# Hybrid Trust Model for Node-Centric Misbehavior Detection in Dynamic Behavior-Homogeneous Clusters
## 4 Segmentation of Dynamic Behavior-Homogeneous Vehicular Cluster
### Dynamic Cluster Head Selection  
In a vehicular network environment, the formation of a vehicle cluster occurs when at least two vehicles are within a range that allows mutual reachability, as determined by their respective Received Signal Strength (RSS). In other words, two vehicles must be within each other's RSS communication range to form a cluster. A vehicle cluster is a collection of vehicles within a 300 m radius centered around a mobile vehicle cluster head. The cluster head vehicle generates and distributes group keys within the vehicle cluster. The dynamism and flexibility of the vehicular network are evidenced by the possibility of multiple vehicle clusters and the same vehicle being a member of different clusters. The selection of a dynamic Cluster Head (CH) is categorized into three scenarios: initialization, update, and departure.  
* Cluster Initialization  
At the initiation of a region, the first vehicle to initiate communication authentication through the RSU and succeed is selected as the Cluster Head (CH). The second vehicle to initiate communication authentication within the same range is chosen as the Backup Cluster Head (BCH).  
* Cluster Head Update  
The trust value is assessed based on vehicle behavior, and potential cluster head vehicles are elected based on this trust value. The vehicle with the highest trust value in the group is considered the potential CH, and the one with the second-highest trust value is seen as the potential backup CH.  
* Cluster Head Departure  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Notations** & **Description** \\ \hline \(k\) & Constant parameter \\ \(T_{r}(v_{i})\) & The indirect trust value of vehicle \(v_{i}\) \\ \(T_{tot}(v_{i})\) & The total trust value \\ \(\mu,\gamma\) & The weights of direct and indirect trust values \\ \(T_{tot}(v_{i})\) & The total trust list of neighboring vehicles \\ \(T_{totar}(v_{i})\) & The average total trust value of \(v_{i}\) \\ \(n\) & The frequency of occurrence of the total trust value of vehicle \(v_{i}\) \\ \(T_{tot}^{i}(v_{i})\) & The total trust value of vehicle \(v_{i}\) computed by vehicle \(v_{j}\) \\ \(T_{glob}(v_{i})\) & The global trust value \\ \(T_{totar}^{i}(v_{i})\) & The average total trust value \\ \(T\) & The time range for direct trust calculation \\ \(L(t_{0}-t_{k})\) & Time distance \\ \(T_{glob}(v_{i})^{T}\) & The direct trust within the sliding time window T \\ \(A\
u(v_{i})\) & The consistency parameter \\ \(T_{thresh}^{o}(v_{i})\) & The trust threshold of vehicle \(v_{i}\) at the vehicle layer \\ \(T_{thresh}^{c}(v_{i})\) & The trust threshold of vehicle \(v_{i}\) at the cluster head layer \\ \(\omega_{t}\) & The periodic check parameter \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._There are two scenarios for the departure of the cluster head from the current area: the CH voluntarily leaving the vehicle cluster and the CH being out of the current range. When the CH voluntarily leaves, it notifies the area's RSU of its departure and delegates the CH responsibilities to the BCH. Not all vehicles selected by the previous CH may be within the communication range. Therefore, after the BCH becomes the new CH, the vehicle cluster needs to be reorganized and updated according to the current situation and the group key. If the CH is out of range, the vehicle members of the group will detect whether it is still within communication range by periodically receiving messages from the CH. If no message from the CH is received within a certain time (e.g., 300 ms), the cluster members will delete the cluster ID and apply to join another vehicle cluster.