# Analysis of LTE-M Adjacent Channel Interference in Rail Transit
## 3 Interference Analysis of LTE-M Underground System  
### Interference Analysis When LTE-M Uses Directional Antenna Radiations Pattern  
When the LTE-M system uses the directional antenna radiations pattern, the scene of interference is shown in Figure 2.  
The source of interference is LTE FDD UE, which may be located in the platform area or inside the carriage, and the sources of victimization are LTE-M BS and LTE-M TE. This paper focuses on two types of interference, one is LTE FDD UE interfering with the LTE-M BS (UE-BS), and the other is LTE FDD UE interfering with LTE-M TE (UE-TE). The path loss of signal in the transmission process is greatly affected by the frequency, environment, distance, antenna height, and some other factors. Selection of an appropriate propagation model is a necessary condition to analyze the interference. Assuming that the distance between UE and the BS is less than 100 m and the UE is located in the platform area, the propagation model can be approximately conceived as the free-space loss according to Equation (8), \(f\) represents the frequency of electromagnetic wave in MHz, and \(d\) represents the spatial distance between transceivers. \[L_{free}=32.44+20\lg(d)+20\lg(f) \tag{8}\]  
When the UE is located inside the carriage, the UE needs to penetrate the carriage to reach the receiving end. The Keenan-Motley model [42], which was derived from the free space propagation model, accounts for penetration loss in the propagation environment, given as follows  
\[L_{k}=L(d_{0})+20\lg\left(\frac{d}{d_{0}}\right)+kF(k) \tag{9}\]  
where \(L(d_{0})\) is the path loss of the free space with a reference distance of \(d_{0}\), \(F(k)\) is the reference value of the penetration loss, \(k\) is the number of layers of penetration. In this paper, the penetration is 1 layer, and the penetration loss is 8 dB. Assuming that the distance between UE and the BS is greater than 100 m, the vehicle-mounted propagation model can be estimated as  
\[L_{\text{UE-BS}}=40(1-0.004\Delta h_{\text{BS}})lg(d)-18-18 lg(\Delta h_{\text{ BS}})+21 lg(f)+80 \tag{10}\] \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Spectrum Emission Limit (dBm)/Channel Bandwidth**} \\ \hline \(\Delta\mathbf{f_{OOB}}\) (MHz) & \(1.4\) MHz & \(3.0\) MHz & \(5\) MHz & \(10\) MHz & \(15\) MHz & \(20\) MHz & **Measurement Bandwidth** \\ \hline \(\pm 0\)–\(1\) & \(-10\) & \(-13\) & \(-15\) & \(-18\) & \(-20\) & \(-21\) & \(30\) kHz \\ \(\pm 1\)–\(2.5\) & \(-10\) & \(-10\) & \(-10\) & \(-10\) & \(-10\) & \(1\) MHz \\ \(\pm 2.5\)–\(5\) & \(-25\) & \(-10\) & \(-10\) & \(-10\) & \(-10\) & \(1\) MHz \\ \(\pm 5\)–\(6\) & & \(-25\) & \(-13\) & \(-13\) & \(-13\) & \(1\) MHz \\ \(\pm 6\)–\(10\) & & & \(-25\) & \(-13\) & \(-13\) & \(-13\) & \(1\) MHz \\ \(\pm 10\)–\(15\) & & & & \(-25\) & \(-13\) & \(-13\) & \(1\) MHz \\ \(\pm 15\)–\(20\) & & & & & \(-25\) & \(-13\) & \(1\) MHz \\ \(\pm 20\)–\(25\) & & & & & & \(-25\) & \(1\) MHz \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Spectrum emission mask. Figure 2: Interference analysis of LTE-M with directional antenna radiations pattern. we assume this value as 5 m, \(f\) represents the frequency of the electromagnetic wave in MHz, and \(d\) represents the spatial distance between transceivers. When the UE is located in the platform area and the distance between the UE and the TE is less than 50 m, the free-space loss model (8) can be used to examine the entire transmission process. When the UE is located inside the carriage, the transmission model uses the Keenan-Motley model as in Equation (9).