# Target Localization Based on Bistatic T/R Pair Selection in GNSS-Based Multistatic Radar System
## 4 Simulation and Experimental Results
### Experimental Results of CMF Method  
The selection of bistatic T/R pairs is equivalent to select visible satellites in the GNSS-based passive multistatic radar. Therefore, CMF method is used to select the optimal combinations of 4, 5,..., 11 satellites from 12 visible satellites. Using AIS data as a reference, we calculate Root Mean Square (RMS) of the optimal combinations. At the same time, the theoretical error is calculated as the reference for the upper limit of positioning performance. The specific calculation process will not be repeated in this paper, which has been demonstrated in literature [29]. And the error curves of CMF method are shown in Figure 9.  
As shown in Figure 9, the positioning error is still in the trend: the measured RMS and the theoretical result both decrease as the number of satellites increases. It is not difficult to see that there are still some small fluctuations in the measured RMS curve in the figure. The reason for this phenomenon is that when observing complex targets such as arircrafts and ferries, these targets can be regarded as a collection of many independent scatterers. When scatterers are unstable, a small change on the viewing angle will cause the echoes synthesized by each scatterer to produce larger fluctuations, thereby affecting the positioning effect of these complex targets.  
In addition, in order to evaluate the performance of CMF method more intuitively, we also compared the measured RMS and the theoretical results before and after selecting satellites (Figures 10 and 11), respectively. From Figures 10 and 11, the measured RMS curve and the theoretical result curve after selecting satellites by CMF method are obviously lower than those before selection, that is, the positioning error is significantly reduced.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Satellite** & **Azimuth** & **Elevation** \\ \hline
1 & Galileo-GSAT0206 (PRN30) & 63.8–63.1\({}^{\circ}\) & 55.2–54.7\({}^{\circ}\) \\
2 & Galileo-GSAT0211 (PRN02) & 40.27–40.33\({}^{\circ}\) & 7.3–6.7\({}^{\circ}\) \\
3 & Glonass-COSMOS2457 & 314.2–313.6\({}^{\circ}\) & 67.8–68.8\({}^{\circ}\) \\
4 & Glonass-COSMOS2425 & 42.4–42.1\({}^{\circ}\) & 53.5–52.5\({}^{\circ}\) \\
5 & Glonass-COSMOS247 & 317.9–318.1\({}^{\circ}\) & 16.1–16.9\({}^{\circ}\) \\
6 & Glonass-COSMOS2459 & 305.4–304.7\({}^{\circ}\) & 5.1–4.5\({}^{\circ}\) \\
7 & GPS-BIIR09 (PRN13) & 293.2–293.9\({}^{\circ}\) & 66.8–67.6\({}^{\circ}\) \\
8 & GPS-BIIR04 (PRN20) & 289.0–288.0\({}^{\circ}\) & 46.4–46.8\({}^{\circ}\) \\
9 & GPS-BIIR05 (PRN28) & 118.0–117.1\({}^{\circ}\) & 44.2–44.8\({}^{\circ}\) \\
10 & GPS-BIIF05 (PRN30) & 63.7–63.5\({}^{\circ}\) & 52.6–51.8\({}^{\circ}\) \\
11 & GPS-BIIRM04 (PRN15) & 288.1–288.3\({}^{\circ}\) & 35.4–36.2\({}^{\circ}\) \\
12 & GPS-BIIRM06 (PRN07) & 58.1–58.3\({}^{\circ}\) & 19.6–18.9\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Satellite parameters.  
Figure 9: The positioning error of the Covariance Matrix Fusion (CMF) method.  
It shows that positioning accuracy has been improved after selecting satellites, and shows the correctness of the proposed method.