## 7 Results and Analysis
### Reliability  
Figure 15 shows the CAM reliability for various sample latency thresholds. Here, the reliability is only plotted for the three individual technologies without incorporating the hybrid V2X. Reliability for DSRC is always 100% if the distance is less than \(D_{thr1}\). For \(L_{thr}\) of 20 ms, the CAM reliability percentage is 37.4% and 38.5% for C-V2X PC5 and 5G, respectively. However, for higher thresholds of 25 ms and 30 ms, C-V2X PC5 is 18.43% and 13.83%, respectively, more reliable than 5G long-range. This is also evident from Figure 12 as the CDF plots of one-way end-to-end CAM latency for C-V2X PC5 and 5G long-range are more distant at 25 ms and 30 ms mark, as compared to the 20 ms mark. \(L_{thr}\) can be selected appropriately for any V2X application depending on the QoS constraints.  
Contrary to Figure 15, in Figure 16, CAM reliability has been plotted versus the distance for a fixed \(L_{thr}\) of 20 ms, as used in the hybrid V2X technology selection algorithm. It can be observed that the CAM transmission via DSRC is 100% reliable for distance up to 160 m. This is also evident from the CAM latency CDF in Figure 12. After 160 m, CAMs are no more reachable implying infinite transmission time, as replicated by 0% reliability values for DSRC. However, it is important to clarify that CAM PDR is badly affected if the distance increases beyond \(D_{thr1}\). Hence, it will be inefficient if CAM transmissions are continued via DSRC after \(D_{thr1}\). A sudden drop in CAM reliability is observed once the distance is higher than \(D_{thr1}\) for hybrid scenario, implying usage of C-V2X PC5 or 5G. It is justified because the CAM PDR is still 100% for these two technologies past \(D_{thr1}\). As also observed from Figure 13, when the distance is between \(D_{thr1}\) and \(D_{thr2}\), the hybrid V2X technology selection algorithm mostly chooses C-V2X PC5. However, depending on  
Figure 14: Packet Delivery Rate (PDR) maximization with hybrid approach along with the latency improvement shown in Figure 12.  
the latency constraints of a particular V2X application, occasional use of 5G long-range is also observed. Due to this flexibility, CAM reliability is sometimes slightly better between the range of \(D_{thr1}\) and \(D_{thr2}\). When the distance goes beyond the \(D_{thr2}\) threshold, and as the PDR of C-V2X PC5 is also adversely affected, it is crucial to rely on long-range 5G communication link for which the PDR stays very high over the longer distances. Over the whole distance sweep till \(D_{thr2}\), C-V2X PC5 and 5G have almost similar CAM reliability. It is important to clarify that the behaviour could be different if the latency threshold changes to any other value. For example, for latency threshold of 30 ms, in can be observed from Figure 12 that the 95% of the CAMs received via C-V2X PC5 have latency less than 30 ms, while for 5G, only 80% of them have latency less than 30 ms. These values are based on actual measurements in our testbed. Nonetheless, it is important to mention that depending on the number of V2X nodes in a broader setup and the load on any particular technology, these numbers can change. These variations have been catered via different branches of the proposed hybrid V2X technology selection decision tree, as shown in the Appendix A. The CAM reliability curve for the hybrid scenario showcases the usefulness of hybrid V2X technology selection as it strives to constantly maximize the CAM transmission reliability irrespective of the distance.  
Figure 16: CAM reliability maximization with hybrid approach for Lthr = 20 ms.  
Figure 15: CAM reliability percentage for different latency thresholds at any distance \(\leq D_{thr1}\).