## 4 Performance Evaluation
### LTE Mode 3  
Unlike LTE mode 4, the standard does not define a specific resource allocation mechanism in mode 4. Thus, there is the possibility of defining different mechanisms to reduce channel congestion and packet losses, especially in environments with a high density of vehicles on the roads. In order to carry out simulations in mode 3, an analytical model defined in [20] is applied. This model, called DIRAC (aDaptive spatial Reuse of rAdio resourCes), is developed on MATLAB and allows us to set up scenarios similar to those considered in mode 4. This model takes advantage of the geographic location of the vehicles to establish a dynamic configuration so that all vehicles experience a similar level of interference. In addition, this model reduces the signaling overhead inherent in a centralized mode. The reference parameters considered in the model are the same as described in Table 3. Thus, Figure 10 shows the variation of the PDR as a function of distance for different packet transmission rates in mode 3. A vehicle density of 0.06 vpm on the road is considered. The results show, as in mode 4, that increasing the packet transmission rate limits the distance range for a given PDR. However, in all cases, the performance of mode 3 is better than mode 4. For packet transmission rates of 10 and 20 pps, the PDR is above 95%. For 50 pps, the same PDR level is maintained, but the coverage range is limited to 200 m.  
Figure 10: PDR variation as a function of distance for different V2V packet transmission rates in LTE mode 3. Figure 9: PDR as a function of propagation distance under different transmission powers. Figure 11 shows the variations of PDR considering different densities of vehicles on the road. In this case, in slow scenarios the PDR are significantly affected compared to highway fast scenarios due to a higher density of vehicles on the road. However, for 50 pps, a PDR above 80% is guaranteed for distances less than 100 m.  
Both LTE mode 3 and LTE mode 4 simulations show that a PDR above 90% can only be guaranteed for short distances. Table 2 shows that use cases require a range of coverage to function properly. For example, for extended sensors, the required coverage distance can be up to 1 km. Whether using centralized or non-centralized LTE modes, the required network reliability of 90 to 99.999% cannot be guaranteed. Worse still, conditions degrade when the packet transmission frequency or the density of vehicles on the roads increase, and when transmission power is reduced. Given that advanced use cases involve demanding potential requirements such as bandwidths, latencies, reliability and coverage ranges that cannot be offered by LTE networks, it is necessary to network architectures that allow us to meet such indicators. One solution that has been envisioned to solve the challenges presented in this scenario relates to the use of multi Radio Access Technologies (RAT)-Dual Connectivity (DC) architectures. In this sense, the combination of different technologies (LTE V2X, NR V2X) and communication interfaces (LTE Uu, NR Uu, PC5 for LTE SL and NR SL) is possible. This involves the need to combine V2V, V2I and V2N communications. The MR-DC approach can ensure robust and reliable communications because the same information is sent redundantly over several interfaces. On the other hand, thanks to V2I and V2N communications, the communications range can be extended. However, in both cases, an increase in communication latency must be taken into account because the traffic must pass through transmission nodes. Thus, different forms of communication can be used depending on the potential requirements of each service, as shown in Tables 1 and 2.