# 5G V2X Performance Comparison for Different Channel Coding Schemes and Propagation Models
## 4 Simulation Results
### Simulation Results for 256-Bit Frame Length  
Figure 3 shows BER performance of the simulated system for 256-bit frames, i.e., for scenarios 6 to 10 in Table 6. BCJR and logBCJR have almost identical performance and maxlogBCJR has a constant offset of 0.2 to 0.3 dB, driven by its suboptimal approximation in all five scenarios. Unlike the first five scenarios, the error floor is so smooth that it never appears and, eventually, BER in all three algorithms falls to zero in all 256-bit frame scenarios. Furthermore, the BER convergence rate is the same in these three algorithms and is increasing vastly. This leads to the BER becoming zero very fast, even in the NLOS and NLOSv scenarios. SOVA decreases more slowly as maxlogBCJR decreases, although it initially starts from the same BER. As a result, SOVA remains the worst turbo algorithm, independent of the traffic and channel state. Further, SOVA is worse than LDPC and polar coding in the high SNR region, although it has better performance in the low SNR region. Similar to the first five scenarios, SOVA does not zero BER below 10 db SNR, except in the case of the highway-LOS scenario. Even though polar coding does not have the best performance, its behaviour is the most interesting of all algorithms. It initially has the worst  
BER, even worse than the uncoded case, having an almost 40% error rate. Gradually, the rate of convergence increases and, eventually, the slope of BER is the steepest. LDPC has an inferior performance at the low SNR region, but above 2 to 3 dB, it starts to converge vastly at a pace similar to polar decoding. The error floor is absent from the LDPC in the 256-bit frame scenarios, except from the urban-NLOS scenario, in which it is negligible. Eventually, BER in all scenarios becomes zero. Unfortunately, LDPC and polar never attain the performance of BCJR-based algorithms because the latter converges rapidly at low SNR. To conclude, BCJR-based algorithms perform best, not only at low and middle SNR but also at high SNR for 256-bit frames in simulated scenarios 6-10. Table 9 shows the SNR required to attain 0.001 and 0.000001 BER for all 256-bit frame scenarios. We can easily conclude that BCJR-based algorithms are the best choice in both cases. Considering both efficiency and complexity, maxlogBCJR is obviously the best candidate for 256-bit frames, as it is by far the least complex algorithm among them, and the gap from optimality is only 0.2 to 0.3 dB for the first case and 1 dB maximum for the second. Polar and LDPC fail to converge fast, resulting in having 1.7 and 2.2 dB offset, on average, for the first case, although their performance gradually accelerates as the SNR increases. SOVA is the only algorithm that reaches the second threshold only in the LOS-based scenarios. Table 10 shows the BER efficiency for specific signal-to-noise ratios. From this table, we can extract many useful results, concerning the impact of the traffic model and the channel state on the system performance. From scenarios 6 and 7, we can conclude that an LOS channel state improves system performance for highway traffic around 10-times, on average, at low SNR, compared to the NLOSv channel state. Scenarios 8, 9 and 10 show that an LOS channel state increases the system's performance for urban traffic above 10-times, on average, and approximately 40-times for BCJR-based algorithms at low SNR. Taking these facts into account, we can conclude that BCJR-based algorithms are more resistant in multi-obstacle environments, as is the case in urban areas. The high SNR case in Table 10 implies something more important. At 9 dB SNR, all algorithms drop to zero, excluding SOVA. This means that the choice of the algorithm is independent of the performance, so we can choose the less complex algorithm for such situations. Figure 3: _Cont._  
Figure 3: BER vs. SNR for scenarios 6-10 and 256-bit frame length. **(a)** highway-LOS scenario; **(b)** highway-NLOSv scenario; **(c)** urban-LOS scenario; **(d)** urban-NLOS scenario; **(e)** urban-NLOSv scenario.