# Analysis of LTE-M Adjacent Channel Interference in Rail Transit
## 2 LTE-M Adjacent Channel Interference
### Principle of Adjacent Channel Interference
The transmission loss occurs when the actual received interference signal power meets \(I_{threshold}\), which represents the MCL [40]; that is, the minimum spatial isolation, as given follows  
\[\mathrm{MCL}=P_{Imax}+G_{\mathrm{TR}}-\mathrm{ACIR}-I_{threshold} \tag{7}\]  
Suppose the path loss of signal transmission in the interfering LTE FDD UE and the LTE-M system is \(L\), when \(L>\mathrm{MCL}\), the path loss exceeds the minimum spatial isolation, and when \(L<\mathrm{MCL}\), the path loss meets the minimum spatial isolation requirement. In the case of \(L=\mathrm{MCL}\), this paper uses different wireless channel propagation models to estimate the minimum safe distance between different systems. Table 2 shows the steps involved in calculating the LTE-M system's interference parameters, where \(P_{noise}\) can be obtained by substituting different system receiving bandwidths and the receiver noise values into Equation (6), then substituting the \(P_{noise}\) and different sensitivity loss into Equation (5) to obtain \(I_{threshold}\). Since both the transmitter and the receiver filters are non-ideal, the frequency band interval and the received signal bandwidth is related to the component of transmitted power falling into the adjacent receiver bandwidth and the attenuation of transmitted power by the receiver filter. According to the spectrum emission mask in [41], as shown in Table 3, the UE's spectrum emission mask is applied to the frequency of the out of band emission (\(\Delta G_{\mathrm{COB}}\)), starting from the edge of the assigned channel bandwidth and the value of ACLR and ACS under different guard band intervals and different receiving channel bandwidths can be obtained by the method of integration. Then, the value of ACLR and ACS can substituted into Equation (4) to obtain the value of ACIR. According to [41], the maximum transmitted power of UE is 23 dBm, the antenna gain of LTE-M BS is 15 dBi, and the antenna gain of LTE-M TE is 0. Moreover, the MCL under different interference links can be obtained by substituting \(P_{Imax}\), \(G_{TR}\), ACIR, and \(I_{threshold}\) into Equation (7). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Interference Link** & & \multicolumn{3}{c}{**UE-BS**} & \multicolumn{5}{c}{**UE-TE**} \\ \hline Received BW (MHz) & & 5 & & 10 & & 5 & & 10 & \\ Guard band (MHz) & 0 & 5 & 0 & 5 & 0 & 5 & 0 & 5 \\ \(P_{Imax}\) (dBm) & 23 & & & 23 & & 23 & & 23 & \\ \(G_{TR}\) (dBi) & 15 & & & 15 & & 0 & & 0 & \\ \(P_{noise}\) (dBm) & \(-102\) & & & \(-99\) & & \(-98\) & & \(-95\) & \\ \(I_{threshold}\) (dBm) & \(-109\) & & & \(-106\) & & \(-98\) & & \(-95\) & \\ ACS (dB) & 53.27 & & 50.26 & & 49.27 & & 46.26 & \\ ACLR (dB) & 21.37 & 35.02 & 21.19 & 35.02 & 21.37 & 35.02 & 21.19 & 35.02 \\ ACIR (dB) & 21.37 & 34.96 & 21.19 & 34.89 & 21.36 & 34.86 & 21.18 & 34.71 \\ MCL (dB) & 125.63 & 112.04 & 122.81 & 109.11 & 99.64 & 86.14 & 96.82 & 83.29 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Interference calculation parameters of LTE-M with directional antenna radiations pattern.