## 7 Results and Analysis
### Simultaneous CAM and DENM Transmission  
In conjunction with the periodically transmitted CAMs, there may be a necessity to transmit dynamically triggered DENMs for various reasons. DENMs can be sent for notifications such as Slow or Stationary Vehicle (SSV), Road Works Warning (RRW), Accident Notification (AN), and Emergency Vehicle Alert (EVA), among others. The proposed hybrid V2X technology selection algorithm also accommodates DENMs and tries to create a balance between CAMs and DENMs. In this regard, multiple approaches can be considered, such as: (a) to pause CAMs for a certain duration, (b) to use different technologies for CAMs and DENMs, and (c) to adapt CAM and DENM frequency in order to minimize the load on the network, meaning, the traffic densities for CAMs and DENMs. In this study, option (c) has been considered. For highly dense traffic scenarios, combination of option (b) and (c) could also be considered along with the underlying pros and cons. This is outside the scope of this paper and will be considered in our future work. Table 5 summarizes CAM/DENM transmission frequencies being used by the proposed hybrid V2X technology selection algorithm for (1) CAM only, and (2) CAM with DENM scenarios. For CAM only scenario, the decision about CAM transmission frequency is based on the CAM density in the last sensing window and its comparison with the density threshold for a particular technology. The vehicle speed is also considered for the selection of CAM transmission frequency. Contrary to it, for joint CAM and DENM transmission scenario, the proposed algorithm considers the minimum possible frequency for CAMs i.e., 1 Hz, whereas, for a better dissemination of crucial time-limited DENMs, the average frequency value has been used i.e., 5 Hz. The reason behind this DENM frequency selection is to create a balance between putting too much load on the network, in turn optimizing resource utilization, and also avoiding the usage of minimum DENM frequency value, in turn, optimizing the reachability of DENMs. Figure 17 shows the results for the test where both CAMs and DENMs are sent intelligently. The distance between \(OBU1\) and \(OBU2\) is shown in Figure 17a. The observed one-way end-to-end latency for hybrid CAMs and hybrid DENMs is plotted in Figure 17b as the \(OBU2\) (the vehicle) moves towards and away from the \(OBU1\). The same latency and distance thresholds have been used for this experiment as well. As the distance is varied, the hybrid V2X technology selection algorithm selects different technologies, as in Figure 17c for sending the next scheduled CAM/DENM. The highest latency values were observed when the distance was greater than \(D_{thr2}\), implying long-range 5G as the only possible technology for maximizing CAM/DENM PDR. It can also be compared with the CDF of the received CAM latency from Figure 12, where the curve for 5G accounts for the portion of values greater than 40 ms. For distance greater than \(D_{thr2}\), irrespective of the fact that both CAMs and DENMs also experience high latency values as in Figure 17b, C-V2X PC5 and/or DSRC are not considered due to their limited transmission ranges. For distances between \(D_{thr1}\) and \(D_{thr2}\), it is observed that mostly both CAMs and DENMs are sent via C-V2X PC5. However, to maximize the reliability of CAMs and DENMs between \(D_{thr1}\) and \(D_{thr2}\), CAMs and DENMs are occasionally sent via 5G if the average one-way end-to-end CAM reception latency via C-V2X PC5 falls below the \(L_{thr}\). As emphasized in Table 5, the proposed hybrid V2X technology selection algorithm adapts the CAM transmission frequency in order to better accommodate the DENMs without burdening the network in the presence of DENMs.