## 3 The Experimental Results
### Packet Delivery Ratio  
The DSRC was confirmed to have a high reliability in a dynamic network topology. The PDR had a high rating with minimal deviations. We could say that the trend was more or less constant, as it was very close to the maximum PDR value (Figures 2a, 3a, 4a, 5a, 6a and 7a); that is, for the most part, the communication perimeter and the message generation frequency did not play a role in this case. When we compare the results obtained for the DSRC and LTE technologies, we can conclude that the PDR values obtained were much worse in both LTE scenarios, i.e., the LTE-Infrastructural (Figures 2b, 3b, 4b, 5b, 6b and 7b), and LTE-D2D mode (Figures 2c, 3c, 4c, 5c, 6c and 7c). The best PDR (around 92%) was obtained for the LTE-Infrastructural mode. With the increase in the message generation frequency for the two lowest traffic intensities, the PDR was a bit higher. On the other hand, the PDR decreased with higher values of the traffic intensity. The communication perimeter had a rather minor impact when it came to the lowest traffic intensities. The impact was more severe for the higher ones, but was still rather negligible in comparison to the LTE-D2D scenario. It achieved the worst results when the high message generation frequency and the largest perimeter were combined. In the LTE-D2D case, the behavior was quite different (Figures 2c, 3c, 4c, 5c, 6c and 7c). The increased value of the perimeter caused a higher PDR. This was also the case for the higher message generation frequency, except with the communication perimeter of 200 m. The best results were achieved for the combination of the greater perimeter and higher message generation frequency. This sounds rather unintuitive at first glance; however, the reason for this behavior lies in the topology of the communication network. On one hand, with a decreasing perimeter, the communicating vehicle is closer to the RSU. On the other hand, its distance from the serving eNodeB increases, which results in less reliable resource scheduling for the transmitting vehicles, and collisions start to occur. Hence, the simulation results suggest that in the case of the LTE-D2D mode 3 communication, the distance between the transmitter and the eNodeB might have an even greater impact on the PDR than the distance between the transmitter and receiver. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Carrier frequency & 5900 MHz \\ Channel bandwidth & 10 MHz \\ Data rate & 6 Mbps \\ Transmit power & 20 dBm \\ Path loss model & Two Ray Interference \\ TX antenna gain & 0 dBi \\ RX antenna gain & 0 dBi \\ \hline \hline \end{tabular}
\end{table} 
Table 4: DSRC-specific parameters. Figure 3: Packet delivery ratio obtained for the traffic intensity of 500 vehicles per hour. Figure 2: Packet delivery ratio obtained for the traffic intensity of 250 vehicles per hour. Figure 4: Packet delivery ratio obtained for the traffic intensity of 750 vehicles per hour. Figure 5: Packet delivery ratio obtained for the traffic intensity of 1000 vehicles per hour. Moreover, a comparison of the LTE scenarios is rather interesting, as the opposite trends are nicely visible in the graphs, i.e., the communication perimeter played a rather important role in the case of LTE-D2D, which was not the case when it came to the LTE-Infrastructural mode. Moreover, the PDR in the LTE-D2D scenario was very dependent on the number of nodes, which is the case for LTE-D2D. Figure 6: Packet delivery ratio obtained for the traffic intensity of 1250 vehicles per hour. Figure 7: Packet delivery ratio obtained for the traffic intensity of 1500 vehicles per hour. the distance of the transmitter from the serving eNodeB. This was probably due to the fact that the resource scheduling was unreliable over long distances, and collisions occurred. We can conclude that the traffic intensities of 250 and 500 vehicles per hour in the LTE-Infrrastructural mode offered the best results (Figures 1(b) and 2(b)).