## 5 Performance Analysis
Although scheduled NG-V2X not only requires a more preliminary procedure including timing  
Figure 12: Average delay and PLR in two bands transmission case: (**a**) Conventional IEEE 802.11p channel access scenario; (**b**) Proposed V2X-UORA channel access scenario. synchronization and RU indication but is also less adaptive than nonscheduled NG-V2X, it shows attractive user capacity performance gains. Figure 14: Average delay and PLR in a single band transmission with 30 sensor STAs: (**a**) Conventional IEEE 802.11p channel access scenario; (**b**) Proposed V2X-UORA channel access scenario with the dedicated RU method. Figure 13: Overall average delay and PLR: (**a**) Conventional IEEE 802.11p channel access scenarios; (**b**) Proposed V2X-UORA channel access scenarios. So far, performance comparison results are focused on their performance comparison under the error-free situation for fair and easy comparison. However, in real world, there exist fading and shadowing in wireless channel and system performance can be degraded by fading and shadowing leading to a smaller coverage range than 1000 m. In order to examine the effect of fading and shadowing in wireless channel, additional simulations with fading and shadowing for 250 m coverage range and 1000 m coverage range are performed. In the simulation, more realistic simulation environment are considered. Unlike the previous results, which are with an ideal channel environment scenario using the ITU-R channel model in Urban Macro (UMa) scenario, which only considers LOS path loss without any consideration on shadowing and non-LOS (NLOS) path loss, additional simulations employ the UMa channel model with shadowing and NLOS transmission probabilities per distance considering actual environment [43]. Channel model parameters used in the simulations are listed in Table 2 and the result is shown in Figure 16. The specific channel model parameters in Table 2 are based on the recent channel model document of IEEE 802.11 working group [44]. As shown in Figure 16, the performance of the legacy channel access procedure is degraded dramatically for case 1. It means that 1000 m, which is an ideal coverage range of IEEE 802.11p-based system, may not be achievable in real world. Although the proposed NG-V2X shows much better performance thanks to its narrow signal bandwidth, the performance also drops significantly for case 1. For case 2, 250 m coverage range case, legacy channel access procedure shows the user capacity threshold performance that is relatively close to the ideal case performance, even though the delay increases. The proposed NG-V2X shows almost the same performance as the ideal case for case 2. It means that not only the proposed NG-V2X shows better user capacity as mentioned in the previous simulation results, but also it provides better coverage range performance for the next-generation V2X systems. In addition to performance comparisons among channel access schemes we have proposed, we also performed the delay and PLR performance simulation under various \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Index** & **Channel Model** & **Scenario** & **Vehicles (STAs) Distribution Radius** & **Shadowing** \\ \hline \multirow{3}{*}{Ideal} & ITU-R & Line of sight (LOS) only & 1000 m (Uniformly) & No \\  & (UMa) & LOS and non-LOS (NLOS) & 1000 m (Uniformly) & 3 dB \\ \multirow{3}{*}{Case 1} & ITU-R & \multirow{3}{*}{LOS and NLOS} & \multirow{3}{*}{250 m (Uniformly)} & \multirow{3}{*}{3 dB} \\  & (UMa) & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Channel model parameters for simulation. Figure 15: Average delay and PLR comparison for legacy, High Priority EDCA, proposed NG-V2X, proposed Scheduled NG-V2X channel access. it is easily expected that a too small OCW may cause frequent collisions and a too large OCW may cause unnecessary channel access delay. To check the exact influence of the OCW, we performed V2X-UORA channel access simulation multiple times with different OCW values and a fixed number of users.