# 5G V2X Performance Comparison for Different Channel Coding Schemes and Propagation Models
## 4 Simulation Results
### Simulation Results for 128-Bit Frame Length  
Figure 2 illustrates BER performance of the simulated system for a 128-bit frame, i.e., for scenarios 1-5 in Table 6. We observe that every decoding algorithm improves the BER \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Simulation** & **Data Frame Size** & **Traffic Model** & **Channel State** \\
**Scenario** & & & \\ \hline
1 & 128 & Highway & LOS \\ \hline
2 & 128 & Highway & NLOSv \\ \hline
3 & 128 & Urban & LOS \\ \hline
4 & 128 & Urban & NLOS \\ \hline
5 & 128 & Urban & NLOSv \\ \hline
6 & 256 & Highway & LOS \\ \hline
7 & 256 & Highway & NLOSv \\ \hline
8 & 256 & Urban & LOS \\ \hline
9 & 256 & Urban & NLOS \\ \hline
10 & 256 & Urban & NLOSv \\ \hline
11 & 512 & Highway & LOS \\ \hline
12 & 512 & Highway & NLOSv \\ \hline
13 & 512 & Urban & LOS \\ \hline
14 & 512 & Urban & NLOS \\ \hline
15 & 512 & Urban & NLOSv \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Simulation scenarios. as the SNR increases at a rate superior to the uncoded case. BCJR and logBCJR coding algorithms have identical behaviour. MaxlogBCJR has a loss of 0.2-0.3 dB at the same BER relative to BCJR and logBCJR in all scenarios, which is expected, since their performance is suboptimal [64]. Figure 2: _Cont._  
Apart from gap, all three algorithms have the same rate of convergence, and above a threshold, an error floor appears [65], limiting the rate of BER convergence. This error floor is smooth for all five scenarios, and it always appears between 5 and 7 dB SNR. Despite the presence of the error floor, these three algorithms have a high rate of reduction. The SOVA decoding algorithm is also suboptimal [66] relative to the turbo-based algorithms. Further, it has better performance compared to LDPC and polar coding for low SNR. As the SNR increases, the BER decreases at a slow pace and, eventually, SOVA becomes the worst of all the coding algorithms above 5.5 to 6.8 dB according to the scenario. Polar coding has the worst initial BER (0 dB), worse than the uncoded case, but as the SNR increases, BER diminishes rapidly in all scenarios. The result is that the BER nulls for SNR greater than 7 dB in highway-LOS and urban-LOS scenarios. Further, it nulls above 8 dB in highway-NLOSv and urban-NLOSv scenarios and above 9 dB in the urban-LOS scenario. LDPC has a much slower rate of convergence for low SNR, and as the SNR increases, the slope of the BER gradually increases in all 128-bit scenarios. This diminishing rate slightly increases in all scenarios except the highway-LOS scenario, indicating the presence of an error floor [67; 68], which is also present in LDPC, limiting its performance. Table 7 shows the SNR needed to achieve a BER of value 0.001 and 0.000001 for all the aforementioned scenarios and for the 128-bit frame length. If our goal is to achieve BER equal to 0.001, then BCJR-based algorithms need less signal power than the rest of the algorithms. If our goal is to achieve BER equal to 0.000001, instead, then polar is the best coding scheme, as it is the only algorithm that achieves this objective in all five scenarios. Analysing the performance of the first two scenarios, we can extract a qualitative measure of the impact that the highway traffic model has on different channel states (LOS, NLOSv). The presence of moving obstacles in the NLOSv state has an impact on BER by approximately an order of magnitude, on average, as shown by Table 8.  
Figure 2: BER vs. SNR for scenarios 1-5 and frame length 128 bits. (**a**) Highway-LOS scenario; (**b**) highway-NLOSv scenario; (**c**) urban-LOS scenario; (**d**) urban-NLOS scenario; (**e**) urban-NLOSv scenario. The first and third scenario involve having LOS channel state and different traffic environments, urban and highway, respectively. If we compare them, we can observe the effect of the traffic model on the system performance. As we can deduce, the effect of the model is greater for small SNR and decreases as the SNR increases. Table 8 shows the achieved BER values for SNR equal to 4 and 9 dB, respectively.