## 3 Construction of the Model
### Level 3 Evaluation: Receiver Sensitivity  
At Level 3, the EMC evaluation focuses on the decrease in receiver sensitivity. The radio wave propagation model of a vehicular radio station depends on the actual communication environment, which includes factors such as terrain, working frequency, communication distance, and antenna characteristics. Hence, analyzing a decrease in receiver sensitivity requires the consideration of radio wave propagation loss, antenna polarization mismatching loss, and feed loss, which is shown in Figure 2.  
The loss of radio wave propagation in free space is given by Equation (12)  
\[L_{bf}=20\text{lg}\bigg{(}\frac{4\pi d}{\lambda}\bigg{)}=20\text{lg}d+20\text{lg }f+32.44, \tag{12}\]  
where \(\lambda\) is radio wavelength, \(d\) is communication distance, and \(f\) is working frequency. The calculation formula of the radio wave transmission loss of Egli model is as follows. \[L_{\text{M}}=88+20\text{lg}(f)-20\text{lg}(h_{1}h_{2})+40\text{lg}(d)+K_{\text {h}} \tag{13}\]  
Here, \(L_{\text{M}}\) is propagation loss, \(f\) is working frequency, \(h_{1}\) and \(h_{2}\) denote the height of the transmitting and receiving antennae, \(d\) is communication distance, and \(K_{\text{h}}\) is the topographic correction factor, which can be expressed as follows:  
\[K_{\text{h}}=1.667-0.1094\Delta h\quad 25\text{ MHz}<f<150\text{ MHz} \tag{14}\]  
\[K_{\text{h}}=2.25-0.1476\Delta h\quad 150\text{ MHz}<f<162\text{ MHz} \tag{15}\]  
\[K_{\text{h}}=3.75-0.2461\Delta h\quad 450\text{ MHz}<f<470\text{ MHz} \tag{16}\]  
Here, \(\Delta h\) is relief height, and the unit is m.  
Compared to the propagation of radio waves in free space, the actual topography is complex and variable. When vehicles communicate, terrain fluctuations and surface obstructions may impede the linear propagation of radio signals, causing reflection, diffraction, and scattering, increasing the propagation loss of radio waves and reducing the actual received power at the receiver. To ensure the accuracy of an evaluation, it is necessary to correctly predict the propagation loss while taking into account the terrain factor. Since vehicular communication systems do not satisfy the applicable conditions of the existing propagation loss model, the accuracy of the results is not high, which will lead to inaccurate evaluations. Therefore, accurate topography and landforms were obtained based on digital maps, and computational models for the radio wave propagation loss in a specific environment were developed to achieve higher computational accuracy. \[L_{b}=L_{bf}+L_{\text{C}}+L_{\text{T}}+L_{\text{R}} \tag{17}\]  
Figure 2: Vehicle-communication-propagation-model-based graphical depiction of terms used in the transmission loss. Here, \(L_{b}\) is the propagation loss, \(L_{C}\) is the polarization mismatching loss, \(L_{T}\) is the feed loss from the transmitting antenna to the feeding network, and \(L_{R}\) is the feed loss from the feeding network to the receiving antenna. The polarization mismatching loss \(L_{C}\) depends on the polarization type and gain of the transmitting and receiving antenna. The antenna polarization mismatching loss is shown in Table 3.  
The feed losses \(L_{T}\) and \(L_{R}\) can be obtained by measuring the voltage standing wave ratio (VSWR)  
\[\Gamma=\frac{\text{VSWR}-1}{\text{VSWR}+1} \tag{18}\]  
\[L_{bf}=20\text{lg}\bigg{(}\frac{4\pi d}{\lambda}\bigg{)}=20\text{lg}d+20\text{lg }f+32.44, \tag{12}\]0  
\[L_{bf}=20\text{lg}\bigg{(}\frac{4\pi d}{\lambda}\bigg{)}=20\text{lg}d+20\text{lg }f+32.44, \tag{12}\]1  
where \(\Gamma\) is the voltage reflection coefficient. The actual power received by the receiver can be expressed as  
\[L_{bf}=20\text{lg}\bigg{(}\frac{4\pi d}{\lambda}\bigg{)}=20\text{lg}d+20\text{lg }f+32.44, \tag{12}\]2  
where \(P_{t}\) is the is the transmitting power of the transmitter, \(P_{r}\) is the actual power received by the receiver, \(G_{t}\) is the gain of the transmitting antenna, and \(G_{r}\) is the gain of the receiving antenna.