# 5G V2X Performance Comparison for Different Channel Coding Schemes and Propagation Models
## 4 Simulation Results
### BER Performance Analysis for maxlogBCJR  
In the previous subsections, we presented the simulation results for 128-, 256- and 512-bit frames, where miscellaneous results were observed. Other aspects that we can examine include the impact of the frame length, the velocity, the channel state and the traffic model on BER performance. The simulations show clearly that the research findings are common for all the decoding algorithms on average. For that reason, we choose maxlogBCJR as a representative algorithm and we will demonstrate its results only. For this purpose, we study the percent average improvement in BER based on these parameters. Figure 5 presents the impact of changing the frame length on all the simulation scenarios, i.e., highway-LOS, highway-NLOSv, urban-LOS, urban-NLOS and urban-NLOSv. Comparing Figure 5a with Figure 5b, we can observe the great impact that the frame length has on the BER performance. Although the frame size is doubled in both cases, in the second case, the improvement is much greater, indicating an exponential growth in efficiency, because the frame sizes are larger. The coding schemes for 128-bit frames are not efficient, due to the small number of parity bits. If we combine this with the poor performance that the NLOS and NLOSv scenarios have in general relative to the LOS, we can conclude that the LOS scenarios have greater BER performance from the NLOS and NLOSv scenarios. The coding schemes for 256 bits have more parity bits, accelerating the performance of the scenarios, but not in the same way. From Figure 5a, we can conclude that when the frame length changes from 128 to 256 bits, the NLOS and NLOSv scenarios have greater improvements compared to the LOS scenarios, mainly because the long error floors that affect the NLOS and NLOSv scenarios for 128-bit frames eventually vanish. Figure 5b shows that highway scenarios are more affected than urban scenarios when the frame size changes from 256 to 512 bits, because the good highway propagation model better exploits the increase in the parity bits. In Figure 6, we present the effect of change in speed, i.e., the change between the urban and highway traffic model, in both LOS and NLOSv channel states. To this end, the percent mean BER improvement versus the change in velocity is illustrated for 128-, 256- and 512-bit frames. Urban-NLOSv and highway-NLOSv scenarios (Figure 6a) have common large-scale characteristics, so the difference in performance is due to the doppler phenomenon only. From this figure, we can infer that by doubling velocity, the BER deteriorates by 6.75 to 10.47 percent. This comparison is the best representative of the study of the speed change, since in urban LOS and highway-LOS scenarios (Figure 6b), in addition to speed, different large-scale characteristics play an important role in the performance. The second comparison describes the impact of traffic model on BER efficiency for certain channel states, i.e., LOS. Given the small effect of the speed change, we conclude that the absence of obstacles in the highway-LOS scenario compared to the urban-LOS scenario results in a massive improvement in BER. This improvement is limited in the case of 128- and 256-bit frames due to the existence of an error floor, but the absence of error floor in 512-bit frames shows the substantial improvement brought about by the change of the traffic model. Figure 7 illustrates the impact of channel state on BER performance. We can conclude that the poor propagation environment in the NLOS and NLOSv cases dominates the performance, due to the permanent or partial absence of LOS component signals. This situation affects the system so severely that when the channel state changes to LOS, the difference in performance is significantly large in all cases (Figure 7a-c). Figure 5: Mean percentage BER improvement vs. frame length for maxlogBCJR and for all simulated scenarios. (**a**) BER improvement when the frame length changes from 128 to 256 bits. (**b**) BER improvement when the frame length changes from 256 to 512 bits.