## 4 Application of the Model
### Level 5 Evaluation: Communication Performance
#### 4.5.2 Communication Quality  
In the application example, the communication system is a digital communication system, and the communication signal is an audio signal. Therefore, the fifth-level evaluation is based on the BER, and the IM criterion is defined based on the maximum acceptable BER. As we can see in Table 10, the maximum BER threshold for audio signals is \(P_{\mathrm{e}}=1\times 10^{-3}\). Therefore, \(P_{\mathrm{e}}=1\times 10^{-3}\) was identified as the fifth-level IM criterion.  
In practice, there are various factors that affect the BER, such as the modulation mode and the channel-coding mode. Hence, these two factors are discussed in this paper. To compute the BER of the audio signal in the proposed example, we selected some channel-coding modes and modulation modes commonly used in armored vehicle communication systems and constructed a simplified simulation model of a typical communication link, which is shown in Figure 12.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Signal Type** & **BER Threshold** \\ \hline Audio Signals & \(P_{\mathrm{e}}\leq 1\times 10^{-3}\) \\ Image Signals & \(P_{\mathrm{e}}\leq 1\times 10^{-5}\) \\ Video Signals & \(P_{\mathrm{e}}\leq 1\times 10^{-9}\) \\ \hline \hline \end{tabular}
\end{table}
Table 10: BER thresholds for different types of digital signals.  
Figure 11: Relationship between the receiver VHF3 sensitivity reduction and the communication distance reduction.  
(1) The influence of the modulation type  
Figure 13 shows the relationship between BER and SNR for seven modulation types: 2 PSK coherent modulation, 2 DPSK coherent modulation, 2 DPSK incoherent modulation, 2 FSK coherent modulation, 2 ASK incoherent modulation. The broken red line in Figure 12 represents the maximum BER threshold for distinguishable audio signals.  
As shown in Figure 13, the degrees of electromagnetic compatibility of the seven modulation modes of the armored vehicle's digital communication system are ranked from highest to the lowest: 2 PSK coherent modulation, 2 DPSK coherent modulation, 2 PSK incoherent modulation, 2 FSK coherent modulation, 2 FSK incoherent modulation, and 2 ASK incoherent modulation. From the point of view of systematic EMC evaluation, it can be argued that 2 PSK coherent modulation has the best EMC.  
(2) The influence on the channel-coding mode  
Figure 14 shows the relationship between BER and SNR for seven channel-coding modes: convolutional coding, BCH coding, cyclic coding, Golay coding, linear coding, Hamming coding, and RS coding. The broken red line in Figure 13 represents the maximum BER threshold for distinguishable audio signals.  
Figure 12: Simulation model of the communication link.  
Figure 13: Relationship between BER and SNR for seven modulation types.  
As shown in Figure 14, the levels of electromagnetic compatibility of the seven channel-coding modes of the armored vehicle digital communication system are ranked from the highest to the lowest: convolutional coding, BCH coding, cyclic coding, Golay coding, linear coding, Hamming coding, and RS coding. From the point of view of systematic EMC evaluation, it can be argued that convolution coding has the best EMC.  
Based on the BER simulation results, the evaluation result of this level is \(\text{IM}>0\), which indicates that a potential EMI is present in this system.  
In summary, all evaluation processes have been completed. There is a potential for EMI and a possible risk of electromagnetic incompatibility in the communications system of the armored vehicle according to our review of the evaluation results.