## 4 Simulations and Results
### Simulation Settings and Results Format  
The main simulation settings are summarized in Table 4. A highway scenario is assumed, with vehicles uniformly distributed over six lanes (three per direction) with variable density. Each vehicle is equipped with one of the two technologies, selected randomly with different proportions. Both a balanced distribution, with 50-50% IEEE 802.11p and NR-V2X, and an unbalanced distribution, with 33-66% are considered. In the case of unbalanced, the case with a majority of VUEs equipped with IEEE 802.11p is denoted as the _more-V\({}_{11p}\) scenario_ and the one with a majority of VUEs equipped with NR-V2X is denoted as the _more-V\({}_{\text{NR}}\) scenario_. It can be noted that the 33-66% distribution is far from the worst case and allows us to investigate a quite common situation under normal traffic where the local distribution of technologies cannot be controlled and would be presumably highly variable. \begin{table}
\begin{tabular}{l l} \hline \hline
**Common Settings** & \\ Scenario & Highway, 3 + 3 lanes, variable vehicle density, average speed 120 km/h with 12 km/h std. deviation \\ Data traffic & Packets with 350 bytes payload generated periodically every 100 ms or following the CAM generation rules \\ Channel and power & Single 10 MHz channel at 5.9 GHz, Tx power 23 dBm (not including antenna gain), antenna gain 3 dBi, noise figure 6 dB \\ Propagation & Modified ECC Report 68 rural [27] path-loss model, log-normal shadowing with 3 dB variance and decorr. dist. 25 m \\ Other settings & Ideal synchronization, congestion control disabled \\ \hline
**For IEEE 802.11p** & \\ MAC settings & \multirow{2}{*}{Rx} & Contention window 15, AIFS 110 μs, SIFS 32 μs \\ MCS-11p & & \(-\)65 dBm with unknown signals; 85 dBm with known signals or when M\({}_{\text{B}}\)-E-signals is assumed \\ thresholds & \\ \hline
**For NR-V2X** & \\ MCS-NR & MCS 8 (QPSK, CR \(\approx\) 0.60), with SINR threshold 7.7 dB [15] \\  & Each packet (350 bytes) occupies 2 subchannels \\ PHY layer & SCS 30 kHz, 12 physical resource blocks (PRBs) in each subchannel, which means 2 subchannels in the 10 MHz channel \\  & The first-stage sidelink control information (SCI) occupies 3 OFDM symbols and 12 PRBs \\  & 18 resource elements (REs) are used as demodulation reference signal (DMRS) during each TTI \\  & Blind retransmissions are disabled \\ \hline
**Coexistence** & \\ Superframe & \(\text{T}_{\text{SF}}\) = 25 ms, \(\text{T}_{\text{NR}}\) = 13 ms, \(\text{T}_{\text{11p/bd}}\) = 12 ms \\ Technology Ratio & Balanced (\text{V}_{\text{NR}}\):V\({}_{\text{11p}}\) = 1:1) or unbalanced with More-V\({}_{\text{11p}}\) (V\({}_{\text{NR}}\):V\({}_{\text{11p}}\) = 2:1) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Main simulation parameters and settings. Figure 8: Illustration of M\({}_{\text{E}}\)-reservation-&-preamble. It is a combination of methods C and D. Only V\({}_{\text{NR}}\) know the superframe structure and they would use both the IEEE 802.11p preamble and reservation message to reserve resources. The subfigure (**a**) is from the V\({}_{\text{NR}}\) perspective, and the subfigure (**b**) is from the V\({}_{\text{11p}}\) perspective. Packets of 350 bytes are assumed, which is consistent with the average CAM packet size observed in [28]. The packets are either generated periodically every 100 ms (the highest frequency for CAM messages) or following the CAM rules. Regarding the propagation, the modified version of the ECC Report 68 path-loss model detailed in [27] is used in this paper, which is characterized by a path-loss exponent of 3.3 and range in good agreement with on-field measurements (the same model is used for both technologies). Log-normal shadowing is also considered, with a variance of 3 dB and decorrelation distance of 25 m. Fast fading is taken into account by the PHY layer abstraction as detailed in [29]. It can be observed that the studied scenario is 2-D; different models, such as those proposed in [30; 31; 32] could be used when a 3-D scenario was investigated in the future.