## 4 Simulation Experiments and Results
### Simulation Experiments and Results
The RMSE of angle estimation when interference transmitting power gradually increases is shown in Figure 9.  
In Case 2, three RFI sources of the same type are set in the system, and their geolocation coordinates in the ENU coordinate system respectively are \(P_{j}^{1}=\left(-5.77\times 10^{4},-5.45\times 10^{4},479.82\right)_{\text{ENU}}\), \(P_{j}^{2}=\left(0,0,863\right)_{\text{ENU}}\), and \(P_{j}^{3}=\left(6.32\times 10^{4},5.90\times 10^{4},-388.83\right)_{\text{ENU}}\), all these coordinates are expressed in meters. As ISR is 10 dB, the angle estimation results are shown in Figure 10. The RMSE in this case is shown in Figure 11. Similar to Figure 8, each point in Figure 10 represents the error between the estimated DOA and the true DOA in azimuth \(\varphi\) and elevation \(\theta\). In Case 3, the number of RFI sources and geographic coordinates are the same as Case 2. As ISR is 10 dB, the angle estimation result is shown in Figure 12. The RMSE in this case and Case 2 are integrated and shown in Figure 13.  
Then, we verify the performance of the PSO algorithm to calculate the spatial coordinates of the RFI source. The parameter selection refers to the principle of parameter setting in [28], \(\beta\) equal to 0.5, \(\
u_{1}\) and \(\
u_{2}\) both equal to 2.0. Figure 14 indicates the process of using the PSO algorithm to solve the optimization problem in Equation (47). Figure 8: Angle estimation accuracy for Case 1 where a single RFI source transmits one of the three types of RFI in one experiment. The horizontal axis represents the error of the azimuth angle, and the vertical axis represents the error of the elevation angle in these figures: (**a**) DOA error of single RFNI source; (**b**) DOA error of single NBLFMI source; (**c**) DOA error of single WBLFMI source. Figure 9: The root mean square error (RMSE) of angle estimation under different interference-to-signal ratio (ISR) for Case 1. \[RMSE_{DOA}=\frac{1}{K}\sum\limits_{k=1}^{K}\sqrt{\frac{1}{N_{MC}\cdot N_{a}} \sum\limits_{l=1}^{N_{MC}}\sum\limits_{i=1}^{N_{a}}\Bigl{[}\left(\theta_{i}^{k }-\hat{\theta}_{i}^{k}\right)^{2}+\left(\varphi_{i}^{k}-\hat{\varphi}_{i}^{k} \right)^{2}\Bigr{]}}. \tag{49}\]0 RMSE of angle estimation for Case 2. \[RMSE_{DOA}=\frac{1}{K}\sum\limits_{k=1}^{K}\sqrt{\frac{1}{N_{MC}\cdot N_{a}} \sum\limits_{l=1}^{N_{MC}}\sum\limits_{i=1}^{N_{a}}\Bigl{[}\left(\theta_{i}^{k }-\hat{\theta}_{i}^{k}\right)^{2}+\left(\varphi_{i}^{k}-\hat{\varphi}_{i}^{k} \right)^{2}\Bigr{]}}. \tag{49}\]1 Angle estimation result for Case 3 where three RFI sources transmit the different types of interference simultaneously. The horizontal axis represents the error of the azimuth angle, and the vertical axis represents the error of the elevation angle in these figures. (**a**) RFI source locates at \(P_{j}^{1}\); (**b**) RFI source locates at \(P_{j}^{2}\); (**c**) RFI source locates at \(P_{j}^{3}\). \[RMSE_{DOA}=\frac{1}{K}\sum\limits_{k=1}^{K}\sqrt{\frac{1}{N_{MC}\cdot N_{a}} \sum\limits_{l=1}^{N_{MC}}\sum\limits_{i=1}^{N_{a}}\Bigl{[}\left(\theta_{i}^{k }-\hat{\theta}_{i}^{k}\right)^{2}+\left(\varphi_{i}^{k}-\hat{\varphi}_{i}^{k} \right)^{2}\Bigr{]}}. \tag{49}\]2 Angle estimation accuracy for Case 2 where three RFI sources transmit the same type of interference simultaneously. The horizontal axis represents the error of the azimuth angle, and the vertical axis represents the error of the elevation angle in these figures: (**a**–**c**) DOA error of RFNI sources; (**d**–**f**) DOA error of NBLFMI sources; (**g**–**i**) DOA error of WBLFMI sources. (**a**,**d**,**g**) RFI source locates at \(P_{j}^{1}\)(**b**,**e**,**h**) RFI source locates at \(P_{j}^{2}\); (**c**,**f**,**i**) RFI source locates at \(P_{j}^{3}\).