## 3 Vehicle Clustering Algorithms
### Vehicle Clustering Method Based on DBSCAN Algorithm
### Simulation Scenario and Parameter Settings

(1) Road Environment Parameter Settings

According to the _Technical Standards of Highway Engineering_ (JTG B01-2014) [34], the width of a dual carriageway with four lanes in each direction is 3.75 \(\times\) 2 \(\times\) 2 m. Considering the presence of emergency lanes and the width required for RSU installation in actual highway scenarios, the road width for this simulation was set to 20 m. The specific parameters for the road environment simulation are shown in Table 2.

(2) Vehicle Parameter Settings

It was assumed that CAV vehicles in the heterogeneous traffic flow are equipped to communicate wirelessly, and that the communication radius of RSUs is much larger than the width of the highway. The mixed density \(\lambda\) is the number of mixed vehicles per kilometer of highway lane, expressed in vehicles/km; according to the service level of the highway, there can be a maximum of 80 vehicles within a 1000 m long dual carriageway with four lanes in each direction. In this study, a random selection of 0 to 80 vehicles, consisting of both CAVs and non-CAVs, was chosen for simulation. The specific vehicle parameter settings are shown in Table 3.

(3) Communication Environment Parameter Settings

In this simulation, the IEEE 802.11 communication protocol is used with UDP as the communication mode. The specific parameters for the communication environment are shown in Table 4. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Type/Value** \\ \hline Channel type & WirelessChnnel \\ Network interface type & WirelessPhy \\ Interface queue type & PriQueue \\ Link layer type & LL \\ Wireless transmission model & TwoRayGround \\ Antenna type & OmniAntenna \\ Communications protocol & IEEE 802.11 p \\ Frequency band & 5.8 GHz \\ Data stream type & CBR \\ User Datagram Protocol & UDP \\ Data transfer rate & 2 Mbps \\ Bandwidth & 75 MHz \\ Packet size & 1000 Bytes \\ Number of simulation rounds & 4000 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Communication Environment Simulation Parameters. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Type/Value** \\ \hline Simulation region & 1000 m \(\times\) 20 m \\ RSU communication radius R (m) & 200, 300, 400, 500 \\ RSU deployment coordinates & (500, 10) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Road Environment Simulation Parameters. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Type/Value** \\ \hline Speed (m/s) & 17–33 \\ Number of mixed vehicles & 0–80 \\ Vehicle communication radius RV (m) & (200, 300, 400, 500) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Vehicle Simulation Parameters. ### Simulation Results and Analysis

Under the assumption that the arrival of vehicles on the highway follows a Poisson distribution, using a mixed traffic density of 0.03 and based on the simulation parameter settings in Section 4.1, 30 vehicle nodes were randomly generated within a simulated section of a 1000 m \(\times\) 20 m highway. The distribution of the vehicle nodes is shown in the figure below. The RSU was placed at the center of the four-lane highway, with coordinates (500, 10). Figure 3 shows the distribution of vehicle nodes before and after the establishment of vehicle cluster in vehicle-road communication network. The figure on the left of Figure 3 represents the distribution positions before the randomly generated vehicle clustering, and each hollow circle \"\(\bigcirc\)\" represents the location of a vehicle node. The solid circles \"\(\bullet\)\" in different colors on the right of Figure 3 all represent vehicle nodes. According to the DBSCAN clustering algorithm, all vehicle nodes are divided into three vehicle clusters, which are distinguished by different colors. The node closest to the cluster center in each cluster is the cluster head, which is represented by a black hollow circle \"\(\bigcirc\)\" in the figure, and a red five-pointed star \"\(\times\)\" represents the position of roadside units.