# Priority-Driven Resource Allocation with Reuse for Platooning in 5G Vehicular Network
## 4 System Modeling and Resource Allocation Algorithm
### System Model  
As shown in Figure 5, the network model comprises platoon vehicles, general vehicles, and Roadside Units (RSUs) within a multi-lane V2X network. Platoon vehicles perform direct V2V communication with their adjacent platoon members, while general vehicles engage in V2I communication with RSUs or V2V communication with nearby vehicles [40,41]. Both communication types share the same frequency band, with resources allocated using NR-V2X Mode 1. This configuration reflects real-world scenarios where resource competition intensifies due to mixed communication demands. Prior to resource allocation, the base station periodically communicates with platoon vehicles within the cell and stores their identifiers. The set of stored platoon vehicles is then further divided into subsets based on the respective platoons and is defined as follows  
\[V_{p}=\{V_{p}^{(1)},V_{p}^{(2)},\ldots,V_{p}^{(m)}\} \tag{1}\]  
\(V_{p}^{(m)}\) represents the set of vehicles in the \(m\)-th platoon. This set is used in the proposed algorithm to prioritize platoon vehicles during the resource allocation process. For the purpose of resource reuse, identifiers for each platoon are separately stored to distinguish between them. In the network, when vehicles require communication resources, they send a resource request message at time \(t\) using the DG method. The base station allocates the available resource blocks to the vehicles. As shown in Figure 6, vehicles that are present in the cell at time \(t\) and have sent resource request messages to the base station are defined as resource-requesting vehicles, which can be expressed as follows:  
\[V_{t}=P_{t}+G_{t} \tag{2}\]  
Figure 5: V2X communication model in NR-V2X network. \(P_{t}\) represents the set of platoon vehicles that send resource requests at time \(t\), expressed as \(P_{t}=\{1,\ldots,n\}\), and these vehicles belong to the set of platoon identifiers \(V_{p}\), which is pre-stored by the base station. \(G_{t}\) represents the set of general vehicles that send resource requests at time \(t\) but do not belong to \(V_{p}\), expressed as \(G_{t}=\{1,\ldots,m\}\). Each vehicle requires resources according to its data transmission needs. Each Resource Block (RB) is defined as a physical resource element available for use at time \(t\). Each RB consists of a combination of time and frequency and represents the unit resource for data transmission. The set of resource blocks at time \(t\) is denoted as \(RB_{t}\). Each vehicle has varying resource demands depending on the size of the data to be transmitted and the transmission rate. The resource demand of a vehicle is determined by the size of the packet data it intends to transmit and the amount of data it can send using a single resource block. The resource block demand \(Rq(v)\) for each vehicle is calculated as follows:  
\[Rq(v)=\left\lceil\frac{D(v)}{C(v)}\right\rceil\quad(v\in V_{t}) \tag{3}\]  
In this case, \(D(v)\) represents the data size of a packet to be transmitted by vehicle \(v\), which is obtained through a resource request message sent via the PUCCH. \(C(v)\) denotes the amount of data that vehicle \(v\) can transmit per resource block, which is determined by the communication state of the vehicle and may vary depending on the modulation scheme. As the resource block is divided into discrete units, the required resources are calculated by applying a ceiling function to round up any fractional values during the resource requirement calculation. In scenarios where a large number of vehicles are requesting resources, the cumulative resource demand may exceed the number of available resource blocks. To address this, one approach involves reusing already allocated resources, and it is crucial to establish criteria for efficient resource reuse. Since a general vehicle does not know the destination address of the packet during resource allocation, it is challenging to calculate interference  
Figure 6: Request Resource in Resource block. and channel gain between communicating vehicles.