## 4 Proposed Algorithm
### Vehicle Cluster Formation  
In V2X communication, _SidelikeUEInformation_ message to request resource allocation and _MeasurementReport_ message to report location information use the same communication channel [8]. Therefore, in environments where there are many VEs, the RRHs are under heavy traffic load because of periodic messages. To solve this problem, multiple VEs form one cluster, and a cluster head (CH) receives a message from each cluster member (CM) and configures the messages into a jumbo message. A message, called a single frame, consisting of a header and payload, is transmitted periodically between VEs to examine the surrounding environment for ID, time, location, velocity, and so on. CH creates a jumbo frame with multiple single frames consisting of one header and one large payload. Because the headers of multiple single frames become one jumbo frame header, the message size and communication overhead decrease. When a single frame is transmitted at every time unit \(t\), the traffic associated with the single frames is  
\[\sum_{t\in\mathbb{T}}\left(l_{header}+l^{t}_{payload}\right)\cdot N^{t}_{u} \tag{10}\]  
where \(l_{header}\) is the length of the header; \(l^{t}_{payload}\) is the length of the payload; and \(N^{t}_{u}\) is the number of VEs at time \(t\). When CH configures a jumbo frame with multiple single frames, the traffic of the jumbo frames is  
\[\sum_{t\in\mathbb{T}}\left(l_{header}+l^{t}_{payload}\cdot N^{t}_{CM}\right) \tag{11}\]  
where \(N^{t}_{CM}\) is the number of CM. The cluster formation step consists of as followings. 1. First step is initializing step, and it occurs when no cluster is configured or the initial step of algorithm. If the initial step, all the VE associate with RRH serving the highest SINR and are set V2I mode. In first step, V2I mode VE with the highest value \(F_{\text{C}}H^{u}\) is selected as first CH and \(F^{u}_{CH}\) are calculated as follows: \[F^{u}_{CH}=\gamma^{c}_{k}\cdot PPPP^{u}\] (12) where \(PPPP^{u}\) is the prose-per-packet-priority (PPPP) value of VE \(u\). PPPP is the feature of priority in V2X data transmission. Frames to which different PPPP values are assigned wait for transmission of messages from different VEs, where the packets are ordered with PPPP values between 0 and 1 [21]. This ensures that the CH is the first to be placed in the jumbo frame during configuration of the frame to satisfy the PPPP. That is, a payload of CH is located at the first of the jumbo frame. Next, payloads are sequentially arranged according to the \(F^{u}_{CH}\), and CM following CH becomes the next CH. 2. Next step is cluster formation and deformation step, and it occurs in the following situations: (i) When the VE moves to another cell; (ii) when the payload of the jumbo frame exceeds the capacity of the acceptable payload; (iii) when the communication distance between CM and CH exceeds the V2V communication distance constraint. In cluster formation and deformation step, the neighboring vehicles decide whether associating with the cluster or not through comparing receiving SINR between serving RRH and adjacent CH. In this process, the SINR of the serving RRH is compared for each vehicle with those of the neighboring CHs using the messages that each vehicle broadcasts consisting of ID, location, and mobility speed at every time unit. If the SINR of one CH is higher than that of another, then that CH will be clustered with the CH providing the highest SINR. 3. The last step occurs when VEs cannot join any cluster or receive higher SINR from RRH than the SINR from neighboring CHs. Then, the VEs that do not belong to the cluster are set to the V2I mode. However, if the same vehicle becomes CH in succession, an additional load, such as constructing jumbo frames as CH, will be added. In other words, maintaining the CH status for the same vehicle would incur significant overhead and therefore would have to be handed over to other vehicles at certain time intervals. The CH designates the VE, following the current CH in the jumbo frame, as the next CH.