## 5 Performance Analysis
This means that the V2X-UORA channel access shows a much better user capacity threshold property compared to the conventional channel access case in the two-band transmission case. If the V2X system requires a quality of service (QoS) delay threshold less than 10 ms, the V2X-UORA channel access could meet the QoS requirement with the averaged delay and it uses the extended bandwidth more efficiently than the conventional wideband channel access case. Figure 11: Average delay and PLR in a single band transmission case (dashed circle is the converged delay range): (**a**) Conventional IEEE 802.11p channel access scenario; (**b**) Proposed V2X-UORA channel access scenario. To show the tendency of wideband operation more obviously, the four-bands case is also examined. Because four-band transmission is commonly applied in recent IEEE 802.11 systems and eight-band transmission is usually implemented by 4 bands + 4 bands transmission structure, examining up to 4 bands wideband operation is reasonable. Figure 13a shows the overall average delay and the PLR of the conventional IEEE 802.11 DCF procedure with a single, two, and four bands cases. This shows that the wideband procedure of the conventional channel access procedure can result in a shorter delay when the number of users is small, but the user capacity threshold does not increase linearly despite the number of bands increasing linearly. Figure 13b shows the overall average delay and the PLR of the proposed V2X-UORA channel access procedure with a single, two, and four bands cases. Unlike Figure 13a, Figure 13b shows that using wideband transmission enhances the user capacity threshold performance more efficiently although it does not enhance delay performance and it only meets the QoS delay requirement. In addition to the V2X-UORA performance analysis, we need to consider the extra optimization method we mentioned in the previous section. We have assumed that NG-V2X systems can have an association procedure for some special STAs including sensor STAs deployed to gather traffic information near a V2X infrastructure STA. In this case, dedicated RUs can be allocated in the UORA trigger frame for the STAs. Because of the dedicated RUs, the number of UORA RUs decreases but the dedicated RU is always occupied by the indicated STA if there are no frame errors. This means that using the dedicated RUs increases RU utilization and hence can enhance the overall delay performance as well. Figure 14a shows that the delay and the PLR performance of the proposed V2X with and without dedicated RUs. We assumed 30 sensor STAs and the X-axis represents the extra number of V2X STAs that excludes the 30 sensor STAs. Each STA generates its data packet including traffic information every 100 ms. Figure 14b shows how the dedicated RU with an association procedure enhances the user capacity threshold performance. Unless the dedicated RU is used, the 30 sensors are also considered as contention STAs. However, replacing only a single UORA RU in the UORA trigger frame to a dedicated RU makes the sensor STAs not participate in the UORA contention procedure. As the number of sensor STAs increases, the dedicated RU method becomes more effective. To examine the performance of the scheduled NG-V2X channel access, we compared the performance with that of legacy channel access, high-priority EDCA (HP-EDCA) and (nonscheduled) NG-V2X in Figure 15. HP-EDCA is the IEEE 802.11p channel access procedure with high priority channel access parameters (AC_VO). Some studies have shown that applying the highest priority access category (AC_VO) to IEEE 802.11p channel access procedure improves its channel access efficiency through their analysis and simulation results [41; 42]. As can be observed, scheduled NG-V2X shows higher user capacity performance than legacy channel access, HP-EDCA and NG-V2X cases we have stated.