## 3 SD-QGrid Routing Platform and Algorithms
### SD-QGrid Online Routing Decision Process
### Simulation Results

First, we compare the impact of the transmission range (distance) on the performance of the routing algorithm. Figure 14 shows that the distance gradually increases, and the transmission success rate also increases. On the contrary, because the packet arrives at the end point faster, the end-to-end delay and the overall network environment overhead will be reduced accordingly. Among the four methods, the GPSR method simply selects the neighbor node closest to the end point for packet forwarding; thus, the end-to-end delay is the lowest, but the transmission success rate is also the lowest, and the overhead is also the highest. The advQGrid transmission success rate and overhead are better than that of QGrid because the vehicle node will continue to carry packets until arrival at the destination grid, but in exchange for the highest end-to-end delay. On the contrary, although our proposed SD-QGrid method considers the real vehicle movement trajectory and the source-to-destination directionality in different time periods, compared with QGrid and its improved method advQGrid, it pays slightly more overhead, but achieves the highest delivery ratio and considerably reduces its end-to-end delay. In conclusion, compared with QGrid, our method increases the average delivery ratio by 17%, reduces the end-to-end delay by 27.09%, and pays a 1.04% overhead, which is shown in Table 9. Compared with advQGrid, the average delivery ratio increases by 10.22%, the end-to-end delay decreases by 31.93%, and the overhead is 1.24%. We compare the impact of the packet time-to-live (TTL) on the performance of the routing algorithm. Figure 15 shows that the packet time-to-live (TTL) gradually increases, the transmission success rate increases accordingly, and the end-to-end delay and the overall network environment overhead also increase. Compared with QGrid and its improved method, advQGrid, although our proposed SD-QGrid method pays slightly more overhead, it can achieve the highest transmission success rate and minimize the \begin{table}
\begin{tabular}{l c c c} \hline \hline  & **Average Delivery** & **Average End-to-End** & **Average Transmission** \\  & **Ratio** & **Delay** & **Overhead** \\ \hline QGrid & +17.00\% & \(-\)27.09\% & +1.04\% \\ advQGrid & +10.22\% & \(-\)31.93\% & +1.24\% \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Performance improvement of SD-QGrid compared to routing protocols with distances. end-to-end delay. As the TTL gradually increases, compared with QGrid and advQGrid, the end-to-end delay of SD-QGrid increases more smoothly. In conclusion, compared with QGrid, our method increases the average delivery ratio by 21.01%, reduces the end-to-end delay by 24.7%, and pays a 1.09% overhead, which is shown in Table 10. Compared with advQGrid, the average delivery ratio increases by 13.66%, the end-to-end delay decreases by 34%, and the overhead is 1.53%. Figure 14: Simulation comparison among different routing protocols vs. different distances. Figure 15: Simulation comparison among different routing protocols vs. different TTLs. Finally, we compare the effect of the packet generation interval (message time) on the performance of the routing algorithm. As shown in Figure 17, as the message time gradually increases, the number of packets in the overall network decreases, and the transmission success rates of the four methods increase. The overhead decreases, and the end-to-end delay remains relatively stable. As shown in the data graphs of the three horizontal-axis parameters mentioned above, compared with QGrid and its improved advQGrid method, \begin{table}
\begin{tabular}{l c c c} \hline \hline  & **Average Delivery** & **Average End-to-End** & **Average Transmission** \\  & **Ratio** & **Delay** & **Overhead** \\ \hline QGrid & +21.01\% & \(-\)24.70\% & +1.09\% \\ advQGrid & +13.66\% & \(-\)34.00\% & +1.53\% \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Performance improvement of SD-QGrid compared to routing protocols with TTLs.