## 6 Results
### Experimental Results  
#### 6.2.1 Parameter Selection  
Choosing a good value for \(\alpha,\beta,d_{limit}\) can enhance the stability of the cluster and control the number of clusters. In the experiment, we used the dichotomy method to roughly determine the value of \(\alpha\) in \([0,2.0]\), the value of \(\beta\) in \([-50,-200]\), and the value of \(d_{limit}\) in \([100,300]\). After determining the value range, each different parameter combination was tested in 20 different road simulation environments, and the clustered results were obtained. Figure 5 is a box plot obtained in the test of the effect of different values of \(\alpha,\beta,d_{limit}\) on the number of clusters and cluster stability.  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Parameter** & **Value** \\ \hline Parameter \(\alpha\) of Equation (1) & 0.1 \\ Parameter \(\beta\) of Equation (1) & \(-150\) \\ Maximum allowable distance that two clusters can be merged \(d_{limit}\)(meter) & 170 \\ Threshold for establishing a robust communication link \(D_{threshold}^{vehicle}\) & 6 \\ Length of road (meter) & 2000 \\ Number of vehicles & \(\mathcal{N}(130,5)\) \\ Communication radius of DSRC \(R\) (meter) & 400 \\ DSRC sub-carrier spacing (KHz) & 156.25 \\ Speed of vehicle \(v\) (meters per second) & \([18,28]\) \\ Data transfer rate of DSRC \(f^{DSRC}\) (Mbps) & 200 \\ Data packet _Size_ (Byte) & \([200,1800]\) \\ Maximum delay allowed \(l_{ik}\) for \(b_{ik}\) (ms) & \(\mathcal{N}(17,8)\) \\ Vehicle’s data generation rate \(r\) (Mbps) & \([0.4,8]\) \\ The unit price of C-V2X traffic charges \(p\) (per MB) & 0.1 \\ Upper limit of vehicles in a cluster \(N\) & 15 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Experimental parameter settings.  
According to Equation (1), \(\alpha\) is the weight of \(Y_{ij}\), but \(Y_{ij}\) is only affected by the current state of the vehicle, and the vehicle state may change at any time. Thus, reducing the influence of \(Y_{ij}\) on \(D_{ij}^{cluster}\) can increase the stability of the cluster. With a continuous decrease in \(\alpha\), the stability of the cluster shows an increasing trend and the outliers gradually decrease. So, the value of \(\alpha\) is 0.1. If two clusters of \(c_{i}\) and \(c_{j}\) at the edge of each other's DSRC communication range are merged, the resulting cluster may be very unstable. By increasing \(\beta\), the \(D_{ij}^{cluster}\) value of the two clusters can be reduced, thereby limiting the merging of these two clusters. However, as shown in Figure 5b,e, when \(\beta\) is greater than \(-160\), the beta has less effect on cluster stability and the number of clusters. This is because the D-limit limits the maximum distance that clusters are allowed to merge, which makes it less likely that clusters at the edge of mutual DSRC communication can merge. At \(\beta=-160\), the mean of the number of clusters increases, and in some cases the number of clusters starts to increase. So we take the value of BETA as \(-150\). As shown in Figure 5e,f, \(d_{limit}\) has an important impact on the number and stability of clusters. The larger the \(d_{limit}\) is, the more distant the clusters can be merged. When \(d_{limit}\) is 170, a reasonable number of clusters can be obtained while maintaining good stability. At this time, the number of clusters will be reduced, and the clusters containing more CMs will be less stable. Therefore, as increases, both the stability of the cluster and the number of clusters tend to decrease. The final values of the three parameters are 0.1, \(-150\), and 170.