## 7 Results and Analysis
### One-Way End-to-End Latency  
Figure 12 shows the Cumulative Distribution Function (CDF) of the observed one-way end-to-end CAM reception latency on OBU2 (the vehicle). The distance between OBU1 and OBU2 is varied from 1 to 350 m for this experiment and multiple trials were conducted to ensure statistical significance. Being built on top of 802.11p, DSRC uses CSMA/CA for accessing the wireless medium. Considering a small scale experimental setup, DSRC channel is always available and the CDF of DSRC is concentrated between 3-5 ms. This makes DSRC as a top contender for latency critical applications in low dense scenarios. However, as explained later, the drawback for DSRC lies in its limited coverage compared to the 5G long-range. Also, CSMA/CA can have an impact on latency in more dense scenarios. For C-V2X PC5 operating in mode 4, sensing-based SPS is used for radio resource selection. It can be observed that the one-way end-to-end CAM transmission latency for C-V2X PC5 and 5G long-range is higher than the one for DSRC but both of them provide better coverage than DSRC in our setup. For the hybrid scenario where technology selection decision is based on a number of selection criteria as described in Section 5, DSRC is preferred mode of communication for distances less than \(D_{thr1}\). The intelligent algorithm senses the variation in distance and as soon as the distance between V2X nodes is higher than \(D_{thr1}\), C-V2X PCS is selected. Similarly, when the distance between V2X nodes is higher than \(D_{thr2}\), 5G is selected. The curve for hybrid communication is a mixture of DSRC, C-V2X PC5 and 5G owing to the intelligent real-time statistics-driven V2X technology selection.  
Figure 13 shows the distance variation between \(OBU1\) and \(OBU2\), the observed one-way end-to-end CAM transmission latency and the intelligently selected V2X technology. The distance and latency thresholds used for the tests are also plotted in Figure 13a and Figure 13b, respectively. \(OBU1\) maintains a stationary position, while \(OBU2\) (the vehicle) drives both away from and towards the \(OBU1\). It should be noted that \(D_{thr1}\) and \(D_{thr2}\) are  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Testing rounds & 10 \\ Total testing days & 5 \\ Total CAMs sent & 22,000 \\ Total DENMs sent & 52,000 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Experimental statistics.  
tuneable parameters and could be adapted based on the transmission ranges for DSRC and C-V2X PC5. Similarly, \(L_{thr}\) is another tuneable parameter and depends on the QoS requirements of the considered use case. Again, it can be observed from Figure 13 that DSRC is the only technology being used in hybrid scenario when the distance is less than \(D_{thr1}\). However, when the distance is between \(D_{thr1}\) and \(D_{thr2}\), both C-V2X PC5 and 5G have been selected intelligently as in Figure 13c. The reason for this is the \(L_{thr}\) of 20 ms. If the average C-V2X PC5 latency during the previous sensing window goes beyond the \(L_{thr}\), CAMs are also sent via 5G as well in an attempt to reduce the transmission latency of CAM(s).  
Figure 12: CDF of one-way end-to-end CAM latency showcasing improvement with hybrid V2X technology selection.  
Figure 13: CAM transmission using hybrid V2X, (**a**) distance between OBU1 and OBU2, (**b**) observed one-way end-to-end CAM latency on OBU2, and (**c**) intelligently selected V2X technology on OBU1.