# 3 GPP 5G V2X Scenarios: Performance of QoS Parameters Using Turbo Codes
## 3 QoS Analysis
### Link Reliability QoS Parameter  
Generally, link reliability QoS parameter is affected by BER performance and the corresponding SNR value (the higher SNR value, the better reliability value) [20]. At Figures 4 and 5 two histograms of link reliability (%) vs. Table 1 scenario and different SNR values are shown. The values are calculated using BER performance values from Figures 2 and 3 and the link reliability formula from [20]. We show the results only for SOVA algorithm since for log-MAP and max-log-MAP we obtain similar results. For SNR values between 0 and 4 dB (small values), Figure 4 shows the calculated reliability values for the different scenarios, while at Figure 4 the SNR values are between 5 and 10 dB (larger values). It is obvious that as the SNR value increases, the reliability also increases. Particularly, at Figure 4 for SNR = 4 dB we observe that for scenarios 5 and 7 the reliability increases instantly to 100%. This is because in these two scenarios we have a large frame length of 512 bits and a small data rate of 6 Mbps, while terminal speed seems to have a small effect on BER and the resulting reliability. Moreover, at Figure 5 for SNR values higher than 7 dB the reliability reaches its highest value (100%) for all 8 scenarios. Figure 3: BER vs. SNR for GEMV channel, 5 different Table 2 scenarios, different decoding algorithms, 3 iterations, frame length of 512 bits. Figure 4: Link Reliability (%) for the different Table 2 scenarios, considering BER for SNR values between 0 and 4 dB, SOVA decoding algorithm and GEMV channel. Figure 5: Link Reliability (%) for the different Table 2 scenarios, considering BER for SNR values between 5 and 10 dB, SOVA decoding algorithm and GEMV channel. At the same Figure for SNR = 5 dB and scenarios 1, 3, 5, 7 (6 Mbps data rate) the reliability is 100%, while at the other scenarios (12 Mbps) we observe that the reliability has smaller values. Furthermore, at Figure 5 for SNR = 6 dB and scenarios 1, 3, 5, 6, 7, 8 (6 Mbps data rate for both frame lengths and 12 Mbps only for 512 bits) the reliability is 100%, while at scenarios 2, 4 (12 Mbps and frame length of 256 bits) we observe that the reliability has smaller values. Thus, we conclude that data rate and frame length play an important role on the link reliability value mainly for medium SNR values (between 4 and 6 dB). On the other hand, mobile terminal speed's effect on reliability is negligible. Table 3 illustrates the recommended Table 1 scenarios for implementation scenarios 1 to 8 examined at Table 2 (rows of Table 5). Moreover, the recommended values are based on the accepted values mentioned for each scenario at Table 1, on SNR values from 0 to 10 dB (columns of Table 3) and on the calculated link reliability values for all three decoding algorithms (the reliability values for SOVA are shown at Figures 4 and 5). Table 3 shows that for SNR values between 0 and 3 dB only scenario 5 from Table 1 can be established. Subsequently, we examine Table 1 scenarios that can be implemented for SNR values between 4 and 6 dB. Here, for these SNR values the choice of the suitable Table 1 scenario depends on data rate and on the decoding algorithm (SOVA is recommended). For high SNR values between 7 and 10 dB, scenarios 2, 3, 6 from Table 1 are recommended. We consider only SOVA decoding algorithm, because for this algorithm we observe the best end-to-end delay results with the simulated scenario 6 of Table 2 (a frame length of 512 bits, a data rate of 12 Mbps and a vehicle speed of 60 km/h) because the vehicle speed increase does not significantly affect the throughput performance, as shown at the following Section 3.4. We take two important metrics (BER and throughput) to measure whether the QoS is affected by the realistic traffic conditions on the road. These simulation results are presented in Figures 7 and 8.