## 3 Experimental Results
### Fixed Infrastructure Density Scenario
#### 3.1.1 Packet Delivery Ratio  
As it can be seen in Figures 2a, 3a, 4a, 5a, 6a and 7a, 4G-based C-V2X in the infrastructural mode has steadily maintained very high values (up to 99.7%) of PDR in the perimeter of up to 1000 m. Beyond 1000 m, PDR has started to drop, reaching the lowest value of around 80% for the largest simulated perimeter, i.e., 1400 m.  
The simulation results for the 4G-based C-V2X communication in device-to-device mode 3 obtained for the traffic intensities ranging from 250 to 1500 vehicles per hour are depicted in Figures 2c, 3c, 4c, 5c, 6c and 7c. It can be seen from the above-listed figures that the best performance in terms of PDR is achieved when the messages are transmitted with the message generation frequency ranging from 4 to 10 Hz and the communication perimeters up to 1000 metres are considered. Increasing the perimeter beyond 1000 m results in a considerable drop in PDR. Interestingly, for the lowest simulated value of the message generation frequency, i.e., 2 Hz, the 4G-based C-V2X in device-to-device mode 3 has experienced approximately 10% drop of PDR compared to the higher message generation frequencies, considering the same perimeter. This performance drop was not observed among the other simulated technologies and is likely caused by an inefficient scheduling of the short and relatively infrequent messages. The 4G-based C-V2X in device-to-device mode 3 has maintained an average PDR value above 75% under all the combinations of simulation variables. Figure 3: PDR simulated for all the investigated modes of the 4G-based and 5G-based C-V2X technologies and traffic intensity of 500 vehicles per hour. Figure 2: Packet Delivery Ratio (PDR) simulated for all the investigated modes of the 4G-based and 5G-based C-V2X technologies and traffic intensity of 250 vehicles per hour. Figure 4: PDR simulated for all the investigated modes of the 4G-based and 5G-based C-V2X technologies and traffic intensity of 750 vehicles per hour. Figure 5: PDR simulated for all the investigated modes of the 4G-based and 5G-based C-V2X technologies and traffic intensity of 1000 vehicles per hour. In both simulated modes of 4G-based C-V2X, no significant impact of the traffic intensity on PDR has been observed, contrary to the results presented in [16]. While in [16], the whole area was served by two cells only, in this study, the same area is divided into four cells, resulting in a better load balancing between the cells. By increasing the traffic intensity in [16], the density of the network nodes, i.e., vehicles, approached the capacity of the cells. The similar phenomenon was not observed in this study thanks to the increased number of the cells and therefore the increased capacity of the network. The 5G-based C-V2X in the infrastructural mode (Figures 2b, 3b, 4b, 5b, 6b and 7b) has achieved very high PDR values (up to 98.8%) for the communication perimeters below 800 m. The PDR has dropped significantly beyond 800 m and remained relatively stable, reaching values around 75% for the perimeters of up to 1400 m. This seems to be caused by an insufficient signal strength due to the rather long communication link. A slight impact of the traffic intensity can be seen in the case of the 5G-based C-V2X in the infrastructural mode, where the minimum achieved PDR decreases with the increasing traffic intensity. No significant impact of the message generation frequency on PDR was observed when using the 5G-based C-V2X in the infrastructural mode for V2I communication in the simulated urban scenario. The 5G in the device-to-device mode 3 (Figures 2d, 3d, 4d, 5d, 6d and 7d) has achieved the lowest performance in terms of PDR from all the investigated technologies. The technology has achieved its peak PDR performance, i.e., 98.8%, in the lowest traffic intensity scenario (Figure 2d) and for the perimeters of up to 400 m. This decrease of PDR is more severe as the traffic intensity increases, as it can be seen in Figures 5d, 6d and 7d.