection of four satellites can  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Simulation 1** & \(r\)**/km** & \(\varphi_{r}\) & **v/m/s** & \(\varphi_{\mathbf{v}}\) & **Interval/m** & **Number** \\ \hline Target 1 & 1 & \(150^{\circ}\) & 15 & \(-120^{\circ}\) & 30 & 1 \\ \hline Target 2 & 1.5 & \(135^{\circ}\) & 20 & \(-135^{\circ}\) & 30 & 5 \\ \hline Target 3 & 2 & \(60^{\circ}\) & 20 & \(-120^{\circ}\) & 30 & 3 \\ \hline
**Simulation 2** & \(r\)**/km** & \(\varphi_{r}\) & **v/m/s** & \(\varphi_{\mathbf{v}}\) & **Length/Width(m)** \\ \hline Target 1 & 1 & \(150^{\circ}\) & 15 & \(-120^{\circ}\) & 141/20 \\ \hline Target 2 & 1.5 & \(135^{\circ}\) & 20 & \(-135^{\circ}\) & 314.6/40.8 \\ \hline Target 3 & 2 & \(60^{\circ}\) & 20 & \(-120^{\circ}\) & 142/18 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Target parameter.  
Figure 7: Geometry schematic diagram of multi-signal and multi-target detection simulation.  
Figure 10: DDM of point targets under the detection of 4 BDS satellites: (**a**) satellite 1; (**b**) satellite 2; (**c**) satellite 3; and (**d**) satellite 4.  
Figure 9: One-dimensional range detection results of point target 3 under the detection of 4 BDS satellites with 33-meter echo sampling: (**a**) satellite 1; (**b**) satellite 2; (**c**) satellite 3; and (**d**) satellite 4.