# Performance Analysis of Ground Target Detection Utilizing Beidou Satellite Reflected Signals
## 4 Experimental Results
### Results of the Second Experiment  
The results of the first experiment suggest that the target information can be clearly seen by the reflection signals of the PRN9 satellite. The reflection signals of PRN16 and PRN24 satellites showed no obvious changes. However, due to the design of the experiment, there were several problems, as follows: (1) the target was put in and out by a human, which would have had some influence on the detection results (as shown in Figure 13); (2) because the target was placed in the same position each time, the impact of the target on the PRN16 and PRN24 satellite reflection signals could not be accurately judged, and the effective range of target detection could not be judged by the first experiment; (3) the CNR information showed obvious changes in the PRN9 satellite which coincided with the target placement time, but PRN24 increased. Through the results of the first experiment, this phenomenon cannot be explained accurately. In order to solve these problems, the second experiment was designed to build on the first experiment; the specific experimental information is detailed in Section 3. The location information and data acquisition time of the experimental site were used to obtain the BeiDou satellite sky map, as shown in Figure 15. The direction indicated by the black arrow is the direction of the reflection antenna. Five satellites, PRN2, PRN3, PRN8, PRN23 and PRN27, were captured and tracked by processing the collected BeiDou satellite reflection signals. The state information of the five satellites was obtained with the satellite sky map, as shown in Table 4.  
Figure 14: Carrier-to-noise ratio (CNR) information of the three BeiDou reflected signals. The I branch component data of the PRN2 satellite changed very little; amplitude changes were seen, but the phenomenon was not obvious. As shown in Figure 17d, the change trend of the phase difference had several protrusions, but the change range was not large, and there was no regularity, so it was difficult to find a reasonable judgment threshold. The phase bulge time was very different from the time when the target passes under the antenna, and the overall judgment effect was poor. Combined with the carrier-to-noise ratio information in Figure 16a, the signal-to-noise ratio information of the satellite increased or decreased several times at the time that the target appeared, which indicates that the target has a certain influence on the reflection signal of the satellite. A shown in Figure 18, the change trend of phase difference of PRN3 was close to that of PRN2, and the appearance of the target cannot be accurately achieved by phase difference information alone. However, there was a distinct difference between the PRN2 and PRN3 satellites. The I branch component data of the PRN3 satellite changed obviously and increased obviously. Moreover, the time when the magnitude increases coincided with the time when the target appeared. From Figure 16b, we can see that the CNR information of PRN3 satellite increased at 14 time nodes, which indicates that the intensity of the reflected signal from the PRN3 satellite increased when the target appeared. It can see that there were 14 obvious signal changes in the I branch component data of the PRN8 satellite from Figure 19. Unlike the PRN3, PRN23 and PRN27 satellites, the I branch component of the PRN8 satellite changed in a \"depression\" state. The changing trend of the phase difference shows that the change was consistent with the number of times the target passes through, and the time duration of each change was 2 s. It should be mentioned that the change in the PRN8 phase difference was the same as that of the PRN9 satellite in the first experiment. At the same time, combined with the carrier-to-noise ratio information of PRN8 shown in Figure 16e, we can see that there were 14 notches in the carrier-to-noise ratio, which indicates that the reflected signal intensity from PRN8 satellite decreased when the target passed under the antenna.