## 3 The Experimental Results
### Average End-To-End Message Latency  
It is worth reiterating here that the presented values represent the average delay, i.e., averaged over all communication sessions realized in the corresponding simulation runs. Similarly to with the PDR, the DSRC also obtained much better results when it came to the end-to-end delay (Figures 7(a), 7(a), 7(a), 7(a) and 7(a)). With increasing values of the message generation frequency and communication perimeter, the delay also increased. Naturally, the lowest delay values were reported for the lowest values of the perimeter and message generation frequency. Moreover, decreasing traffic intensity led to better values of the delay, especially for higher values of the perimeter and message generation frequency. For both LTE modes, i.e., LTE-Infrrastructural (Figures 7(b), 7(b), 7(b), 7(b), 7(b) and 7(b)) and LTE-D2D (Figures 7(c), 7(c), 7(c), 7(c) and 7(c)), the behavior was the same as that reported for the DSRC. So, the delay values increased with the increase in the perimeter or frequency of the generated messages. Regarding the traffic intensity, the trend was again the same as that reported for the DSRC. Please note that the values of the average end-to-end delay were approximately four orders of magnitude lower in the case of the DSRC than for both LTE-based technologies. Figure 8: End-to-end delay obtained for the traffic intensity of 250 vehicles per hour. Figure 10: End-to-end delay obtained for the traffic intensity of 750 vehicles per hour. Figure 9: End-to-end delay obtained for the traffic intensity of 500 vehicles per hour. Figure 11: End-to-end delay obtained for the traffic intensity of 1000 vehicles per hour. Figure 12: End-to-end delay obtained for the traffic intensity of 1250 vehicles per hour. Generally, we can conclude that neither mode of LTE was suitable for perimeters greater than 600 m. A lower frequency of message generation (two or four) could also be used for perimeters of 800-1000 m in the infrastructural mode. The D2D mode was applicable only for very short distances/perimeters. With greater perimeters, the traffic intensity began to play a more important role. It is worth noting here that the absolute value of the delay was significantly reduced in the LTE communications when the infrastructural mode was deployed. However, with the increasing number of communicating vehicles, it was easy to see how the end-to-end delay started to fluctuate as the PDR grew and HARQ retransmissions began to occur, as illustrated in Figures 11(b) and 11(b). This effect was observed when there were more than 90 simultaneously communicating vehicles within the same cell, and its significance grew with the increasing traffic intensity. The PDR in these cases was as low as 50%. Putting the obtained results into the context of the networking and connectivity requirements of the most popular V2I services [22], the DSRC was able to fulfill the latency requirements for all the types of V2I services in all of the investigated urban scenarios. The LTE in the infrastructural mode was able to partially fulfill the requirements within a limited communication perimeter (<600 m) for the services that required less frequent updates (1-2 Hz) and that had less stringent latency requirements (<500 milliseconds). V2I services that require low-latency communication (<100 milliseconds) combined with less frequent updates (1-2 Hz) could be served by the LTE-Infrastructural technology within a limited perimeter (<600 m) and for traffic intensities of up to 1000 vehicles per hour. The LTE in the D2D mode 3 was not able to serve any of the most popular V2I services in the selected use case. Moreover, the simulation results suggest that in all of the investigated scenarios, only the DSRC was able to support the V2I services with the most stringent requirements in terms of latency and message generation frequency.